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  • if a female carrier and a normal male give birth to a daughter, she has a 1 in 2 chance of being a carrier of the trait (like her mother). If the child is a son, he has a 1 in 2 chance of being affected by the trait (for example, colorblindness). If a female carrier and an affected male give birth to a daughter, she will either be affected or be a carrier. If the child is a son, he will either be affected or be entirely free of the gene. See the following Punnett squares (The letters X and Y represent their respective normal chromosomes; X underlined represents the colorblindness allele).
  • if a female carrier and a normal male give birth to a daughter, she has a 1 in 2 chance of being a carrier of the trait (like her mother). If the child is a son, he has a 1 in 2 chance of being affected by the trait (for example, colorblindness). If a female carrier and an affected male give birth to a daughter, she will either be affected or be a carrier. If the child is a son, he will either be affected or be entirely free of the gene. See the following Punnett squares (The letters X and Y represent their respective normal chromosomes; X underlined represents the colorblindness allele).
  • Unit 1 Notes

    1. 1. BIOLOGY 40S Unit 1 Understanding Biological Inheritance
    2. 2. Members of a family show many similarities in appearance, but are not identical (except in the case of identical twins). Why do offspring inherit certain characteristics from their parents, but not others? Unit 1 – Understanding Biological Inheritance
    3. 3. Heredity <ul><li>In biology, heredity refers to the transference of biological characteristics from a parent organism to offspring. </li></ul>Unit 1 – Understanding Biological Inheritance
    4. 4. homozygous recessive heterozygous trait allele purebred dihybrid Independent assortment dominant phenotype genotype gene Unit 1 – Understanding Biological Inheritance
    5. 5. Traits <ul><li>It is common knowledge today that organisms inherit characteristics from their parents. During sexual reproduction, parents pass on traits to their offspring by means of genetic material within the egg and sperm. </li></ul><ul><li>A trait is described as a distinguishing feature or characteristic of an organism that has been passed on due to the transmission of genes. </li></ul>Unit 1 – Understanding Biological Inheritance
    6. 6. Traits - continued <ul><li>Sexual reproduction introduces variation within a species because offspring inherit characteristics from both parents. Traits are inherited because discrete units called genes are passed from parent to child when the child is conceived. These genes are a unique blueprint for an individual organism, providing all the biological information needed for its pre-birth development and life, as well as for the characteristics that make that individual unique. </li></ul>Unit 1 – Understanding Biological Inheritance
    7. 7. Mendel's Contribution The story of Gregor Mendel and his work provides a fascinating glimpse into the nature of science. Mendel was born in 1822 and as a young man attended the University of Vienna. There he studied chemistry, biology and physics, but left before graduating, probably for health reasons. He entered the Augustinian monastery in Brno, and with the support of the abbot, began his investigation of the inheritance of certain traits in pea plants ( Pisum sativum ). His choice of pea plants as the experimental subject was excellent as peas grow and reproduce quickly, their mating can be controlled, and the plants have a number of distinct traits that are readily observed. Over the course of the next eight years, Mendel conducted experiments and maintained detailed records of his results. His university training led him to design simple experiments that permitted him to observe the inheritance of one trait at a time. His use of mathematics allowed him to formulate conclusions based on his results. These conclusions are known as Mendel’s Laws or Principles.
    8. 8. Gregor Mendel Early Principles of Inheritance
    9. 9. Gregor Mendel Gregor Mendel’s Research & Principles
    10. 10. Gregor Mendel Using Terms in Modern Genetics to Review Mendel’s Work
    11. 11. Mendel's Laws or Principles <ul><li>Genes In Pairs : </li></ul><ul><li>Genetic characteristicss are controlled by unit factors (genes) that exist in pairs in individual organisms and are passed from parents to their offspring. When two organisms produce offspring, each parent gives the offspring one of the factors from each pair. </li></ul>
    12. 12. Mendel's Laws or Principles <ul><li>Dominance and Recessiveness : </li></ul><ul><li>When two unlike factors responsible for a </li></ul><ul><li>single characteristic are present in a single individual, one factor can mask the </li></ul><ul><li>expression of another factor. </li></ul><ul><li>That is, one factor is dominant to the other, which is said to be recessive. </li></ul>
    13. 13. Mendel's Laws or Principles <ul><li>The Principle of Segregation : </li></ul><ul><li>During the formation of gametes, the paired </li></ul><ul><li>factors separate (segregate) randomly so that each gamete receives one factor or the other. </li></ul>
