1 Mendelelian Genetics

2 Gregor Mendel ( ) Austrian monkAustrian monk Studied the inheritance of traits in pea plantsStudied the inheritance of traits in pea plants Developed the laws of inheritanceDeveloped the laws of inheritance

3 Site of Gregor Mendel’s experimental garden in the Czech Republic

4

5

6 Mendel Performed “crosses” on different pea plants: Parents: Yellow Seeds X Green Seeds F1 : All offspring had yellow seeds

7 Parents: X F1 : X F2 : 3: 1

8 Generation “Gap” Parental P 1 Generation = the parental generation F 1 generation = the first-generation F 2 generation = the second-generation

9  Mendel found plants were able to pass on traits  He said these physical traits are inherited as “factors”  Mendel’s “factors” are actually genes Inheritance

10 What we know now: Genes code for traits We have two copies of each gene – because we have two copies of each chromosome

11 Genetics Terms  Gene – codes for a trait (tallness)  Alleles - forms of a gene:  Dominant – “stronger” of two alleles; always expressed;(T)  Recessive - allele that shows only if dominant is NOT there; (t)  Dominant MASKS the recessive

12  Homozygous – SAME alleles (TT or tt); also called pure  Homozygous – SAME alleles (TT or tt); also called pure  Heterozygous DIFFERENT alleles (Tt); also called hybrid

13 More Terminology  Genotype – what GENE is there (e.g. TT, Tt, tt)  Phenotype - the PHysical feature (e.g. tall, short)

14 Genotype & Phenotype in Flowers Genotype of alleles: T = tall plant t = short plant GenotypesTT Tttt Phenotypestall tall short

15 Punnett Square Used to predict outcomes of genetic crosses

16 Genetic Practice Problems

17 Breed the P 1 generation tall (TT) x dwarf (tt) pea plants t t TT

18 Solution: t t TT Tt All Tt = tall (heterozygous tall) produces the F 1 generation tall (TT) vs. dwarf (tt) pea plants

19 Breed the F 1 generation tall (Tt) vs. tall (Tt) pea plants T t Tt

20 Solution: TT Tt tt T t Tt F 2 generation 1/4 (25%) = TT 1/2 (50%) = Tt 1/4 (25%) = tt 1:2:1 genotype 3:1 phenotype 3:1 phenotype tall (Tt) x tall (Tt) pea plants

21 Monohybrid Crosses

22 Trait: Seed Shape Alleles: R – Roundr – Wrinkled Cross: Round seeds x Wrinkled seeds RR x rr P 1 Monohybrid Cross R R rr Rr Genotype:Rr Genotype: Rr PhenotypeRound Phenotype: Round Genotypic Ratio:All alike Genotypic Ratio: All alike Phenotypic Ratio: All alike

23 P 1 Monohybrid Cross Review  Homozygous dominant x Homozygous recessive  Offspring all Heterozygous (hybrids)  Offspring called F 1 generation  Genotypic & Phenotypic ratio is ALL ALIKE

24 Trait: Seed Shape Alleles: R – Roundr – Wrinkled Cross: Round seeds x Round seeds Rr x Rr F 1 Monohybrid Cross R r rR RR rrRr Genotype:RR, Rr, rr Genotype: RR, Rr, rr PhenotypeRound & wrinkled Phenotype: Round & wrinkled G.Ratio:1:2:1 G.Ratio: 1:2:1 P.Ratio: 3:1

25 F 1 Monohybrid Cross Review  Heterozygous x heterozygous  Offspring: 25% Homozygous dominant RR 50% Heterozygous Rr 25% Homozygous Recessive rr  Offspring called F 2 generation  Genotypic ratio is 1:2:1  Phenotypic Ratio is 3:1

26 Mendel’s Laws

27 Law of Dominance Some alleles are dominant and other alleles are recessive. (T or t) An organism with at least one dominant allele for a trait will always have that trait. (TT, Tt) Recessive traits are only seen in homozygous recessive organisms. (tt)

28 Law of Segregation During the formation of gametes (eggs or sperm), the two alleles responsible for a trait separate from each other: Tt can make two gametes: T gamete T gamete t gamete t gamete

29 Applying the Law of Segregation

30 Law of Independent Assortment Alleles for different traits are distributed to gametes independently of one another. This law can be illustrated using dihybrid crosses.

31 Dihybrid Cross Traits: Seed shape & Seed color Alleles: Alleles: R round Y yellow r wrinkledy green What gametes are possible in an individual that is heterozygous for both traits?

32 Dihybrid Cross Traits: Seed shape & Seed color Alleles: Alleles: R round Y yellow r wrinkledy green RrYy x RrYy RY Ry rY ry All possible gamete combinations

33 Dihybrid Cross RYRyrYry RYRy rY ry

34 Dihybrid Cross RRYY RRYy RrYY RrYy RRYy RRyy RrYy Rryy RrYY RrYy rrYy RrYy Rryy rrYy rryy Round/Yellow: 9 Round/green: 3 wrinkled/Yellow: 3 wrinkled/green: 1 9:3:3:1 phenotypic ratio RYRyrYryRY Ry rY ry

35 Dihybrid Cross Round/Yellow: 9 Round/green: 3 wrinkled/Yellow: 3 wrinkled/green: 1 9:3:3:1

36 Incomplete Dominance and Codominance

37 Incomplete Dominance F1 hybrids in betweenphenotypes F1 hybrids have an appearance somewhat in between the phenotypes of the two parental varieties. Example:snapdragons (flower) Example: snapdragons (flower) RR = red flower WW = white flower RW = pink Cross a red x white on your 1 st box

38 Incomplete Dominance RWRWRWRW W WRR All RW = pink (heterozygous pink) produces the F 1 generation

39 Now cross two pink snapdragons on your paper.

40 Codominance Two alleles are expressed at same time Example: blood type has 3 alleles: A, B, O (this is called MULTIPLE alleles)

41 Codominance 3 alleles: A, B, O 1.type A= AA or AO (_______) 2.type B= BB or BO (____) 3.type AB= AB (codominant) 4.type O= OO (______)

42 Codominance Problem Example:Example: male Type O (OO) x female type AB AOBO AOBO 1/2 = I A i 1/2 = I B i O AB O

43 Sex-linked Traits Traits (genes) located on the sex chromosomes – mostly X chromosome

44 Sex-linked Traits Sex Chromosomes XX chromosome - femaleXy chromosome - male fruit fly eye color Example: Eye color in fruit flies

45 Sex-linked Trait Problem Example: Eye color in fruit flies Cross a (red-eyed male) x (white-eyed female)

46 Sex-linked Trait Problem (red-eyed male) x (white-eyed female) X R Y x X r X r. XrXr XRXR y XrXr

47 Sex-linked Trait Solution: X R X r X r y 50% red eyed female 50% white eyed male XrXr XRXR y XrXr

48 Female Carriers

49 Polygenic Traits Most traits have more than one gene involved Example: height in humans