Unit 6 Bio Test: Punnet Squares

Allele

A version of a gene

Codominant

A relationship where both alleles in a heterozygous genotype are fully expressed (e.g., AB blood type).

Dominant

An allele that is expressed in the phenotype even if only one copy is present (e.g., Aa or AA shows the A trait).

Incomplete dominant

A relationship where the heterozygous phenotype is a blend of the two alleles (e.g., red and white flowers producing pink offspring).

Recessive

An allele that is only expressed when two copies are present (e.g., aa).

Autosomal

A gene or trait located on a non-sex chromosome, meaning it affects individuals regardless of biological sex.

Chromatin

The form DNA takes when it is not undergoing cell division; DNA wrapped around histones. Loosely wrapped chromatin allows gene expression, while tightly wrapped chromatin prevents it.

Epigenetics

The study of changes in gene expression that do not alter the DNA sequence; gene activity can be influenced by environmental factors like diet, stress, and toxins.

Gene

A segment of DNA that contains instructions to make a protein.

Genotype

The genetic makeup of an organism (e.g., AA, Aa, or aa); it determines the phenotype.

Gregor Mendel

A scientist who studied inheritance in pea plants and published his findings in 1866, though they were not understood until 1900.

Heterozygous/heterozygote

Having two different alleles for a gene (e.g., Aa).

Histones

Proteins that DNA wraps around to form chromatin; they help regulate gene expression by controlling how tightly DNA is packed.

Homozygous/homozygote

Having two identical alleles for a gene (e.g., AA or aa).

Mendelian trait

a single gene determines the trait with dominant and recessive alleles.

Non-Mendelian trait

Includes incomplete dominance, codominance, multiple alleles (A B O blood), polygenic (influenced by ≥2 genes) traits, and environmental influences.

Phenotype

The physical expression of a genotype (e.g., brown eyes, tall plant). genotype + enviornment

Sex chromosomes

Chromosomes that determine biological sex; most individuals assigned male at birth have XY, and those assigned female at birth have XX