    14. 14. Mendel's Laws or Principles <ul><li>The Principle of Independent Assortment : </li></ul><ul><li>During gamete formation, segregating pairs of factors assort independently of each other. </li></ul>
    15. 15. Mendel’s laws cont’d. <ul><li>What we know now </li></ul><ul><ul><li>Genes are sections of chromosomes </li></ul></ul><ul><ul><li>Chromosomes come in pairs called homologous pairs </li></ul></ul><ul><ul><ul><li>Homologous pairs have genes controlling the same traits </li></ul></ul></ul><ul><ul><ul><li>Genes are located at the same point or locus, on each member of the pair </li></ul></ul></ul><ul><ul><ul><li>Information contained within the homologous genes is not necessarily the same (ex: blues vs. brown eyes) </li></ul></ul></ul><ul><ul><ul><ul><li>Alternative forms of a gene for a trait are called alleles </li></ul></ul></ul></ul>
    16. 16. Gene locus
    17. 17. Gene Linkage
    18. 18. Mendel’s laws cont’d. <ul><li>Inheritance of a single trait </li></ul><ul><ul><li>Capitol letter- represents the dominant allele </li></ul></ul><ul><ul><li>Small letter- represents the recessive allele </li></ul></ul><ul><ul><ul><li>Dominant -a certain trait will result if the individual has at least 1 dominant allele </li></ul></ul></ul><ul><ul><ul><li>Recessive - for a recessive trait to result the individual must have 2 copies of the recessive allele </li></ul></ul></ul>
    19. 19. Mendel’s laws cont’d. <ul><ul><li>Genotype - genetic composition of an individual with regard to a specific trait </li></ul></ul><ul><ul><ul><li>2 copies of the dominant allele- homozygous dominant </li></ul></ul></ul><ul><ul><ul><li>1 copy of the dominant allele and 1 of the recessive- heterozygous </li></ul></ul></ul><ul><ul><ul><li>2 copies of the recessive allele- homozygous recessive </li></ul></ul></ul><ul><ul><li>Phenotype - physical appearance of the individual with regard to a trait </li></ul></ul><ul><ul><ul><li>Homozygous dominant individual and heterozygous individual will have the same phenotype in this instance </li></ul></ul></ul><ul><ul><ul><li>Homozygous recessive individual will have a different phenotype </li></ul></ul></ul>
    20. 20. Mendel’s laws cont’d. <ul><ul><li>Gamete formation </li></ul></ul><ul><ul><ul><li>During meiosis, homologous chromosomes separate so there is only 1 member of each pair in a gamete </li></ul></ul></ul><ul><ul><ul><li>There is one allele for each trait, such as hairline, in each gamete </li></ul></ul></ul><ul><ul><ul><li>No two letters in a gamete can be the same letter of the alphabet </li></ul></ul></ul><ul><ul><ul><ul><li>If genotype is Ww, then gametes from this individual will contain either a W or a w </li></ul></ul></ul></ul><ul><ul><ul><ul><li>If the genotype is WwLl (looking at 2 traits), gametes can contain any of the following combinations </li></ul></ul></ul></ul><ul><ul><ul><ul><ul><li>WL, Wl, wL, or wl </li></ul></ul></ul></ul></ul>
    21. 21. Monohybrid Crosses <ul><li>One trait crosses-monohybrid cross </li></ul><ul><ul><li>Let’s consider a specific cross </li></ul></ul><ul><ul><ul><li>If a homozygous woman with a widow’s peak reproduces with a man with a straight hairline, what kind of hairline will their children have? </li></ul></ul></ul><ul><ul><ul><ul><li>Use W= widow’s peak, w=straight hairline </li></ul></ul></ul></ul><ul><ul><ul><ul><li>figure out the genotype of each parent </li></ul></ul></ul></ul><ul><ul><ul><ul><ul><li>Woman has a widow’s peak and we are told she is homozygous so she is WW </li></ul></ul></ul></ul></ul><ul><ul><ul><ul><ul><li>Man has a straight hairline so he must be ww </li></ul></ul></ul></ul></ul><ul><ul><ul><ul><li>Determine their gametes: her eggs will all have W and his sperm will all have w </li></ul></ul></ul></ul><ul><ul><ul><ul><li>Put together all possible combinations: all offspring will receive a W from her and a w from him so all Ww </li></ul></ul></ul></ul>
    22. 22. Monohybrid Crosses <ul><li>One-trait cross cont’d. </li></ul><ul><ul><li>In this example there was only 1 combination of eggs and sperm possible </li></ul></ul><ul><ul><li>What if the parents were each Ww? </li></ul></ul><ul><ul><ul><li>Then sperm could have either W or w, and eggs also could have W or w </li></ul></ul></ul><ul><ul><li>One way to figure out the possible combinations of eggs and sperm that could occur is to use a Punnett square </li></ul></ul><ul><ul><li>This is illustrated on the following slide </li></ul></ul>
    23. 24. Monohybrid Crosses <ul><li>One-trait cross cont’d. </li></ul><ul><ul><li>After the genotypes and phenotypes of offspring are determined, we can determine the ratios </li></ul></ul><ul><ul><ul><li>In our previous example, in the Punnett square we had the following offspring: WW, Ww, Ww, and ww </li></ul></ul></ul><ul><ul><ul><ul><li>The genotypic ratio is 1 WW:2 Ww:1 ww </li></ul></ul></ul></ul><ul><ul><ul><ul><li>The phenotypic ratio is 3 individuals with a widow’s peak to 1 individual with a straight hairline </li></ul></ul></ul></ul><ul><ul><ul><li>Another way to phrase the phenotypic ratio is in terms of probability </li></ul></ul></ul><ul><ul><ul><ul><li>This couple has a 75% chance of producing a child with a widow’s peak and a 25% chance of producing a child with a straight hairline </li></ul></ul></ul></ul><ul><ul><ul><li>The probability will be the same for each pregnancy between this couple </li></ul></ul></ul>
