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  • Figure 12.2 ( a ) Punnett-square diagram showing the sex determination pattern in humans. ( b ) An early human embryo appears neither male nor female. Then tiny ducts and other structures that can develop into male or female reproductive organs start forming. In an XX embryo, ovaries form in the absence of the Y chromosome and its SRY gene. In an XY embryo, the gene product triggers formation of testes, which secrete a hormone that initiates development of other male traits. ( c ) External reproductive organs in human embryos.
  • Figure 12.2 ( a ) Punnett-square diagram showing the sex determination pattern in humans. ( b ) An early human embryo appears neither male nor female. Then tiny ducts and other structures that can develop into male or female reproductive organs start forming. In an XX embryo, ovaries form in the absence of the Y chromosome and its SRY gene. In an XY embryo, the gene product triggers formation of testes, which secrete a hormone that initiates development of other male traits. ( c ) External reproductive organs in human embryos.
  • Figure 12.2 ( a ) Punnett-square diagram showing the sex determination pattern in humans. ( b ) An early human embryo appears neither male nor female. Then tiny ducts and other structures that can develop into male or female reproductive organs start forming. In an XX embryo, ovaries form in the absence of the Y chromosome and its SRY gene. In an XY embryo, the gene product triggers formation of testes, which secrete a hormone that initiates development of other male traits. ( c ) External reproductive organs in human embryos.
  • Figure 12.3 Karyotyping, a diagnostic tool that reveals an image of a single cell’s diploid complement of chromosomes. This human karyotype shows 22 pairs of autosomes and a pair of X chromosomes. Figure It Out: Was this cell taken from a male or female? Answer: Female
  • Figure 12.3 Karyotyping, a diagnostic tool that reveals an image of a single cell’s diploid complement of chromosomes. This human karyotype shows 22 pairs of autosomes and a pair of X chromosomes. Figure It Out: Was this cell taken from a male or female? Answer: Female
  • Figure 12.4 ( a ) Example of autosomal dominant inheritance. A dominant allele ( red ) is fully expressed in heterozygotes. Achondroplasia, an autosomal dominant disorder, affects the three men shown above. At center, Verne Troyer (Mini Me in the Mike Myers spy movies), stands two feet, eight inches tall. ( b ) An autosomal recessive pattern. In this example, both parents are heterozygous carriers of the recessive allele ( red ).
  • Figure 12.4 ( a ) Example of autosomal dominant inheritance. A dominant allele ( red ) is fully expressed in heterozygotes. Achondroplasia, an autosomal dominant disorder, affects the three men shown above. At center, Verne Troyer (Mini Me in the Mike Myers spy movies), stands two feet, eight inches tall. ( b ) An autosomal recessive pattern. In this example, both parents are heterozygous carriers of the recessive allele ( red ).
  • Figure 12.9 Left, what red–green color blindness means, using ripe red cherries on a green-leafed tree as an example. In this case, the perception of blues and yellows is normal, but the affected individual has difficulty distinguishing red from green. Right , two of many Ishihara plates, which are standardized tests for different forms of color blindness. ( a ) You may have one form of red–green color blindness if you see the numeral 7 instead of 29 in this circle. ( b ) You may have another form if you see a 3 instead of an 8.
  • Figure 12.9 Left, what red–green color blindness means, using ripe red cherries on a green-leafed tree as an example. In this case, the perception of blues and yellows is normal, but the affected individual has difficulty distinguishing red from green. Right , two of many Ishihara plates, which are standardized tests for different forms of color blindness. ( a ) You may have one form of red–green color blindness if you see the numeral 7 instead of 29 in this circle. ( b ) You may have another form if you see a 3 instead of an 8.
  • Figure 12.9 Left, what red–green color blindness means, using ripe red cherries on a green-leafed tree as an example. In this case, the perception of blues and yellows is normal, but the affected individual has difficulty distinguishing red from green. Right , two of many Ishihara plates, which are standardized tests for different forms of color blindness. ( a ) You may have one form of red–green color blindness if you see the numeral 7 instead of 29 in this circle. ( b ) You may have another form if you see a 3 instead of an 8.
