Introduction to Veterinary Anatomy and Physiology Textbook - E-Book by Aspinall Victoria; Cappello Melanie; & Melanie Cappello

Author:Aspinall, Victoria; Cappello, Melanie; & Melanie Cappello [Aspinall, Victoria & Cappello, Melanie]
Language: eng
Format: epub
Publisher: Elsevier Health Sciences
Published: 2015-03-25T00:00:00+00:00

Back-crossing to the recessive

This is a technique using test matings to ascertain whether an animal is carrying a particular recessive gene. This may be a gene that causes a harmful condition such as the eye disease progressive retinal atrophy or, in more minor cases, an unwanted coat colour. A recessive gene will only be expressed if an animal is homozygous for that gene. If the animal is heterozygous, the gene will not be expressed but the animal will carry the gene and may pass it on to its offspring.

For example: progressive retinal atrophy (PRA) is a condition seen in breeds such as Labradors, Golden Retrievers, Collies and Spaniels. It causes gradual deterioration of the retinal blood vessels and results in blindness by the time the dog is about 18 months old. It is important to identify carriers of the gene so that they do not pass it on to their puppies.

Let the gene for normal sight be S.

Let the gene for PRA be s.

Thus dogs with:

• the genotype SS will have normal sight

• the genotype ss will have PRA and go blind by 18 months old

• the genotype Ss will have normal sight but will be carriers of this recessive gene

The suspect bitch under investigation could have the genotype Ss or SS.

1. Suppose the suspect bitch is Ss.

Mate her to a dog who is known to have PRA and will therefore have the genotype ss.

The F1 generation will be:

Download

Copyright Disclaimer:
This site does not store any files on its server. We only index and link to content provided by other sites. Please contact the content providers to delete copyright contents if any and email us, we'll remove relevant links or contents immediately.