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10. patterns of inheritance

Bio Lecture ppt
Patterns of Inheritance

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10. patterns of inheritance

  1. 1. Patterns of Inheritance
  2. 2. Chromosome Review
  3. 3. Genetics • Study of the patterns of inheritance • Mendelian Genetics – Gregor Mendel – Pea plant experiments • Grow easily • Distinguishable characteristics – Round/Wrinkly, Yellow/Green, Tall/Short • Can control mating
  4. 4. Terminology • Allele—Alternate forms of a gene • Dominant Allele—trait that exerts its effects whenever present – Symbolized by capitol letter (B) – Ex. Dwarfism, Huntington’s disease • Recessive Allele—trait that is masked if a dominant trait is present – Symbolized by lower case letter (b) – Ex. Blue eyes
  5. 5. Terminology • Genotype—Genetic makeup of an organisms – Homozygous—2 alleles that are the same (BB or bb) – Heterozygous—2 different alleles (Bb) • Phenotype—Observable characteristics – Brown eyes, brown hair, tall, short • Generation—group of organisms born around the same time – P Generation—Parental – F1—offspring of parent, first filial generation – F2—1st generation of offspring
  6. 6. Genetic Terminology Term Definition Generations P First (parental) generation F1 children (Latin filii) of generation P F2 children of generation F1 Chromosomes and Genes chromosome macromolecules found in cells, consisting of DNA, protein and RNA gene the unit of heredity of a living organism locus specific location of a gene, DNA sequence, or position on a chromosome allele one of a number of alternative forms of the same gene or genetic locus Term Definition Dominant and recessive dominant allele an allele that is always expressed if present recessive allele an allele that is only expressed if the dominant allele is not present Genotypes and Phenotypes genotype the genetic makeup of a cell, an organism, or an individual homozygous contains two of the same allele of a gene heterozygous contains two different alleles of a gene phenotype an organism's observable characteristics or traits true breeding pure-bred, is an organism that always passes down a certain phenotypic trait to its offspring wild type most common phenotype in nature mutant physical or genetic difference from a mutation in a gene
  7. 7. Tracking Inheritance • Monohybrid Cross—Mating between individuals that are BOTH heterozygous • Dihybrid Cross—Mating between individuals that are heterozygous for 2 traits (genes) • Punnett Square—diagram showing genotypes in a monohybrid cross – Test cross—a Punnett square done to figure out the genotype of an unknown • Always use a homozygous recessive individual with unknown
  8. 8. Male parent Female parent Yy Yy Female gametes (1:1) Y y Y y YY Yy Yy yy Genotypic ratio 1:2:1 (1 YY: 2 Yy: 1 yy) Phenotypic ratio 3:1 (3 yellow: 1 green) Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Male gametes (1:1) Monohybrid Cross
  9. 9. If plant is homozygous dominant (YY): y y Y y Y Male gametes y Y y y Male gametes y YY Female gametes Yy Yellow seeds (Yy): 100% chance Yy Yy Yy yy If plant is heterozygous (Yy): Yy Female gametes Yellow seeds (Yy): 50% chance Green seeds (yy): 50% chance Yy yy Yy yy
  10. 10. Law of Segregation • Two alleles of each gene are packed into separate gametes – Alleles move apart during meiosis – Occurs during meiosis 1—Metaphase • Homologous chromosome move to opposite ends of poles
  11. 11. Law of Segregation Every individual contains a pair of alleles for each particular trait which segregate or separate during cell division (assuming diploidy) for any particular trait and that each parent passes a randomly selected copy (allele) to its offspring. Gametes will be paired randomly with gametes from the other parent.
  12. 12. Example 1. P generation 2. F1 generation 3. F2 generation
  13. 13. Genetics Problem The ability to curl your tongue up on the sides (T, tongue rolling) is dominant to not being able to roll your tongue. A woman who can roll her tongue marries a man who cannot. Their first child has his father’s phenotype. What are the genotypes of the mother, father, and child? What is the probability that their second child will be a tongue roller?
  14. 14. Law of Independent Assortment • The segregation of alleles of one gene does not influence the alleles for another gene – Alleles are RANDOMLY packaged in gametes • Since we have SO MANY genes, can’t keep doing punnett square. – Use Product Rule—The chance that 2 independent events will both occur = the product of individual chances that each event will occur
  15. 15. Product Rule
  16. 16. Law of Independant Assortment
  17. 17. Law of Independent Assortment and Dihybrid Crosses About 70% of Americans perceive a bitter taste from the chemical phenylthiocarbamide (PTC). The ability to taste this chemical results from a dominant allele (T) and not being able to taste PTC is the result of having two recessive alleles (t). Albinism is also a single locus trait with normal pigment being dominant (A) and the lack of pigment being recessive (a). A normally pigmented woman who cannot taste PTC has a father who is an albino taster. She marries a homozygous, normally pigmented man who is a taster but who has a mother that does not taste PTC. What percentage of the children will be albinos? What percentage of the children will be non-taster of PTC?
