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 ZWpair of chromosomes are always female (ZWf), while individuals with a ZZ pair of chromosomes can be either male (ZZm) or female (ZZf). Scientists mated ZWf or 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.

(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.

(b) Using the template, construct an appropriately labeled graph, including error bars, to represent the data in Table 1. Based on the data, compare the ZZm×ZWf crosses and the ZZm×ZZf crosses to determine whether there is a significant difference between the two crosses in the fraction of female progeny produced at 24°C, 32°C, and 36°C.

(c) For each cross, describe whether genetics or temperature determines the sex of progeny produced from eggs incubated at 35°C. For each cross, describe whether genetics or temperature determines the sex of progeny produced from eggs incubated at 24°C.

(d) Predict the effect of increasing global temperatures on the continued presence of the W chromosome in this species of lizard. Scientists claim that, in this species, the W chromosome is unimportant in sex determination. Instead, proteins that are encoded by a gene or genes on the Z chromosome, and that are maximally expressed only at certain temperatures, are responsible for determining whether embryos will develop as females or males. Use the data to support this claim

Answer 1

Answer:

A) The Z chromosome trait is sex-linked. Theoretically, the lizards with the ZW(f)genotype would be more likely to express the recessive trait because it would only need one recessive allele. The lizards with the ZZ(m) genotype would need two recessive alleles (one from each parent) to express the trait.

Explanation:

Answer 2

This research data show that the sex determination is affected by temperature.

(A) It is because ZW only need only one recessive allele to be expressed while ZZ need two recessive allele to express the gene.

(B) At $\rm \bold {36^\cdot C}$ only female offspring will produce. For graph find the attachment.

(C) According to given data, At $\rm \bold {35^\cdot C}$ the sex is completely determined by temperature. While at $\rm \bold {24^\cdot C}$ the sex is affected by genes because ZZ produce only males at this temperature.

(D)  According to the data if there will be permanent increase in temperature more than  $\rm \bold {30^\cdot C}$. There will no need of W chromosome to produce female offspring. Hence it might be lost.

ZZ is male below $\rm \bold {28^\cdot C}$. This proves temperature affect the sex determination.

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