1. Rat Genetics

2. Male Rat (Dad)
Phenotype
Black Hair
Genotype
BB / Bb

3. Female Rat (Mom) Phenotype Genotype Gray (shade of Black) Hair Coat
BB / Bb

4. 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)

5. 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 B b b B B B B
100% 0%
50% B B B b B
50%

6. 1st Mating Offspring / F1 Generartion (babies)
9 lived
Phenotype
100% Black Hair Coat
Genotype
100% BB / Bb

7. 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 B b B B B B b
75%
25% b B b b b
25%
25%
50%

8. 2nd Mating / F2 Generation Offspring
phenotype
75% Black Hair Coat
25% White Hair Coat
Genotype
75% BB / Bb
25% bb

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

10. 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