Dominance Allele = Alternative version of gene Dominant allele P Recessive allele p Each individual inherits 2 alleles/gene GenotypePhenotype? PP homozygous dominant pp homozygous recessive P p heterozygous
Dominant allele masks expression of recessive allele Find the dominant allele Pick symbols What is the phenotype of plant with genotype Rr? What is genotype of a green plant?
Segregation The 2 alleles segregate in gametes during meiosis Random segregation Human chromosome 11 gene for beta globin Genotype Hbb/Hbb Pea chromosome 1 Genotype of plant? Phenotype of plant?
Mendel did not know about: – DNA/chromosomes/genes – Crossing over or the cell cycle – Linked alleles
In mice, black fur is dominant over white fur Cross heterozygous mouse with homozygous recessive mouse Possibilities?
In mice, black fur is dominant over white fur Cross heterozygous mouse with homozygous recessive mouse 1.Make an allele key 2.Show the cross 3. Write the phenotypes under the genotypes 4. Determine the parental gametes (random segregation) 5. Add to Punnett square 6. Determine offspring
Punnett square What is the expected ratio of phenotypes? Genotypes? In a litter of 3, how many are expected to be white? Which phenotype is the recessive phenotype?
In cats striping is dominant over non-stripes. Mate two heterozygous cats.
The Scottish fold is a dominant trait Genotypes FF Ff ff Phenotypes? The original Scottish Fold was a white barn cat named Susie, found in Scotland
Test cross Scottish fold cat -> Is she Ff or FF? If FF, then cross to ff kittens? If Ff, then cross to ff kittens? A test cross is always a cross to a homozygous individual.
Review All possible one gene crosses B = black fur allele b = white fur allele BB X BB all black BB X Bb BB X bb Bb X Bb Bb X bb bb X bb all white
Independent Assortment 2 genes Y = yellow pea allele R = round pea allele y = green pea alleler = wrinkled Phenotypes of peas
True-breeding yellow, round X true-breeding green, wrinkled Allele key? P Genotype? Gametes? (always 4 per parent in 2 gene cross) X R = round allele Y = yellow r = wrinkled y = green rryy RRYY RY and ry
Parental generation: RRYY X rryy Gametes ? F1 generation? Gametes of F1 generation? F2 generation?
F2 generation Ratio of genotypes? Ratio of phenotypes?
Extensions of Mendel Codominance Both alleles expressed in phenotype Ex. Blood type I gene Alleles I A I B Phenotype of I A I B ?
multiple alleles Ex. blood type Alleles I A I B i I A I A I B I B I A I B I A i I B iii