    24. 25. Monohybrid Crosses <ul><li>One-trait crosses and probability </li></ul><ul><ul><li>Product rule of probability </li></ul></ul><ul><ul><ul><li>The chance of 2 or more independent events occurring together is the product of their chance of occurring separately </li></ul></ul></ul><ul><ul><ul><ul><li>In the cross Ww X Ww, what is the chance of obtaining either a W or a w from a parent? </li></ul></ul></ul></ul><ul><ul><ul><ul><ul><li>Chance of W = ½ and the chance of w = ½ </li></ul></ul></ul></ul></ul><ul><ul><ul><ul><ul><li>Therefore the probability of having these genotypes is as follows </li></ul></ul></ul></ul></ul><ul><ul><ul><ul><ul><li>Chance of WW= ½ X ½ = ¼ </li></ul></ul></ul></ul></ul><ul><ul><ul><ul><ul><li>Chance of Ww = ½ X ½ = ¼ </li></ul></ul></ul></ul></ul><ul><ul><ul><ul><ul><li>Chance of wW= ½ X ½ = ¼ </li></ul></ul></ul></ul></ul><ul><ul><ul><ul><ul><li>Chance of ww = ½ X ½ = ¼ </li></ul></ul></ul></ul></ul>
    25. 26. Monohybrid Crosses <ul><li>One-trait crosses and probability cont’d. </li></ul><ul><ul><li>Sum rule of probability -the chance of an event that can occur in more than one way is the sum of the individual chances </li></ul></ul><ul><ul><ul><li>To calculate the chance of an offspring having a widow’s peak, add the chances of WW, Ww, or wW from the preceding slide </li></ul></ul></ul><ul><ul><ul><ul><li>¼ + ¼ + ¼ = ¾ or 75% </li></ul></ul></ul></ul>
    26. 27. Dihybrid Crosses <ul><li>The inheritance of two traits </li></ul><ul><ul><li>Mendel reasoned from the results of his pea plant crosses that each pair of factors assorts independently into gametes </li></ul></ul><ul><ul><ul><li>If one pair of homologous chromosomes has a W on one and w on the other, and a second pair has an R on one and an r on the other, when gametes form all possible combinations of these letters are possible: WR, Wr, wR, and wr </li></ul></ul></ul><ul><ul><ul><li>Called the Law of Independent Assortment </li></ul></ul></ul>
    27. 28. Segregation and independent assortment
    28. 29. Dihybrid Crosses <ul><li>The law of independent assortment states : </li></ul><ul><ul><li>Each pairs of factors assorts independently (without regard to how the others separate) </li></ul></ul><ul><ul><li>All possible combinations of factors can occur in the gametes </li></ul></ul>
    29. 30. Dihybrid Crosses <ul><li>Two-trait crosses-dihybrid cross </li></ul><ul><ul><li>Let’s consider two traits, hairline and finger length </li></ul></ul><ul><ul><ul><li>We’ll use the W and w as before, and now S=short fingers and s=long fingers </li></ul></ul></ul><ul><ul><li>A person who is WwSs widow’s peak and short fingers and a person who is also WwSs have children </li></ul></ul><ul><ul><ul><li>Figure the gametes for each parent </li></ul></ul></ul><ul><ul><ul><ul><li>WS, Ws, wS, and ws for both </li></ul></ul></ul></ul><ul><ul><ul><li>Make a big Punnett square as illustrated on the following slide </li></ul></ul></ul><ul><ul><ul><li>Figure the genotypes of the offspring </li></ul></ul></ul><ul><ul><li>Phenotypic ratio: 9 widow’s peak, short fingers: 3 widow’s peak, long fingers; 3 straight hairline, short fingers; 1 straight hairline, long fingers </li></ul></ul>
    30. 31. Dihybrid cross
    31. 32. Dihybrid Crosses <ul><li>Two-trait crosses and probability </li></ul><ul><ul><li>Probability laws </li></ul></ul><ul><ul><ul><li>Probability of widow’s peak = ¾ </li></ul></ul></ul><ul><ul><ul><li>Probability of short fingers= ¾ </li></ul></ul></ul><ul><ul><ul><li>Probability of straight hairline= ¼ </li></ul></ul></ul><ul><ul><ul><li>Probability of long fingers= ¼ </li></ul></ul></ul><ul><ul><li>Using the product rule </li></ul></ul><ul><ul><ul><li>Probability of widow’s peak and short fingers = ¾ X ¾ = 9/16 </li></ul></ul></ul><ul><ul><ul><li>Probability of widow’s peak and long fingers = ¾ X ¼ = 3/16 </li></ul></ul></ul><ul><ul><ul><li>Probability of straight hairline and short fingers = ¼ X ¾ = 3/16 </li></ul></ul></ul><ul><ul><ul><li>Probability of straight hairline and long fingers = ¼ X ¼ = 1/16 </li></ul></ul></ul>
    32. 33. Review <ul><li>monohybrid cross, dihybrid cross, P generation, F1 generation, F2 generation, phenotypic ratio, genotypic ratio, dominant alleles, recessive alleles, purebred, hybrid, carrier </li></ul>
    33. 34. Beyond Simple Inheritance Patterns <ul><li>When Gregor Mendel crossed a purple-flowered pea plant with a white-flowered pea plant, the flowers in the next generation are all purple. However, the cross between a red-flowered snapdragon and a white-flowered snapdragon produces pink-flowered snapdragons. </li></ul><ul><li>1) What is the dominant flower colour in pea plants? </li></ul><ul><li>2) How does the snapdragon cross differ from the pea plant cross? </li></ul><ul><li>3) Can you come up with an explanation for the results of the snapdragon cross? </li></ul>
    34. 35. Incomplete Dominance
