Question
TOPIC – 5.3 Mendelian Genetics
(a) – TOPIC – 5.3 Mendelian Genetics
(b) – TOPIC – 5.3 Mendelian Genetics
In the tongue sole fish (Cynoglossus semilaevis), sex is determined by a combination of genetics and environmental temperature. Genetically male fish have two Z chromosomes (ZZ), and genetically female fish have one Z chromosome and one W chromosome (ZW). When fish are raised at 22℃, ZZ fish develop into phenotypic males and ZW fish develop into phenotypic females. However, when fish are raised at 28℃, the Z chromosome is modified (denoted as Z*). Z*W individuals develop as phenotypic males that are fertile and can pass on the Z* chromosome to their offspring even when the offspring are raised at 22℃. A cross between a ZW female and a Z*Z male is shown in the Punnett square below.
(a) Predict the percent of phenotypic males among the 22℃ \(F_{1}\) offspring of the cross shown in the Punnett square if the offspring are raised at .
(b) At least one Z or Z* chromosome is necessary for survival of the fish. A researcher crossed two fish and observed a 2:1 ratio of males to females among the offspring. Based on the information, identify the genotype of the male parent in the cross. Describe ONE fitness cost to the female of mating with this particular male.
Answer/Explanation
Ans:
(a) Predict the percent of phenotypic males among the \(F_{1}\) offspring of the cross shown in the Punnett square if the offspring are raised at 22°C.
Prediction (1 point)
75%
(b) At least one Z or Z* chromosome is necessary for survival of the fish. A researcher crossed two fish and observed a 2:1 ratio of males to females among the offspring. Based on the information, identify the genotype of the male parent in the cross. Describe ONE fitness cost to the female of mating with this particular male.
Identification (1 point)
Z* W
Description (1 point)
• Fewer offspring will develop/survive.
• 1/4 of the offspring are predicted to die.
• Some of her offspring will have the Z* chromosome/all of her male offspring will have a Z* chromosome.
(a) The percent of pherotupremales among the F1 offspring of the cross shown the Punnett square if the offspring are raised at 220C is about 75%.
(b) The genotypes of the male parentin the cross is Z*W. A fitness cost of the female of marting with pastaularmale would be that only 75% of their offspring will survive, as 25% percent of the offspring will have a genotype of WW; which in turn shows the reduction of offspring surround.