• self-fertilizing
• true-breeding
• cross-breeding

Gene

Locus

Diploid cells

Alleles

 

Homozygous

Heterozygous

Dominant

Homozygous dominant

Homozygous recessive

Two alleles separate during meiosis

Genotype

Phenotype

P

F₁

• Single trait
• Cross true-breeding parents
• Homozygous dominant
• Homozygous recessive

 

• Phenotype = Purple flowers
• Genotype =

 

• White flowers =

Punnett Square method:

 

Genotypic Ratio ____ AA: _____ Aa: _____aa

• to find out genotype of individual with dominant phenotype
• could be either AA or Aa
• cross that individual with

2 different outcomes possible:

- 2 traits

- assume they are on

Flower color and height

Purple

White

Tall

Short

Cross true-breeding parents

Purple tall X white short

What gametes can each parent produce?

What will be the genotype and phenotype of the offspring?

Cross: AaBb X AaBb

What gametes are produced?

How many possible combinations of eggs and sperm?

Draw the Punnett square for the cross.

What are the genotypic and phenotypic ratios of the offspring?

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- Diploid cells have pairs of genes

- on pairs of homologous chromosomes

- two genes of a pair separate

- At end of meiosis:

Genes on pairs of homologous chromosomes have been sorted out independent of genes on other chromosomes

Dominance Relations

Example: Snapdragons: red X white --> pink

Example: ABO blood typing

- (also a multiple allele system)

Blood types (Fig. 11.11):

Phenotype: Genotype(s)

A :

AB :

B :

O :

- Example - Marfan Syndrome

 

-loose jointed

- abnormally curved spine

 

Example: Hair Color in Mammals

- Black, yellow and chocolate labrador retrievers

Gene 1 = codes for melanin

- BB or Bb

- bb

Gene 2 - codes for deposition of melanin in hairs

- EE or Ee

- ee

Gene 3 - codes for tyrosinase (enzyme in melanin pathway)

- CC or Cc

- cc

Consider first 2 genes

Cross true-breeding black dog X yellow dog

F₁ =

Now cross the offspring (F₁ X F₁ ) BbEe X BbEe

Another example of epistasis

Comb shape in poultry

Continuous Variation

Environmental Effects

Review

- Review questions 1-5

-Self quiz 1-8

Critical Thinking Genetics Problems 1-15