Pedigrees & More Genetics

Pedigree

MaleFemale

HeterozygousShows trait

Probabilities

Aa aaChild will have recessive trait?

aa

Chance of “a” allele from dad?

1/2

Chance of “a” allele from mom?

2/2 (1)

Total

1/2 x 1 = 1/2

Recessive characteristics

Inheritance pattern•Trait tends to skip generations

Dominant characteristics•Trait does not skip generations•Occurs frequently within a family

Pedigree Analysis

Sex linked characteristics•Tend to occur more in males than in females

•Color-blindness •Hemophilia

X-linked Recessives: More commonly seen in Males

• Why?• Males only need one recessive

allele to see trait.• E.g. Color-blindness

• XcY = colorblind male• XcXc = colorblind female• XcX = carrier female

A woman with normal vision whose father was colorblind marries a colorblind male. What percent of the couple’s sons will be colorblind?

1. All

2. 75%

3. 50%

4. 25%

A woman with normal vision whose father was colorblind marries a colorblind male. What percent of the couple’s sons will be colorblind?

1. All

2. 75%

3. 50%

4. 25%

Xc X

Xc XcXc XcX

Y XcY XY

Incomplete Dominance

Codominance &Multiple Alleles

Epistasis

• A gene at one locus alters the expression of a gene at another locus.

• Example: – Black coat (B) is

dominant to brown (b)– Pigment color (C) is

dominant to no pigment color (c)

Polygenic Traits

• Additive effect of multiple genes on a single phenotype

• Results in normal distribution

• Examples: skin color, height

Effect of Environment on Phenotype

More acidic soil Less acidic soil

Pleiotropic Effects