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Bio 178 Lecture 26 Genetics. Reading Chapters 13 & 14 Quiz Material Questions on P 276-278 & 300 Chapters 13 & 14 Quizzes on Text Website (

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Presentation on theme: "Bio 178 Lecture 26 Genetics. Reading Chapters 13 & 14 Quiz Material Questions on P 276-278 & 300 Chapters 13 & 14 Quizzes on Text Website ("— Presentation transcript:

1 Bio 178 Lecture 26 Genetics

2 Reading Chapters 13 & 14 Quiz Material Questions on P & 300 Chapters 13 & 14 Quizzes on Text Website (

3 Outline Genetics Human Genetics (cntd) Chromosomes and Genetics DNA  Experiments - DNA is hereditary material

4 Human Genetic Disorders Hemophilia Sickle Cell Anemia Huntington’s Disease

5 Dominantly Inherited Disorders - Huntington’s Disease The Disease Degenerative disease of the nervous system - progressive neural cell death caused by build up of the protein huntingtin (mutated form). No cure. Terminal years post-diagnosis. Cause Associated with a triplet (CAG) repeat in the gene for huntingtin. Genetics Lethal in heterozygotes. 50% chance of passing the disease to progeny.

6 Huntington’s Disease (Cntd.) Why does the allele persist? Late onset of disease - symptoms at 35 to 40 years old. _disease.htm /huntington.htm

7 Basal Ganglia of HD Patient Caudate Nucleus


9 Chromosomal Theory of Inheritance Walter Sutton, 1902 Pre-Sutton Chromosomes, 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, ) 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.

10 Chromosomal Theory of Inheritance (Cntd.) Sutton’s evidence (Cntd.) 2. Mendel’s Laws Chromosomes segregate and assort independently in meiosis. Response of the Scientific Community There are more genes than chromosomes! The Final Evidence Thomas Hunt Morgan, eye color in Drosophila. Read P

11 Morgan’s Experiment - Sex Linkage

12 Morgan’s Experiment - Sex Linkage (Cntd) Crossed the F 1 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.

13 Autosomes and Sex Chromosomes Autosomes Sex Chromosomes Principle 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).

14 Sex Determination in Different Organisms

15 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.

16 Nondisjunction The failure of homologues or sister chromatids to separate in meiosis  aneuploidy. Nondisjunction of Autosomes Effects are either fatal or severe. Down Syndrome (Trisomy 21)

17 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.

18 Klinefelter Syndrome chromosome_abnormalities.shtml Klinefelter calico cat - evidence that Y chromosome determines maleness.

19 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. chromosome_abnormalities.shtml

20 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.

21 Nondisjunction

22 Abnormal ity F Meiosis I F Meiosis II M Meiosis I M Meiosis II Trisomies75-95%5-25%0 45, X20%80% 3N~25%0-25% 4N

23 Nondisjunction Chromosome Abnormality Spontaneous Abortion (%) All50 Trisomy Trisomy 13, 18, XXX, XXY, XYY0.3 All other trisomies , X8.7 3N6.4 4N2.4 Structural Abnormalities2.0

24 Pedigree Example The above pedigree is for a rare kidney disease. Deduce the inheritance (autosomal, sex-linked, dominant, recessive).


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