  • Figure 12.9 Left, what red–green color blindness means, using ripe red cherries on a green-leafed tree as an example. In this case, the perception of blues and yellows is normal, but the affected individual has difficulty distinguishing red from green. Right , two of many Ishihara plates, which are standardized tests for different forms of color blindness. ( a ) You may have one form of red–green color blindness if you see the numeral 7 instead of 29 in this circle. ( b ) You may have another form if you see a 3 instead of an 8.
  • Figure 12.10 Cri-du - chat syndrome. ( a ) This infant’s ears are low relative to his eyes. ( b ) Same boy, four years later. The high-pitched monotone of cri-du-chat children may persist into their adulthood.
  • Figure 12.10 Cri-du - chat syndrome. ( a ) This infant’s ears are low relative to his eyes. ( b ) Same boy, four years later. The high-pitched monotone of cri-du-chat children may persist into their adulthood.
  • Figure 12.11 Banding patterns of human chromosome 2 ( a ), compared with two chimpanzee chromosomes ( b ). Bands appear because different regions of the chromosomes take up stain differently.
  • Figure 12.12 Evolution of the Y chromosome. Mya stands for million years ago.
  • Figure 12.13 ( a ) A case of nondisjunction. This karyotype reveals the trisomic 21 condition of a human female. ( b ) One example of how nondisjunction arises. Of the two pairs of homologous chromosomes shown here, one fails to separate during anaphase I of meiosis. The chromosome number is altered in the gametes that form after meiosis.
  • Figure 12.13 ( a ) A case of nondisjunction. This karyotype reveals the trisomic 21 condition of a human female. ( b ) One example of how nondisjunction arises. Of the two pairs of homologous chromosomes shown here, one fails to separate during anaphase I of meiosis. The chromosome number is altered in the gametes that form after meiosis.
  • Figure 12.14 Relationship between the frequency of Down syndrome and mother’s age at childbirth. The data are from a study of 1,119 affected children. The risk of having a trisomic 21 baby rises with the mother’s age. About 80 percent of trisomic 21 individuals are born to women under thirty-five, but these women have the highest fertility rates, and they have more babies.
  • Figure 12.14 Relationship between the frequency of Down syndrome and mother’s age at childbirth. The data are from a study of 1,119 affected children. The risk of having a trisomic 21 baby rises with the mother’s age. About 80 percent of trisomic 21 individuals are born to women under thirty-five, but these women have the highest fertility rates, and they have more babies.

Transcript

  • 1. Chromosomes andHuman Inheritance Chapter 12
  • 2. Impacts, Issues:Strange Genes, Tortured Minds Exceptional creativity often accompanies neurobiological disorders such as schizophrenia, autism, chronic depression, and bipolar disorder • Examples: Lincoln, Woolf, and Picasso
  • 3. 12.1 Human Chromosomes In humans, two sex chromosomes are the basis of sex – human males have XY sex chromosomes, females have XX All other human chromosomes are autosomes – chromosomes that are the same in males and females
  • 4. Sex Determination in Humans Sex of a child is determined by the father • Eggs have an X chromosome; sperm have X or Y
  • 5. Sex Determination in Humans The SRY gene on the Y chromosome is the master gene for male sex determination • Triggers formation of testes, which produce the male sex hormone (testosterone) • Without testosterone, ovaries develop and produce female sex hormones (estrogens)
  • 6. Sexual Development in Humans
  • 7. diploid diploid germ cells germ cells in female in malemeiosis, gameteformation in both eggs spermfemale and male: X × Y X × Xfertilization: X X X XX XX Y XY XY sex chromosome combinations possible in the new individual Fig. 12-2a, p. 186
