Performing Monohybrid Crosses

A monohybrid cross is addressing the inheritance of one gene.Answer the following questions:

Question 1:

Drosophila melongaster, more commonly known as thefruit fly, can have red or white eyes. You breed a red-eyed fly toa white-eyed fly and get 50 offspring that all have red eyes. Whichtrait is dominant?

Question 2:

Consider an offspring from the previous question. Its phenotypeis red eyes.

What is its genotype? (Circle one of the choices below)

Homozygous dominant, Heterozygous, or Homozygous recessive

Question 3: (2pts)

Next, you perform a cross of two heterozygous, red-eyed flies.They have 100 offspring. How many of these offspring do you predictwill have red eyes? Show your work using a Punnett square. [Useletters R and r to designate the alleles]

Question 4:

Suppose you found a fly that had escaped and was flying aroundyour lab. He has red    eyes, but you do not know hisgenotype. To find out, you cross him with a white eyed fly (sinceyou know her genotype). The result is 50% white eyed and 50% redeyed offspring. What is the escaped fly’s genotype? Explain how youknow.

X-linked Inheritance

Consider this imaginary animal, the tree rat. They are usuallyblack, but sometimes they can be purple. The allele for the purplecolor is X-linked. You manage to capture two of these animals fromthe same family, a black female and her purple male offspring.

Question 5:

What is the genotype of the black female mother?

Question 6

Do you know the phenotype of the father based on the maleoffspring? Why or why not?

Question 7: (2pts)

Next you breed the tree rats to each other (inbreeding isacceptable in this case). What percent of the offspring do youexpect to be purple? Are any of them female? Use a Punnett squareto show your work. [Use the letters B (black) and b (purple) torepresent the alleles.]