Exam 2: Chromosome Abnormalities

Question 1

Define a mutation

Answer 1

A mutation is a change in genome nucleotide sequence that deviates from the norm.

-Allelic variation is generated via mutation

–Phenotypic variations result from changes in individual genes due to allelic variation

Question 2

At what phase of mitosis are karyotypes typically done?

Answer 2

Metaphase

Question 3

Define aneuploidy

Answer 3

Change in the number of individual chromosomes due to a addition or loss (no longer a balanced set)

Question 4

What are the kinds of aneuploidy?

Answer 4

Nullisomy: Loss of both members of a homologous pair

2n-2

Monsomy: Loss of one member of a homologous pair

2n-1

Trisomy: Gain of one chromosome, resulting in 3 homologous pairs

2n+1

Tetrasomy: Gain of two chromosomes

2n+2

Question 5

Discuss the use and limitations of karyotyping to identify chromosome abnormalities.

Answer 5

Use: Karyotyping is a test to examine chromosomes in a sample of cells. This test can help identify genetic problems as the cause of a disorder or disease.

Limitations: Karyotyping could miss small chromosomal mutations such as small structural abnormality like a a 5bp inversion.

Question 6

Describe the relationship between nondisjuction and eu- or aneuploidy.

Answer 6

Nondisjunction is the most common mechanism resulting in aneuploidy. Nondisjunction is an error in which there is unequal distribution of the members of a single chromosome pair in cell division.

Question 7

Describe advantages and disadvantages of chromosomal abnormalities.

Answer 7

Mutations are neither positive nor negative. Mutations can cause disease or death. However, some mutations have given species advantages that lead to speciation.

Question 8

Define autoployploidy, allopolyploidy, and endoployploidy

Answer 8

Autopolyploidy: Addition of one or more sets of chromosomes identical to haploid complement of same species (ex: all human)

Allopolyploidy: Combination of chromosome sets from different species as consequence of hybridization (ex: mule– different homologous chromosomes, from horse and one from donkey)

Endopolyploidy: Condition where only certain cells in diploid organism are polyploid. Set of chromosomes replicates repeatedly without cytokinesis (endoreplication)

Question 9

Define euploidy/polyploidy

Answer 9

Addition of complete chromosome set

Question 10

What are the different of structural chromosomal rearrangements?

Answer 10

-Deletion
-Insertion
-Inversion
-Nonreciprocal translocations
-Reciprocal translocations

Question 11

A diploid organism with only 1 chromosome has

Answer 11

Monosomy

Question 12

A haploid organism with 2 chromosomes has

Answer 12

Disomy–which is abnormal here

Question 13

Define nondisjunction

Answer 13

The failure of one or more pairs of homologous chromosomes or sister chromatids to separate normally during nuclear division, usually resulting in an abnormal distribution of chromosomes in the daughter nuclei.

Question 14

Jimsom weed nondisjunction (Trisomy: 2n+1) is an example of a ________ chromosomal abnormality

Answer 14

positive

Question 15

Trisomy of chromosome 21 causes

Answer 15

Down syndrome

Question 16

Trivalent vs Bivalent & Univalent

Answer 16

Three copies of chromosome are synapsed

vs

Prior to first meiotic division, one bivalent and one univalent (an unpaired chromosome) may be present instead of a trivalent

Question 17

Do duplications and/or deletions always cause gene dosage problems?

Answer 17

For some genes, having an extra copy may not cause any detectable problems.

For others though, it can upset the carefully regulated interactions tons inside the cell.

Question 18

Deletions

Answer 18

Missing regions of chromosome where chromosome breaks in one or more places.

-Terminal deletion (near one end)
–Intercalary deletion (interior of the
chromosome)

Question 19

Compensation Loop

Answer 19

Synapsis between chromosome with large intercalary deletion and normal complete homolog requires unpaired region of normal homolog to loop out of linear structure into deletion or compensation loop.

Be able to draw this

Question 20

Duplications

Answer 20

Repeated segment of chromosome

Single locus is present more than once in genome

Arise from unequal crossing over between synapsed chromosomes during meiosis

Lead to the production compensation loops

Question 21

Is the compensation group on the normal or abnormal chromosomes for deletions vs duplications?

Answer 21

Deletions– normal

Duplications– abnormal

Question 22

What supports the theory that gene duplication plays a role in evolution?

Answer 22

Hypothesis supported by discovery of genes with substantial DNA sequence in common, but distinct gene products

Example: digestive enzymes trypsin and chymotrypsin

Question 23

Inversions

Answer 23

-Rearrangement of linear gene sequence

-No loss of genetic information

-Segment of chromosome turned 180° within chromosome

-Requires two breaks in chromosome, and reinsertion inverted segment

-May arise from chromosomal looping

Question 24

Paracentric vs Pericentric Inversion

Answer 24

Paracentric: Does not change lengths
of two arms of the chromosome. Centromere not part of inverted segment.

Pericentric: Centromere is part of inverted segment. Does change lengths of two arms of chromosome.

Question 25

Do inverted and non inverted chromosomes pair in meiosis?

Answer 25

Yes but onlyyy if they form an inversion loop

Question 26

Translocation

Answer 26

Movement of a chromosome segment to a non homologous chromosome or to another region of the same chromosome.

Nonreciprocal- no exchange

Reciprocal- exchange between segment

Question 27

Segregation Patterns After a Reciprocal Translocation

Answer 27

Alternate segregation
-Segregation pattern at first meiotic
division
-Has complete complement of genetic information

Adjacent segregation
-Leads to gametes containing
duplications and deficiencies

Question 28

Robertsonian Translocation

Answer 28

Involves breaks at extreme
ends of short arms of two nonhomologous acrocentric chromosomes

Large submetacentric or
metacentric chromosome
produced

Ex: Familial Down syndrome

Be able to draw out process

Question 29

Fragile Sites

Answer 29

More susceptible to chromosome breakage when cultured in absence of folic acid or other chemicals

Sites indicate regions of non-tightly coiled chromatin

Question 30

Fragile-X Syndrome

Answer 30

CGG repeat near to the gene FMR-1 (fragile-X mental retardation 1)
may cause the gene to be turned off as the size of the repeat increases.