Question
A pedigree of an inheritable disease is shown below. 
The correct answer is
X-linked recessive
The pedigree described in the question is designed to determine the pattern of inheritance for a specific disease. Let's analyze the pedigree step-by-step:
- In the pedigree chart, males are represented by squares, and females by circles. Affected individuals are filled, and unaffected are open. Carrier states, if represented, are often shown with half-filled shapes.
- In X-linked recessive inheritance:
- Males (with only one X chromosome) will express the disease if they inherit the affected X chromosome.
- Females (with two X chromosomes) must inherit two affected X chromosomes to express the disease; if they inherit only one, they become carriers.
- Affected males pass the affected X chromosome to all their daughters (making them carriers if the mother is unaffected) and none to their sons.
- Check the generations in the pedigree chart:
- First Generation: One male is affected which suggests that the disease might be X-linked since he could have inherited the X chromosome from a carrier mother.
- Second Generation: An affected male from an unaffected father points to an X-linked pattern, as he must have received the affected X from his carrier mother.
- The pattern where no affected sons come from an affected father supports the X-linked recessive inheritance mode.
- Verify against the options:
- Autosomal dominant: Not possible, as not all generations show affected offspring from affected parents.
- X-linked dominant: Unlikely, as affected fathers would pass the disease to all daughters.
- X-linked recessive: Fits the observed pattern where mainly males are affected, and females are carriers.
- Autosomal recessive: Unlikely given the skewed gender distribution of affected individuals.
Thus, the correct answer is X-linked recessive.
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Important Questions from Mendelian Inheritance
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)
- 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 ________.
- 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 ________.
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