  • 8. Fig. 12-2bc, p. 186
  • 9. At seven weeks, appearance of At seven weeks, appearance “uncommitted” duct system of of structures that will give embryo rise to external genitaliaY chromosome Y chromosome Y chromosome Y chromosome present absent present absent testes ovaries 10 weeks 10 weeks ovary penis vaginal opening uterus penis vagina testis birth approaching b c Fig. 12-2bc, p. 186
  • 10. Animation: Human sex determination
  • 11. Karyotyping Karyotype • A micrograph of all metaphase chromosomes in a cell, arranged in pairs by size, shape, and length • Detects abnormal chromosome numbers and some structural abnormalities Construction of a karyotype • Colchicine stops dividing cells at metaphase • Chromosomes are separated, stained, photographed, and digitally rearranged
  • 12. Karyotyping
  • 13. Fig. 12-3a, p. 187
  • 14. Fig. 12-3b, p. 187
  • 15. Animation: Karyotype preparation
  • 16. 12.1 Key ConceptsAutosomes and Sex Chromosomes All animals have pairs of autosomes – chromosomes that are identical in length, shape, and which genes they carry Sexually reproducing species also have a pair of sex chromosomes; the members of this pair differ between males and females
  • 17. 12.2 Autosomal Inheritance Patterns Many human traits can be traced to autosomal dominant or recessive alleles that are inherited in Mendelian patterns Some of those alleles cause genetic disorders
  • 18. Autosomal Dominant Inheritance A dominant autosomal allele is expressed in homozygotes and heterozygotes • Tends to appear in every generation • With one homozygous recessive and one heterozygous parent, children have a 50% chance of inheriting and displaying the trait • Examples: achondroplasia, Huntington’s disease
  • 19. Autosomal Recessive Inheritance Autosomal recessive alleles are expressed only in homozygotes; heterozygotes are carriers and do not have the trait • A child of two carriers has a 25% chance of expressing the trait • Example: galactosemia
  • 20. Autosomal Inheritance
  • 21. Fig. 12-4a, p. 188
  • 22. Fig. 12-4b, p. 188
  • 23. Animation: Autosomal dominantinheritance
  • 24. Animation: Autosomal recessiveinheritance
  • 25. Galactosemia
  • 26. Neurobiological Disorders Most neurobiological disorders do not follow simple patterns of Mendelian inheritance • Depression, schizophrenia, bipolar disorders Multiple genes and environmental factors contribute to NBDs
  • 27. 12.3 Too Young to be Old Progeria • Genetic disorder that results in accelerated aging • Caused by spontaneous mutations in autosomes
  • 28. 12.2-12.3 Key ConceptsAutosomal Inheritance Many genes on autosomes are expressed in Mendelian patterns of simple dominance Some dominant or recessive alleles result in genetic disorders
  • 29. 12.4 Examples of X-Linked Inheritance X chromosome alleles give rise to phenotypes that reflect Mendelian patterns of inheritance Mutated alleles on the X chromosome cause or contribute to over 300 genetic disorders
  • 30. X-Linked Inheritance Patterns More males than females have X-linked recessive genetic disorders • Males have only one X chromosome and can express a single recessive allele • A female heterozygote has two X chromosomes and may not show symptoms Males transmit an X only to their daughters, not to their sons
  • 31. X-Linked Recessive Inheritance Patterns
  • 32. Animation: X-linked inheritance
  • 33. Some X-Linked Recessive Disorders Hemophilia A • Bleeding caused by lack of blood-clotting protein Red-green color blindness • Inability to distinguish certain colors caused by altered photoreceptors in the eyes Duchenne muscular dystrophy • Degeneration of muscles caused by lack of the structural protein dystrophin
  • 34. Hemophilia A in Descendentsof Queen Victoria of England
  • 35. Red-Green Color Blindness
  • 36. Fig. 12-9a, p. 191
  • 37. Fig. 12-9b, p. 191
  • 38. Fig. 12-9c, p. 191
  • 39. Fig. 12-9d, p. 191
