epistasis

PROBLEM ON EPISTASIS

WHATIS EPISTASIS?EPISTASIS IS THE INTERACTION OF ONE GENE IS MODIFIED BY ONEOR SEVERAL OTHER GENES, WHICH ARE SOMETIMES CALLED MODIFIERGENES. THE GENE WHOSE PHENOTYPE IS EXPRESSED IS SAID TO BEESPISTATIC, WHILE THE PHENOTYPE ALTERED OR SUPPRESSED IS SAID TO BEHYPOSTATIC. THE NORMAL F2 DIHYBRID PHENOTYPIC RATIO IS 9:3:3:1 -EPISTASIS RESULTS IN DEBVIATIONS FROM THE RATIO.

1.) A WOMAN WITH BLOND HAIR AND RECEDING CHIN MARRIES A MAN WHO HASDARK HAIR AND HAS NORMAL CHIN.WHAT ARE THE POSSIBLE GENOTYPESAND PHENOTYPES OF THEIR OFFSPRING?

MALE FEMALE

P HHCC X hhcc F1 ALL FOUR WILL HAVE THE HhCc ALLELES F2 HC Hc Ch hc

HC Hc hC hc

HC HHCC HHCc HhCC HhCc

Hc HHCc HHcc HhCc Hhcc

hC HhCC HhCc hhCC HhCc

hc HhCc Hhcc hhCc hhcc

PHENOTYPES-DARK HAIR, NORMAL CHIN- 9 – 56%-DARK HAIR, RECEEDING CHIN- 3 – 19%-BLONDE HAIR, NORMAL CHIN- 3 – 19%-BLONDE HAIR, RECEEDING CHIN- 1 – 6%

PHENOTYPIC RATIO9:3:3:1

56%:19%:19%:6%

PROBLEM ON SEX-LINKED TRAITS

2.) A MOTHER WHO CARRIES AN ALLELE FOR HEMOPHILIA AND HAS A LARGE EAR IS MARRIED TO A MAN WHO IS NON-HEMOPHILIAC AND HAS A SMALL EARS. WHAT ARE THE POSSIBLE GENOTYPES AND PHENOTYPES OF THEIR OFFSPRING?

MALE FEMALE

P XHeY XHEXhE

F1 ONLY 3 IS NORMAL F2

XHe Y Xhe Y

XHE XHEXHe XHEY XHEXhe XHEY



XhE XhEXHe XhEY XhEXhe XhEY

PHENOTYPES-FEMALE, NORMAL – 3 –19%-MALE, NORMAL - 7 – 44%-FEMALE, CARRIER OF HEMOPHILIA - 4 – 25 %-FEMALE, HEMOPHILIAC, SMALL EARS - 1 – 6%-MALE, HEMOPHILIAC, BIG EARS – 1 – 6%

PHENOTYPIC RATIO

3:7:4:1:1

19%:44%:25%:6%:6%



MALE FEMALE

P XHeY XHEXhE

F1 ONLY 2 IS NORMAL F2

XHe Y Xhe Y






PHENOTYPIC RATIO

3:7:4:1:1

19%:44%:25%:6%:6%



MALE FEMALE

P XHeY XHEXhE

F1 ALL IS NORMAL F2

XHe Y Xhe Y






PHENOTYPIC RATIO

3:7:4:1:1

19%:44%:25%:6%:6%

epistasis

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