Can a recessive trait be a dominant trait as well? I ask this because I have a science problem that says this:
A Bb guinea pig crosses with a Bb guinea pig, and four offspring are produced. All the offspring are black. Explain how this could happen.
I tried making a Punnett square, but it never turned out that all the offspring had the dominant trait. I thought that if a recessive trait can also be a dominant trait, that it would be the answer.
Please help. Getting really frustrated.
B=allele for black color
b=allele for the recessive color
When you perform a cross between the two guinea pigs, there is a 75% chance that EACH offspring will express black as the phenotype, and there is 25% chance that EACH guinea pig will express the recessive phenotype. Out of four offspring, you would expect one of the offspring to display the recessive phenotype, but the chances that all of the offspring from the cross between the guniea pigs will display black as the phenotype are higher compared to at least one of the offspring displaying the recessive phenotype.
The results of a cross are the following:
Genotype frequency:
1 BB : 2 Bb : 1bb
Phenotype frequency:
3 Black : 1 Recessive
You can look at the results of a cross in two ways: One, the chances of ONE offspring expressing the black phenotype is 3/4 or 75%, or two, you can say that the out of four children, three should express the black phenotype, and one should express the recessive phenotype. However, the results are indicative of the chances that ONE offspring will inherit a specific combination of alleles, or express a specific phenotype.
The chances that all four will express the dominant phenotype is the following:
(3/4)^4=81/256 or 32%
The chances that three will express the dominant phenotype and one will will express the recessive phenotype is the following:
(3/4)^3*(1/4)=27/256 or 11%
So, is it basically just that the guinea pig offspring will have a higher chance of being black than it would for 3 offspring being black and the other one being the recessive color?
Yes.
Thanks!
i don't understand
I understand that you are frustrated with the Punnett square not giving you the expected results. Let's break down the problem and try to understand how all the offspring can be black even though the trait involved is considered recessive.
In this case, the guinea pigs have the genotype Bb, which means that they have one dominant gene (B) and one recessive gene (b) for coat color. The dominant gene (B) produces a black coat color, while the recessive gene (b) produces a different coat color, such as brown.
To determine the possible outcomes, we need to create a Punnett square. Since both parents have the same genotype (Bb), the Punnett square would look like this:
| B | b |
-------------------------
B | BB | Bb |
-------------------------
b | Bb | bb |
From the Punnett square, we can see that there are four possible combinations of alleles (genotypes) for the offspring: BB, Bb, Bb, and bb.
Now, it's important to note that the dominant gene (B) produces a black coat color, while the recessive gene (b) produces a different coat color, such as brown. Since all the offspring in your problem have a black coat color, this means that all of them must have at least one dominant gene (B).
If we carefully examine the Punnett square, we can see that all four offspring genotypes (BB, Bb, Bb, and bb) have at least one dominant gene (B), resulting in a black coat color.
Therefore, the reason why all the offspring are black is that they inherited at least one dominant gene (B) from their parents, even though the trait itself (brown coat color) is considered as recessive.
I hope this explanation helps!