Chromosome Structure Changes

Question 1

What are the four basic types of chromosome rearrangements?

Answer 1

Deletion = loss of chromosome segment

Duplication = doubling of chromosome segment

Inversion = orientation within chr reversed

Translocation = segment moved to different site

Question 2

What parts of the chromosome are required for survival of cell after meiosis?

Answer 2

Centromere and 2 telomeres

Question 3

Why is a lack of centromere problematic for meiosis?

Answer 3

Chromosome is acentric so there’s nowhere for the spindle to attach causing DNA to be lost

Question 4

What is 2 centromeres problematic?

Answer 4

Chromosome is dicentric so it isn’t incorporated into progeny cell

Question 5

What happens if telomere is lost?

Answer 5

It impacts DNA stability and replication.

Question 6

What is the “.” in the chromosome abbreviation AB.CDEFG?

Answer 6

The centromere

Question 7

What is deletion?

Answer 7

Loss of a chromosome segment. AB.CD__G

Question 8

Is deletion viable?

Answer 8

In many cases it isn’t viable especially when multiple genes are lost. (gene dosage effect)

Question 9

What are the effects of duplications?

Answer 9

Can be advantageous.

Question 10

What does it mean to be homozygous for duplication?

Answer 10

Individuals that are homozygous for duplication carries duplication on both homologous chromosomes.

Question 11

How are gene duplications detected?

Answer 11

There is a characteristic loop structure

Question 12

How do gene duplications take place?

Answer 12

Chromosomes do not align properly resulting in unequal crossing over. This results in a gene moving from one chromosome to the other.

Unequal crossing over between chromosomes containing 2 copies of the gene takes place resulting in another gene being added to the chromosomes.

Question 13

How do homologous chromosomes meet when one has a duplication?

Answer 13

The duplicated gene loops out of the chromosome

Question 14

How do inversions take place?

Answer 14

For inversion chromosome must break in 2 places.

Question 15

What is the effect of gene inversions?

Answer 15

May break gene in 2 parts.

If between genes it can cause inverted gene order and mis-expression of gene.

Question 16

What are the types of inversions?

Answer 16

Paracentric (does not include centromere)

Pericentric (Includes centromere)

Question 17

How is the result different for inversions if the individual is homozygous for a particular inversion compared to being heterozygous?

Answer 17

If homozygous the homologous chromosomes can pair and separate normally.

If heterozygous an inversion loop forms resulting in a dicentric chromosome and an acentric chromosome which are not viable.

Question 18

How does a heterozygous paracentric inversion result in viable and non viable gametes?

Answer 18

A dicentric chromatid is produced due to formation of bridge between chromatids.

Question 19

What is the overall effect of inversions on fertility?

Answer 19

Individuals with inversions are semi-sterile due to 50% of their sperm/eggs being non-viable.

Question 20

What is a translocation?

Answer 20

Movement of genetic material between non-homologous chromosomes. or within the same chromosome

Question 21

What is a non-reciprocal translocation?

Answer 21

Material moves from one chromosome to another without recpiprocal exchange

Question 22

What is a reciprocal translocation?

Answer 22

2 way exchange

Question 23

What are the effects of translocations?

Answer 23

Can physically link genes that were previously on different chromosomes and this changes gene expression as genes may be under control of different regulatory sequences. (eg philadelphia chromosome)

Chromosomal breaks may take place within a gene,

Deletions frequently accompany translocations eg: Robertsonian translocation

Question 24

What is a robertsonian translocation?

Answer 24

Translocation that is identical to down’s syndrome caused by reciprocal translocation between chromsome 21 and 14.

Question 25

Why does the Robertsonian translocation cause symptoms of Down’s syndrome?

Answer 25

The translocation adds expression of chromosome 21 for a third time due to its attachment to chromsome 14. This overexpression increases chromosome 21’s gene dosage resulting in symptoms of Down’s syndrome.

Question 26

What are the possible phenotypes resulting from the Robertsonian translocation?

Answer 26

25% Down’s syndrome

25% translocation carriers

25% normal

25% lethal (non-viable)