The allele associated with albinism in humans is recessive ($c$). The probability that an albino male ($cc$) and a carrier female ($Cc$) will have an offspring with normal skin pigmentation is _________. (Round off to one decimal place)
Understanding Albinism Inheritance
The question concerns the inheritance of albinism, a condition caused by a recessive allele ($c$). We need to find the probability that an offspring will have normal skin pigmentation when an albino male (genotype $cc$) mates with a carrier female (genotype $Cc$). Normal skin pigmentation requires at least one dominant allele ($C$).
Genetic Cross Analysis
We can determine the possible genotypes of the offspring using the parents' genotypes:
- Male parent genotype: $cc$ (produces only $c$ gametes)
- Female parent genotype: $Cc$ (produces $C$ and $c$ gametes with equal probability)
Punnett Square Method
A Punnett square helps visualize the possible combinations of alleles in the offspring:
| $c$ | $c$ | |
| $C$ | $Cc$ | $Cc$ |
| $c$ | $cc$ | $cc$ |
The possible genotypes for the offspring are $Cc$ and $cc$. The phenotypes are:
- $Cc$: Normal skin pigmentation (inherits one dominant $C$ allele)
- $cc$: Albinism (inherits two recessive $c$ alleles)
Calculating Probability
From the Punnett square, 2 out of the 4 possible offspring genotypes are $Cc$. Therefore, the probability of an offspring having normal skin pigmentation is:
$ P(\text{Normal Pigmentation}) = P(Cc) = \frac{\text{Number of } Cc \text{ outcomes}}{\text{Total number of outcomes}} = \frac{2}{4} = \frac{1}{2} $
Converting the fraction to a decimal:
$ \frac{1}{2} = 0.5 $
The question asks to round the answer to one decimal place. The probability is 0.5.
Important Questions from Mendelian Inheritance
- The blood group of the mother is A⁺ and that of the father is AB⁺. Which of the following statements is/are correct?
- Fabry disease in humans is a X-linked disease. The probability (in percentage) for a phenotypically normal father and a carrier mother to have a son with Fabry disease is ________.
A pedigree of an inheritable disease is shown below.
- In tomato plant, red (R) is dominant over yellow (r) for fruit color and purple (P) is dominant over green (p) for stem color. Fruit color and stem color assort independently. The number of progeny plants of different fruit/stem colors obtained from a mating are as follows:
Red fruit, purple stem - 145
Red fruit, green stem – 184
Yellow fruit, purple stem - 66
Yellow fruit, green stem - 47
What are the genotypes of the parent plants in this mating? - Assuming independent assortment and no recombination, the number of different combinations of maternal and paternal chromosomes in gametes of an organism with a diploid number of 12 is ________.
