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Heredity- Part 2

Heredity- Part 2

Author: Sam Youts

1. Identify the three types of genotypes and their corresponding phenotypes.

2. Construct a Punnett square to determine the possible genotypes and phenotypes of offspring.

The term HOMOZYGOUS describes a pair of alleles (or gene) where both of the alleles are the same.  Either they are both dominant or both recessive.  A homozygous pair would be written as either AA or aa.

The term HETEROZYGOUS  describes a pair of alleles that are different, with one being dominant and the other being recessive.  A heterozygous pair would be written as Aa.  Although one recessive allele is in the gene, the organism will express (show) the dominant form, because only one dominant allele is required for that form of the trait to show up.

A person's PHENOTYPE is the physical expression of a trait, or what they "look like."  The phenotype is determined by the genes, although we cannot see the genes.  For example, if a person has these genes for ear lobes:  LL   then that person will have loose ear lobes.  We say their PHENOTYPE is loose ear lobes.

The GENOTYPE is the actual alleles in a pair.  The genotype is written as a pair of letters, capitol or lower-case depending on if the alleles are dominant or recessive.  There are three possible combinations of alleles, so there are three possible genotypes:  AA, Aa, or aa.

A PUNNETT SQUARE is a grid used to determine all of the possible outcomes of a genetic cross using the alleles of two parents. 

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Use this video to complete the Heredity vocabulary, and bring it to class on Friday. We will use this information for our Punnett Square examples and our Punnett Races!

Source: Sam Youts