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In chickens, males have two Z sex chromosomes (ZZ) and females have one Z and one W sex chromosome (

Emma

Answers

Yes - this is on the OCR Biology syllabus isn't it? The situation in chickens is that the males are XX (or ZZ they call it to prevent confusion) while in humans this would be a female of course. Females chickens are XY (or ZW). There are rather complex reasons for this in terms of evolution that you don't need to know. You just need to be able to do a punnett square. Thanks Jon

Jonathan C.

05 April 2013

mapping gene

The genes for ruby eyes (rb), tan body (t) and cut wings (ct) are all found on the X-chromosome of Drosophila melanogaster. All of these are recessive traits. They map in the order rb, ct, t with 12.5 map units between rb and ct and 7.5 map units between ct and t. Suppose you cross a cut wing male with a homozygous female that is both tan and has ruby eyes.
What will the F1 females look like?
Draw map of the section of the X chromosomes that has these 3 genes for the F1 females
Assume you testcross your F1 females.
What progeny classes would you expect? ii. Give approximate numbers for each class based on a total of 2000 progeny.
Assuming the i=1 and there are no double crossovers.
Assuming the i=0 and there are the expected number of double crossovers.

Emma