Heredity

Facts:

gene A sequence of DNA that occupies a specific location on a chromosome and determines a particular characteristic in an organism. For example: The gene for eye color.

allele One member of a pair of genes that occupy a specific position on a specific chromosome.

dominant allele Represented by a capital letter. The gene that when present produces the characteristic it represents.

probability The chance of an offspring inheriting a certain characteristic.

Punnet square A grid used to predict the probable outcome of a genetic cross.

recessive allele Represented by a lower case letter. It takes a pair of recessive alleles for the characteristic to be present.

In Drosophila melanogaster (fruit flies), red eye color (R) is dominant over brown eye color (r). If the flies shown were crossed, what percent of their offspring would be expected to have brown eyes?

Think:
1. Compare the male and female diagrams of fruit flies. How does one determine the gender?

The female fly has a pointed abdomen (tail end).

2. The female fly has these alleles for eye color, Rr, which means she has one dominant gene for red eyes and one recessive gene for brown eyes. The male has two recessive genes for brown eyes, rr. What are the possible combination of the alleles from these parent flies?