Chapter 5 Flashcards
(26 cards)
How do sex chromosomes contrast with autosomes?
In some species, the lack of sex chromosomes (one or both) is not lethal to the organism.
In a diploid organism, one member of the sex chromosome pair may be inactivated without significant consequences.
Sex chromosomes carry genes responsible for the development of male or female gonads.
- In sexual ______, genes signal developmental pathways whereby the sexes are generated.
- Sexual ________ is the complex set of responses by cells, tissues, and organs to those genetic signals.
- Determination
- Differentiation
In humans, the genetic basis for determining the sex “male” is accomplished by the presence of ________.
a portion of the Y chromosome
Klinefelter syndrome in humans, which leads to underdeveloped testes and sterility, is caused by which chromosomal condition?
47, XXY
Which of the following elements is responsible for determining male sex in humans?
SRY
Which of the following elements allows for homologous pairing in meiosis?
PARS
Klinefelter syndrome (47, XXY) and Turner syndrome (45, X) are due to __________
improper segregation of sex chromosomes during meiosis
Which of the following statements regarding sexual differentiation in humans is FALSE?
“The embryo is hermaphroditic until primordial germ cells migrate to gonadal ridges.
Because gonadal ridges can form either ovaries or testes, they are called bipotential gonads.
The presence of two X chromosomes determines whether the gonadal ridges develop into ovaries or testes.
Sexual differentiation occurs very early in embryonic development.”
The presence of two X chromosomes determines whether the gonadal ridges develop into ovaries or testes.
Which of the following statements about XYY males is true?
They are generally taller than average.
What are pseudoautosomal regions (PARs) on the sex chromosomes?
They are homologous regions of the X and Y chromosomes.
How does nondisjunction in human female gametes give rise to Klinefelter and Turner syndrome offspring following fertilization by a normal male gamete?
Nondisjunction results in ova that carry either two X chromosomes or none. The former results in Klinefelter syndrome when fertilized by a Y-containing sperm, and the latter results in Turner syndrome when fertilized by an X-containing sperm.
It is believed that any male-determining genes contained on the Upper Y chromosome in humans are not located in the limited region that synapses with the X chromosome during meiosis.
What might be the outcome if such genes were located in this region?
It would be detrimental to sex-determining mechanisms due to crossing over.
The sex of birds, some insects, and other organisms is determined by a ZW chromosomal arrangement in which the males have like sex chromosomes (ZZ) and females are ZW (similar to XY in humans). Assume that a recessive lethal allele on the Z chromosome causes death of an embryo in birds. What sex ratio would result in the offspring if a cross were made between a male heterozygous for the lethal allele and a normal female?
2:1 male to female
If a population of humans carries an X-linked lethal recessive allele that causes spontaneous abortions in the first trimester, how would you expect this to affect the sex ratio of that population?
There would be a reduced number of males
For an individual with the XXY chromosomal composition, the expected number of Barr bodies in interphase cells is ________.
One
Which of the following has one Barr body?
Klinefelter’s and normal female
Which of the following elements represents a large untranslated transcript involved in inactivation?
Xist
Which of the following statements about Barr bodies is true?
The formation of Barr bodies ensures that males and females have equal doses of genes on the X chromosome.
A human with the karyotype 49, XXXYY forms _______ Barr bodies.
Two
How do mammals, including humans, solve the “dosage problem” caused by the presence of an X and Y chromosome in one sex and two X chromosomes in the other sex?
In females, one of the X chromosomes is condensed and largely inactive so that each sex has one active X chromosome.
What is a Barr body, and where is it found in a cell?
- It is a darkly stained region near the nuclear envelope of interphase cells.
- It is seen in nuclei of mammals with two or more X chromosomes
- It is an inactivated X chromosome.
-There will be one less Barr body than the number of X chromosomes.
Define the Lyon hypothesis.
Inactivation of an X chromosome occurs at random early in embryonic development.
Inactivated X chromosomes are in some way “marked” such that all clonally related cells have the same X chromosome inactivated.
What does the apparent need for dosage compensation mechanisms suggest about the expression of genetic information in normal diploid individuals?
Many genes required for normal cellular and organismic function in both males and females are located on the Upper X chromosome.
Dosage compensation is necessary to balance of the products of genes located on the Upper X chromosome for normal development.
The products of genes located on the Upper X chromosome have nothing to do with sex determination or sex differentiation.
A fruit fly with a chromosome formulation of 2X:3A would be which of the following?
Intersex
