bio 178 lecture 26
DESCRIPTION
Bio 178 Lecture 26. Genetics. Reading. Chapters 13 & 14. ?. Quiz Material. Questions on P 276-278 & 300 Chapters 13 & 14 Quizzes on Text Website (www.mhhe.com/raven7). Outline. Genetics Human Genetics (cntd) Chromosomes and Genetics DNA - PowerPoint PPT PresentationTRANSCRIPT
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Bio 178 Lecture 26Genetics
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Reading
• Chapters 13 & 14
Quiz Material
• Questions on P 276-278 & 300
• Chapters 13 & 14 Quizzes on Text Website (www.mhhe.com/raven7)
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Outline
• Genetics
Human Genetics (cntd)
Chromosomes and Genetics
• DNA
Experiments - DNA is hereditary material
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Human Genetic Disorders
• Hemophilia
• Sickle Cell Anemia
• Huntington’s Disease
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Dominantly Inherited Disorders - Huntington’s Disease
• The DiseaseDegenerative disease of the nervous system - progressive neural cell death caused by build up of the protein huntingtin (mutated form).
No cure. Terminal 10-30 years post-diagnosis.
• CauseAssociated with a triplet (CAG) repeat in the gene for huntingtin.
• GeneticsLethal in heterozygotes.
50% chance of passing the disease to progeny.
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Huntington’s Disease (Cntd.)• Why does the allele persist?
Late onset of disease - symptoms at 35 to 40 years old.
http://www.thesahara.net/huntingtons_disease.htm
http://www.genephile.com.tw/Tests/huntington.htm
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Basal Ganglia of HD Patient
http://www.stanford.edu/group/hopes/causes/neuro/d3.html
Caudate Nucleus
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Chromosomal Theory of InheritanceWalter Sutton, 1902
• Pre-SuttonChromosomes, centrioles, and mitochondria all divide and segregate in meiosis.Which of these structures are responsible for heredity (follow Mendel’s rules)?
• Sutton’s Evidence (Sutton, 1877-1916)1. Gametes
(a) Must have equal hereditary contributions - sperm contain little cytoplasm, but do have nuclei. Hereditary material probably in the nucleus.
(b) Somatic cells have 2 homologous chromosomes, but gametes have only 1. Consistent with Mendel’s model.
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Chromosomal Theory of Inheritance (Cntd.)• Sutton’s evidence (Cntd.)2. Mendel’s Laws
Chromosomes segregate and assort independently in meiosis.
• Response of the Scientific CommunityThere are more genes than chromosomes!
• The Final EvidenceThomas Hunt Morgan, 1910 - eye color in Drosophila.
Read P 265-266.
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Morgan’s Experiment - Sex Linkage
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Morgan’s Experiment - Sex Linkage (Cntd)
• Crossed the F1 females with the male parent.
• What ratio would you predict?
• Obtained a 1:1:1:1
Segregation of white eyed trait had a 1:1 correspondence with segregation of the X chromosome Mendel’s observation of segregation of alternate traits reflected chromosome behavior.
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Autosomes and Sex Chromosomes• Autosomes
• Sex ChromosomesPrinciple function - sex determination.
• Which sex determines progeny sex (human)?
• Features of the Y Chromosome (human)Carries 78 active genes, including a sex-determining gene (SRY).
• Sex Linked Genes
Any gene (does not have to be involved with sex) that is carried on the sex chromosomes (usually on X).
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Sex Determination in Different Organisms
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Barr Body 1 X chromosome in each female somatic cell is inactivated early in development female cells produce the same amount of protein from the X as do male cells.
http://www.carolguze.com/text/442-4-chromosome_abnormalities.shtml
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NondisjunctionThe failure of homologues or sister chromatids to separate in meiosis aneuploidy.
• Nondisjunction of Autosomes
Effects are either fatal or severe.
Down Syndrome (Trisomy 21)
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Nondisjunction (Cntd.)• Nondisjunction of Sex Chromosomes
Generally, the effects are not as severe as nondisjunction of autosomes.
1. X Chromosome
(a) Triple X Syndrome
Usually taller than average females, generally “normal” and most are *fertile.
(b) Klinefelter Syndrome
XX + Y XXY
Sterile male with female characteristics and sometimes mildly impaired intelligence.
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Klinefelter Syndrome
http://www.carolguze.com/text/442-4-chromosome_abnormalities.shtml
Klinefelter calico cat - evidence that Y chromosome determines maleness.
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Nondisjunction of Sex Chromosomes (Cntd.)
(c) Turner Syndrome (Monosomy X)
X + O XO
Short females with edema (resulting in webbed neck) that are almost always sterile.
http://www.carolguze.com/text/442-4-chromosome_abnormalities.shtml
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Nondisjunction of Sex Chromosomes (Cntd.)
(d) OY
O (egg) + Y OY
Lethal - genes on the X chromosome are necessary for survival.
2. Y Chromosome
X + YY (sperm) XYY
Tall, fertile males.
Genetic Counseling
Read P 274.
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Nondisjunction
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Nondisjunction
Abnormality
F Meiosis I
F Meiosis II
M Meiosis I
M Meiosis II
Trisomies 75-95% 5-25% 0
45, X 20% 80%
3N ~25% 0-25%
4N
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Nondisjunction
Chromosome AbnormalitySpontaneous Abortion (%)
All 50
Trisomy 16 7.5
Trisomy 13, 18, 21 4.5
XXX, XXY, XYY 0.3
All other trisomies 13.8
45, X 8.7
3N 6.4
4N 2.4
Structural Abnormalities 2.0
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Pedigree Example
The above pedigree is for a rare kidney disease. Deduce the inheritance (autosomal, sex-linked, dominant, recessive).
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