Lecture 9

Question 1

What are the two types of chromosomal mutation?

Answer 1

Changes in structure which do cause alterations in the DNA molecule and changes in number which involve novel DNA sequence arrangements

Question 2

What are the two origins of chromosomal rearrangements?

Answer 2

Through breakage and rejoining or through crossing over and rearrangements

Question 3

How does breakage and rejoining lead to the formation of chromosomal mutations?

Answer 3

Two or more double strand breaks occur in a chromosome
If this is not repaired then a segment will be lost causing a deletion mutation
If the strand is repaired but inverted then an inversion mutation occurs
If there are breaks on different chromosomes then the the wrong ends can be joined leading to a translocation
If there is a break in the broken off segment of the chromosome then one chromosome may end up with multiple copies of the same gene while the other chromosome loses these genes

Question 4

How does crossing over and rearrangements lead to the formation of chromosomal mutations?

Answer 4

Through non-allelic homologous recombination, where organisms with multiple repeat sequences can having crossing over through the incorrect sequences
If the regions are on the same chromosome then a segment may be looped out and lost causing a deletion or they may cause an inversion depending on the relative orientation of the strands at the time of crossing over
If the regions are on nonhomologous chromosomes then they can cross over to cause a translocation
If the regions are on two homologous chromosomes then the cross over can move some genes between the chromosomes causing a deletion on one chromosome and duplication on the other

Question 5

What are terminal deletions?

Answer 5

When the deletion is at the end of the chromosome

Question 6

What are interstitial deletions?

Answer 6

When the deletion is within a chromosome arm

Question 7

What are intragenic deletions?

Answer 7

A small deletion within a gene that inactivates the gene

Question 8

What are multigenic deletions?

Answer 8

Severe deletions involving several or many genes

Question 9

How can deletions be detected through chromosome structure?

Answer 9

There is a loop formed when the chromosomes pair up and the homologous regions pair up

Question 10

What is pseudodominance and how can it be used for genetic mapping?

Answer 10

Pseudodominance is when a deletion allows the expression of a recessive allele
Which can be used to map genes to specific chromosome segments

Question 11

What are tandem duplications?

Answer 11

When a duplicated copy of a gene is present right next to the original

Question 12

What are insertional duplications?

Answer 12

When a duplication is placed in a non adjacent position to the original

Question 13

How can duplications be detected?

Answer 13

Looking for duplicated banding patterns or loops at meiosis in heterozygotes

Question 14

What are the effects of duplications?

Answer 14

Can have major effects on phenotype e.g. the Bar mutation in drosophila is a small duplication on the X chromosome which reduces the size of the eye and makes it bar shaped

Question 15

What are segmental duplications?

Answer 15

Regions of duplication which range from 10-50 kbp and can include genes and regions inbetween genes can be both tandem and dispersed

Question 16

What is a paracentric inversion?

Answer 16

When the centromere is outside the inversion

Question 17

What is a pericentric inversion?

Answer 17

An inversion where the centromere is inside the inversion

Question 18

What are the consequences of inversions?

Answer 18

As these do not typically change the overall amount of genetic material individuals with these mutations frequently appear normal

Question 19

How can inversions be detected?

Answer 19

Through use of an inversion heterozygote cells undergoing meiosis will have one of the chromosomes twist at the ends of the inversion inorder to pair up leading to the formation of an inversion loop

Question 20

What are consequences of an inversion loops in meiosis if the inversion is paracentric?

Answer 20

A paracentric inversion leads to crossing over within the loop causing formation of a dicentric bridge and an acentric fragment to form
The acentric fragment is then lost due to lack of a centromere
The dicentric bridge will then randomly break leading to formation of two chromosomes both of which will have deletions

Question 21

What are the consequences of an inversion loop at meiosis if it is formed due to a pericentric inversion?

Answer 21

A cross over event where various duplication and deletion chromosomes form