Question

The sex of an organism is typically determined genetically, but environmental factors can also play a role. Scientists examined the roles of genes and environmental temperature in the sex determination of a lizard species. Individuals with a ZW pair of chromosomes are always female (ZWf), while individuals with a ZZ pair of chromosomes can be either male (ZZm) or female (ZZf). Scientists mated ZWfor ZZf females with ZZm males and incubated the eggs produced in 20 clutches at temperatures ranging from 23°C to 36°C. When the young hatched, the scientists determined their sexes (Table 1). Among the eggs that did not hatch, the mortality of embryonic lizards was approximately the same for both males and females.

Table 1. Fraction of female progeny produced as a function of egg incubation temperature

 

a) If a particular gene is located on the Z chromosome of this lizard species, describe why a lizard with a ZW genotype has a greater probability of expressing the recessive phenotype for the trait than a lizard with the ZZ genotype does.

Answer 1

(a) According to the question, phenotype is recessive & gene for that phenotype is present in the Z chromosome is

In order to develop the recessive phenotype in ZZ individuals, two Z chromosomes must contain the responsible gene that develops the recessive phenotype.

If only one Z chromosome contains the recessive gene & other contains gene responsible for dominate phenotype, then ZZ individuals will show dominate phenotype because dominate characteristic will override the recessive one. But ZW individuals have only one Z chromosome & if it contains the recessives gene, the individuals will show the recessive phenotype.

Thus, a lizard with ZW genotype has greater probability to express the recessive phenotype compare to the ZZ genotype due to the fact that there is lower chance that both Z chromosomes of ZZ individuals will contain the recessive gene compare to the single Z chromosome of ZW genotype.

THANK YOU If any queries please leave your valuable comment in the comment box.