1. Bio 178 Lecture 26
Genetics

2. ? Reading Quiz Material Chapters 13 & 14 Questions on P 276-278 & 300
Chapters 13 & 14 Quizzes on Text Website (

3. Outline Genetics DNA Human Genetics (cntd) Chromosomes and Genetics
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.

7. Basal Ganglia of HD Patient
Caudate Nucleus

8. Chromosomes & Genetics

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 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.

13. Autosomes and 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 Nondisjunction of Autosomes
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
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.

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. Nondisjunction Abnormality F Meiosis I F Meiosis II M Meiosis I
M Meiosis II
Trisomies
75-95%
5-25%
45, X
20%
80% 3N
~25%
0-25% 4N

23. Chromosome Abnormality Spontaneous Abortion (%)
Nondisjunction
Chromosome Abnormality
Spontaneous 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

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

25. Exam 4 to Here!