1. Inheritance of Single-Gene Differences I.Transmission genetics – link between meiosis & Mendel’s postulates II.Mendel: father of genetics A.Mendel’s Empirical approach B.Contrasting characters III.Monohybrid cross A.Mendel’s results B.Mendel’s First “law” equal segregation C.Punnent Square IV.Dihybrid cross A.Mendel’s Second “law” independent assortment B.Using the testcross

2. I. Transmission genetics – link between meiosis & Mendel’s postulates The transmission of discrete units (genes located on chromosomes) from parent to offspring Correlation between the behavior of chromosomes during meiosis and the transmission of traits

4. Terminology review Genes come in different forms = ALLELES Phenotype = expressed form of a character (what an individual looks like) Genotype = specific set of alleles carried by an individual (the actual genetic composition) Homozygous = the alleles of a gene are identical (AA) Heterozygous = the alleles of a gene are different (Aa) Dominant allele = an allele that expresses its phenotypic effect even when heterozygous… therefore AA and Aa have the same phenotype Recessive allele = An allele whose phenotypic effect is notexpressed in a heterozygote… therefore (a) can only be expressed when the individual is homozygous – (aa).

5. Genetic Crosses Self Cross = Haploid Cross = simplest, each gene present in 1 copy only (fungi) Diploid Cross = each gene present in 2 copies

6. II. Gregor Johann Mendel “Father of Genetics”

7. Mendel’s success Came up with an elegant model of experimental design –chose a good “model” organism: Pisum sativum –restricted his examination to one or very few pairs of contrasting traits in each experiment –took meticulous notes with accurate quantitative records

9. A. Mendel’s Empirical approach Mendel’s experiments were designed to determine the quantitative relationships from which laws could be discovered

10. B. Contrasting characteristics of the garden pea

11. III. Monohybrid cross Hybridization = when two plants of the same species but with different characteristics are crossed (mated) to each other. Mono = dealing with one pair of contrasting characteristics P – F1 – F2 –

12. A. Mendel’s results ParentalF1F2F2 ratio Round x wrinkledAll round 5474 round 1850 wrinkled 2.96:1 Yellow x green seedsAll yellow 6022 yellow 2001 green 3.01:1 Purple x whiteAll purple 705 purple 224 white 3.15:1 Inflated x pinchedAll inflated 882 inflated 229 pinched 2.95:1 Green x yellow podsAll green 428 green 152 yellow 2.82:1 Axial x terminalAll axial651 axial 207 terminal 3.14:1 Long x shortAll long787 long 277 short 2.84:1

13. Mendel’s explanation 1)the existence of “factors” – particulate theory of inheritance 2)genes are in pairs, 3)the principle of segregation, 4)gametic content – the F 2 3:1 ratio is based on a 1:1 segregation in a heterozygote 5)random fertilization – gametes are brought together for fertilization in a random manner

16. B. Mendel’s First Law Equal Segregation = The two members of a gene pair segregate from each other into the gametes; so half the gametes carry one member of the pair and the other half of the gametes carry the other member of the pair.

19. C. Using Punnett Squares in Genetic Crosses Punnett squares –Considers only genes of interest –List sperm genotypes across top –List egg genotypes down side –Fill in boxes with zygote genotypes

20. Pp Frequencies Phenotypes Genotypes Frequencies Making a Punnett Square: Heterozygous X Heterozygous Eggs of Heterozygous Plant Pollen of Heterozygous Plant 11 2 P p pP PpPP pp PPpppPPp

21. IV. Dihybrid Cross Follows the inheritance of two different traits within the same individual.

24. A. Mendel’s Second Law Independent Assortment = two different genes will randomly assort their alleles during gamete formation

26. F 1 cross: GgWw x GgWw

27. (Hair color) & (Hair length) Black/Brown Short/Long P: Black, short x Brown, long

30. B. Using the testcross

31. Pedigree Analysis

32. How do doctors know if a trait is inherited? They take a “family history”, and show it in a diagram form known as a pedigree

33. Pedigree Symbols

34. Example 1: Grandparents had two children: a son and a daughter. Their son had the trait in question. He marries a woman without the trait. One of the son’s four children (a boy) had the trait.

35. Example 2: Grandpa has the trait, grandma doesn’t. Of their five children, one son and two daughters have trait. One son and one daughter don’t have trait. One daughter with trait marries man without. Of their five kids, one son and one daughter have trait.

36. Can you tell from a pedigree if a trait is dominant or recessive?

37. Could this trait be dominant? If it’s dominant, the affected daughter would have to be either DD or Dd. If she’s DD or Dd, she would have had to get a dominant D allele from a parent. But, if were dominant and the parent had a D allele, the parent would have the trait, too. Therefore, trait is recessive, NOT dominant; daughter is dd

38. What are the genotypes? Parents don’t have the trait, so they can’t be dd. But, since they each passed a recessive d allele to daughter, they must each be Dd. Since the trait is recessive, daughter must be dd. dd Dd DD or Dd

39. Could this trait be dominant? If it’s dominant, the affected daughter would have to be either DD or Dd. If she’s DD or Dd, she would have had to get a dominant D allele from a parent. Dad has the trait, so he could have given her a D allele. So, trait is dominant.

40. What are the genotypes? Since the trait is dominant, mom can’t have a D, or she would show the trait. So, mom is dd. The son doesn’t have trait, so he must be dd, too. If son is dd, he got one d from mom; one from dad. Dad must be Dd; daughter is Dd. dd Dd dd