    35. 36. <ul><li>Incomplete dominance </li></ul><ul><ul><ul><li>Heterozygous individual has a phenotype intermediate to the two homozygous individuals </li></ul></ul></ul><ul><ul><ul><li>Ex: curly-haired Caucasian woman and a straight-haired Caucasian man produce wavy-haired children </li></ul></ul></ul><ul><ul><ul><ul><li>When 2 wavy-haired people have children, the phenotypic ratio is 1 curly: 2 wavy: 1 straight </li></ul></ul></ul></ul>Beyond Simple Inheritance Patterns
    36. 37. Incomplete Dominance
    37. 38. <ul><li>Polygenic inheritance </li></ul><ul><ul><li>Controlled by 2 or more sets of alleles </li></ul></ul><ul><ul><li>Each dominant allele codes for a product and effects are additive </li></ul></ul><ul><ul><li>Result is a continuous range of phenotypes </li></ul></ul><ul><ul><ul><li>Ex: human height, skin pigmentation </li></ul></ul></ul>Beyond Simple Inheritance Patterns
    38. 39. Beyond Simple Inheritance Patterns
    39. 40. <ul><li>Polygenic inheritance cont’d. </li></ul><ul><ul><li>Skin color </li></ul></ul><ul><ul><ul><li>Controlled by many gene pairs and many alleles </li></ul></ul></ul><ul><ul><ul><li>Assuming the simplest model, 2 alleles at loci </li></ul></ul></ul><ul><ul><ul><ul><li>A and B </li></ul></ul></ul></ul><ul><ul><ul><ul><li>When an AaBb person has children with another AaBb person, children can range from very light to very dark </li></ul></ul></ul></ul>Beyond Simple Inheritance Patterns
    40. 41. <ul><li>Polygenic inheritance cont’d. </li></ul>Beyond Simple Inheritance Patterns Very light aabb Light Aabb or aaBb Medium brown AaBb, AAbb, aaBB Dark AABb or AaBB Very dark AABB
    41. 42. <ul><li>Multiple allele inheritance and codominance </li></ul><ul><ul><li>The gene exists in several allelic forms, but each person still has only 2 of the possible alleles </li></ul></ul><ul><ul><li>ABO blood types </li></ul></ul><ul><ul><ul><li>I A = A antigens on RBCs </li></ul></ul></ul><ul><ul><ul><li>I B = B antigens on RBCs </li></ul></ul></ul><ul><ul><ul><li>i = has neither A nor B antigens on RBCs </li></ul></ul></ul><ul><ul><li>Both I A and I B are dominant over I; I A and I B are codominant (when both alleles are equally expressed) </li></ul></ul><ul><ul><li>Phenotype Genotype </li></ul></ul><ul><ul><li>A I A I A or I A i </li></ul></ul><ul><ul><li>B I B I B or I B i </li></ul></ul><ul><ul><li>AB I A I B </li></ul></ul><ul><ul><li>O ii </li></ul></ul>Beyond Simple Inheritance Patterns
    42. 43. Inheritance of blood type
    43. 44. Multiple Allele Inheritance and Codominance
    44. 45. <ul><li>Epistasis </li></ul><ul><ul><li>a form of gene interaction whereby one gene interferes with the phenotypic expression of another nonallelic gene or genes. Gene A is said to be epistatic to gene B if an allele of gene A masks the encoded effects of gene B. </li></ul></ul>Beyond Simple Inheritance Patterns
    45. 46. Beyond Simple Inheritance Patterns
    46. 47. <ul><li>Lethal Genes </li></ul><ul><ul><li>a gene that leads to the death of an individual; these can be either dominant or recessive in nature </li></ul></ul>Beyond Simple Inheritance Patterns
    47. 48. <ul><li>The sex of an individual is determined at the time of fertilization by the type of sex chromosome (X or Y) present in the sperm. If the sperm contains an X chromosome, the zygote will be female (XX). If the sperm contains a Y chromosome, the zygote will be male (XY). </li></ul><ul><li>The following diagrams show the complete set of chromosomes for a male. Notice the last pair of chromosomes. They are labeled as XY for the male. A female would have XX chromosomes. </li></ul><ul><li>It is the presence of the Y chromosome that creates a male. In its absence, the individual becomes a female. </li></ul>Sex Determination in humans
    48. 49. Karyotype
    49. 50. Karyotype
    50. 51. <ul><li>During meiosis in males, when the pair of chromosomes segregate, the X and the Y chromosomes also separate. Half of the sperm produced would carry the Y chromosome and the other half would carry the X chromosome. There are therefore two types of sperm: </li></ul><ul><li>1. If a sperm with the Y chromosome fertilizes an egg, the new life will be a male. 2. If a sperm with the X chromosome fertilizes an egg, the new life will be female. </li></ul><ul><li>During meiosis in females, all eggs receive a X chromosome. </li></ul>Sex Determination in humans
    51. 52. <ul><li>Through the first six weeks of pregnancy, the embryo develops as a female. </li></ul><ul><li>Sex differentiation occurs in the seventh week of embryonic development. Genes on the Y chromosome trigger the release of androgens that stimulates the development of male reproductive organs. Should androgens not be released, the embryo continues to develop as a female in response to the release of estrogens. </li></ul><ul><li>Sex-linked traits are recessive and carried on the X chromosome. Consequently, because males carry one copy of the gene and females carry two copies of the gene, sex-linked genes are expressed more often in males than in females. </li></ul>Sex Determination in humans
    52. 53. <ul><li>Sex-linked traits are recessive and carried on the X chromosome. Consequently, because males carry one copy of the gene and females carry two copies of the gene, sex-linked genes are expressed more often in males than in females. </li></ul>Sex Determination in humans
    53. 54. Genetics of Parenthood
