When a normal female (XX, +/tra) Drosophila is crossed with a normal male (XY, tra/tra), what would be the percentage of males ?
To determine the percentage of males in the offspring of a cross between a normal female Drosophila (XX, +/tra) and a normal male Drosophila (XY, tra/tra), we need to understand the principles of Drosophila genetics.
In Drosophila, the sex determination system is based on the presence or absence of the Y chromosome. Males have one X and one Y chromosome (XY), while females have two X chromosomes (XX). Additionally, there is a gene called transformer (tra) that plays a crucial role in sex determination.
In this specific cross, the female is normal (XX, +/tra) and the male is normal (XY, tra/tra). The "+" symbol indicates that the gene involved in sex determination is functional.
To determine the percentage of males in the offspring, we need to consider the genetic inheritance patterns.
1. The female parent (XX, +/tra) will contribute an X chromosome to all of her offspring, as she only possesses X chromosomes.
2. The male parent (XY, tra/tra) will contribute either an X or a Y chromosome to its offspring.
Now we can analyze the possible combinations of sex chromosomes that result from this cross:
- Female offspring: When the female parent contributes an X chromosome, and the male parent contributes an X chromosome, the result is XX, which corresponds to a normal female.
- Male offspring: When the female parent contributes an X chromosome, and the male parent contributes a Y chromosome, the result is XY, which corresponds to a normal male.
Based on the above analysis, we can conclude that all the offspring from this cross will be either XX (female) or XY (male), with a 1:1 ratio. Therefore, the percentage of males would be 50%.
To summarize, when a normal female (XX, +/tra) Drosophila is crossed with a normal male (XY, tra/tra), the resulting offspring will have a 50% chance of being males.