  • 40. 12.4 Key ConceptsSex-Linked Inheritance Some traits are affected by genes on the X chromosome Inheritance patterns of such traits differ in males and females
  • 41. 12.5 Heritable Changesin Chromosome Structure On rare occasions, a chromosome’s structure changes; such changes are usually harmful or lethal, rarely neutral or beneficial A segment of a chromosome may be duplicated, deleted, inverted, or translocated
  • 42. Duplication DNA sequences are repeated two or more times; may be caused by unequal crossovers in prophase I
  • 43. normalchromosomeone segmentrepeated p. 192
  • 44. Deletion Loss of some portion of a chromosome; usually causes serious or lethal disorders • Example: Cri-du-chat
  • 45. segment C deleted p. 192
  • 46. Deletion: Cri-du-chat
  • 47. Fig. 12-10a, p. 192
  • 48. Fig. 12-10b, p. 192
  • 49. Inversion Part of the sequence of DNA becomes oriented in the reverse direction, with no molecular loss
  • 50. segmentsG, H, Ibecomeinverted p. 192
  • 51. Translocation Typically, two broken chromosomes exchange parts (reciprocal translocation)
  • 52. chromosome nonhomologous chromosomereciprocal translocation p. 192
  • 53. Does Chromosome Structure Evolve? Changes in chromosome structure can reduce fertility in heterozygotes; but accumulation of multiple changes in homozygotes may result in new species Certain duplications may allow one copy of a gene to mutate while the other carries out its original function
  • 54. Differences AmongClosely Related Organisms Humans have 23 pairs of chromosomes; chimpanzees, gorillas, and orangutans have 24 • Two chromosomes fused end-to-end
  • 55. human chimpanzee gorilla orangutan Fig. 12-11, p. 193
  • 56. Evolution of X and Y Chromosomesfrom Homologous Autosomes
  • 57. Ancestral reptiles Ancestral reptiles Monotremes Marsupials Monkeys Humans (autosome pair) Y X Y X Y X Y X Y X areas that can cross over areas that SRY cannot cross overA Before 350 B SRY gene C By 320–240 mya, the D Three more times, 170–130 mya,mya, sex was evolves 350 mya. two chromosomes have the pair stops crossing over indetermined by Other mutations diverged so much that another region. Each time, moretemperature, not accumulate and they no longer cross changes accumulate, and the Yby chromosome the chromosomes over in one region. The chromosome gets shorter. Today, tdifferences. of the pair diverge. Y chromosome begins he pair crosses over only at a small to degenerate. region near the ends. Fig. 12-12, p. 193
  • 58. 12.6 Heritable Changes inthe Chromosome Number Occasionally, new individuals end up with the wrong chromosome number • Consequences range from minor to lethal Aneuploidy • Too many or too few copies of one chromosome Polyploidy • Three or more copies of each chromosome
  • 59. Nondisjunction Changes in chromosome number can be caused by nondisjunction, when a pair of chromosomes fails to separate properly during mitosis or meiosis Affects the chromosome number at fertilization • Monosomy (n-1 gamete) • Trisomy (n+1 gamete)
  • 60. Nondisjunction
  • 61. Autosomal Change and Down Syndrome Only trisomy 21 (Down syndrome) allows survival to adulthood • Characteristics include physical appearance, mental impairment, and heart defects Incidence of nondisjunction increases with maternal age Can be detected through prenatal diagnosis
  • 62. Trisomy 21
  • 63. n+1 n+1 n−1 n−1chromosome CHROMOSOMEalignments at NONDISJUNCTION alignments at NUMBER metaphase I AT ANAPHASE I metaphase II anaphase II IN GAMETES Fig. 12-13b, p. 194
  • 64. n+1 n+1 n−1 n−1chromosome CHROMOSOMEalignments at NONDISJUNCTION alignments at NUMBER metaphase I AT ANAPHASE I metaphase II anaphase II IN GAMETES Stepped Art Fig. 12-13b, p. 194
  • 65. Down Syndrome and Maternal Age
  • 66. Fig. 12-14a, p. 195
  • 67. Fig. 12-14b, p. 195
