Terminology
- True-Breeding
- Homozygous
- P
- Parental generation
- F1
- Offspring of P
- 1st generation.
- F2
- Offspring of F1
- Second generation.
Mendel
Only autosomal chromosomes
- Genotype
- 2 alleles
- 3 genotypes
- homozygous dominant / heterozygous, homozygous recessive
- Phenotype
- 2 alleles
- 2 phenotypes for dominant/recessive alleles.
- The expressed trait in an organism.
Dominance
- Complete Dominance
- Dominant allele completely masks the recessive allele.
Phenotypes
- Expressivity
- ?
- Penetrance
- ?
Different genotypes can produce the same phenotypes.
Punnet Squares
- Punnet Squares
- Shows gamete genotypes of parent genes.
Monohybrid Crosses
- Heterozygote X Heterozygote
- Genotypic ratio = 1:2:1 - 4 total
- Phenotypic ratio = 3:1 - 4 total
As a fraction, 3:1 reads 3/4 : 1/4, 4 total.
Multiply fractions by total number of offspring to find approx counts of each phenotype.
Can check if ratio matches up w/ pop by dividing pop # dominant by # recessive to find ratio amount pop.
Test Cross
Use a dominant hetero or homozygote and cross them with a homozygous recessive mate
- Tells if the parent is homozygous or heterozygous dominant trait.
- Homozygote Dominant
- Would show a 4:0 ratio.
- Heterozygote
- Would show a 2:2 ratio.
Reciprocal Crosses
- Is this gene on autosomal or sex chromosomes?
- Must switch male/female phenotypes in second cross.
- Cross 1
- Female white X male purple
- Cross 2
- Female purple X male white
Look at the offspring ratio of each cross
- Ratios are the same -> autosomal chromosome.
- Ratios are different -> Sex-linked chromosome.