The Genetics of Inheritance

Why do we look the way we do?

• All organisms are made of cells.• Inside of these cells, a chemical called

DNA contains the “instructions” that control the way we look.

DNA

DNA: the instruction manual• The segments in the DNA that carry the “instructions”

are called GENES.

• Every individual has two of every gene.

Blue Eyes

Brown EyesBrown Hair Black Hair

Fair SkinOlive Skin

• There is more than one version of each gene. The different versions are called alleles.

Dominant & Recessive Human TraitsEarlobes: Widow’s peak:

# Students w/free lobes

# Students w/attached lobes

Free Attached

# Students w/ a widow’s peak

# Students w/out aWidow’s peak

One allele is dominant and the other allele is recessive. The dominant allele covers the expression of the recessive allele.

Genotype & Phenotype

# Students w/ free lobes # Students w/ attached lobes

• The observable traits of an organism is called the phenotype.

• The genotype is the combination of all of the different alleles that make up an individual

Incomplete Dominant TraitsBlood types: Flower color:

In incomplete dominance, the dominant allele does not cover up the expression of the recessive allele.

Why do we look like our parents?

Aa aa

Aa

Aa aa

Aa

Aa aa

Aa

Aa aa

aa

Punnett Squares• A diagram that is used to predict the

genotype and phenotype of the offspring based on the genotype of the parents.

p p

P Pp Pp

p pp ppPp

ppIt’s a probability problem!

½ purple pea plants; ½ white pea plants

Punnett Squares1. What is the probability that this couple will

have a child with brown eyes?

Bb

Bb

2. What is the probability that this couple will have 3 children with brown eyes?

BB= bb=Bb=

More Punnett SquaresThere are 10 guinea pigs in a litter. Five of the guinea pigs have long hair, and five have short hair. Long hair is dominant and short hair is recessive. What are the genotypes of the parents?

Genotypefor long hair:

Genotypefor short hair:

Applications of math in genetics

Selective breeding—The selection of certain seeds or animals for reproduction so that the next generation has the same desirable traits.