Nondisjunction during either meiosis I or II in the female gamete.
The incidence of Down syndrome, also known as trisomy 21, increases with increasing maternal age. Which of the following errors most likely produces this condition?
False,
Females with only one X chromosome are viable but have Turner syndrome, which is characterized by underdeveloped ovaries. Males that lack an X chromosome do not develop; this condition is lethal.
Females with only one X chromosome are viable but have Turner syndrome, which is characterized by underdeveloped ovaries. Males that lack an X chromosome do not develop; this condition is lethal.
Females with only one X chromosome do not develop; this condition is lethal.
Two products of the second meiotic division have both the maternal and paternal chromosomes of a set and the other two products have none for that set.
Which of the following statements about the products produced when nondisjunction occurs during meiosis I is true?
Homologs fail to separate during meiosis I.
Which of the following accurately describes a possible meiotic nondisjunction event?
Two haploid gametes fuse to form a diploid cell.
All of the following events occur during normal meiosis except _______.
False,
Nondisjunction during either meiosis I or meiosis II creates gametes that will generate trisomies if fertilized.
Nondisjunction during either meiosis I or meiosis II creates gametes that will generate trisomies if fertilized.
In order to create the possibility of generating a trisomy, nondisjunction must occur during meiosis II
True,
During meiosis, the presence of a chromosomal loop signals that a duplication or deletion has occurred.
During meiosis, the presence of a chromosomal loop signals that a duplication or deletion has occurred.
Duplications and deletions can be detected during meiosis by the presence of extrachromosomal loops that do not pair properly with their homolog.
Normal, because they have a normal amount of genetic material.
Balanced translocation heterozygotes have a normal amount of genetic material, but it is in a translocated configuration. As long as there are no position effects, these individuals can be phenotypically normal.
Balanced translocation heterozygotes have a normal amount of genetic material, but it is in a translocated configuration. As long as there are no position effects, these individuals can be phenotypically normal.
What phenotype would be expected in balanced translocation heterozygotes in the absence of position effects?
Fragile X syndrome – deletion
Which of the following syndromes is not paired with its causative chromosomal aberration?
Huntington disease – duplication
Fragile X syndrome – deletion
Cri du chat syndrome – deletion
Down syndrome – Robertsonian translocation
Huntington disease – duplication
Fragile X syndrome – deletion
Cri du chat syndrome – deletion
Down syndrome – Robertsonian translocation
the loss of part of a chromosomal segment.
Deletion
the repetition of a segment. The repeated segment may be located next to the original or at a different location, and its orientation may be the same as the original or the reverse.
Duplication
the removal of a segment followed by its reinsertion into the same chromosome in the reverse orientation.
Inversion
the transfer of a segment to a nonhomologous chromosome. Translocations may be reciprocal (two nonhomologous chromosomes exchange segments) or nonreciprocal (one chromosome transfers a segment without receiving one).
Translocation
3 only
Diploid cell with three pairs of homologous chromosomes (2n = 6) enters meiosis:
Meiosis occurs normally (no nondisjunction).
Meiosis occurs normally (no nondisjunction).
2 or 4
If one chromosome pair undergoes nondisjunction in meiosis I, half the gametes will have an extra chromosome (n +1), and half will be missing a chromosome (n – 1).
If one chromosome pair undergoes nondisjunction in meiosis I, half the gametes will have an extra chromosome (n +1), and half will be missing a chromosome (n – 1).
Diploid cell with three pairs of homologous chromosomes (2n=6) enters meiosis:
Nondisjunction of one chromosome pair in meiosis I.
Nondisjunction of one chromosome pair in meiosis I.
0 or 6
If all chromosome pairs undergo nondisjunction in meiosis I, half the gametes will have twice the normal haploid number of chromosomes (2n), and half will have no chromosomes.
If all chromosome pairs undergo nondisjunction in meiosis I, half the gametes will have twice the normal haploid number of chromosomes (2n), and half will have no chromosomes.
Diploid cell with three pairs of homologous chromosomes (2n=6) enters meiosis:
Nondisjunction of all three chromosome pairs in meiosis I (all chromosomes go to one pole).
Nondisjunction of all three chromosome pairs in meiosis I (all chromosomes go to one pole).
2, 3, or 4
If one chromosome undergoes nondisjunction in meiosis II, half the gametes will have the normal haploid number of chromosomes (n), one-quarter will have an extra chromosome (n +1), and one-quarter will be missing a chromosome (n – 1).
If one chromosome undergoes nondisjunction in meiosis II, half the gametes will have the normal haploid number of chromosomes (n), one-quarter will have an extra chromosome (n +1), and one-quarter will be missing a chromosome (n – 1).
Diploid cell with three pairs of homologous chromosomes (2n=6) enters meiosis:
Nondisjunction of one chromosome in one daughter cell in meiosis II.
Nondisjunction of one chromosome in one daughter cell in meiosis II.
0, 3, or 6
If all chromosomes undergo nondisjunction in meiosis II, half the gametes will have the normal haploid number of chromosomes (n), one-quarter will have twice the haploid number (2n), and one-quarter will have no chromosomes.
If all chromosomes undergo nondisjunction in meiosis II, half the gametes will have the normal haploid number of chromosomes (n), one-quarter will have twice the haploid number (2n), and one-quarter will have no chromosomes.
Diploid cell with three pairs of homologous chromosomes (2n=6) enters meiosis:
Nondisjunction of all three chromosomes in one daughter cell in meiosis II (if all chromosomes go to one pole).
Nondisjunction of all three chromosomes in one daughter cell in meiosis II (if all chromosomes go to one pole).
13
2n
2n
Species has diploid number of 26:
Haploid
Haploid
39
3n
3n
Species has diploid number of 26:
Triploid
Triploid
52
4n
4n
Species has diploid number of 26:
Tetraploid
Tetraploid
27
Trisomy 2n+1.
Trisomy 2n+1.
Species has diploid number of 26:
Trisomic
Trisomic
25
Monosomy 2n-1.
Monosomy 2n-1.
Species has diploid number of 26:
Monosomic
Monosomic
Karyotype analysis of spontaneously aborted fetuses has shown that a significant percentage are trisomic and every chromosome can be involved.
Which one of the following statements best describes the evidence that indicates that humans with aneuploid karyotypes occur at conception but are usually inviable?
The father must have contributed the abnormal X-linked gene.
A boy with Klinefelter syndrome (47,XXY) is born to a mother who is phenotypically normal and a father who has the X- linked skin condition called anhidrotic ectodermal dysplasia:
Which parent contributed the abnormal gamete?
Which parent contributed the abnormal gamete?
Son is XXY and heterozygous for anhidrotic dysplasia, he must have received both the defective gene and the Y chromosome from his father.
Non-Disjunction must have occurred during meiosis I.
Non-Disjunction must have occurred during meiosis I.
Boy with Klinefelter syndrome (47, XXY):
Using the appropriate genetic terminology, describe the meiotic mistake that occurred. Be sure to indicate in which division the mistake occurred.
Using the appropriate genetic terminology, describe the meiotic mistake that occurred. Be sure to indicate in which division the mistake occurred.
Son’s mosaic phenotype is caused by X-chromosome inactivation, a form of dosage compensation in mammals.
Boy with Klinefelter syndrome (47, XXY):
Using the appropriate genetic terminology, explain the son’s skin phenotype.
Using the appropriate genetic terminology, explain the son’s skin phenotype.
