You may wish to open the assessment now so you can see the questions you need to answer as you work through the next few pages. The assessment can be found in CMB1005 on Canvas in the Strand D under Genetics Practical 3: gene Linkage. If you cannot see your assessment please email Dr Jeremy Brown.

You will also investigate eye colour genetics as you have observed that in Rusty and Brown rats, Red eyes are common, in Tan rats Orange eyes are common. You will use true breeding lines again to set up crosses.

The answers from crosses 7, 8 and 9 will provide the answers you need for the post-practical assessment.

To check your hypothesis regarding dominance of eye colour you set up a new cross. You cross a Brown coated, Red eyed rat with a Tan coated, Orange eyed rat and get all Rusty coloured, Red eyed rats (litter 7).

In order to determine if there is a linkage relationship you set up two test crosses where only 2 characteristics are heterozygous per cross. You should test both of these using the Punnett calculator; note one parent in these crosses is homozygous recessive for two characteristics; in the other parent these characteristics are heterozygous.

Therefore, you decide to cross: Rusty coated, Red eyed rats x Brown coated, Orange eyed rats

Next you cross Rusty coated, Red eyed rats x Tan coated, Orange eyed rats.