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What does it mean for an X-chromosome deletion to be lethal when hemizygous or homozygous?
In the fruit fly (D. melanogaster), a known deletion on the X chromosome removes both a gene involved in the fly's development and the gene for eye color. The deletion is lethal when homozygous or hemizygous. Flies that are heterozygous for the mutation are viable, but have indentations at the wing margin. Therefore, the deletion is named the Notch mutation. The allele for wild type eyes is dominant over the allele for white eyes. Predict the phenotypic ratio of the offspring from from a cross between a white-eyed notched female and a wild-type male.
a) 1 wild type female; 1 notched female; 1 white-eyed male; 1 white-eyed notched male
b) 1 white-eyed female; 1 notched female; 1 white-eyed male
c) 1 white-eyed notched female; 1 wild type female; 1 white-eyed notched male; 1 wild-type male
d) 1 wild-type female; 1 notched female; 1 white-eyed male
3 Answers
- SmegheadLv 75 years ago
Homozygous for the mutation means you have two X chromosomes (you're a female) and both copies have the mutation on them.
Hemizygous for the mutation means you only have one X chromosome (you're a male) and it has the mutation on it.
- 5 years ago
You have to understand what Hemi/homozygous means first. Hemizygous is when only one chromosome is present. Homo is when both chromosomes are the same. Therefore, if you only have one chromosome and its' deleted, its' fatal. And if you have two of the same, they are both deleted, and it is equally fatal. However, if you have a mix it is not fatal, rather, it results in a notched wing.
Mixes make
