Chapter 15 Chromosomes

Transcription

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 Development <2 months gestation embryo has rudimentary gonads

5 2 mos. SRY gene on Y chromosome active -> testes develop -> testosterone -> male If no SRY ovaries female SRY discovered in 1990 Y chromosome has ~78 genes

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7 Chromosome theory of inheritance Genes located on chromosomes = gene locus Thomas Morgan

8 Drosophila 2n = 8 3 prs autosomes X and Y sex chromosomes

9 Bithorax Wildtype White eye Wildtype = normal Mutant = abnormal Wingless eyeless

10 Drosophila genetics White eye allele = w Wildtype allele = w + on X chromosome Sex-linked gene! Genotype? ww, w + w w + w +

11 Sex-linked genes Cross a red female with a white male (pg. 288)

12 X w+ X w+ X X w Y Punnett square Cross f1 females with f1 males

13 f1 X w+ X w X X w+ Y f2

14 X-linked genes in humans Female genotypes Male genotypes X C X C X C X c X c X c X C Y X c Y 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?

15 No green photoreceptors

16 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.

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

18 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

19 Genes on this X are not expressed Lyon hypothesis Females mosaics for X-linked traits

20 X C X c Patches of colorblind cells in retina Normal phenotype Blue colorblindness is rare

21 Genotype of orange female? Genotype of black female? Genotype of orange male? Genotype of black male?

22 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)

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

24 Drosophila

25 Chromosomal abnormalities Disjunction anaphase of meiosis

26 If chromosome do not disjoin Non-disjunction Meiotic spindle error Gametes?

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28 Fertilization (human) Aneuploidy abnormal number of chromosomes

29 Nondisjunction anaphase I Nondisjunction anaphaseii Fertilization animation at Learn Genetics

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

31 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)

32 2. Trisomy (2n+1) Ex. Trisomy 21 (Down syndrome) 1/700 births Higher risk in women > 35 Abnormal meiosis

33 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.

34 Chromosome structure abnormalities 1. Deletion fragment lost 2. Duplication repeated fragment 3. Translocation fragment attaches to other chromosome 4. Inversion fragment inverts Univ. Wisc. Genetics center tumors

35 Chromosome 12 deletion along with an inversion (in the long arm) of chromosome 12 Chromosome 6p25.1 deletion and 7q21.13 duplication This is Hayes. He was born in July 2007 with a rare chromosome disorder Chromosome 13 deletion This is a story of Maya who has a chromosome abnormality. She has a gross motor delay in which she isn't walking or crawling 22q13 deletion syndrome Insulin treatment. The family of a little child born with a deletion of the 22q13 region of his chromosome 22 Chromosome 16 Deletion Ace's Story Chromosome 15q Duplication Syndrome - Cody's Poem

36 Inheritance of mitochondrial DNA and chloroplast DNA (plants) Extranuclear

37 Maternal inheritance (cytoplasm)

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