Chapters 7/8 - Clinical Cytogenetics Flashcards
What are pseudoautosomal regions on the sex chromsomes?
- Homozygous regions of autosomal chromosomes
- Regions of the X and Y chromosomes that don’t recombine during meiosis
- Hemizygous regions of the X and Y chromosomes
- Homologous regions of the X and Y chromosomes
Homologous regions of the X and Y chromosomes.
(The pseudoautosomal regions refer to regions of homology between the X and Y chromosomes in humans that undergo recombination during meiosis.)
In humans, the genetic basis for determining the sex “male” is accomplished by the presence of _____.
- A balance between the number of X chromosomes and the number of haploid sets of autosomes
- Multiple alleles scattered throughout the autosomes
- One X chromosome
- High levels of estrogen
- A portion of the Y chromosome
A portion of the Y chromosome.
Klinefelter syndrome in humans, which leads to underdeveloped testes and sterility, is caused by which chromosomal condition?
- 47, XYY
- Triploidy
- 45, X
- 47, 21+
- 47, XXY
47, XXY
A recessive gene for red-green color blindness is located on the X chromosome in humans. Assume that a woman with normal vision (her father is color blind) marries a color blind male. What is the likelihood that this couple’s first son will be color blind?
- 100%
- 75%
- 50%
- 0%
- 25%
50%
Normally in humans, all the sons of a male showing a sex-linked phenotype will inherit the trait.
- True
- False
False
Normally in humans, all the sons of a female homozygous for a sex-linked recessive gene will inherit the trait.
- True
- False
True
The condition that exists when an organism gains or loses one or more chromosomes but not a complete haploid set is known as _____.
- Triploidy
- Polyploidy
- Aneuploidy
- Euploidy
- Trisomy
Aneuploidy
What is the specific term that describes the loss of a single chromosome (2n-1)?
- Polyploidy
- Trisomy
- Aneuploidy
- Monosomy
Monosomy.
Monosomy involves the loss of a single chromosome (e.g., an X chromosome in Turner syndrome).
Trisomy 21, or Down Syndrome, occurs when there is a normal diploid chromosomal complement but one (extra) chromosome 21. Although fertility is reduced in both sexes, females have higher fertility rates than males. Van Dyke et al. (1995; Down Syndrome Research and Practice 3(2):6569) summarize data involving children born of Down Syndrome individuals. Assume that children are born to a female with Down Sydrome and a normal 46-chromosme male. What proportion of the offspring would be expected to have Down Syndrome?
None of the offspring would be expected to have Down Syndrome
-One-half of the offspring would be expected to have Down Syndrome
-One-third of the offspring would be expected to have Down Syndrome
-All the children would be expected to have Down Syndrome
-Two-thirds of the offspring would be expected to have Down Syndrome
One-half of the offspring would be expected to have Down syndrome.
An individual with Patau syndrome would be called a triploid.
- True
- False
False
Chorionic villus sampling (CVS) is sometimes preferred to amniocentesis because results can be provided earlier in the pregnancy.
- True
- False
True
Assume that an organism has a diploid chromosome number of 14. There would be 28 chromosomes in a tetraploid.
- True
- False
True
The condition known as cri-du-chat syndrome in humans has a genetic constitution designated as _____.
- 46, 5p-
- Trisomy
- Heteroplasmy
- Triploidy
- 45, X
46, 5p-
Gene duplications provide an explanation for the origin of gene families.
- True
- False
True
A pericentric inversion includes the centromere.
- True
- False
True
A paracentric inversion is one whose breakpoints do not flank the centromere.
- True
- False
True
In general, inversion and translocation heterozygotes are as fertile as organisms whose chromosomes are in the standard arrangement.
- True
- False
False
A 3-year-old exhibited some early indication of TUrner syndrome, which results from a 45, X chromosome composition. Karyotypic analysis demonstrated two cell types: 46,XX (normal) and 45, X. propose a mechanism for the origin of this mosaicism,
- Dispermic fertilization
- Mitotic nondisjunction of X chromosomes
- Reciprocal translocation between two X chromosomes
- Meiotic nondisjunction of X chromosome
- Inactivation of X chromosomes
Mitotic nondisjunction of X chromosomes.
Which of the following accurately describes a possible meiotic nondisjunction event?
- Homologs fail to separate during meiosis I.
- Meiosis fails to proceed to completion.
- Sister chromatids fail to separate during meiosis I.
- Fusion of gametes results in trisomy.
Homologs fail to separate during meiosis I.
(Correct. Ordinarily, homologs separate during meiosis I. Failure of this separation is one of the ways in which nondisjunction can occur.)
All of the following events occur during normal meiosis except _______All of the following events occur during normal meiosis except _______.
- homologous chromosomes separate from one another during meiosis I
- two haploid gametes fuse to form a diploid cell
- one diploid cell produces four haploid cells
- sister chromatids separate from one another during meiosis II
two haploid gametes fuse to form a diploid cell.
Fusion of haploid gametes occurs after meiosis.
In order to create the possibility of generating a trisomy, nondisjunction must occur during meiosis II.
- True
- False
False.
Nondisjunction during either meiosis I or meiosis II creates gametes that will generate trisomies if fertilized.
Which of the following arrangements would yield the greatest reduction in gamete viability?
- An inversion heterozygote for a large inversion
- An inversion homozygote for a small inversion
- An inversion homozygote for a large inversion
- An inversion heterozygote for a small inversion
An inversion heterozygote for a large inversion.
(A large heterozygous inversion will result in greater numbers of genes that are duplicated or deleted when crossing over occurs.)
All of the following could result from meiosis in a pericentric inversion heterozygote in which a single crossover occurred within the inversion loop except a _______.
- chromosome with some duplicated regions
- completely normal chromosome
- chromosome with two centromeres
- chromosome with some deleted regions
-chromosome with two centromeres
When the centromere is contained within the inversion, it is neither duplicated nor deleted.
Inversion loops do NOT form during meiosis in paracentric inversion heterozygotes.
- True
- False
False
(Loop formation allows pairing within inverted regions of homologous chromosomes regardless of whether the centromere is included in the inversion.)
