Answer:
1. Read the problem.
2. Determine what traits are dominant and which are recessive. Often you must marshal background knowledge to do this – which may not be explicitly mentioned in the problem.
3. Are any letters assigned to the genes? If not, make some up. We usually take the dominant characteristic and use the first letter of that word. For example, if polydactyly ( extra fingers ) is dominant over the normal five–fingered condition, we would pick P for the dominant gene, and small p for the recessive normal allele.
4. Determine, if possible, the genotypes of the parents. In 9 out of 10 problems this information is given, or at least implied. Sometimes you have to deduce it from other information given. Write it down so that you can remember what it is, e.g. Pp.
5. Determine all the possible kinds of gametes that can be made by each parent. Be careful, remember that a gamete can ordinarily receive only one gene of a pair of alleles. This is the part that most people have trouble with! e.g. P p.
6. Make a Punnett square, using each of the gametes for one parent across the top of each column, those of the other parent go vertically. If you have done step 5 properly you shouldn’t have any trouble with this step.
7. Work the cross carefully.
8. Now read the problem again. Find out exactly what it is asking for. Don’t assume too much. This is another place where many people get lost.
9. In most problems, these steps should get you through adequately. Some are slightly altered – for example, if the genotype of one of the parents is unknown, and that is what the problem wants you to discover. You may assign that parent something like A_ or __ genotype and see if that helps. Put the offspring genotypes in the square and work backward. Remember this won’t get all the problems – there is still nothing like real understanding – but it can help organize your attack on a genetic problem. and of curse, unless you understand the terms, such as homozygous, heterozygous, dominant, recessive, allele, and so on, you cannot begin to think of working problems.
10. Finally, the actual genetic information you need to solve these problems often appears concealed rather than revealed by the wording of the problem. learn to translate such a sentence, “Mary is normally pigmented but had an albino father”, into its logical consequence: “Mary is heterozygous for albinism” and then into “Mary is Cc”. Notice that, in this kind of a problem you may need to solve several subsidiary problems before you can proceed with the final solution.
