Genetic Crosses Chapter 9: Section 2

5 Minute warm up Describe how Mendel artificially cross pollinated pea plants and how he prevented self fertilization. – Use correct anatomical terminology of pea plants – E.g. Stamen, Pistil Use a half sheet of paper Complete Sentences – Can use notes from last class period – Work alone

Particulate Inheritance  Mendel stated that physical traits are inherited as “particles”  Mendel did not know that the “particles” were actually Chromosomes & DNA

Types of Genetic Crosses  Monohybrid cross - cross involving a single trait e.g. flower color  Dihybrid cross - cross involving two traits e.g. flower color & plant height

Punnett Square Used to help solve genetics problems Used to help solve genetics problems

More Terminology  Genotype - gene combination for a trait (e.g. RR, Rr, rr)  Phenotype - the physical feature resulting from a genotype (e.g. red, white, fire breathing, non-fire)

Genotype & Phenotype in Flowers Genotype of alleles: R = red flower r = yellow flower Genotype of alleles: R = red flower r = yellow flower Genes occur in pairs, so 2 alleles affect a characteristic Genes occur in pairs, so 2 alleles affect a characteristic Possible combinations are: Possible combinations are: GenotypesRR Rrrr PhenotypesRED RED YELLOW

Genotypes  Homozygous genotype - gene combination involving 2 dominant or 2 recessive genes (e.g. RR or rr); also called pure- breeding/true-breeding  Homozygous genotype - gene combination involving 2 dominant or 2 recessive genes (e.g. RR or rr); also called pure- breeding/true-breeding  Heterozygous genotype - gene combination of one dominant & one recessive allele (e.g. Rr); also called hybrid  What generation was composed of all hybrid plants in Mendel’s experiment?

Monohybrid Crosses Crosses

11 Trait: Seed Shape Trait: Seed Shape Alleles: R – Roundr – Wrinkled Alleles: R – Roundr – Wrinkled Cross: Round seeds x Wrinkled seeds Cross: Round seeds x Wrinkled seeds RR x rr 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

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

13 Trait: Seed Shape Trait: Seed Shape Alleles: R – Roundr – Wrinkled Alleles: R – Roundr – Wrinkled Cross: Round seeds x Round seeds Cross: Round seeds x Round seeds Rr x Rr 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

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

…And Now the Test Cross In peas both TT and Tt result in a tall plant In peas both TT and Tt result in a tall plant How could you tell if a tall plant is Homozygous (TT) or Heterozygous (Tt)? How could you tell if a tall plant is Homozygous (TT) or Heterozygous (Tt)? Testcross – an individual of unknown genotype is crossed with a homozygous recessive individual to determine it’s genotype Testcross – an individual of unknown genotype is crossed with a homozygous recessive individual to determine it’s genotype

16 Trait: Seed Shape Trait: Seed Shape Alleles: R – Roundr – Wrinkled Alleles: R – Roundr – Wrinkled Cross: Wrinkled seeds x Round seeds (unknown genotype) Cross: Wrinkled seeds x Round seeds (unknown genotype) rr x RR rr x RR F 2 Testcross (1st) r r RR Rr Genotype:Rr Genotype: Rr PhenotypeAll Round Phenotype: All Round G. Ratio:All Alike G. Ratio: All Alike P.Ratio: All Alike

17 Trait: Seed Shape Trait: Seed Shape Alleles: R – Roundr – Wrinkled Alleles: R – Roundr – Wrinkled Cross: Wrinkled seeds x Round seeds (unknown genotype) Cross: Wrinkled seeds x Round seeds (unknown genotype) rr x Rr rr x Rr F 2 Testcross (2nd) r r rR Rr rrRr rr Genotype:Rr, rr Genotype: Rr, rr PhenotypeRound, Wrinkled Phenotype: Round, Wrinkled G. Ratio:1:1 G. Ratio: 1:1 P.Ratio: 1:1

Bottom Line Offsping all dominant phenotype (Tall, Purple) tested individual = Homozygous dominant (TT,PP) Offspring ½ dominant, ½ recessive phenotype (Tall/Short, Purple/White) tested individual = Heterozygous dominant (Tt,Pp)