Answer to Question #194298 in Genetics for bianca

Question

 Indicate whether to cross (i) mutant females with wild-type males, or (ii) mutant males with wild-type females, or (iii) both (i.e. reciprocal crosses), to produce an F1 generation that will enable you to determine if the traits are dominant or recessive, and if they are sex-linked (on the X chromosome). Draw mating diagrams and Punnett squares to support your answer.

To determine whether the mutant genes are independent or linked, a testcross is more appropriate than using data from the F2 generation. Knowing which are the recessive genes, indicate which individuals you would mate in this testcross. Draw a mating diagram & use the forked line method to predict the outcome of this cross.

 

Conduct the appropriate testcross using Drosophila Lab, record your results and indicate whether the three mutant genes are inherited independently or whether they are linked? Include a chi square analysis to support your conclusion.

 

Answer 1

(a)

The reciprocal cross is the two parallel crosses and involves the same genotype of both the parents but the sex is opposite in the two crosses. For example, the reciprocal cross of female AA and male aa and female aa and male AA. The autosomal inheritance will result in the same genotypes as the autosomal transfer occurs in the same way from parent to offspring for both sexes. The transfer of plastids and chloroplast does not occur in the same way for both sexes. The genes will always inherit from the mother in the reciprocal cross in case of maternal inheritance. 

Therefore, option (iii) given as "both (i.e. reciprocal crosses)" is the correct answer.

(b)

Mutant gene possess loci that are usually sort out together at a higher frequency than fore cased by random assortment of chromosomes. The mutant gene specify that the loci are present on the alike chromosome. Hence it is known as linked gene for the said loci.

Below there is using a forked line method to represent the mating diagram:

(c)

Let's consider X^w X^w as the mutant female whereas X⁺ Y is the wild-type male. and X^R X^R is the wild type female for red-eye and X^w Y is the white-eyed male.

  i.mutant females with wild-type males

Mutant female (X^w X^w) x wildtype male (X⁺ Y) will give 2X⁺X^w,2 X^w Y. which means female wild type and male mutant.

ii. mutant males with wild-type females

Wildtype female (X^R X^R) x Mutant male (X^w Y) will give 2 X^R X^w,2 X^R Y. All red-eyed.

(iii)both (i.e., reciprocal crosses) 

 

X^R X^w X X^R Y will give X^R X^R, X^R Y, X^w Y, X^R X^w

 The gene for White-eye color in Drosophila has located on the X chromosome but not the Y chromosome. Genes on the X chromosome that determine a trait are called sex-linked. Hence the pattern is known as crisscross inheritance as the father passes a trait to his daughter, chi-squared test, cannot be obtained without the appropriate observed and expected values given.