Terminology

Central Dogma

DNA -> RNA -> Proteins

Genes

DNA that makes proteins.

Genes never change location.

Allele

Variant of gene.

A collection of base pairs.

Base Pair

A,T,C,G's that make up a gene.

May change inside of a gene.

Changes the allele of the gene.

Law of Segregation

50% chance for each allele to be chosen.

Mono-Hybrid Crosses

A cross that follows the inheritance of 1 trait.

Trait

Characteristics of organisms.

Discrete

Either/or, no in-between.

Controlled by single genes.

True Breeding

Plants that always produce offspring identical to themselves.

A true-breeding plant is homozygous, has discrete genes.

Cross-Mating

Each parent passes on one allele.

Self-Crossing

Allele crosses with the same allele.

Generations

P Generation

Parental Generation

F1 First Filial

Offspring of P.

F2 Second Filial

Offspring of F1.

Law of Independent Assortment

Alleles for different traits separate independently. In a typical di-hybrid cross, the two genes are unrelated.

Mono-hybrid Cross 1 trait

Punnet square has 4 outcomes.

Di-hybrid Cross 2 traits

Punnet square has 16 outcomes.

Gametes get one allele from each gene, not both.

• Gametes are listed on the outside of the punnet square.

• RRyy × rrYY leads to gametes Ry, Ry, Ry, Ry × rY, rY, rY, rY.

Law of Dominance

How two genes interact with each other to determine the phenotype.

Dominance or recessiveness is not absolute.
One allele may be dominant some of the time and recessive if it shows with another allele.
Dominant just means it shoes up with 1 copy of the allele.

Dominance

Describes how alleles interact, not the frequency of which they are passed on.

Gene is functioning to produce a specific phenotype.

Think of alleles as two speakers, if either works, the sound will play.

Dominant Gene

Denoted by uppercase letters.

If exists, will express.

Recessive Gene

Denoted by lowercase letters.

Only expresses when the dominant trait is absent.

Types of Dominance

Complete Dominance

If it exists, it produces the pigment. Overrides the recessive allele.

Red producing allele always produces a red phenotype if it exists.

Incomplete Dominance

Phenotypes blend. Looks different from each parent.

Red and white producing alleles combine to make pink.

Co-Dominance

Both parent alleles show up.

Both red and white and simultaneously expressed. Spotted colors.

Punnet Squares

Multiplication tables for genetics. Shows combination %s.

Homozygous

Both alleles of the homologous gene pairs are the same.

Heterozygous

In the homologous gene pairs, there are two different alleles from each parent.

Genotype Ratio

The allele ratios from a punnet square.

YY, Yy, yY, yy is a 1:2:1 genotypic ratio.

Phenotype Ratio

The expressed trait ratios from a punnet square.

Y produces yellow, y produces green.
YY, Yy, yY, yy is a 3:1 yellow to green phenotypic ratio.

Y_

Underscore is wildcard, doesn't matter what allele.

Only needs one copy of big Y because it is dominant.