Science (Biology)
In a species of rodent, fur colour may be black or brown and their tail length either long or short.
A pair of rodents were crossed, and their progeny then allowed to interbreed. The result in the F2 were as follows:
29 with brown fur with long tails; 9 long tailed with black fur; 10 short tailed with brown fur; 3 short tailed with black fur;
Using the information provided, explain these results as fully as possible justifying your answers with written text and genetic diagrams (with Keys) to show your logic as you proceed backwards through the generations of rodents and identify their possible genotypes
To understand the results of the F2 generation, we need to start by assuming that the fur color and tail length are determined by two separate gene pairs. Let's use the letters B and b to represent the different alleles for fur color (black and brown) and the letters T and t to represent the different alleles for tail length (long and short).
Now let's analyze the given information step-by-step:
1. The F2 generation consists of the offspring resulting from the interbreeding of the F1 generation. This means that the F1 generation must have been heterozygous for both fur color and tail length, as the F2 offspring exhibit various combinations of traits.
2. Let's assume that the black fur color allele (B) is dominant over the brown fur color allele (b), and the long tail allele (T) is dominant over the short tail allele (t). This information will help us construct the genetic diagrams.
3. The first set of data provided states that 29 rodents had brown fur with long tails. This suggests that both parents in the F1 generation must have been heterozygous for both traits (BbTt).
Using the principles of Mendelian genetics, let's construct a Punnett square to display the potential crosses in the F1 generation:
| BT | Bt |
------|----------|----------|
BT | BBTT | BBTt |
------|----------|----------|
Bt | BbTT | BbTt |
From the Punnett square, we can see that 25% (BBTT), 25% (BBTt), 25% (BbTT), and 25% (BbTt) of the F1 offspring will have both brown fur and long tails.
4. The next set of data states that 9 rodents had long tails and black fur. This means that these rodents must have inherited the dominant alleles for both traits (BBTT).
5. The third set of data states that 10 rodents had short tails and brown fur. This can be explained as these individuals having inherited the recessive alleles for both traits (bbTt).
6. The final set of data states that 3 rodents had short tails and black fur. This can only occur if these individuals inherited the recessive alleles for both traits (bbTT).
Now, let's summarize the possible genotypes of the parents (F1 generation) and the resulting genotypes of the F2 generation rodents:
- F1 Generation: BbTt
- F2 Generation:
- 25% BBTT: Long tails, black fur
- 25% BBTt: Long tails, black fur
- 25% BbTT: Long tails, brown fur
- 25% BbTt: Long tails, brown fur
- 0% bbTT
- 25% bbTt: Short tails, brown fur
I hope this explanation and genetic diagram help you understand the results in the F2 generation and the possible genotypes of the rodents in the previous generations.
To understand the results of the F2 generation, we need to start by identifying the possible genotypes of the parent rodents. Let's assign variables to represent the different traits: B for black fur, br for brown fur, L for long tail, and l for short tail.
From the given information, we know that the F2 generation consisted of 29 rodents with brown fur and long tails, 9 rodents with black fur and long tails, 10 rodents with brown fur and short tails, and 3 rodents with black fur and short tails.
To determine the possible genotypes of the parent rodents, let's consider the phenotypes of the F2 generation and work our way backward. We can start by identifying the possible genotypes for each phenotype in F2.
1. Brown fur and long tail (29 rodents):
This phenotype can be expressed by the genotype brbrLL or brbrLl. Both of these genotypes would result in brown fur, and the presence of at least one L allele would lead to a long tail.
2. Black fur and long tail (9 rodents):
This phenotype can only be produced by the genotype B_B_LL, where B represents the dominant allele for black fur.
3. Brown fur and short tail (10 rodents):
This phenotype can be expressed by either the genotype brbrll or brbrLl. The presence of at least one l allele would lead to a short tail.
4. Black fur and short tail (3 rodents):
This phenotype can be produced by either the genotype B_B_ll or B_bll. In both cases, the presence of two l alleles would result in a short tail.
Now, let's construct a genetic diagram to represent the possible genotypes of the parent rodents:
| B br
---|-------------
B | B_B_ B_br
br| B_br brbr
| L l
---|-------
L | LL Ll
l | Ll ll
From this genetic diagram, we can see that the possible genotypes for the parent rodents are B_brLL, B_brLl, B_BLL, and B_ll. These genotypes would explain the observed phenotypes in the F2 generation.
Note: The genetic diagram represents the possible genotypes that can result from the initial cross. The letters in each box represent alleles inherited from each parent. The capitalized letters represent dominant alleles, while lowercase letters represent recessive alleles.
By understanding the phenotypes and using the principles of Mendelian genetics, we can logically deduce the possible genotypes of the parent rodents, leading to the observed results in the F2 generation.