Friday 2/20/13 -notebook page 22

Genetics- Punnett Square Notes First…some vocab!

Vocab: Heredity- the passing of traits from parents to offspring Trait- physical characteristic that we see Gene- the section on a strand of DNA that has the code for a certain trait Allele-alternate forms of a gene for a single trait(dominant or recessive) Dominant- expressed allele (overpowers and covers up recessive allele, if present) Recessive- unexpressed allele (covered up by dominant gene)

Genotype- the genes of an organism; for one specific trait we use two letters to represent the genotype. Capital= dominant allele; lowercase= recessive allele. Phenotype- the physical appearance of a trait in an organism Homozygous- two same alleles (2 dominant or 2 recessive) Heterozygous- two different alleles

Tt QQ Ff rr Yy hh mm Ss GG PP Ll Bb dd Underline the following that are homozygous and circle the ones that are heterozygous: Tt QQ Ff rr Yy hh mm Ss GG PP Ll Bb dd

B= brown eyes b= blue eyes What would the genotype be for an individual who is heterozygous? ______ What would be the phenotype be for an individual who is heterozygous? _________   If a person has blue eyes, what must their genotype be? _______

Step-by-Step Punnett square review 1st. Draw your square Parental Cross: Tt x tt

2nd. Then place the parent’s genotypes on the outside 2nd. Then place the parent’s genotypes on the outside. Each allele goes next to its own box!!

3rd. Complete the square.

Genotypes (letters): Phenotypes (physical appearance): 4th. Summarize your results using percentages and ratios.

Practice Problem #1 1. An elephant with large ears (EE) is crossed with an elephant with small ears (ee). What are the expected offspring?

Practice Problem #2 2. A heterozygous white chicken, which is the dominant allele, is crossed with a red chicken (recessive). What is the probability of having a red chicken?

Practice Problem #3 3. A heterozygous dominant dog with black fur is crossed with another heterozygous black dog. The recessive allele results in brown fur color. What are the predicted offspring ratios?