  • 68. Change in Sex Chromosome Number Changes in sex chromosome number may impair learning or motor skills, or be undetected Female sex chromosome abnormalities • Turner syndrome (XO) • XXX syndrome (three or more X chromosomes) Male sex chromosome abnormalities • Klinefelter syndrome (XXY) • XYY syndrome
  • 69. Turner Syndrome XO (one unpaired X chromosome) • Usually caused by nondisjunction in the father • Results in females with undeveloped ovaries
  • 70. 12.5-12.6 Key Concepts: Changes inChromosome Structure or Number On rare occasions, a chromosome may undergo a large-scale, permanent change in its structure, or the number of autosomes or sex chromosomes may change In humans, such changes usually result in a genetic disorder
  • 71. 12.7 Human Genetic Analysis Charting genetic connections with pedigrees reveals inheritance patterns for certain alleles Pedigree • A standardized chart of genetic connections • Used to determine the probability that future offspring will be affected by a genetic abnormality or disorder
  • 72. Studying Inheritance in Humans Genetic studies can reveal inheritance patterns or clues to past events • Example: A link between a Y chromosome and Genghis Khan?
  • 73. Defining Genetic Disordersand Abnormalities Genetic abnormality • A rare or uncommon version of a trait; not inherently life threatening Genetic disorder • An inherited condition that causes mild to severe medical problems, characterized by a specific set of symptoms (a syndrome)
  • 74. Some Human Genetic Disordersand Genetic Abnormalities
  • 75. Stepped ArtTable 12-1, p. 196
  • 76. Recurring Genetic Disorders Mutations that cause genetic disorders are rare and put their bearers at risk Such mutations survive in populations for several reasons • Reintroduction by new mutations • Recessive alleles are masked in heterozygotes • Heterozygotes may have an advantage in a specific environment
  • 77. A Pedigree for Huntington’s Disease A progressive degeneration of the nervous system caused by an autosomal dominant allele
  • 78. Constructing a Pedigree for Polydactyly
  • 79. Animation: Pedigree diagrams
  • 80. 12.8 Prospects in Human Genetics Genetic analysis can provide parents with information about their future children Genetic counseling • Starts with parental genotypes, pedigrees, and genetic testing for known disorders • Information is used to predict the probability of having a child with a genetic disorder
  • 81. Prenatal Diagnosis Tests done on an embryo or fetus before birth to screen for sex or genetic problems • Involves risks to mother and fetus Three types of prenatal diagnosis • Amniocentesis • Chorionic villus sampling (CVS) • Fetoscopy
  • 82. Amniocentesis
  • 83. Animation: Amniocentesis
  • 84. Fetoscopy
  • 85. Preimplantation Diagnosis Used in in-vitro fertilization • An undifferentiated cell is removed from the early embryo and examined before implantation
  • 86. After Preimplantation Diagnosis When a severe problem is diagnosed, some parents choose an induced abortion In some cases, surgery, prescription drugs, hormone replacement therapy, or dietary controls can minimize or eliminate symptoms of a genetic disorder • Example: PKU can be managed with dietary restrictions
  • 87. Genetic Screening Genetic screening (widespread, routine testing for alleles associated with genetic disorders) • Provides information on reproductive risks • Identifies family members with a genetic disorder • Used to screen newborns for certain disorders • Used to estimate the prevalence of harmful alleles in a population
  • 88. 12.7-12.8 Key ConceptsHuman Genetic Analysis Various analytical and diagnostic procedures often reveal genetic disorders What an individual, and society at large, should do with the information raises ethical questions
  • 89. Animation: Deletion
  • 90. Animation: Duplication
  • 91. Animation: Inversion
  • 92. Animation: Morgan’s reciprocal crosses
  • 93. Animation: Translocation
  • 94. Video: Strange genes, richly torturedminds