every person has two copies (alleles) for each gene. how those two alleles interact determines what...

BASICS OF GENETICS

Every person has two copies (alleles) for each gene. How those two alleles interact determines what you see for an organism, their phenotype.

Dominant Alleles

Represented by a CAPITAL LETTER

Dominant alleles hide recessive alleles when it is present in a genotype with one

It is expressed when an organism has 1 OR 2 copies of this allele

Recessive Alleles

Represented by a lower case letter

Recessive alleles are hidden by dominant alleles when present in a genotype with one May not be expressed, but is still present

and can be passed onto offspring

It is expressed only when organisms have 2 copies of a recessive alleles

The majority of alleles interact in a dominant/recessive relationship.

Some interact in a co-dominance or incomplete dominance relationship.

Co-Dominance

“Co”—think of cooperation, they share the spotlight, you see both

2 dominant alleles—dominant trait is seen 2 recessive alleles—recessive trait is seen

1 dominant and 1 recessive allele—you see BOTH the dominant and recessive phenotype

Ex.: If R=red and r=white, Rr would be a red flower with white spots

Incomplete Dominance

2 dominant alleles—dominant trait is seen

2 recessive alleles—recessive trait is seen

1 dominant and 1 recessive allele—you see a combination of the dominant and recessive

Ex: If R=red and r=white, Rr would have a blend of the two, a pink flower

Genotype

The genetic make-up of an organism, what genes (letter) combination the organism has.

Represented by 2 letter pairs

Ex: HH, Hh, hh

Phenotype

How the genotype is expressed, the actual physical characteristics you see

Ex: long hair, brown hair

How are genotypes related to phenotypes?

GENOTYPE DETERMINES PHENOTYPE The genes you have determine the

traits you express.

Homozygous An organism that has 2 of the same

alleles for a trait. Homozygous dominant: 2 capital letters Homozygous recessive: 2 lower case

letters

Prefix “homo” means same AKA—pure, or purebred Ex: HH, aa, GG, bb

Heterozygous

An organism that has 1 dominant and 1 recessive allele for a trait

Prefix “hetero” means different

AKA—hybrid

Ex: Aa, Hh, Gg, Bb

Examples

GG=homozygous dominant Same, and 2 dominant

gg=homozygous recessive Same, and 2 recessive

Gg= heterozygous

Practice Questions

1. Aa_______________________________

2. cc_______________________________ 3. RR

______________________________ 4. Bb

______________________________

Practice Questions

1. Aa ___Heterozygous________ 2. cc_Homozygous

recessive_________ 3. RR __Homozygous

dominant________ 4. Bb ___Heterozygous_________