Fruit flies with one allele for curly wings (cm and one allele for normal wings (cy+) have curly wings. when two curly- winged flies were crossed, 203 curly-winged and 98 normal-winged flies were obtained. in fact, all crosses between curly- winged flies produce nearly the same curly : normal ratio among the progeny. a. whet is the approximate phenotypic ratio in these offspring? b. suggest an explanation for these date. c. if a curly-winged fly was mated to e normal- winged fly. how many flies of each type would you expect among 180 total offspring?

a) 2:1 (Curly:normal); b) The mutation is lethal in homozygosis; c) 90 will have curly wings, 90 will have normal wings.

Explanation:

The mutation for curly wings Cy is dominant over the recessive wild-type allele Cy+.

In order to see normal-winged flies in the progeny, the curly-winged parentals must have been heterozygous.

The cross was:

CyCy+ x CyCy+

The expected offspring (obtained from a Punnett Square of the cross) is:

The expected phenotypic ratios are 3:1.

However, those were not the observed proportions.

a) Out of a total of 301 progeny, 203 were curly-winged and 98 were normal-winged. 203/301 is approximately 2/3, and 98/301 is approximately 1/3, so the observed phenotypic ratio is 2:1.

b) The observed phenotypic ratio in all crosses suggests that the genotype CyCy is lethal and never appears in adult flies.

c) From a Punnett Square we can determine that a cross between the flies CyCy+ (curly winged) and Cy+Cy+ (normal winged) would give the offpsring:

Among 180 total offspring, half of them (90) will have curly wings, and half (90) will have normal wings.

the menstrual cycle – higher tier. negative feedback mechanisms affect the production of hormones in the menstrual cycle. oestrogen also stimulates the release of lh (luteinising hormone) from the pituitary gland, which in turn controls the production of progesterone.