developed by Biology Staff, Thurgood Marshall Academic High School,
Genetics: The study of inheritance.
Trait: A physical characteristic
we can describe.
Example 1: Pea shape is a trait.
Example 2: Eye color is a trait.
Gene: A particular sequence of DNA
located on a specific point on a chromosome, that tells a cell to produce
a specific protein.
Example 1: Gene for hair color.
Example 2: Gene for blood type.
Alleles: are a variation of a gene
and are located on chromosomes.
For the gene for eye color, one variation could be a brown allele, and
another variation could be a blue allele. Notice that each allele is located
on the same place on the chromosome (the location of the gene for eye
Example 1: For pea plant height H = tall plants or h
= short plants.
Example 2: For eye color E = brown eyes or e = blue
Dominant: an allele that is shown
even if it is present in only one copy.
Example: Being able to roll your tongue is dominant over not being
able to roll your tongue. If we chose the letter "T",
we could show it this way:
T = tongue roller, t = not being able to roll their tongue.
Recessive: An allele that is shown
ONLY if it is present in two copies.
Example: In the gene for eye color, the blue allele is recessive. A person
with blue eyes will have two blue alleles.
ee = blue eyes
Genotype: MUST be two alleles
that RESULT in a particular trait or disorder.
Example 1: Gene for pea plant height -- Genotypes could
be HH, or Hh, or hh
Example 2: Gene for eye color -- Genotypes could be EE,
or Ee, or ee