    54. 55. <ul><li>Sex-linkage is another common alternative-inheritance pattern. In sex-linked traits, such as color-blindness, the gene for the trait is found on the X chromosome (a sex chromosome). </li></ul><ul><li>Sex-linked traits affect primarily males, since they have only one copy of the X chromosome (male genotype: XY). </li></ul><ul><li>Females, who have two copies of the X chromosome, are affected only if they are homozygous for the trait. Females can, however, be carriers for sex-linked traits, passing their X chromosomes on to their sons. </li></ul>Sex Linked Inheritance
    55. 56. <ul><li>Sex-linked inheritance works as follows: </li></ul>Sex Linked Inheritance
    56. 57. <ul><li>Sex-linked inheritance works as follows: </li></ul>Sex Linked Inheritance
    57. 58. Meiosis <ul><li>How is it possible that genes from two parents unite to form a new life that still has the critically correct number of chromosomes? To understand the transfer of traits from parents to offspring, a clear concept of the nature of DNA, chromosomes, and genes is vital. </li></ul><ul><li>Meiosis is the process that results in egg and sperm cells having one half of the normal number of chromosomes. </li></ul><ul><li>Egg and sperm then unite to form a new individual with the correct amount of genetic material. </li></ul>Unit 1 - Genetics
    58. 59. Meiosis Diploid & Haploid <ul><li>Most cells in the human body have 46 chromosomes. When new cells are made, they also have 46 chromosomes. The process of mitosis describes how this is done. Forty-six is the normal number of chromosomes found in human cells; this is called the diploid number. Any more or less causes abnormalities. </li></ul><ul><li>A special type of cell division produces sperm and egg cells with half the diploid number. Having half the normal number of chromosomes is called haploid. </li></ul>Unit 1 - Genetics
    59. 60. Meiosis Diploid & Haploid <ul><li>In effect, a sperm cell ends up with 23 chromosomes and fertilizes an egg with 23 chromosomes. This new cell is the beginning of life and it has 46 chromosomes--the normal number. </li></ul><ul><li>The special type of cell division that ensures that each sperm and egg has the haploid number of chromosomes is called meiosis. </li></ul>Unit 1 - Genetics
    60. 61. Meiosis Unit 1 - Genetics
    61. 62. Meiosis <ul><li>http://www.csuchico.edu/~jbell/Biol207/animations/meiosis.html </li></ul><ul><li>http:// www.pbs.org/wgbh/nova/baby/divide.html # </li></ul><ul><li>http:// www.cellsalive.com/meiosis.htm </li></ul><ul><li>http:// www.biologyinmotion.com/cell_division / </li></ul><ul><li>http://highered.mcgraw-hill.com/sites/0072437316/student_view0/chapter12/animations.html# </li></ul><ul><li>http://www.sumanasinc.com/webcontent/anisamples/majorsbiology/meiosis.html </li></ul>Unit 1 - Genetics
    62. 63. Reducing the chromosome number <ul><li>Overview of meiosis </li></ul><ul><ul><li>2 divisions, 4 daughter cells </li></ul></ul><ul><ul><li>Cells are diploid at beginning of meiosis </li></ul></ul><ul><ul><li>Pairs of chromosomes are called homologues </li></ul></ul>
    63. 64. nucleolus Overview of meiosis centromere 2n = 4 DNA replication 2n = 4 synapsis sister chromatids n = 2 n = 2 Meiosis II Sister chromatids separate, becoming daughter chromosomes. Meiosis I Homologous pairs separate. n = 2 n = 2
    64. 65. nucleolus centromere 2n = 4
    65. 66. nucleolus centromere 2n = 4 DNA replication 2n = 4 synapsis sister chromatids
    66. 67. nucleolus centromere 2n = 4 DNA replication 2n = 4 synapsis sister chromatids Meiosis I Homologous pairs separate. n = 2 n = 2
    67. 68. nucleolus centromere 2n = 4 DNA replication 2n = 4 synapsis sister chromatids n = 2 n = 2 Meiosis II Sister chromatids separate, becoming daughter chromosomes. Meiosis I Homologous pairs separate. n = 2 n = 2
    68. 69. Reducing the chromosome number <ul><li>Meiosis I </li></ul><ul><ul><ul><li>Homologues line up side by side at equator-synapsis </li></ul></ul></ul><ul><ul><ul><li>When pairs separate, each daughter cell receives one member of the pair </li></ul></ul></ul><ul><ul><ul><li>Cells are now haploid </li></ul></ul></ul>
    69. 70. Reducing the chromosome number cont’d. <ul><li>Meiosis II </li></ul><ul><ul><ul><li>No replication of DNA occurs in this division </li></ul></ul></ul><ul><ul><ul><li>Centromeres divide and sister chromatids migrate to opposite poles to become individual chromosomes </li></ul></ul></ul><ul><ul><ul><li>Each of the four daughter cells produced has the haploid chromosome number and each chromosome is composed of one chromatid </li></ul></ul></ul>
    70. 71. Reducing the chromosome number cont’d. <ul><li>Phases of meiosis I </li></ul><ul><ul><li>Prophase I </li></ul></ul><ul><ul><ul><li>Synapsis occurs, nuclear membrane breaks down </li></ul></ul></ul><ul><ul><ul><li>Homologues line up side by side and crossing over occurs </li></ul></ul></ul><ul><ul><li>Metaphase I </li></ul></ul><ul><ul><ul><li>Homologous pairs line up at equator such that maternal or paternal member may be oriented toward either pole </li></ul></ul></ul><ul><ul><li>Anaphase I </li></ul></ul><ul><ul><ul><li>Homologous chromosomes (each still consisting of 2 chromatids) undergo independent assortment into daughter cells </li></ul></ul></ul><ul><ul><li>Telophase I </li></ul></ul><ul><ul><ul><li>Cytokinesis produces 2 daughter cells which are haploid </li></ul></ul></ul>
