Bio 178 Lecture 26 Genetics

? Reading Quiz Material Chapters 13 & 14 Questions on P 276-278 & 300 Chapters 13 & 14 Quizzes on Text Website (www.mhhe.com/raven7)

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

Human Genetic Disorders Hemophilia Sickle Cell Anemia Huntington’s Disease

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 10-30 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.

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

Basal Ganglia of HD Patient Caudate Nucleus http://www.stanford.edu/group/hopes/causes/neuro/d3.html

Chromosomes & Genetics

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, 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.

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, 1910 - eye color in Drosophila. Read P 265-266.

Morgan’s Experiment - Sex Linkage

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.

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).

Sex Determination in Different Organisms

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

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)

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.

Klinefelter Syndrome http://www.carolguze.com/text/442-4-chromosome_abnormalities.shtml Klinefelter calico cat - evidence that Y chromosome determines maleness.

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

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.

Nondisjunction

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

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

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

Exam 4 to Here!