When we study genetics, we examine the following genetic entities (from most complex to least complex)Chromosome: A long,

continuous thread of DNA that consists of numerous genes and regulatory information

Gene: A piece of DNA that provides a set of instructions to a cell to make a certain protein.

Allele: Variation of a gene for a particular trait

Remember Mendel’s Findings Mendel found that even though two

traits can be present in an organism, some traits “masked” others.

A dominant trait is one that “masks” another and is expressed

A recessive trait is one can be “masked” be another trait and is only expressed when a copy of the trait is present

Genotypes and PhenotypesAlleles are represented using letters. We usually choose a letter corresponding to the dominant trait. For example, if we are looking at eye color, we can compare both green and brown eyes. If brown is the dominant trait, we will represent the brown allele with an uppercase B. If green is recessive, we will represent the green allele with a lowercase b.

We call the combination of alleles an organism’s Genotype (the letters). Using the above example, the here are the possible genotypes for eye color: BB, Bb, bb

We call an organism’s observable characteristic due to its allele pairs it’s Phenotype. Using the above example, here are the possible phenotypes for eye color: Brown eyes, Green eyes.

A closer look at Dominance and Recessiveness

Each organism has two alleles for a trait. One allele comes from the organism’s mother and the other allele comes from an organism’s father. Organisms can be homozygous (have two of the same alleles), also known as purebred, for a trait or be heterozygous (have two different alleles) for a trait.

Father Father BB BB Mother Mother

Example: Brown Eyes (B) and Green eyes (b)Homozygous Dominant: BBHomozygous Recessive: bbHeterozygous: Bb

Lets Practice Allele Notation!A certain species of parrot is known to have two body color variations. The dominant variation is red. The recessive variation is yellow. Write all possible genotypes for the parrot. State what phenotype will go with which genotype.

African elephants are known for their large ears, while Indian elephants are known for their small ears. The dominant condition in elephants is small ears and the recessive condition is large ears. Write all possible genotypes for the elephant. State what phenotype will go with which genotype.

Different ways that genes can affect organisms

EpistasisPolygenic Traits:

When one gene interferes with the expression of another gene.

Example: Albinism in mice is

caused by one gene blocking four other genes

Traits produced by two or more traits.Examples: Eye color is controlled by 3 genesSkin color is controlled by 4 genes

Can the environment affect genotypes and phenotypes?

Example of Genotype Example of Phenotype

Sea turtles lay their eggs in the sand. Eggs that mature in warmer temperatures develop into female turtles. Eggs that mature in cooler temperatures develop into male turtles.

Identical twin studies have shown that twins raised in the same environment are more similar than those raised in separate environments. Also, twins raised with different treatments may show different physical features.