The fruit fly Drosophila melanogaster is one of the most important model organisms in genetics. Much of what we know about linkage, sex-linkage and chromosome mapping came from breeding experiments with it, starting with Thomas Hunt Morgan in the early 1900s.It is ideal for genetic crosses because:• it has a short life cycle (about 10 days at 25 °C), so many generations can be studied quickly
• each female lays hundreds of eggs, giving large samples and reducing sampling error
• it is small, cheap and easy to keep in bottles on simple food
• males and females are easy to tell apart
• it has only four pairs of chromosomes
• many mutations have easily seen phenotypesCommon mutant phenotypes include vestigial wings (short, crumpled wings), ebony body (dark body), white eyes instead of the normal red, and curly wings. The normal phenotype found in wild populations is called the wild type.Worked example: in Drosophila, the allele for normal wings (V) is dominant to the allele for vestigial wings (v). Two heterozygous flies (Vv × Vv) are expected to give 3 normal-winged : 1 vestigial-winged offspring. From 400 offspring, about 300 would have normal wings and 100 vestigial wings.Morgan's discovery that the white-eye mutation appeared mostly in males led to the idea of sex-linked genes. Crosses involving several Drosophila genes at once also showed that some genes do not assort independently.
• each female lays hundreds of eggs, giving large samples and reducing sampling error
• it is small, cheap and easy to keep in bottles on simple food
• males and females are easy to tell apart
• it has only four pairs of chromosomes
• many mutations have easily seen phenotypesCommon mutant phenotypes include vestigial wings (short, crumpled wings), ebony body (dark body), white eyes instead of the normal red, and curly wings. The normal phenotype found in wild populations is called the wild type.Worked example: in Drosophila, the allele for normal wings (V) is dominant to the allele for vestigial wings (v). Two heterozygous flies (Vv × Vv) are expected to give 3 normal-winged : 1 vestigial-winged offspring. From 400 offspring, about 300 would have normal wings and 100 vestigial wings.Morgan's discovery that the white-eye mutation appeared mostly in males led to the idea of sex-linked genes. Crosses involving several Drosophila genes at once also showed that some genes do not assort independently.