Lesson hub

## Can't find the answer? Try online tutoring

We have the UK’s best selection of online tutors, when and for how long you need them.

Getting 1-on-1 support is cheaper than you might think.

### Participating users

Welcome to our free-to-use Q&A hub, where students post questions and get help from other students and tutors.

You can ask your own question or look at similar Biology questions.

To answer the last part you need to know the expected number of double crossovers which you normally calculate using observed data e.g. 498 flies had ruby eyes

1b) ......ct.....

rb<-----20...>t

1c) cut wing 500, ruby eyed and tan body 500, normal 1000

There are lots of things to consider when answering this question.

Firstly all of the traits are recessive.

Males = XY Females =XX

Homozyous means both chromosomes have the same alleles (form of a gene)

I would start by mapping out the traits like this:

rb<---12.5----->ct<----7.5----->t

We start by crossing a ct Male (who therefore has the chromosomes XY) with the female (XX) who is homogenous.

This means the male only has the ct trait on his X chromosome and the female has the recessive versions of rb and t on each X chromosome.

To cross them make a grid like on the whiteboard.

The F1 female will inherit one X chromosome from the male and one from the female. So on one X chromosome will have the ct and the other will have rb and t. However because all the traits are recessive and feature on only one of the two chromosomes none of these traits will actually display themselves and so the F1 female will normal. Or wont have cut wings, ruby eyes or tan body.

i need help finding the answer for this question