How can this fly can produce gametes containing four different combinations of alleles?Which are recombinant gametes?how are recombinants produced?
In fruit flies, the genes for wing shape and body stripes are linked. In a fly whose genotype is WwSs, W is linked to S, and w is linked to s. Also, which are parental-type gametes?
Boy, this is confusing, isn't it? Let me see if I can make some sense for you.
First of all, understand each one of those letters stands for an allele, which is a form of a gene that codes for the expression of a certain phenotype, or how that trait will appear physically. For example, the W probably is the allele for the dominant wing shape, while the w is the allele for recessive wing shape. The S is the allele for stripes, while the s is the allele for non-striped.
From those four different letters, it is possible to come up with four different types of genotypes. You could have WWSS, which would be purebred homozygous dominant wing/striped body. You could also have WwSs, which would be heterozygous dominant wing/striped body. You could get the combinations, WWSs, or WwSS. And last but not least, you could get an expression of the recessive traits, wwss, purebred homozygous recessive for recessive wing/non-striped body.
Do not think all the capital letters have to stick together; it is possible for the W to link to an s, just as well as a w could link to an S. The capital letter simply stands for the dominant allele, while the lower case stands for the recessive allele.