Genetics

Definitions:
Trait - Characteristic

Gene - Segment of DNA controlling a trait

Alleles - Different forms of a gene

“Flower color” is a gene

“Purple” & “White” are alleles


Lessons
Traits are controlled by gene pairs

Pairs separate during meiosis ⇒

Law of Segregation

Each gamete has only one allele

Law of Independent Assortment

Which allele gets into which gamete is random

Dominant allele masks recessive allele

Same alleles = “true breeding”/homozygous

Different alleles = “hybrids”/heterozygous

An individual’s looks (phenotype) does not always represent its alleles (genotype)


Genetic Symbolism
Use the first letter of dominant allele

Capital = dominant

Lower case = recessive

If purple is dominant to white:

“P” = allele for purple

, “p” = allele for white


Making a Punnett Square: Monohybrid Cross




Test Cross (backcross)

An individual with the dominant phenotype (brown rabbit) and an individual
with the recessive phenotype (white rabbit)

Reveals the genotype of the dominant individual

Incomplete Dominance

A heterozygous phenotype is intermediate between 2 homozygous phenotypes




Dihybrid Crosses