Patterns of Inheritance

1. aka Genetics Parents pass heritable traits to offspring (genes) Gregor Mendel 1860’s, Austrian monk experimented with garden peas tracked traits from parents to subsequent generations Patterns of Inheritance

2. Cross fertilization Pollen from one plant to fertilize another plant P = Parents F1 = 1st generation of offspring Hybrid (cross) = offspring of two different varieties e.g. purple vs. white flowers How?

3. Mendel tracked 7 characteristics Each had two distinct forms Controlled Started with pure varieties

4. Monohybrid cross Differs by one characteristic No blending (pink) What happened to the white? Showed up in F2

5. Mendel’s 4 hypotheses • Alternate versions of each gene = alleles (Purple or White) • Offspring inherit 2 alleles, 1 from each parent for each characteristic (color) • Homozygous = each allele is the same (PP or pp) • Heterozygous = different alleles (Pp) • Dominant = determines appearance, and Recessive = not apparent • Gametes (sperm or egg) carry only one allele as a result of pair separation during meiosis = Law of segregation

6. Pure parent plants • All purple (PP) • All white (pp) • Gametes will be either P or p • F1 are all purple because of dominance (Pp) • F2 results in a mathematically predictable 3:1 ratio • Phenotype = expressed traits • Genotype = genetic makeup • Punnett square • Hybrid posibilities

7. Alleles of a gene reside at the same locus on homologous chromosomes • Separated by independent assortment in meiosis…ultimately within separate gametes

8. Are they packaged together? Or, independently from one another? Seed characteristics (alleles) Round (R) or wrinkled (r) Yellow (Y) or green (y) Hypothesis: They are packaged together. What happens if there are 2 characteristics?

9. F1 produces equal amounts of 4 possible genotypes F2 reveals even more genotypic possibilities (9:3:3:1) Dihybrid cross is equivalent to two monohybrid crosses (12:4 or 3:1) Law of independent assortment Hypothesis: Each pair of alleles are independent of one another

10. Black coat is dominant (B) Chocolate coat is recessive (b) Normal vision (N) vs. blind (n) What are the results of a dihybrid cross of heterozygous parents (black, normal vision) ? *progressive retinal atrophy (PRA) causes blindness Phenotype of heterozygous parents? Genotype of heterozygous parents? Gamete possibilities Sperm? Eggs?

11. Black coat is dominant (B) Chocolate coat is recessive (b) Normal vision (N) vs. blind (n) What are the results of a dihybrid cross of heterozygous parents (black, normal vision) ? Phenotype of heterozygous parents? black, normal vision Genotype of heterozygous parents? BbNn x BbNn Gamete possibilities Sperm: BN, bN, Bn, bn Eggs: BN, bN, Bn, bn

12. Sperm: BN, bN, Bn, bn Eggs: BN, bN, Bn, bn What is the genotypic ratio of the offspring? What is the phenotypic ratio of the offspring? BN bN Bn bn BN bN Bn bn

13. Sperm: BN, bN, Bn, bn Eggs: BN, bN, Bn, bn 9 3 3 1 BN bN Bn bn BNBN BNbN BNBn BNbn BN bN bNBN bNbN bNBn bNbn Bn BnBN BnbN BnBn Bnbn bn bnBN bnbN bnBn bnbn

14. Can you know the genotype by looking at the phenotype? What are their genotype possibilities?

15. Can you know the genotype by looking at the phenotype? What are their genotype possibilities? bb BB or Bb

16. Perform a testcross to determine an unknown genotype Mate an unknown genotype (black lab) X homozygous recessive (chocolate lab) Testcross

17. Some examples of dominant and recessive traits in humans (at one gene locus)

18. Class total • Bent pinky – dominant (BB or Bb) • Blue eyes – recessive (ee) • No mid-digital hair – recessive (mm) • Tongue rolling – dominant (RR or Rr) • Widow’s Peak – dominant (WW or Ww) • Right over left Thumb – recessive (cc) • Attached ear lobes – recessive (aa) • Hitchhiker’s thumb – recessive (hh)

19. Can’t Testcross Pedigree – family tree of genetic history E.g. tracking deafness (dd) in an isolated family Since deafness appeared in F1 of grandparents…carriers Abigail? John? Hepzibah? How do we determine inheritance of human traits?

20. Recessive Albinism Cystic fibrosis Thick mucous excretion of lungs and other organs; requires life long treatment Sickle cell anemia Probability increases with less variability (inbreeding) Dominant Extra fingers, toes Webbed fingers, toes Dwarfism Normal body; short arms and legs DD die, Dd survive, non-dwarfs (99.99% pop.) are dd Dominant lethal disorders less common; usually kill embryo Other single gene disorders David Rappaport

21. Identifying disorders: • Amniocentesis is sampling of amniotic fluid • Chorionic villus sampling (CVS) of placental tissue • Ultrasound

22. Incomplete dominance E.g. snapdragons Heterozygotes differ from homozygotes Predictable 1:2:1 ratio Different than “blending” hypothesis No testcross necessary Traits that don’t conform to Mendel’s laws

23. More than two alleles per gene • 3 alleles in blood type – OAB • 4 possible phenotypes = O, A, B, AB • 6 possible genotypes; co-dominance

24. Rh factor = “+” and “-” along with O, B, A • Rhesus incompatibility disease • 30 combinations; much more complicated • “O-” was considered universal donor; but new research shows not always the case

25. Gene influences multiple characteristics Pleiotropy

26. Additive effects of multiple genes on a single phenotypic characteristic Polygenic Inheritance

27. X-linked recessive alleles More common in males than females Males only needs to inherit one sex-linked recessive allele from mom to be expressed Females has to inherit two sex-linked recessive alleles for expression Examples Red-green color blindness Hemophilia Sex-linked genes