Question

Suppose you have a trait in which males exhibit the trait with much greater frequency than females. Females can pass the trait to all of their offspring even if they themselves don’t exhibit the trait while males pass the trait to only their female offspring. A) Explain what pattern of inheritance is described in this scenario. B) Give a specific example of a genetic trait that shows this pattern of inheritance. C) If you have a female offspring that exhibits a trait with this pattern of inheritance, what can you conclude about the genotypes of her parents? D) If you have a man that exhibits a trait like this, who is married to a woman whose father also exhibited a trait like this, what would be the expected phenotype ratios of their offspring? E) SHOW YOUR WORK.

Answer 1

Answers:

A) The above scenario describes an X-linked recessive trait. Males have two sex chromosomes X and Y while females have two X chromosomes. Hence due to presence of a normal X-chromososme, females will be less affected but males having only single X chromosome they show the trait.

B) Examples of common X-linked recessive traits are Hemophilia and Colourblindness.

C) An X-linked recessive trait, when manifested in female means that she has both the chromosomes affected. The phenotypes of the parents will be Father - affected; mother - normal or affected. Genotypically father is showing the trait as X is affected and mother can be either carrier with one X affected and one normal or is herself affected if both x chromosome carry the trait. Hence if we consider for example, she is colourblind then, her father is colourblind and her mother is a carrier for the trait (normal vision) or is colourblind.
Mother - X^a X or X^a X^a
Father - X^a Y

D) An affected man has X- chromosome that carries the trait. Mother will have inherited one affected X chromosome from her father and hence will be a carrier. All the work is shown belowtaking Hemphilia as the X - linked trait under study

Hence, 50% of all offspring will be thermophilic irrespective of sex. In other words half of females and half of males will be affected and other half will be normal.

E) The work is shown as above.