Download - Extra credit problem for Lecture #4
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Extra credit problem for Lecture #4
An agouti mouse is crossed to a white mouse and all the F1 offspring are agouti.
An F1 female is crossed to an F1 male, and the offspring are:
11 agouti: 5 white: 4 black
Q: Test the hypothesis that the original parental genotypes were BBCC and bbcc. Give the 2 value, the df, the P value, and state whether or not you reject the hypothesis.
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Cytogenetics: Chromosome Mutations, Aberrations &
Evolution
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Chromosomes
Prokaryote Eukaryote4.2 X 106 base pairs Has 1000x more DNADNA essentially naked DNA complexed w/ RNA & proteinmRNA translated as mRNA is transcribed in nucleus, it's transcribed translated in the cytoplasmmRNA is often polycistronic mRNA is almost never
polycistronic
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Eukaryotic chromosomes
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Metacentric Submetacentric Acrocentric
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Human karyotype
Homologous pair
Sex chromosomesautosomes
Sister chromatids
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Why do we care?
Many diseases and birth defects are a direct result of missing, broken, or extra chromosomes.
• Down Syndrome
• Cri du chat Syndrome
• Patau Syndrome
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Mutations at the level of the homologous pair
• EUPLOIDY: "true" ploidy, meaning two members of each homologous pair.
• ANEUPLOIDY: "not true" ploidy, meaning more or fewer members than two of each homologous pair.
• MONOSOMY - one homolog; partner is missing
• TRISOMY - three homologs• NULLISOMY- one entire homologous pair is
missing.
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Monosomy and Trisomy
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Down Syndrome
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How does it happen? Nondisjunction
Each chrom.has twochromatids
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Trisomy: Patau Syndrome
• 1/20,000 births
• severe mental retardation
• heart and organ defects
• polydactyly
• death by the age of one year
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Chromosomal Abnormalities Occurring in Human Fetuses
Type of Abnormality
% spontaneously abortedfetuses with the
abnormality
% fetuses with theabnormality thatsurvive to term
All abnormalities 50 5Autosomal Trisomies 16 7.5 0 13, 18, & 21 4.5 15 All others 13.8 0Trisomies of Sex chromosomesXXX, XXY, XYY 0.3 75Monosomy for X (XO) 8.7 1Structural Abnormalities 20 45
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Structural Changes
• Deletions (deficiencies)
• Duplications
• Inversions
• Translocations
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w
Psuedo-dominanceHomozygotes
lethal
Deletions (deficiencies)
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How can chromosomes break?
Ionizing radiation (production of free radicals, which act like little atomic "cannon balls", blasting through strands of DNA or c'somes.
Chemical insult.
Break points of chromosomes are highly reactive ("sticky"), whereas normal ends of c'somes are capped by telomeres, which do not readily bond to other molecules.
Why do they rejoin?
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• Breaks that occur before S phase will affect both newly formed chromatids, & all daughter cells arising from them.
• Breaks that occur when the chromosome is in dyad form may affect only one chromatid. (Thereafter, only the progeny carrying the broken chromatid will be affected.)
S Phase
Dyad
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Cri-du-chat Syndrome1/50,000 birthsDeletion short arm chrom 5Mental retardationSlow motor skill
developmentLow birth weight and slow
growthSmall head (microcephaly)Partial webbing of fingers or
toesWide-set eyes
(hypertelorism)High-pitched cry
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Structural Changes
• Deletions (deficiencies)
• Duplications
• Inversions
• Translocations
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Duplication is a source of new genes over evolutionary time:e.g., gene families like globins and MHC genes
Duplications
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Bar eye: caused by duplication
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Duplications: source of evolutionary novelty?
• Ribosomal DNA• Globins (alpha and
beta)• Homeobox genes
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Structural Changes
• Deletions (deficiencies)
• Duplications
• Inversions
• Translocations
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Inversions
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