Re: will breeding a purebred with a mutt affect all future ofspring?

Yes, it certainly will, and I'll briefly explain why, although you'll find some information about this in every encyclopedia etc.

Information about how to 'build organisms' are passed down from generation to generation as genes, made from DNA. These genes are used to make proteins, and small difference in these proteins, due to small differences in the genes, then effect what we look like as well as causing diseases like cystic fibrosis, sickle-cell anemia etc.

The genes come on chromosomes, and we have two copies of each of 23 chromosomes. One of these copies come from our father and one from our mothers, and the copies of these chromosomes they pass on contain material from all of our grandparents - your father received one set of chromosomes from your paternal grandfather and one from your paternal grandmother, but the single set of chromosomes that you received in the sperm that fertilised one of your mother's ova were a combination of these two sets, due to a process called recombination which occurs during the formation of ova and sperm cells.

Because you have two copies of each gene, a phenomenon called dominance means that sometimes you appear to show a characteristic of only one of your parents - for example you might have your mothers' brown eyes because the gene for brown eyes that your mother passed on is dominant to a gene for blue eyes. This doesn't mean that you aren't still carrying a copy of the gene from your father, however, so your children could still get a blue-eye gene from you.

The offspring of your purebred and mongrel dogs would have half the genes from the purebred parent and half from the mongrel, so on average you would expect it to look in-between the two parents - it could have its mothers eyes, fathers pointy ears, mothers kinked tail, fathers wiry hair but mothers coat colour, and a thousand other characteristics - its this that gives it the obvious mixed-up look. Many other characteristics will be a mixture of the parents - for example it might ahve a eyes that are the same colour you'd get if you mixed the two parent's eye colours together, cos many gene work like this instead.

However, its important to remember that it is only the physical appearance of the offspring (the phenotype) that are a mixture - the genes remain distinct, so the next generation will on average have one quarter of the genes from each grandparent, one eight from each great-grandparent, one sixteenth from each great-great-grandparent. Even if you only breed the offspring of the 'mutt' with pedigree animals afterwards, future generations will still have some genes from this dog, and they could be expressed for many generations. Each generation will have fewer and fewer non-pedigree genes, but the dogs probably won't look exactly pedigree. That's why dog breeders are so interested in the breeding history and pedigree of dogs they use to breed from - a dog can look perfectly OK, but be carrying genes that might be expressed in the offspring.

I hope this helps - you can find out more in any school biology textbook, and there are probably loads of books available specifically on dog breeding or dog genetics, too.

Yours, James Cotton