Assume that the allele controlling brown eyes (B) is dominant over that controlling blue eyes (b) in human beings. (In actuality, eye color in humans is an example of multigene inheritance, which is much more complex than this.) A blue-eyed man marries a brown-eyed woman; and they have six children, all brown-eyed. What is the most likely genotype of the father?
mother?
If the seventh child had blue eyes, what could you conclude about the parents’ genotypes?
Father: bb
Mother: BB
all children are Bb.
If the seventh child is bb, then Mother is Bb.
To determine the most likely genotypes of the parents, we can use the principles of Mendelian genetics.
Given that brown eyes (B) is dominant over blue eyes (b), we'll represent the genotypes as follows:
- BB: homozygous dominant for brown eyes
- Bb: heterozygous for brown eyes
- bb: homozygous recessive for blue eyes
Let's analyze each scenario step-by-step:
1. The six children have brown eyes:
Since all six children have brown eyes, the father cannot have the genotype bb (homozygous recessive), as that would result in blue eyes. Therefore, the only possible genotypes for the father are BB (homozygous dominant) or Bb (heterozygous).
The most likely genotype of the father is Bb because if he were homozygous dominant (BB), all of the children would also be homozygous dominant for brown eyes.
Therefore, the most likely genotype of the father is Bb.
As for the mother, the fact that all six children have brown eyes suggests that she must have at least one dominant allele (B), which could be either BB or Bb. However, since the father's most likely genotype is Bb, it is more likely that the mother's genotype is BB to have all brown-eyed children.
Therefore, the most likely genotype of the mother is BB.
2. The seventh child has blue eyes:
If the seventh child has blue eyes, it means that the child inherited the recessive allele (b) from each parent. This indicates that both the father and the mother must carry at least one recessive allele (b) in their genotype.
Since all the children from the previous scenario have brown eyes and the seventh child has blue eyes, it suggests that both parents are heterozygous (Bb) for eye color.
Therefore, if the seventh child has blue eyes, we can conclude that both parents have the genotype Bb.
To determine the genotypes of the parents and the possible genotypes of the children, we need to understand the principles of inheritance in this scenario.
In this case, the allele for brown eyes (B) is dominant over the allele for blue eyes (b). Dominant alleles will always express their traits in the presence of a recessive allele. So, if a person carries either one or two copies of the dominant allele for brown eyes (BB or Bb), they will have brown eyes.
Now let's analyze the information provided:
1. A blue-eyed man marries a brown-eyed woman, and they have six brown-eyed children.
Since the man is blue-eyed, he can only have the genotype bb (two copies of the recessive allele for blue eyes). All his gametes (sperm cells) will carry the allele b.
If all six children have brown eyes, it means that they must have received at least one dominant allele B from their mother. Therefore, the mother must be heterozygous (Bb) or homozygous dominant (BB).
Based on this information, the most likely genotype of the father is bb (homozygous recessive for blue eyes), and the most likely genotype of the mother is Bb (heterozygous for brown eyes).
2. If the seventh child had blue eyes, what could you conclude about the parents’ genotypes?
If the seventh child has blue eyes, it means they inherited two copies of the recessive allele b, one from each parent (bb). So, both parents must carry at least one recessive allele for blue eyes (b). This suggests that the mother, who has brown eyes, could be either homozygous dominant (BB) or heterozygous (Bb) for the brown eye allele. The father, being blue-eyed (bb), is already known to carry two copies of the recessive allele for blue eyes.
In conclusion, based on the information provided, the most likely genotype of the father is bb (homozygous recessive for blue eyes), and the most likely genotype of the mother is Bb (heterozygous for brown eyes). If the seventh child has blue eyes, it would confirm that the mother is heterozygous (Bb) for eye color, while the father remains homozygous recessive (bb).