Rat Genetics

Male Rat (Dad)

• Phenotype– Black Hair

• Genotype– BB / Bb

Female Rat (Mom)

• Phenotype– Gray (shade of

Black) Hair Coat

• Genotype– BB / Bb

Vocabulary Terms• Heterozygous: The 2 alleles for the

trait are different ex. Bb 1 dominate & 1 recessive

• Homozygous: The 2 alleles for the trait are the same ex. BB or bb 2 dominant or 2 recessive

• Phenotype: Physical appearance

• Genotype: Genetic traits (BB /Bb / bb)

What will their offspring’s phenotype and genotype be if female is heterozygous dominant for black hair and the male is

homozygous for black hair?• Female Male

– Bb -BB

• Offspring• Black Hair• White Hair• Homozygous• Heterozygous

1st Mating Offspring / F1 Generartion (babies)

• 9 lived

• Phenotype– 100% Black Hair

Coat

• Genotype– 100% BB / Bb

What will their offspring’s phenotype and genotype be if male and female is heterozygous dominant for black hair?

• Female Male– Bb -Bb

• Offspring• Black Hair• White Hair• Homozygous • Dom. Rec.• Heterozygous

2nd Mating / F2 Generation Offspring

• phenotype– 75% Black Hair Coat– 25% White Hair Coat

• Genotype– 75% BB / Bb– 25% bb

So based on the phenotypes of the second mating offspring we now

know….

• Both Female (mom) and Male (dad) genotype has to be..

–Bb Heterozygous Dominant for black hair

Your Turn: Name: ___________ Per___

What would happen if you breed the white homozygous (bb) rat to an black homozygous rat (BB)?• Phenotype

black ________%white ________ %

• Genotype• ___ ______%• ___ ______%

• Draw/Color picture to show Phenotype of offspring on back of this sheet