    71. 72. Homologous pairs align at the metaphase plate. Metaphase I DNA Replication Homologous chromosomes separate, pulled to opposite poles by centromeric spindle fibers. Anaphase I Daughter cells have one chromosome from each homologous pair. Telophase I Homologous chromosomes pair during synapsis. Prophase I Meiosis I 2n = 4 Chromosomes still consist of two chromatids. Interkinesis n = 2
    72. 73. DNA Replication
    73. 74. DNA Replication Homologous chromosomes pair during synapsis. Prophase I Meiosis I 2n = 4
    74. 75. Homologous pairs align at the metaphase plate. Metaphase I DNA Replication Homologous chromosomes pair during synapsis. Prophase I Meiosis I 2n = 4
    75. 76. Homologous pairs align at the metaphase plate. Metaphase I DNA Replication Homologous chromosomes separate, pulled to opposite poles by centromeric spindle fibers. Anaphase I Homologous chromosomes pair during synapsis. Prophase I Meiosis I 2n = 4
    76. 77. Homologous pairs align at the metaphase plate. Metaphase I DNA Replication Homologous chromosomes separate, pulled to opposite poles by centromeric spindle fibers. Anaphase I Daughter cells have one chromosome from each homologous pair. Telophase I Homologous chromosomes pair during synapsis. Prophase I Meiosis I 2n = 4
    77. 78. Homologous pairs align at the metaphase plate. Metaphase I DNA Replication Homologous chromosomes separate, pulled to opposite poles by centromeric spindle fibers. Anaphase I Daughter cells have one chromosome from each homologous pair. Telophase I Homologous chromosomes pair during synapsis. Prophase I Meiosis I 2n = 4 Chromosomes still consist of two chromatids. Interkinesis n = 2
    78. 79. Reducing the chromosome number cont’d. <ul><li>Interkinesis -period between meiosis I and meiosis II </li></ul><ul><li>Phases of meiosis II </li></ul><ul><ul><li>Prophase II- </li></ul></ul><ul><ul><ul><li>Cells have 1 member of each homologous pair </li></ul></ul></ul><ul><ul><li>Metaphase II </li></ul></ul><ul><ul><ul><li>Chromosomes line up at the equator </li></ul></ul></ul><ul><ul><li>Anaphase II </li></ul></ul><ul><ul><ul><li>Centromeres divide and daughter chromosomes migrate </li></ul></ul></ul><ul><ul><li>Telophase II </li></ul></ul><ul><ul><ul><li>Nuclei form, cytokinesis </li></ul></ul></ul>
    79. 80. Metaphase II Chromosomes align at the metaphase plate. Anaphase II Daughter chromosomes move toward the poles. Telophase II Spindle disappears, nuclei form, and cytokinesis takes place. Meiosis II Prophase II Cells have one chromosome from each homologous pair. n = 2 n = 2 Daughter Cells Meiosis results in four haploid daughter cells. n = 2 n = 2
    80. 81. Meiosis II Prophase II Cells have one chromosome from each homologous pair. n = 2 n = 2
    81. 82. Metaphase II Chromosomes align at the metaphase plate. Meiosis II Prophase II Cells have one chromosome from each homologous pair. n = 2 n = 2
    82. 83. Metaphase II Chromosomes align at the metaphase plate. Anaphase II Daughter chromosomes move toward the poles. Meiosis II Prophase II Cells have one chromosome from each homologous pair. n = 2 n = 2
    83. 84. Metaphase II Chromosomes align at the metaphase plate. Anaphase II Daughter chromosomes move toward the poles. Telophase II Spindle disappears, nuclei form, and cytokinesis takes place. Meiosis II Prophase II Cells have one chromosome from each homologous pair. n = 2 n = 2
    84. 85. Metaphase II Chromosomes align at the metaphase plate. Anaphase II Daughter chromosomes move toward the poles. Telophase II Spindle disappears, nuclei form, and cytokinesis takes place. Meiosis II Prophase II Cells have one chromosome from each homologous pair. n = 2 n = 2 Daughter Cells Meiosis results in four haploid daughter cells. n = 2 n = 2
    85. 87. Reducing the chromosome number cont’d. <ul><li>Meiosis in detail </li></ul><ul><ul><li>Meiosis I- genetic recombination occurs in 2 ways </li></ul></ul><ul><ul><ul><li>Crossing over-exchange of segments of DNA between homologues </li></ul></ul></ul><ul><ul><ul><li>Independent assortment of chromosome pairs </li></ul></ul></ul>
    86. 88. Independent alignment
    87. 89. Synapsis and crossing over
    88. 90. Chromosomal Alterations
    89. 91. Chromosomal Abnormalities <ul><li>Genetic counseling </li></ul><ul><ul><li>Determines risk of chromosomal or genetic mutation in a family </li></ul></ul><ul><ul><li>Allows couples to understand mode of inheritance, medical consequences, and possible decisions </li></ul></ul><ul><li>Counseling for chromosomal disorders </li></ul><ul><ul><li>Disorders result in syndromes -groups of symptoms </li></ul></ul><ul><ul><li>Karyotyping - visual display of chromosomes </li></ul></ul>
    90. 92. Chromosomal Abnormalities <ul><li>Nondisjunction </li></ul><ul><li>Changes in chromosome number </li></ul><ul><ul><li>Abnormalities in chromosome number may be due to nondisjunction </li></ul></ul><ul><ul><ul><li>When it occurs during meiosis I both members of a homologous pair migrate into the same daughter cell </li></ul></ul></ul><ul><ul><ul><li>When it occurs in meiosis II, the centromere fails to divide and both daughter chromatids enter the same gamete </li></ul></ul></ul><ul><ul><ul><ul><li>Egg with 24 chromosomes fertilized by sperm with 23- trisomy </li></ul></ul></ul></ul><ul><ul><ul><ul><li>Egg with 22 chromosomes fertilized by sperm with 23 chromosomes- monosomy </li></ul></ul></ul></ul><ul><ul><li>Normal development depends on the presence of exactly 2 of each kind of chromosome </li></ul></ul>
