1. Genetics

2. Evolution
• Starts with genes and cellular division
• Principle of segregation- pairs of genes are
evenly distributed between gametes (sex
cells) during gamete formation
• Allele-genes that determine expression of a
trait ( Dominant or recessive alleles)
• Phenotype-”what it looks like”
• Genotype-genetic makeup

3. • Homozygous- carries to “same” genes for a
trait (example: Dominant-BB or recessive –bb)
• Heterozygous: different genes Bb
• We use Punnett Squares to predict the results
of these crosses
• Phenotypic ratio: results of cross (example
3Dominant to 1 recessive ) (3:1)
• Genotypic ratio: results of cross according to
genes ( 1:2:1) (one homozygous dominant to 2
heterozygous to one homozygous recessive)

5. What is dominant? Recessive?
What is the phenotypic ratio?
Genotypic ratio?

6. Dihybrid cross
• Cross of 2 kinds of genes and 2 traits.
• 9:3:3:1 is ratio is typical phenotypic ratio for
this cross
• All gene combinations are possible
– b/c of independent assortment that happens in
meiosis