Law of Segregation alleles separate monohybrid cross

1. Law of Segregation alleles separate monohybrid cross Law of Independent assortment allele pairs inherited independently dihybrid cross

2. Rules of Multiplication & Additions • Multiplication – likely that all events coincide • Addition – sum of all possibilities

3. Co-dominance • 2 alleles affect the phenotype in separate, distinguishable ways • ABOblood groups • 3 alleles (MULTIPLE ALLELES) • IA, IB, i • both IA & IB are dominant to i allele • IA & IB alleles are co-dominant to each other • determines presences of oligosaccharides on the surface of red blood cells

4. Polygenic inheritance • Some phenotypes determined by additive effects of 2 or more genes on a single character • phenotypes on a continuum • human traits • skin color • height • weight • eye color • intelligence • behaviors

5. Albinism Johnny & Edgar Winter albinoAfricans

6. Nature vs. nurture • Phenotype is controlled by both environment & genes Human skin color is influenced by both genetics & environmental conditions Coat color in arctic fox influenced by heat sensitive alleles Color of Hydrangea flowers is influenced by soil pH

7. Pleiotropy • Most genes are pleiotropic • one gene affects more than one phenotypic character • wide-ranging effects due to a single gene: • dwarfism (achondroplasia) • gigantism (acromegaly)

8. Acromegaly: André the Giant

9. Epistasis in Labrador retrievers • 2 genes: E & B • pigment (E) or no pigment (e) • how dark pigment will be: black (B) to brown(b)

10. Incomplete dominance • Heterozygotes show an intermediate phenotype • RR = red flowers • rr = white flowers • Rr = pink flowers • make 50% less color

11. Dihybrid heterozygous cross

12. It all started with a fly… • Chromosome theory of inheritance • experimental evidence from improved microscopy & animal breeding led us to a better understanding of chromosomes & genes beyond Mendel • Drosophila studies A. H. Sturtevant in the Drosophila stockroom at Columbia University

13. Thomas Hunt Morgan 1910 | 1933 • embryologist at Columbia University • 1st to associate a specific gene with a specific chromosome • Drosophila breeding • prolific • 2 week generations • 4 pairs of chromosomes • XX=female, XY=male

14. Morgan’s first mutant… • Wild type fly = red eyes • Morgan discovered a mutant white-eyed male • traced the gene for eye color to a specific chromosome

15. 75%red eye female 25%white eye male red eye female white eye male x x Discovery of sex linkage allred eye offspring How is this possible? Sex-linked trait!

16. Genes on sex chromosomes • Y chromosome • SRY: sex-determining region • master regulator for maleness • turns on genes for production of male hormones • pleiotropy! • X chromosome • other traits beyond sex determination • hemophilia • Duchenne muscular dystrophy • color-blind

17. XHXH XHXh XHXh XHXh XH XHY XHY XhY Xh male / sperm XH Y XHXH XHY XH XHY XH female / eggs Y Xh XhY XHXh Sex-linked traits sex-linked recessive Hh x HH

18. Sex-linked traits summary • X-linked • follow the X chromosomes • males get their X from their mother • trait is never passed from father to son • Y-linked • very few traits • only 26 genes • trait is only passed from father to son • females cannot inherit trait

19. Gene Recombination in Linked Genes • In contrast, linked genes, genes located on the same chromosome, tend to move together through meiosis and fertilization. • Under normal Mendelian genetic rules, we would not expect linked genes to recombine into assortments of alleles not found in the parents. • If the seed color and seed coat genes were linked, we would expect the F1 offspring to produce only two types of gametes, YR and yr when the tetrads separate. • One homologous chromosome from a P generation parent carries the Y and R alleles on the same chromosome and the other homologous chromosome from the other P parent carries the y and r alleles.

20. Recombination Frequency# RecombinantsTotal Recombinants = Offspring that vary from parent phenotype. Conclusions: Genes are linked, but not entirely due to crossing over during meiosis.

21. Mechanisms of inheritance • What causes dominance vs. recessive? • genes code for polypeptides • polypeptides are processed into proteins • proteins function as… • enzymes • structural proteins • hormones

22. Prevalence of dominance • Because an allele is dominant does not mean… • it is better • it is more common Polydactyly: dominant allele

23. Polydactyly individuals are born with extra fingers or toes dominant to the recessive allele for 5 digits recessive allele far more common than dominant  399 individuals out of 400 have only 5 digits  most people are homozygous recessive (aa)

24. Hound Dog Taylor

25. Other Genetic Diseases of Interest Blue People! Progeria

26. Chromosomal errors, I • Nondisjunction: members of a pair of homologous chromosomes do not separate properly during meiosis I or sister chromatids fail to separate during meiosis II • Aneuploidy: chromosome number is abnormal • Monosomy~ missing chromosome • Trisomy ~ extra chromosome (Down syndrome) • Polyploidy~ extra sets of chromosomes

27. Chromosomal Abnormalities Turners (XO) Kleinfelters (XXY) Down Syndrome Cri du Chat