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Chapter 15 Chromosomes

Chapter 15 Chromosomes. The chromosomal basis of sex. In humans, Y chromosome determines sex XX X XY Gametes? p(son) p (daughter). Humans X/Y system. Chromosome theory of inheritance. Genes located on chromosomes = gene locus Thomas Morgan. X-linked genes in humans.

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Chapter 15 Chromosomes

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  1. Chapter 15 Chromosomes

  2. The chromosomal basis of sex In humans, Y chromosome determines sex XX X XY Gametes? p(son) p (daughter)

  3. Humans X/Y system

  4. Chromosome theory of inheritance • Genes located on chromosomes = gene locus • Thomas Morgan

  5. X-linked genes in humans Female genotypes Male genotypes XCXCXCXcXcXc XC Y XcY Terms: homozygous, heterozygous, hemizygous Concept check: • From whom do males obtain the Y chromosome? • From whom do females obtain the X chromosomes? • Why are X-linked disorders more prevalent in males?

  6. No green photoreceptors

  7. Example: colorblindness is X-linked • 1/1O males • A man is colorblind. What % of his sons and daughters are expected to be colorblind. His wife does not carry the colorblind allele on either X chromosome.

  8. X-chromosome inactivation in females • One X inactivated during embryonic development  Barr body (see nuclear envelope) • # in female cells? male cells?

  9. FYI • Barr body testing was introduced in the 1966 Olympic games, in an effort to detect male athletes trying to "pass" as females, to gain a competitive advantage .

  10. Genes on this X are not expressed • Lyon hypothesis • Females mosaics for X-linked traits

  11. XCXc • Patches of colorblind cells in retina • Normal phenotype Blue colorblindness is rare

  12. Genotype of orange female? • X-orange X-orange • Genotype of black female? • X-black X black Genotype of calico X-orange X-black • Genotype of orange male? X-orange Y • Genotype of black male? • X-black Y

  13. Linkage Unlinked genes -On different chromosomes -Independent assortment! Example in pea plants: color gene (Chromosome 1) shape gene (Chromosome 7) Example in humans: Blood type (Chromosome 9) Lactose intolerance (Chromosome 2)

  14. Linked Genes • -on same chromosome • -do not assort independently • Example humans: • Freckles (Chromosome 16) • Red hair (Chromosome 16)

  15. Drosophila

  16. Chromosomal abnormalities • Disjunction anaphase of meiosis

  17.  Fertilization (human) Aneuploidy – abnormal number of chromosomes

  18. Nondisjunction anaphase I • NondisjunctionanaphaseII • Fertilization animation at Learn Genetics

  19. 1. Monosomy (2n-1) Ex. Turner syndrome 45, X 1/5,000 births Only viable monosomy in humans

  20. Possible symptoms Short stature Lymphadema of the hands and feet Broad chest Low hairline Low-set ears Reproductive sterility Rudimentary ovaries gonadal streak absence of a menstrual period Increased weight, obesity Shield shaped thorax of heart Shortened hand bones Small fingernails Characteristic facial features Webbed neck Aorta abnormalities Poor breast development Horseshoe kidney Visual impairments Ear infections and hearing loss High waist-to-hip ratio (the hips are not much bigger than the waist) Attention Deficit/Hyperactivity Disorder Nonverbal Learning Disability (problems with math, social skills and spatial relations)

  21. 2. Trisomy (2n+1) Ex. Trisomy 21 (Down syndrome)

  22. Possible symptoms Common physical signs include: Excess skin at the nape of the neck Flattened nose Single crease in the palm of the hand Small ears Small mouth Upward slanting eyes Wide, short hands, short fingers White spots on eye Physical development is often slower than normal. Delayed mental and social development.

  23. Chromosome structure abnormalities • Deletion – fragment lost • Duplication – repeated fragment • Translocation – fragment attaches to other chromosome • Inversion – fragment inverts

  24. Inheritance of mitochondrial DNAand chloroplast DNA (plants) • Extranuclear

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