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Exam 7: Sex Determination and Sex Chromosomes

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Question 21

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Assuming a normal number of autosomes, what would be the sex of the following: XXY mouse, XXY Drosophila?

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male and f...

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Question 22

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List three abnormalities involving numbers of X chromosomes.

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Klinefelter syndrome...

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Question 23

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In Drosophila, sex is determined by the ratio of the number of X chromosomes to the number of haploid sets of autosomes.

How many Barr bodies would one expect to see in cells of Turner syndrome females and Klinefelter syndrome males?

The Protenor mode of sex determination is the ________.

Individuals have been identified who have two different karyotypes, such as 45, X/46, XY or 45, X/46, XX. Such individuals are called ________.

A typical XX human female has one Barr body.

Describe three distinct genetic regions of the human Y chromosome.

What is the composition of a Barr body?

In Drosophila, an individual female fly was observed to be of the XXY chromosome complement (normal autosomal complement) and to have white eyes as contrasted with the normal red eye color of wild type. The female's mother and father had red eyes. The mother, however, was heterozygous for the gene for white eyes. Knowing that white eyes are X-linked and recessive, present an explanation for the genetic and chromosomal constitution of the XXY, white-eyed individual. It is important that you state in which parent and at what stage the chromosomal event occurred that caused the genetic and cytogenetic abnormality.

The accompanying figure is a pedigree of a fairly common human hereditary trait; the boxes represent males and the circles represent females. Filled in symbols indicate the abnormal phenotype. Given that one gene pair is involved, a) Is the inheritance pattern X-linked or autosomal? b) Give the genotype of each individual in the pedigree. If more than one genotypic possibility exists, present all possible alternatives.

What particular karyotype was at one time considered to be related to criminal predisposition?

What can cause phenotypic mosaicism for X-linked genes in female mammals?

A small part of the human Y chromosome contains the gene that is responsible for determining maleness. What is the name of this gene?

A color-blind, chromatin-positive male child (one Barr body) has a maternal grandfather who was color blind. The boy's mother and father are phenotypically normal. Construct and support (using appropriately labeled diagrams) a rationale whereby the chromosomal and genetic attributes of the chromatin-positive male are fully explained.

Dosage compensation leads to a variety of interesting coat color patterns in certain mammals. For instance, a female cat that is heterozygous for two coat color alleles, say black and orange, will usually have the "calico" or mosaic phenotype. Describe the chromosomal basis for the mosaicism (calico) in the female. Explain why chromosomally normal male cats do not show the mosaic phenotype, but XXY male cats can be calico.

Klinefelter syndrome in humans, which leads to underdeveloped testes and sterility, is caused by which chromosomal condition?

Studies done in the 1960s suggested that individuals with the XYY condition were prone to criminal behavior. What conclusions presently seem appropriate concerning this chromosomal condition?

Normally in humans, all the sons of a female homozygous for a sex-linked recessive gene will inherit that trait.

In humans, the male is the homogametic sex.