1) The F2 progeny from a cross exhibits a modified dihybrid ratio of 9:7 instead of 9:3:3:1. What phenotype ratio would be expected from a testcross of the F1 progeny?
2) In Drosophila, mutants a through g all have a white eye phenotype. The following data shows the results of pairwise combinations in a complementation test:
a b c d e f g
g + - + - + + -
f - + - + + -
e + + + + -
d + - + -
c - + -
b + -
a -
How many genes are present?
Which are defects in the same gene?
3) A male Drosophila fly is found with white eyes. How would you determine if the mutant in this fly is the same as Morgan’s original white fly. Show the cross(es) you would do. You must use proper symbols.
4) What does the term complementation mean? If two different mutations that have the same phenotype complement each other, what can you conclude about those two mutations?
Could you help me with these questions to help me study for my next test?
1) The modified dihybrid ratio of 9:7 suggests that two independent genes are involved in the trait, with a recessive allele at one gene masking the expression of both dominant and recessive alleles at the other gene. In a testcross of the F1 progeny, we can expect a phenotypic ratio of 1:1:1:1. This is because the individuals in the F1 generation have a genotype of AaBb (where A and B represent dominant alleles, and a and b represent recessive alleles). When these individuals are testcrossed with individuals that have a genotype of aabb, four different genotypes can be produced: AaBb, Aabb, aaBb, and aabb. Consequently, the phenotypic ratio would be 1:1:1:1.
2) To determine the number of genes present and identify which mutants are defective in the same gene, we can examine the results of the complementation test. Complementation occurs when two mutants with the same phenotype are crossed, and the resulting offspring have a wild-type phenotype. Looking at the data provided, we can identify three groups: group a and group g, group b and group f, and group c, d, and e.
Based on the complementation test, we can conclude the following:
- Mutants within the same group, such as a and g, b and f, and c, d, and e, complement each other. Therefore, they are not defective in the same gene.
- Each group represents a separate gene. Hence, there are three genes present (gene for group a/g, gene for group b/f, and gene for group c/d/e).
3) To determine if the mutant fly has the same mutation as Morgan's original white fly, a complementation test can be performed. The mutant fly is crossed with Morgan's original white-eyed fly, which we will represent using the symbol W.
If the mutant fly is homozygous for the mutant allele, we can represent it as ww. The cross would be performed as follows:
ww (mutant fly) x W (original white fly)
If the resulting F1 generation shows a white-eyed phenotype, it suggests that the mutant in this fly is the same as Morgan's original white fly. On the other hand, if the F1 generation shows a wild-type red-eyed phenotype, it would indicate that the mutations are not the same.
4) In genetics, complementation refers to when two different mutations that have the same phenotype, such as white eye color, result in offspring with a wild-type phenotype when crossed. This indicates that the mutations are in different genes and can complement each other to restore the normal function of the gene or genes in question.
If two different mutations that have the same phenotype complement each other, it can be concluded that the mutations are present in different genes. This means that the mutations do not affect the same molecular pathway or process. If the mutations affected the same gene, they would not be able to complement each other and would result in a non-wild-type phenotype in the offspring.
Of course, I can help you with these questions. Let's go through each question step by step:
1) To determine the phenotype ratio expected from a testcross of the F1 progeny, we need to understand the modified dihybrid ratio observed in the F2 progeny. In a normal dihybrid cross, the phenotypic ratio is expected to be 9:3:3:1. However, in this case, the ratio is modified to 9:7. This modification suggests that the two traits being studied are not segregating independently, which could be due to genetic linkage or some form of interaction between the alleles.
In a testcross, we cross the F1 progeny with a homozygous recessive individual. In this specific scenario, the F1 progeny should be crossed with an individual that is homozygous recessive for both traits being studied.
Based on the modified dihybrid ratio of 9:7, we can determine the expected phenotype ratio from the testcross. The dominant phenotypes in the F2 progeny should be present in a ratio of 9, while the recessive phenotypes should be present in a ratio of 7. Therefore, the expected phenotype ratio from the testcross would be 9:7.
2) The complementation test is used to determine if different mutants with the same phenotype are due to defects in different genes or the same gene. A prefix "+" indicates a wild type phenotype, while a "-" indicates a mutant phenotype.
By examining the complementation matrix given, we can determine the number of genes involved and which mutations are in the same gene.
In this case, we can see that mutations a and f do not complement when crossed since their combination results in a mutant phenotype. This indicates that a and f are defects in the same gene.
To determine the number of genes, we count the rows/columns without any complementation between them. In this example, we have 3 rows/columns (e, f, and g) where at least one combination results in a mutant phenotype. Therefore, we can conclude that there are 3 different genes involved.
3) To determine if the mutant in the male Drosophila fly is the same as Morgan's original white fly, we need to perform a cross involving both flies. To show the cross(es) using proper gene symbols, we need to know the symbols assigned to each gene, which are usually represented by letters.
Let's assume that the mutant in the male Drosophila fly is represented by the symbol "w" (for white eyes) and Morgan's original white fly is also represented by the same symbol "w." In this case, we can perform a cross between the male Drosophila fly (w/Y) and a female fly with red eyes (w+ w+ X) to determine if they are the same mutant.
The expected outcome of this cross would be as follows:
- Approximately 50% of the male progeny will have white eyes (w/Y), confirming that the mutant in the male fly is indeed the same as Morgan's original white fly.
- The female progeny will have red eyes (w+ w+) since they inherited the wild-type allele from their father and mother.
4) The term "complementation" refers to a phenomenon in genetics where two different mutations that have the same phenotype do not affect each other. In other words, the presence of one mutation can compensate for the absence of the other, thus allowing for normal function to occur.
When two different mutations that have the same phenotype complement each other, it implies that the mutations are in different genes. Complementation occurs because the mutations affect different steps or components of a biological process, and their combined effects restore normal function.
Therefore, if two different mutations that have the same phenotype complement each other, it can be concluded that the mutations are in different genes.