Question

Drosophila Dihybrid Cross Chart Red-eyed female x white-eyed male Cross 1: Red tape White-eyed female x red-eyed male) Cross 2: White tape (Reciprocal eross) Vial ID A B Genotype Phenotype Genotype Phenotype P1 Y Y B Vial A Phenotype Genotype Phenotype Genotype ID F1 Y B A Phenotype Vial ID Genotype Phenotype Genotype F2 Y Y Y Y Y Y Y 35

Answer 1

Types of inheritance

Autosomal inheritance scheme is associated to non-sexual chromosomes, meaning that both females and males are the same. In a Sex link or allosome genes inheritance the genotype and the phenotypes depend of sex, where females have three possible genotypes and males only two. In D. melanogaster and in humans males are XY and females XX, where the X chromosome carries the allosome gene .Both types must follow another genetic scheme, the most to be studied are dominant-recessive and codominant scheme. The dominant recessive only has two phenotypes but three genotypes, the codominant has 3 of both were the heterozygous express both the recessive and the dominant. A variation of these is when a homozygous is lethal, meaning that having two of the same allele is not possible.

For a test cross one must always use a homozygous individual. This means that in this exercise we will have an X^WX^W female and an X^w-Y male. Females can only be white eyes in X^w-X^w- genotypes.

Cross1: the P1 ♀ genotype X^WX^W and a ♂ X^w-Y and the phenotypes are ♀ Red eyes ♂ white eyes.

Cross2: the P1 ♀ genotype X^wX^w- and a ♂ X^WY and the phenotypes are ♀ white eyes ♂ red eyes.

F1 is the resulting descendants of the Cross1 and cross 2 with their genotypes and phenotypes below the table

♀ XWXW x ♂Xw-Y	XW	XW
Xw-	XWXw-	XWXw-
Y	XWY	XWY

Cross 1= has 50% of females with red eyes and 50% of males with red eyes. With 100% of females X^WX^w- and 100% of males X^WY.

♀ Xw-Xw- ♂ XWY	XW-	XW-
XW	XWXw-	XWXw-
Y	XW-Y	XW-Y

Cross 2= has 50% of females with red eyes and 50% of males with white eyes. With 100% of females X^WX^w- and 100% of males X^W-Y.

Has you can see only females behave in mendelian proportions but males show that it is sex linked.

F2 is the crees between the descendants of F1( P2), in this case the cross is single has there is only type of female and one type of males.

♀ XwXw- ♂ XWY	XW	XW-
XW	XWXW	XWXw-
Y	XWY	XW-Y

Cross 1 of F2 has 50% of the males with red eyes and 50% with white eyes, females have 100% with red eyes. The genotypes are 50% X^WX^W and 50% X^WX^w- for the females, and 50% X^WY and 50% X^W-Y for males.

♀ XwXw- ♂ Xw-Y	XW	XW-
Xw-	XWXw-	Xw-Xw-
Y	XWY	XW-Y

Cross 1 of F2 has 50% of the males with red eyes and 50% with white eyes, females have 50% with red eyes and 50% with white eyes. The genotypes are 50% X^WX^w- and 50% X^w-X^w- for the females, and 50% X^WY and 50% X^W-Y for males.

The average fitness of the population would decrease because they were selected by a moist environment or the mosquitos.