Mendelian Genetics Chapter 10.2

Gregor Mendel Made the first discoveries in genetics Studied basic traits of Pea pod plants Pea pods are true breeders – always produced offspring with the same trait. Developed Mendel’s laws

Inheritance of traits When Mendel crossed plants with different traits he expected them to blend. Instead all offspring had the trait of one parent.

F1 and F2 Generations P – Cross green And yellow peas F1 – all yellow. Self fertilization - Cross F1 with F1 F2 – mostly yellow Some green

Seven traits Mendel studied Seven characters For all traits he found That one trait was Dominant over the Other trait.

Mendel’s Conclusions Inheritance – factors are passed on from generation to generation These factors are called genes Allele – Different forms of a gene

Mendel’s Conclusions 2) The Principle of Dominance: Some alleles are dominant and some are recessive Dominant covers recessive Recessive only shows if there is no Dominant allele

Mendel’s Conclusions 3) There are two alleles for each gene Genotype - the two alleles (Yy) Phenotype – the observable trait (yellow) Dominant alleles are written as a Capital letter (Y) Recessive alleles are written as a lower case letter (y)

Genotypes and phenotypes Homozygous Dominant (YY) – shows dominant trait (yellow) Homozygous Recessive (yy) –shows recessive trait (green) Heterozygous (Yy) – shows dominant trait (yellow)

Mendel’s conclusions 4) Law of segregation – the two alleles for each character separate during meiosis

Monohybrid cross Hybrid = heterozygote (Yy) Monohybrid cross – cross between two individuals that have different alleles for one gene. Example: Yy X Yy

Punnett squares Predict the possible offspring of a cross between two known genotypes.

Punnett Square rules A. Divide the parent genotype in half (meiosis) B. Put the genotype of each HAPLOID cell along top and left edge of square C. Combine sperm and egg in each box of square D. Capital Letters first, same letters go together

Monohybrid cross Example 2 parents - heterozygous genotypes Purple flower is the dominant trait X

Genotype of each haploid DAD MOM

B= dominant (purple) b= recessive (white) Phenotype 3:1 ratio

Punnett Square practice. Use R = red and r = white flowers 1)Homozygous dominant mom and heterozygous dad 2)Heterozygous mom and homozygous recessive dad 3) True breeding red mom and white dad

Can you cross more than one allele in a punnett square? Dihybrid cross - Cross two organisms that differ in two traits.

Dihybrid cross R- round r – wrinkled Y – Yellow y- green

Law of independent assortment There is a random assortment of alleles that occurs during gamete formation. 4 possible combinations of gametes Genotype – YyRr Gametes: YR, Yr, yR, yr

4 different phenotypes Phenotypic ratio 9:3:3:1 9 different genotypes

Practice Dihybrid Cross S – short tail s – long tail B – Brown b – white Cross SsBb X SsBb