Chromsomal Theory: GeneticsCytology 1860 = Mendel’s theories of heredity 1875 = cytologists work out mitosis 1890 = cytologists work out meiosis 1900 = Correns, DeVries and von Seysenegg rediscover Mendel’s work

1902 = Sutton and Bovari notice parallels between Mendel’s theories and the behavior of chromosomes Thomas Hunt Morgan: starts doing experiments with Drosophila melanogaster

3 pairs of autosomes 1 pair of sex chromosomes

Wild Type = normal and most frequently observed phenotype Mutant Type = phenotypes that are alternatives to the wild type w = white eye allele w+ = wild type/red eye allele

Eye Color: located on the X- chromosome = sex linked P: w+w+ x w 100% w+w (all red eye) Linked Genes = located on the same chromosome and tend to be inherited together; do not assort independently

Unlinked Genes = show independent assortment YyRr x yyrr 25% YyRr 25% yyrr 25% yyRr 25% Yyrr 50% parental types 50% recombinants

Parental type = same phenotype as one of the parents Recombinants = a phenotype that differs from either parent 50% recombination or better means genes assort randomly UNLINKED

If recombinants are less than 50%, genes are probably linked. Recombination frequency = % of crossing over Recombination Frequency = recombinants total offspring x 100

* Probability of crossing over is directly proportional to the distance between the genes. 1 map unit (centimorgan) = 1% recombination frequency

Sex Chromosomes: heterogametic sex homogametic sex Sex Linked Traits: usually X-linked traits hemophilia color blindness Duchenne’s muscular dystrophy

Pedigree for Color Blindness:

X-Inactivation in Females: Lyon Hypothesis Barr Bodies

Chromosomal Alterations: Nondisjunction Aneuploidy Polyploidy Alterations of Chromosome Structure Breakage Duplication Translocation Inversion

Results of Chromosomal Alteration: 1. General Down’s syndrome = trisomy 21 Patau syndrome = trisomy 13 Edward’s syndrome = trisomy In Males Klinefelter syndrome Extra Y

3. In Females Metafemales Turner syndrome 4. Deletions Cri du chat syndrome 5. Translocations chronic myelogenous leukemia (CML)

6. Parental Imprinting Prader-Willi syndrome Angelman syndrome 7. Genomic Imprinting 8. Fragile X Syndrome 9. Uniparental Disomy

Exceptions to Chromosomal Theory of Inheritance: Extranuclear genes Plants