The Punnett Square Approach and Probability Studying Heredity The Punnett Square Approach and Probability

Will individuals with different genotypes have different phenotypes? Maybe? Genotype: T T Phenotype: Tall Genotype: T t Phenotype: Tall Can individuals with different phenotypes have the same genotype? No? Phenotype: Tall Genotype: TT or Tt Phenotype: Short Genotype: tt

Punnett Squares In the early 1900s, Dr. Reginald Punnett developed a square to predict possible offspring of a cross between two known genotypes. Punnett squares are useful for keeping track in a cross.

P1 Monohybrid Cross r r Rr Rr R R Rr Rr Trait: Seed Shape Alleles: R – Round r – Wrinkled Cross: Round seeds x Wrinkled seeds RR x rr r r Genotype: Phenotype: Genotypic Ratio: Phenotypic Ratio: Rr Round All alike All Round Rr Rr R R Rr Rr

P1 Monohybrid Cross Review Homozygous dominant x Homozygous recessive Offspring all Heterozygous (hybrids) Offspring called F1 generation Genotypic & Phenotypic ratio is ALL ALIKE

F1 Monohybrid Cross R r RR Rr R r Rr rr Trait: Seed Shape Alleles: R – Round r – Wrinkled Cross: Round seeds x Round seeds Rr x Rr R r Genotype: Phenotype: G. Ratio: P. Ratio: RR, Rr, rr Round & wrinkled 1:2:1 3:1 RR Rr R r Rr rr

F1 Monohybrid Cross Review Heterozygous x heterozygous Offspring: 25% Homozygous dominant RR 50% Heterozygous Rr 25% Homozygous Recessive rr Offspring called F2 generation Genotypic ratio is 1:2:1 Phenotypic Ratio is 3:1

F2 Monohybrid Cross (1st) Trait: Seed Shape Alleles: R – Round r – Wrinkled Cross: Round seeds x Round seeds RR x Rr R r Genotype: Phenotype: G. Ratio: P. Ratio: RR, Rr, Round 100% Round RR Rr R R RR Rr

F2 Monohybrid Cross (2nd) Trait: Seed Shape Alleles: R – Round r – Wrinkled Cross: Round seeds x Wrinkled seeds Rr x rr r r Genotype: Phenotype: G. Ratio: P. Ratio: RR, Rr, Round & Wrinkled 1:1 Rr Rr R r rr rr

F2 Monohybrid Cross Review Homozygous x heterozygous(hybrid) Offspring: 50% Homozygous RR or rr 50% Heterozygous Rr Phenotypic Ratio is 1:1 Called Test Cross because the offspring have SAME genotype as parents

Did You Learn Anything

See if you can determine the parental genotypes based on the offspring in the Punnett square below. ? ? ? Bb Bb ? bb bb

In Mendel’s original experiment with purple and white pea flowers, why are only purple flowers seen in the F1 generation, but both purple and white flowers found in the next (F2) generation? P1 F1 F2 &

The trait that disappears Complete the Bridge Map below The observed trait Dominant Recessive The trait that disappears

The way an organism looks Complete the Bridge Map below The way an organism looks Phenotype Genotype Allele Combination

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