Disorders in Chromosome Number - Revision

Question 1

What is aneuploidy?

Answer 1

The presence of an abnormal number of chromosomes in a cell, for example a human cell having 45 or 47 chromosomes instead of the usual 46. It does not include a difference of one or more complete sets of chromosomes

Question 2

What is the most common type of aneuploidy?

Answer 2

Trisomy - there is an extra chromosome.

Question 3

What is Trisomy 21?

Answer 3

Down Syndrome

Question 4

What is Trisomy 13?

Answer 4

Patau syndrome

Question 5

What is Trisomy 18?

Answer 5

Edwards syndrome

Question 6

What is monosomy?

Answer 6

Another type of aneuploidy in which there is a missing chromosome.

Question 7

What is an example of monosomy?

Answer 7

Turner syndrome - a female has a missing or damaged X chromosome.

Question 8

What is polyploidy?

Answer 8

Polyploidy is a chromosomal mutation in which a cell has entire extra sets of chromosomes (the cells of an organism have more than two paired sets of chromosomes)

LETHAL

Question 9

What is mosaicism?

Answer 9

Mosaicism is when a person has 2 or more genetically different sets of cells in his or her body. A person with mosaicism may have some cells in his or her body with 46 chromosomes. But other cells have 47 chromosomes.

Question 10

How does aneuploidy arise?

Answer 10

Errors in meisosis –> non-disjunction

Question 11

What is non-disjunction?

Answer 11

Occurs when pairs of homologous chromosomes or sister chromatids fail to separate during meiosis

Question 12

Nondisjunction can occur during either meiosis I or II. What is the result of it occurring during meiosis I?

Answer 12

• 2 gametes that lack a chromosome
• 2 gametes with 2 copies of the chromosome

Question 13

Nondisjunction can occur during either meiosis I or II. What is the result of it occurring during meiosis II?

Answer 13

• 1 gametes that lacks that chromosome
• 2 normal gametes with one copy of the chromosome
• 1 gamete with 2 copies of the chromosome

Question 14

What is euploidy? What does this correspond to in humans?

Answer 14

An individual with the appropriate number of chromosomes - 22 pairs of autosomes and one pair of sex chromosomes in humans

Question 15

What is an individual with an error in chromosome number termed?

Answer 15

Aneuploid; a term that includes monosomy (loss of one chromosome) or trisomy (gain of an extra chromosome)

Question 16

What is a chromosomal inversion? What are its effects?

Answer 16

A chromosome inversion is the detachment, 180° rotation, and reinsertion of part of a chromosome. Unless they disrupt a gene sequence, inversions only change the orientation of genes and are likely to have more mild effects than aneuploid errors.

Question 17

What is a translocation?

Answer 17

A translocation occurs when a segment of a chromosome dissociates and reattaches to a different, nonhomologous chromosome - can be benign or have devastating effects

Question 18

What are reciprocal translocations?

Answer 18

Result from the exchange of chromosome segments between two nonhomologous chromosomes such that there is no gain or loss of genetic information