Chapter 19, Problem 2CT

Still referring to Problem 1, what will be the possible genotypes of offspring from the following matings? With what frequency will each genotype show up?

1. a. AABB × aaBB
2. b. AaBB × AABb
3. c. AaBb × aabb
4. d. AaBb × AaBb

Summary Introduction

To predict: The predicted genotype frequencies among the offspring for the mating AABB × aaBB.

Introduction: The law of independent assortment and law of segregation are the laws proposed by Gregor Johann Mendel, a geneticist. Mendel proposed the law of independent assortment based on the results of monohybrid cross that “two alleles at any locus tend to separate from each other during meiosis, so they end up in different gametes”. Mendel proposed the law of independent assortment based on the results of dihybrid cross that “alleles at one locus tend to assort into gametes independently of alleles at other loci”. The number of possible allele combination for the given genotype is given by the formula 2ⁿ where “n” is the number of heterozygous alleles that are present.

Explanation of Solution

A monohybrid cross is constructed with Punnett square for the parents having the genotype AABB and aaBB.

Conclusion

All the offspring have the same genotype AaBB. Therefore, there is no genotype frequency.

Summary Introduction

To predict: The predicted genotype frequencies among the offspring for the mating AaBB × AABb.

Introduction: The law of independent assortment and law of segregation are the laws proposed by Gregor Johann Mendel, a geneticist. Mendel proposed the law of independent assortment based on the results of monohybrid cross that “two alleles at any locus tend to separate from each other during meiosis, so they end up in different gametes”. Mendel proposed the law of independent assortment based on the results of dihybrid cross that “alleles at one locus tend to assort into gametes independently of alleles at other loci”. The number of possible allele combination for the given genotype is given by the formula 2ⁿ where “n” is the number of heterozygous alleles that are present.

Explanation of Solution

A monohybrid cross is constructed with Punnett square for the parents having the genotype AaBB and AABb.

Conclusion

The following is the frequency of genotypes.

Total number of possible genotypes = 4.

AABB=$\frac{1}{4}$

AABb=$\frac{1}{4}$

AaBB=$\frac{1}{4}$

AaBb =$\frac{1}{4}$

$\frac{1}{4}\times 100=25\%$

The frequency of all four genotypes is 25%.

Summary Introduction

To predict: The predicted genotype frequencies among the offspring for the mating AaBb × aabb.

Introduction: The law of independent assortment and law of segregation are the laws proposed by Gregor Johann Mendel, a geneticist. Mendel proposed the law of independent assortment based on the results of monohybrid cross that “two alleles at any locus tend to separate from each other during meiosis, so they end up in different gametes”. Mendel proposed the law of independent assortment based on the results of dihybrid cross that “alleles at one locus tend to assort into gametes independently of alleles at other loci”. The number of possible allele combination for the given genotype is given by the formula 2ⁿ where “n” is the number of heterozygous alleles that are present.

Explanation of Solution

A monohybrid cross is constructed with Punnett square for the parents having the genotype AaBb and aabb

Conclusion

The following is the frequency of genotypes.

Total number of possible genotypes = 4.

AABB=$\frac{1}{4}$

aaBB=$\frac{1}{4}$

Aabb=$\frac{1}{4}$

aabb =$\frac{1}{4}$

$\frac{1}{4}\times 100=25\%$

The frequency of all four genotypes is 25%.

Summary Introduction

To predict: The predicted genotype frequencies among the offspring for the mating AaBb × AaBb.

Introduction: The law of independent assortment and law of segregation are the laws proposed by Gregor Johann Mendel, a geneticist. Mendel proposed the law of independent assortment based on the results of monohybrid cross that “two alleles at any locus tend to separate from each other during meiosis, so they end up in different gametes”. Mendel proposed the law of independent assortment based on the results of dihybrid cross that “alleles at one locus tend to assort into gametes independently of alleles at other loci”. The number of possible allele combination for the given genotype is given by the formula 2ⁿ where “n” is the number of heterozygous alleles that are present.

Explanation of Solution

A monohybrid cross is constructed with Punnett square for the parents having the genotype AaBb and AaBb.

The following is the frequency of genotypes.

Total number of possible genotypes = 16.

AABB=$\frac{1}{16}$

AABb=$\frac{2}{16}=\frac{1}{8}$

AaBB=$\frac{2}{16}=\frac{1}{8}$

AaBb=$\frac{4}{16}=\frac{1}{4}$

AAbb=$\frac{1}{16}$

Aabb=$\frac{1}{16}$

aaBB=$\frac{2}{16}=\frac{1}{8}$

aaBb=$\frac{2}{16}=\frac{1}{8}$

aabb=$\frac{1}{16}$

$\begin{array}{l}\frac{1}{4}\times 100=25\%\\ \frac{1}{8}\times 100=12.5\%\\ \frac{1}{16}\times 100=6.25\%\end{array}$

The frequency of genotypes AABB, aaBB , AAbb and aabb is 6.25%.

The frequency of genotypes AaBB, AABb, aaBb and Aabb is 12.5%.

The frequency of genotypes AaBb is 25%.