    91. 93. Chromosomal Abnormalities <ul><li>Nondisjunction </li></ul>
    92. 94. Chromosomal Abnormalities <ul><li>Changes in chromosome number cont’d. </li></ul><ul><ul><li>Trisomy </li></ul></ul><ul><ul><ul><li>Three copies of one kind of chromosome </li></ul></ul></ul><ul><ul><ul><li>The only one compatible with a reasonable chance of survival is trisomy 21 Down Syndrome </li></ul></ul></ul><ul><ul><li>Monosomy </li></ul></ul><ul><ul><ul><li>One copy of one kind of chromosome </li></ul></ul></ul><ul><ul><ul><li>Most are incompatible with life </li></ul></ul></ul>
    93. 95. Chromosomal Abnormalities <ul><li>Down Syndrome </li></ul><ul><ul><li>Most common trisomy in humans </li></ul></ul><ul><ul><li>Short stature, eyelid fold, flat face, stubby fingers, a wide gap between the first and second toes, large fissured tongue, round head, palm crease, simian line, mental retardation </li></ul></ul><ul><ul><li>3 copies of chromosome 21 </li></ul></ul><ul><ul><li>Can be detected by a karyotype </li></ul></ul>
    94. 96. Chromosomal Abnormalities <ul><li>Down Syndrome </li></ul>
    95. 97. Chromosomal Abnormalities <ul><ul><li>Chances of survival are greatest if monosomy or trisomy involves the sex chromosomes </li></ul></ul><ul><ul><ul><li>Turner’s syndrome -monosomy X (XO), zygote has one X chromosome and no other X or Y </li></ul></ul></ul><ul><ul><ul><ul><li>Capable of survival, phenotypically female, infertile </li></ul></ul></ul></ul><ul><ul><ul><ul><li>Short, may have malformed features-webbed neck, high palate, small jaw, congenital heart and kidney defects, ovarian failure, infertility </li></ul></ul></ul></ul><ul><ul><ul><ul><li>Generally have normal intelligence, may have learning disabilities </li></ul></ul></ul></ul>
    96. 98. Chromosomal Abnormalities <ul><ul><li>Chances of survival are greatest if monosomy or trisomy involves the sex chromosomes </li></ul></ul><ul><ul><ul><li>Jacob’s syndrome (XYY) is due to nondisjunction in meiosis II </li></ul></ul></ul><ul><ul><ul><ul><li>XYY genotype can only result from nondisjunction in spermatogenesis </li></ul></ul></ul></ul><ul><ul><ul><ul><li>Taller than average, persistent acne, speech and reading problems </li></ul></ul></ul></ul><ul><ul><ul><li>Klinefelter syndrome (XXY) is due to nondisjunction in meiosis II </li></ul></ul></ul><ul><ul><ul><ul><li>Underdeveloped testes and prostate gland, no facial hair </li></ul></ul></ul></ul><ul><ul><ul><ul><li>Phenotypically male, infertile </li></ul></ul></ul></ul><ul><ul><ul><ul><li>Generally have normal intelligence, but may be slow learners </li></ul></ul></ul></ul>
    97. 99. Chromosomal Abnormalities
    98. 100. Chromosomal Abnormalities <ul><li>Changes in chromosome number cont’d. </li></ul><ul><ul><li>Poly-X females </li></ul></ul><ul><ul><ul><li>More than 2 X chromosomes </li></ul></ul></ul><ul><ul><ul><li>XXX females may be unusually tall, with delayed language and motor skills but normal cognitive abilities </li></ul></ul></ul><ul><ul><ul><li>XXXX females are usually severely retarded </li></ul></ul></ul>
    99. 101. <ul><li>Disorders from changes in chromosomal structure </li></ul><ul><ul><li>Deletions and mutations </li></ul></ul><ul><ul><ul><li>Deletion - breaks in a chromosome which result in loss of genes </li></ul></ul></ul><ul><ul><ul><li>Williams syndrome </li></ul></ul></ul><ul><ul><ul><ul><li>Chromosome 7 loses an end piece </li></ul></ul></ul></ul><ul><ul><ul><ul><ul><li>Turned up nose </li></ul></ul></ul></ul></ul><ul><ul><ul><ul><ul><li>Wide mouth with small chin </li></ul></ul></ul></ul></ul><ul><ul><ul><ul><ul><li>Poor academic skills but well-developed verbal and musical skills </li></ul></ul></ul></ul></ul><ul><ul><ul><li>Cri du chat syndrome </li></ul></ul></ul><ul><ul><ul><ul><li>Chromosome 5 loses an end piece </li></ul></ul></ul></ul><ul><ul><ul><ul><li>Small head, mental retardation, cat-like cry </li></ul></ul></ul></ul>Chromosomal Abnormalities
    100. 102. Deletion
    101. 103. <ul><li>Disorders from changes in chromosomal structure cont’d. </li></ul><ul><ul><li>Duplications -may have more than 2 alleles for certain traits </li></ul></ul><ul><ul><ul><li>Inverted duplication of chromosome 15-segment joins in direction opposite from normal </li></ul></ul></ul><ul><ul><ul><ul><li>Poor muscle tone </li></ul></ul></ul></ul><ul><ul><ul><ul><li>Mental retardation </li></ul></ul></ul></ul><ul><ul><ul><ul><li>Seizures, autism </li></ul></ul></ul></ul><ul><ul><li>Translocation -exchange between 2 non-homologues </li></ul></ul><ul><ul><ul><li>Person with both involved chromosomes is normal </li></ul></ul></ul><ul><ul><ul><li>Person who inherits only 1 will have various syndromes </li></ul></ul></ul><ul><ul><ul><ul><li>Depends on which chromosomes are affected </li></ul></ul></ul></ul>Chromosomal Abnormalities
    102. 104. Duplication
    103. 105. Translocation
