Mendelian Genetics

Using Punnett Squares Tool used to predict genetic traits in offspring Can determine phenotypes and genotypes Can be written as percents (75%), fractions(3/4), or ratios (3:1) Monohybrid Cross A cross involving a single trait.

Using Punnett Squares Remember Alleles are represented by letters dominant alleles are represented with a capital letter recessive alleles are represented by a lowercase letter

YOUR TURN ! Describe what a trait is and indicate where it is found. What is the difference between a genotype and phenotype?

Example 1: Your turn A homozygous green fish is crossed with a homozygous yellow fish. If all of the offspring turn out green, what is the genotype of the yellow fish and green fish? What would the genotype be for the offspring?

Example 1: parents Homozygous Green Fish Genotype = GG Homozygous Yellow Fish Genotype = gg

Example 1: offspring Heterozgous Green Fish Genotype = Gg

Example 1: g g G Gg Gg G Gg Gg How to use a Punnett Square to support your predictions on genetic crosses: GG x gg Put the parents’ genotype around the outside. Combine the alleles. Each box represents the percentage of offspring that could result with that genotype. g g G Gg Gg G Gg Gg 100% of the offspring will be heterozygous green.

Example 2: Your turn Cross 2 of the offspring from the 1st generation. Gg x Gg

Example 2 Solution: G g Phenotypes: G GG Gg g Gg gg 75% of the offspring will be green. 25% of the offspring will be yellow. G GG Gg g Gg gg

Testcross Used to test an individual whose phenotype for a trait is dominant, but whose genotype is not known Cross it with an individual whose genotype is homozygous recessive Ex. GG x gg or Gg x gg