  18. 18. Recessive Disorders • Recessive Disorder— disorder is ONLY expressed when both alleles are recessive – Can be “carried” – Heterozygous individuals can carry gene but not express disease Dd Hearing carrier father Dd Hearing carrier mother D d D DD Hearing Dd Hearing (carrier) d Dd Hearing (carrier) dd Deaf
  19. 19. Recessive Disorders
  20. 20. Dominant Disorders • Dominant Disorder – Condition is expressed when an individual has at least one dominant allele Achondroplasia
  21. 21. Autosomal Disorders Disorder Likelihood Symptoms Recessive Disorders Albinism approximately 1 in 17,000 Most people with albinism appear white or very pale. Because individuals with albinism have skin that entirely lacks melanin, their skin can burn more easily from overexposure Galactosemia approximately 1 in 60,000 (Caucasians) In galactosemic patients, galactitol accumulates in body tissues. This can result in an enlarged liver, cirrhosis, renal failure, cataracts, brain damage, and ovarian failure. Without treatment, mortality in infants with galactosemia is about 75%. Phenylketonuria (PKU) approximately 1 in 15,000 (US) Abnormally high levels of phenylalanine accumulate in the blood and are toxic to the brain. Complications intellectual disability, brain function abnormalities, mood disorders, irregular motor functioning, and behavioral problems. Sickle-cell disease approximately 1 in 5,000 (US) Sickle-cell disease may lead to various acute and chronic complications, several of which have a high mortality rate. Sickle-cell anaemia can lead to various complications, including: increased risk of infection, stroke, and chronic pain. Tay–Sachs disease approximately 1 in 3,500 (Ashkenazi Jews) Tay–Sachs disease is typically first noticed in infants around 6 months old displaying an abnormally strong response to sudden noises or other stimulus, known as the “startle response.” There may also be listlessness or muscle stiffness (hypertonia). Dominant Disorders Alzheimer’s disease unknown dementia; memory loss and mental decay; not all cases are the result of genetics Huntington’s disease approximately 5–10 in 100,000 a neurodegenerative genetic disorder that affects muscle coordination and leads to cognitive decline and behavioral symptoms. It typically becomes noticeable in mid-adult life. Hypercholesterolemia unknown the presence of high levels of cholesterol in the blood; can lead to atherosclerosis and other heart problems; can be caused by genetics or lifestyle
  22. 22. Variations on Mendel’s Laws • Incomplete Dominance – Individual who is heterozygous show intermediated phenotype
  23. 23. Variations on Mendel’s Laws • Pleiotropy – One gene has many effects
  24. 24. Variations on Mendel’s Laws • Pleiotropy – One gene has many effects Sickle-cells can cause many problems in a person’s life, including organ damage, chronic illness, and pain.
  25. 25. Variations on Mendel’s Laws Polygenic Inheritance—Many genes control one phenotype
  26. 26. Variations on Mendel’s Laws Polygenic Inheritance—Many genes control one phenotype Read more here: oi/10.1371/journal.pbio.0000069
  27. 27. Sex Linked Genes • Sex Determination – Female – XX – Male - XY
  28. 28. Sex Linked Genes • Can be carried on either X or Y chromosome – More common on X chromosome • Affect more males than females Female Male XAXa XAY
  29. 29. Sex Chromosomes and Sex Linked Genes • Eye color in fruit flies
  30. 30. X-Linked Disorders Disorder Genetics Characteristics X-Linked Recessive Inheritance Duchenne muscular dystrophy mutation in the dystrophin gene early life muscle degeneration and eventual death Fragile X syndrome expansion of the CGG trinucleotide repeat on the X chromosome most widespread single-gene cause of autism and inherited cause of intellectual disability, especially among boys Hemophilia A mutant allele; ~70% of the time it is an X-linked recessive trait, but ~30% of cases arise from mutations deficiency in clotting factor VIII, which causes increased bleeding and usually affects males Red–green color blindness absence or mutation of the genes for red or green color receptors difficulty with discriminating red and green hues Rett syndrome mutations in the gene MECP2 located on the X chromosome typically have no verbal skills, and about 50% of individuals affected do not walk. Scoliosis, growth failure, and constipation are very common and can be problematic. X-Linked Dominant Inheritance Hypertrichosis unknown abnormal amount of hair growth over the body X-linked hypophosphatemia mutation in the PHEX gene sequence (Xp.22) and subsequent inactivity of the PHEX protein It can cause bone deformity including short stature and genu varum (bow leggedness). Retinitis pigmentosa (some forms) unknown degenerative eye disease that causes severe vision impairment and often blindness