The ability to roll the tongue (R) is determined by a dominant gene while the recessive gene results in the inability to roll the tongue (r). A man and his wife can both roll their tongues and are surprised to find that their son cannot. Explain this by showing the genotypes of all three pesons.
I think both the mother and the father's genotypes are Rr (heterozygous).
And the child probably has a homozygous recessive trait (rr).
Am I right?
Please check!
Thanks!
yes. both parents are Rr. That is how the child can be rr.
In humans, the gene for right handeness is dominant to the for left hendeeness. A man and a woman both heterozygous for this trait marry. What percent of their children they expected to be right handed? What percent left handed? What are the genotypic and phenotypc ratios?
Wow- this was posted in 2009
You are correct in your understanding of tongue rolling being determined by a dominant gene (R) and the inability to roll the tongue being determined by the recessive gene (r).
If both the man and his wife can roll their tongues, they must have at least one dominant allele for tongue rolling. So, their genotypes could either be RR (homozygous dominant) or Rr (heterozygous).
Now, let's consider the genotype of their son. Since he cannot roll his tongue, it means he must have received two recessive alleles (rr) from his parents, as the recessive trait is only expressed in individuals who inherit two copies of it.
Given that both parents can roll their tongues (Rr or RR), the most logical conclusion is that their son inherited two recessive alleles (rr) from them. Therefore, your conclusion that the child has a homozygous recessive trait (rr) is correct.
In summary:
- Father: Genotype could be either RR or Rr.
- Mother: Genotype could be either RR or Rr.
- Son: Genotype is rr (homozygous recessive).
Well done on your analysis!