In guinea pigs, the allele for a rough coat (R) is dominant over the allele for a smooth coat (r). A heterozygous guinae pig (Rr) and a homozygous recessive guinea pig (rr) have a total of nine offspring. The punnett square for this cross shows a 50 percent chance that any particular offspring will have smooth coats. Explain how all nine offspring can have smooth coats.
In guinea pigs, rough coats (with lots of swirly cowlicks) are dominant over smooth cats. If a male homozygous recessive guinea pig is crossed with a female homozygous dominant guinea pig, what are the possible genotypes and phenotypes of the offspring? Complete the Punnett square and the percentages of rough and smooth coated offspring.
***Please follow all Punnett square rules to complete this question. (Letters and numbers, only)
Please use the following:Rough=R and Smooth =r
To explain how all nine offspring can have smooth coats, let's first create a Punnett square to determine the possible genotypes of the offspring from crossing a heterozygous (Rr) guinea pig with a homozygous recessive (rr) guinea pig:
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| R | r |
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| Rr | rr |
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Here, the above Punnett square shows the possible combinations of alleles that the offspring can inherit.
From this cross, we can see that 50% of the offspring will inherit the dominant allele (R) and have a rough coat, while the other 50% will inherit the recessive allele (r) and have a smooth coat.
However, in this specific scenario, it is stated that all nine offspring have smooth coats. This indicates that none of the offspring inherited the dominant rough coat allele (R).
To achieve this outcome, all the offspring must have inherited the recessive smooth coat allele (r) from the heterozygous guinea pig (Rr). In other words, they must have received the recessive allele (r) from both parents.
Since the homozygous recessive guinea pig (rr) can only pass on the recessive allele (r), all the offspring will inherit this recessive allele (r) from the homozygous recessive guinea pig (rr).
Therefore, the genotypes of all the nine offspring will be rr, resulting in all of them having smooth coats.
To explain how all nine offspring can have smooth coats, we need to understand the principles of Mendelian genetics and how alleles are inherited from parents to offspring.
In this scenario, the allele for a rough coat (R) is dominant over the allele for a smooth coat (r). A heterozygous guinea pig (Rr) carries one dominant allele (R) and one recessive allele (r), while a homozygous recessive guinea pig (rr) carries two recessive alleles (r).
When these two guinea pigs are crossed, we can create a Punnett square to visualize the potential offspring genotypes and phenotypes:
| R r
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R | RR Rr
r | Rr rr
In this Punnett square, the letters represent the alleles contributed by each parent, where uppercase letters represent dominant alleles (R) and lowercase letters represent recessive alleles (r).
Looking at the Punnett square, we can see that there are four possible combinations for the offspring: RR, Rr, Rr, and rr.
Among these possibilities, the only genotype that results in a smooth coat is when both alleles are recessive (rr). This is because the rough coat allele (R) is dominant over the smooth coat allele (r).
Now, let's consider the information given in the question: A heterozygous guinea pig (Rr) and a homozygous recessive guinea pig (rr) have a total of nine offspring. If all nine offspring have smooth coats, that means all nine must have the genotype rr.
To calculate the probability of all nine offspring having the rr genotype, we need to consider the genotype of the heterozygous parent (Rr). Since there is a 50 percent chance that an individual offspring will inherit the smooth coat allele (r) from the heterozygous parent (Rr), we can use the principle of independent probability to calculate the chance of all offspring having rr genotype.
Each offspring has a 50 percent chance of inheriting the smooth coat allele (r) from the heterozygous parent (Rr). As there are nine offspring in total, we multiply the probabilities together:
(0.5) * (0.5) * (0.5) * (0.5) * (0.5) * (0.5) * (0.5) * (0.5) * (0.5) = 0.5^9
This calculation evaluates to approximately 0.002, which means there is a 0.2 percent chance of all nine offspring having smooth coats.
Thus, it is highly unlikely for all nine offspring to have smooth coats, assuming independent assortment of alleles and following Mendelian genetics.