Can anyone help me with Genetics? I have some problems and answers and need them explained to me.
Here are some of the questions and answers:
1. Assume that a dihybrid cross is made in which the genes' loci are autosomal, independantly assorting, and incompletely dominant. How many different phenotypes are expected in offspring?
Answer: 9
2. Assume that a dihybrid F2 ratio, resulting from epistasis was 9:3:4. If a double heterozygote was crossed to the fully recessive type, what phenotypic ratio is expected among the offspring?
Answer: 1:1:2
3. Assume that a dihybrid F2 ratio, resulting from epistasis, was 15:1. If a double heterozygote was crossed to the fully recessive type, what phenotypic ratio is expected among offspring?
Answer:3:1
If anyone can explain how these are done I would really appreciate it!
for #3. This is a testcross situation that would result in a 3:1 ratio because an ordinary dihybrid testcross would produce a 1:1:1:1, but 15:1 is duplicate dominant epistasis. So three of the genotypes/phenotypes have a dominant allele at one or both 10ci; therefore, 3/4 will show the dominant epistasis phenotype. Only the aabb double homozygote will be different.
Certainly! I can help explain how you can arrive at the answers for these genetics questions.
1. For the first question, you are given that the genes' loci are autosomal, independently assorting, and incompletely dominant. With these conditions, each gene will have two alleles (variants of the gene) that independently assort during the formation of gametes.
To determine the number of different phenotypes expected in the offspring, you can use the formula 2^n, where n is the number of gene pairs involved. In this case, it is a dihybrid cross involving two gene pairs. Therefore, the number of different phenotypes expected is 2^2 = 4.
However, since the genes in question are incompletely dominant, each gene pair will have three possible genotypes and three corresponding phenotypes. Thus, we have to multiply the number of phenotypes for each gene pair: 3 * 3 = 9. Therefore, the expected number of different phenotypes in the offspring is 9.
2. For the second question, you are given a dihybrid F2 ratio of 9:3:4, which indicates the phenotypic ratios of the offspring resulting from a cross. It is also mentioned that the cross involves a double heterozygote (two heterozygous individuals) crossed with the fully recessive type (two homozygous recessive individuals).
To determine the phenotypic ratio expected among the offspring, you need to consider the possible combinations of alleles from both gene pairs. In this case, the resulting phenotypic ratios are determined by the epistatic interaction between the two genes.
Without knowing the specific alleles involved, it's difficult to provide a detailed explanation. However, by looking at the given dihybrid F2 ratio of 9:3:4, we can deduce that there are four different phenotypes observed.
The ratio indicates that for every 9 individuals, 3 will have one phenotype, 3 will have a second phenotype, and 4 will have a third phenotype. Therefore, the expected phenotypic ratio among the offspring is 1:1:2.
3. For the third question, you are given a dihybrid F2 ratio of 15:1. Similar to the second question, this indicates the phenotypic ratios of the offspring resulting from a cross. Again, it involves a double heterozygote crossed with the fully recessive type.
The phenotypic ratio is 15:1, which means that for every 15 individuals, 1 will have one phenotype. Therefore, the expected phenotypic ratio among the offspring is 3:1.
Please note that these explanations are based on the given information and assumptions provided in the questions. Let me know if you need further clarification or have any additional questions!
Sure, I'd be happy to help explain the solutions to these genetics questions!
1. To determine the number of different phenotypes expected in offspring from a dihybrid cross, you need to consider the number of possible combinations of alleles for each gene. If the genes are independently assorting, this means that the alleles for one gene will segregate independently of the alleles for the other gene during gamete formation.
In this scenario, if each gene has 2 alleles (A, a and B, b), there will be 2^2 = 4 possible combinations of alleles for each gene. Since we are dealing with a dihybrid cross, where two genes are involved, you need to multiply the possibilities together: 4 x 4 = 16.
However, if the genes' loci are incompletely dominant, this means that one allele may not be completely dominant over the other, and instead, there may be blending of traits in the heterozygous state. In this case, you would need to consider the additional phenotypes that may arise from incomplete dominance.
If we assume that there are 3 possible phenotypes for each gene combination (assuming homozygous dominant, heterozygous, and homozygous recessive yield different phenotypes), then you need to multiply the possible phenotypes for each gene: 3 x 3 = 9.
Therefore, there are 9 different phenotypes expected in the offspring.
2. In this question, we are dealing with epistasis, which means that the alleles at one gene locus mask or alter the expression of alleles at another gene locus. A dihybrid F2 ratio of 9:3:4 suggests that there are three possible phenotypes.
To determine the phenotypic ratio expected among the offspring when a double heterozygote is crossed with the fully recessive type, consider that the double heterozygote has two alleles for each gene (AaBb), and the fully recessive type has two homozygous recessive alleles (aabb).
When you cross these individuals, you need to consider the possible allele combinations for each gene:
For the A gene: AA, Aa (no aa in the fully recessive type).
For the B gene: BB, Bb (or bb in the fully recessive type).
Therefore, you have two phenotypic possibilities for each gene, resulting in a phenotypic ratio of 1:1:2.
3. Similar to the previous question, this question involves epistasis with a dihybrid F2 ratio of 15:1, indicating two possible phenotypes.
Again, when a double heterozygote is crossed with the fully recessive type, you need to consider the possible allele combinations for each gene:
For the A gene: AA, Aa (no aa in the fully recessive type).
For the B gene: BB, Bb (or bb in the fully recessive type).
In this case, since there is a 15:1 ratio, it suggests that 15 out of 16 possible combinations will yield one phenotype, while only 1 combination will yield the other phenotype.
Therefore, the phenotypic ratio expected among the offspring is 3:1.
I hope this explanation helps you understand how to approach and solve these genetics questions! Let me know if you have any further questions.