BIOS 242 reading 4 - expression of many genes on their sex chromosom...

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BIOS 242 reading 4

• Despite the fact that human males are XY and human females are XX, they have equal

expression of many genes on their sex chromosomes. This phenomenon is called –Answer dosage compensation

• In Drosophila, an X-linked gene confers an apricot eye color. Which of the following would

have a very similar phenotype?–Answer Homozygous females and hemizygous males

• In somatic cells of human females one of the two X chromosomes is ran- domly turned off.

What is this mechanism called?–Answer X-chromosome inactivation

• In C. elegans, dosage compensation occurs in the by

diminishing the expression of X-linked genes on both X chromosomes to approximately 50% of that in the .–Answer hermaphrodite; male

• In birds males are ZZ and females are ZW. Studies have shown that male birds express

twice as much gene product of some Z-linked genes. What does this suggest?–Answer Z-linked genes are not dosage compensated in birds.

• What accounts for equal expression of genes on the sex chromosomes despite the fact that

males and females have an unequal complement of sex chromosomes?–Answer dosage compensation

• Which species achieves dosage compensation by inactivating the paternal- ly derived X

chromosome in all somatic cells of a female?–Answer Marsupial mammals 1 / 2

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• Two copies of the apricot allele in the female fruit fly produce a phenotype that is similar to

that produced by one copy in the male. This is an example of the phenomenon of –Answer dosage compensation

• What is a Barr body?

–Answer An inactivated X chromosome in mammalian somatic cells

• In humans with a typical constitution of chromosomes, X-chromosome inactivation

induces dosage compensation by randomly inactivating one of the X chromosomes in the somatic cells of Blank .–Answer females

• Who first proposed the phenomenon of X inactivation?

–Answer

MARY LYON

• In Drosophila, dosage compensation is accomplished by Blank .

–Answer - doubling the expression of most X-linked genes in the male

• Like X chromosomes in human females, one of the Z chromosomes in female birds is

randomly inactivated in somatic cells.–Answer false

• Dosage compensation can occur by increasing the expression of genes on the X chromosome

in males by twofold. Which of these organisms achieves this?–Answer Drosophila melanogaster

• The inactivated X chromosome in somatic cells of mammals is called a(n)

–Answer barr body

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