How does the inheritance of sex chromosomes result in approximately equal numbers of males and females among the offspring of fruit flies?

The male sex chromosomes are X and Y. One-half of male gametes will contain a Y chromosome and one-half will contain an X chromosme; the number of male offspring and the number of female offspring are approximately equal as a result.

Offer an explanation to why Morgan did not find white-eyed female Drosophila in the F2 generation when he crossed white-eyed males with red-eyed females.

THe mutant allele for white eyes is X-linked, so a female Drosophilia must have two copies of the mutant allele in order to be white-eyed. A male who has only one mutant allele for white eyes will be white-eyed because he has only one X chromosome.

How does crossing-over show that genes are found on chromosomes?

Crossing-over does not create new genes or old ones. It changes the locations of genes among the chromosomes that carry them- new combinations.

How can crossing-over between two alleles be used to map their locations on chromosomes?

The percentage of crossing-over between the genes for two traits is proportional to the distance between them on a chromosome.

What are point mutations?

The substitution, addition, or removal of a single nucleotide.

How can nondisjunction change chromosome number?

If it occurs during human egg formation, one egg will have 22 chr. instead of reg. 23; another will have 24; if one combines with normal sperm-zygote will have 45 or 47 chr. instead of reg. 46.

Is pattern baldness a sex-linked trait or a sex-influenced trait? Explain your answer.

Sex-influenced. Gene expression can be the same on paper (BB'). A woman won't lose her hair, but a man will. Differences in gene expression are due to higher levels of testosterone in men, which interacts with genotype BB' to produce baldness in men.

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CH.12 Sec.1 & 2

Question	Answer
How does the inheritance of sex chromosomes result in approximately equal numbers of males and females among the offspring of fruit flies?	The male sex chromosomes are X and Y. One-half of male gametes will contain a Y chromosome and one-half will contain an X chromosme; the number of male offspring and the number of female offspring are approximately equal as a result.
Offer an explanation to why Morgan did not find white-eyed female Drosophila in the F2 generation when he crossed white-eyed males with red-eyed females.	THe mutant allele for white eyes is X-linked, so a female Drosophilia must have two copies of the mutant allele in order to be white-eyed. A male who has only one mutant allele for white eyes will be white-eyed because he has only one X chromosome.
How does crossing-over show that genes are found on chromosomes?	Crossing-over does not create new genes or old ones. It changes the locations of genes among the chromosomes that carry them- new combinations.
How can crossing-over between two alleles be used to map their locations on chromosomes?	The percentage of crossing-over between the genes for two traits is proportional to the distance between them on a chromosome.
What are point mutations?	The substitution, addition, or removal of a single nucleotide.
How can nondisjunction change chromosome number?	If it occurs during human egg formation, one egg will have 22 chr. instead of reg. 23; another will have 24; if one combines with normal sperm-zygote will have 45 or 47 chr. instead of reg. 46.
A husband and wife have the ABO blood group genotypes IAIB and ii. What ABO blood types can their children have?	AB and O
Inheritance of Huntington's disease.	Autosomal dominant.
Inheritance of Sickle Cell Anemia.	Autosomal recessive.
Is pattern baldness a sex-linked trait or a sex-influenced trait? Explain your answer.	Sex-influenced. Gene expression can be the same on paper (BB'). A woman won't lose her hair, but a man will. Differences in gene expression are due to higher levels of testosterone in men, which interacts with genotype BB' to produce baldness in men.

Created by: bio-williamson

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