The Punnet Square and Its Applications

Advanced in the 20 th century by an English geneticist, Reginald Punnett, the Punnet square is a square diagram consisting of a usually three columns and three rows (Wanjie, 2014). The square is applied to determine and depict all the frequencies and combinations of different phenotypes and genotypes of a cross conducted using Mendel’s first law of inheritance. Despite being used as described, the Punnet square is limited by its lack of information concerning the probable variation in small samples as well as the absence of information concerning the prevalence of parental genotypes in a population. 

Hemophilia is an X-linked disorder, which implies it is transmitted alongside the X chromosome which determines the sex of an individual in the conventional Mendelian fashion. Understandably, the genetic make-up of a woman is XX while that of a man is XY. For this case, the mother, who is a carrier, will bear the hemophiliac trait on one of her X chromosomes while the father will not have any (males are not carriers for sex-linked disorders). The resultant Punnet square depicts the following: 

h—the symbol for the hemophilia trait 

Answers to the Questions 

The probability of a female offspring being hemophiliac is 0% 

The probability of a female offspring being a carrier for the condition is 1 / 4 (25%) 

The probability of a male offspring developing hemophilia is 1 / 4 (25%) 

The probability of a male offspring being a carrier for the condition is 0% 

The probability of any offspring being hemophiliac is 1 / 4 (25%) 

Only male offspring would develop the condition because they only have one X chromosome, which they inherit from their female parents. The recessive gene they inherit alongside the X chromosome causes the condition because they do not have another dominant gene on the Y chromosome to mask the effects of the inherited recessive gene. 

References 

Wanjie, A. (2014).  The Basics of Genetics . New York, NY: Rosen Digital.