    104. 106. <ul><li>Disorders from changes in chromosomal structure cont’d. </li></ul><ul><ul><li>Inversion </li></ul></ul><ul><ul><ul><li>Segment is turned 180 degrees </li></ul></ul></ul><ul><ul><ul><li>Leads to altered gene activity </li></ul></ul></ul>Chromosomal Abnormalities
    105. 107. Inversion
    106. 108. Pedigree Analysis <ul><li>Pedigree: family record that shows how a trait is inherited over several generations </li></ul><ul><li>Can show autosomal (recessive/ dominant) or sex-linked traits </li></ul>
    107. 109. Pedigree Analysis - Symbols
    108. 110. Pedigree Analysis - Symbols Marriage Line: Offspring: Twins:
    109. 111. Pedigrees
    110. 112. <ul><li>Pedigrees for autosomal disorders </li></ul><ul><ul><li>An affected child from 2 unaffected parents indicates an autosomal recessive trait </li></ul></ul><ul><ul><li>Two affected parents produce an unaffected child </li></ul></ul><ul><ul><ul><li>Indicates both parents are heterozygous for an autosomal dominant trait </li></ul></ul></ul><ul><ul><ul><li>Another indicator- when both parents are unaffected, none of their children are either </li></ul></ul></ul>Genetic Disorders
    111. 113. Autosomal Recessive Pedigree Chart <ul><li>Fig. 26.9 </li></ul>
    112. 114. Autosomal Dominant Pedigree Chart <ul><li>Fig. 26.10 </li></ul>
    113. 115. <ul><li>Pedigrees for sex-linked disorders </li></ul><ul><ul><li>X-linked disorders </li></ul></ul><ul><ul><ul><li>X-linked recessive disorders </li></ul></ul></ul><ul><ul><ul><ul><li>To be affected, daughters must inherit it from both parents </li></ul></ul></ul></ul><ul><ul><ul><ul><li>Sons can only inherit it from mother, therefore more males affected than females </li></ul></ul></ul></ul><ul><ul><ul><li>X-linked dominant disorders </li></ul></ul></ul><ul><ul><ul><ul><li>Affected males pass the trait only to daughters </li></ul></ul></ul></ul><ul><ul><ul><ul><li>Females can pass trait to both daughters and sons </li></ul></ul></ul></ul>Genetic Disorders
    114. 116. X-linked Recessive Pedigree Chart
    115. 117. Pedigrees
    116. 118. <ul><li>Genetic disorders of interest </li></ul><ul><ul><li>Autosomal recessive disorders </li></ul></ul><ul><ul><ul><li>Tay-sachs disease </li></ul></ul></ul><ul><ul><ul><ul><li>Jewish people in U.S. of central and eastern European descent </li></ul></ul></ul></ul><ul><ul><ul><ul><li>Lack of hexosaminidase A </li></ul></ul></ul></ul><ul><ul><ul><ul><ul><li>Glycosphingolipid stored in lysosomes </li></ul></ul></ul></ul></ul><ul><ul><ul><ul><ul><li>Build up in brain cells-loss of function </li></ul></ul></ul></ul></ul><ul><ul><ul><ul><li>Symptoms appear in infancy </li></ul></ul></ul></ul><ul><ul><ul><li>Cystic fibrosis </li></ul></ul></ul><ul><ul><ul><ul><li>Most common genetic disorder in Caucasians in U.S. </li></ul></ul></ul></ul><ul><ul><ul><ul><li>Defect in chloride channel proteins in cells </li></ul></ul></ul></ul><ul><ul><ul><ul><li>Thick, abnormal mucus production </li></ul></ul></ul></ul><ul><ul><ul><ul><ul><li>Lungs, bronchial tubes, pancreatic ducts affected </li></ul></ul></ul></ul></ul>Genetic Disorders
    117. 119. <ul><li>Autosomal recessive disorders cont’d. </li></ul><ul><ul><li>Phenylketonuria </li></ul></ul><ul><ul><ul><li>Lack enzyme for phenylalanine metabolism </li></ul></ul></ul><ul><ul><ul><li>Affects nervous system development </li></ul></ul></ul><ul><ul><li>Sickle-cell anemia </li></ul></ul><ul><ul><ul><li>Irregular red blood cells caused by abnormal hemoglobin </li></ul></ul></ul><ul><ul><ul><ul><li>Clog vessels- poor circulation </li></ul></ul></ul></ul><ul><ul><ul><ul><li>Internal hemorrhaging </li></ul></ul></ul></ul><ul><ul><ul><li>Heterozygous individuals are normal unless dehydrated or experience mild oxygen deprivation </li></ul></ul></ul>Genetic Disorders
    118. 120. <ul><li>Autosomal dominant disorders </li></ul><ul><ul><li>Marfan syndrome </li></ul></ul><ul><ul><ul><li>Defect in fibrillin-protein in elastic connective tissue </li></ul></ul></ul><ul><ul><ul><ul><li>Long limbs and fingers, weakened arteries, dislocated lenses in the eyes </li></ul></ul></ul></ul><ul><ul><li>Huntington disease </li></ul></ul><ul><ul><ul><li>Progressive degeneration of brain cells </li></ul></ul></ul><ul><ul><ul><li>Gene for defective protein called Huntington </li></ul></ul></ul><ul><ul><ul><ul><li>Too many copies of the amino acid glutamine </li></ul></ul></ul></ul>Genetic Disorders
    119. 121. <ul><li>X-linked recessive disorders </li></ul><ul><ul><li>Color blindness </li></ul></ul><ul><ul><ul><li>About 8% of Caucasian males have red-green colorblindness </li></ul></ul></ul><ul><ul><li>Duchene's muscular dystrophy </li></ul></ul><ul><ul><ul><li>Absence of a protein called dystrophin </li></ul></ul></ul><ul><ul><ul><ul><li>Causes calcium to leak into muscle cells which actives enzymes that break down the cells </li></ul></ul></ul></ul><ul><ul><li>Hemophilia </li></ul></ul><ul><ul><ul><li>Hemophilia A is due to a lack of clotting factor VIII </li></ul></ul></ul><ul><ul><ul><li>Hemophilia B is due to a lack of clotting factor IX </li></ul></ul></ul><ul><ul><ul><li>Blood clots slowly or not at all </li></ul></ul></ul>Genetic Disorders
    120. 122. Pedigrees

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