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| Question | Answer |
| heterogametic sex | because males produce two different types of gametes with respect to the sex chromosomes (XO), they are said to be the ________. |
| homogametic sex | females that produce gametes that are all the same with respect to the sex chromosomes are the (XX) ________. |
| hemizygosity | males possess (in drosophila) only a single X chromosome and can only carry a single eye-color allele. Males therefore cannot be either homozygous or heterozygous but are said to be ________ for the X-linked loci |
| nondisjunction | about 10% of the time, the two X chromosomes in the females fail to separate in anaphase I of meiosis, a phenomenon known as ________. When ________ of the Xs occurs, half of the eggs receive two copies of the X chromosome and the other half receive only a Y chromosome. |
| 2. Although mammals and fruit flies use XY determination, the mechanisms are different. What determines "maleness" in these two groups? | in drosophila, males have one X chromosome and females have two X chromosomes. In mammals, males have a Y chromosome and females have two X chromosomes. (The gene on the Y chromosome makes them male). |
| 3. Explain how reciprocal crosses can be used to infer that a trait is influenced by a sex-linked gene. | A reciprocal cross allows us to test the role of parental sex on a given inheritance pattern. In one cross, a male expressing the trait of interest will be crossed with a female not expressing the trait. In the other, a female expressing the trait of interest will be crossed with a male not expressing the trait. |
| 4. How did Bridges' study of eye color in fruit flies help establish that genes are on chromosomes? | The significance of Bridges' study is that he was able to link the inheritance of a specific gene (w) to the presence of a specific chromosome (X). The association between genotype and chromosomes gave unequivocal evidence that sex-linked genes are located on the X chromosome and confirmed the chromosome theory of inheritance. |
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