Lecture 9

Question 1

What are the 2 type of chromosomal mutations

Answer 1

structural and number

Question 2

Changes in chromosomal number are refereed to as

Answer 2

polyploid changes

Question 3

Structural mutations involve

Answer 3

novel sequence rearrangements within 1 or more DNA molecule

Question 4

Why are chromosomal mutations important x5

Answer 4

• understand how genes work together
• insights into meiosis and chromosome architecture
• tools for genomic manipulation
• cause of genetic diseases
• insights into evolutionary processes

Question 5

Types of chromosomal mutations x3

Answer 5

• loss of genetic material
• gain of genetic material
• relocation of genetic material

Question 6

What causes loss of genetic material (x2)

Answer 6

• deletion

- missing chromosome

Question 7

what causes a gain in genetic material (x2)

Answer 7

• duplication

- extra chromosome

Question 8

What causes relocation of genetic material (x2)

Answer 8

• Translocation

- inversion

Question 9

How do you form a deletion?

Answer 9

A chromosome segment can be lost

Question 10

How do you form a duplication?

Answer 10

a section can be doubled

Question 11

What sort of breaks are lethal unless repaired, and how can chromosomal rearrangement result from this

Answer 11

Double-stranded breaks; If ends of 2 different breaks are joined a chromosomal rearrangement can result

Question 12

What does a DNA molecule have to have to survive meiosts

Answer 12

• Centromere

- 2 telomeres

Question 13

What is nonallelic homologous recombination

Answer 13

Crossing over between duplicated DNA sequences (this causes rearrangements)

Question 14

How can crossing over occur between non-homologous chromosomes

Answer 14

Repeat sequences on different chromosomes (or within 1 chromosome)

Question 15

If crossing over occurs between repeat DNA sequences that are not if in the same position on homologs then what can be produced?

Answer 15

• Deletions
• Duplications
• inversions
• translocations

Question 16

Why is a deleted segment often lost?

Answer 16

Because it has no centromere

Question 17

What’s a terminal deletion

Answer 17

Segment deleted at the end of a chromosome

Question 18

What’s a interstitial deletion

Answer 18

segment deleted within a chromosome

Question 19

Intragenic deletion

Answer 19

a small deletion within a gene that inactivates the gene

Question 20

Multigenic deletions

Answer 20

Involve several genes and their consequences are more severe

Question 21

When is a loop formed by a chromosome

Answer 21

In meiosis the chromosome of a deletion heterozygote

Question 22

What are the consequences when a multigenic deletion is made homozyous by inbreeding

Answer 22

Lethal consequences

Question 23

What sort of mutations never revert back to the wildtype

Answer 23

Multigenic mutations

Question 24

Pseudodominance (to do with deletions)

Answer 24

Deletions allow the expression of phenotypes carried as recessive alleles

Question 25

Tandem duplications

Answer 25

Duplications that are adjacent

Question 26

Insertional duplications

Answer 26

Duplications that are located elsewhere (not adjacent) in the genome

Question 27

If a duplication has occured, how many copies of that chromosome region will a diploid cell have

Answer 27

Three copies

Question 28

What does detection of duplications involve?

Answer 28

Looking for duplications of chromosome banding patterns + the presence of loops at meiosis in heterozygous individuals

Question 29

Describe the Bar mutation (4 main points)

Answer 29

-Mutation in Drosophila
-that have reduced facests in the eye, making the eye smaller
-the trait is inherited as an incomplete or partial dominant X linked train
-Heterozygous females have smaller eyes, while even smaller is that of homozygous females and hemizygous males
(see image in slides)

Question 30

Segmental duplications

Answer 30

Duplications that range in size from 10-50 kbp and encompass whole genes and the regions between them.

• Most segemental duplications are dispersed but some are tandem.
• About 4% of the genome consists of segmental duplications

Question 31

Paracentric Inversions

Answer 31

The centromere will be outside the inversion

Question 32

Pericentric inversions

Answer 32

The centromere is inside the inversion

Question 33

Are people with inversions usually normal or not?

Answer 33

Yes because inversions dont change the overall amount of genetic material

Question 34

Para or peri centric inversions cause the formation of a dicentric bridge

Answer 34

Paracentric

Question 35

What’s an inversion loop

Answer 35

During meiosis 1 chromosome twists at the ends of the inversions so that it can pair withe the untwisted homolog

Question 36

In para or peri centric inversions does an acentric fragment form

Answer 36

paracentric - this fragment is lost because it has no centromere

Question 37

In para or pericentric inversions can crossing over result in duplications and deletions result

Answer 37

Pericentric

Question 38

Explain what it is meant by: Inversions act as crossover supressors

Answer 38

They dont stop crossing over happening, you just dont see any crossover product as they are not viable

Question 39

Explain what it is meant by: Inversions can lead to the creation of ‘Super Genes’

Answer 39

Gene are linked, can not be broken up as no crossing over

Question 40

What is often detected when patients are having fertility problems

Answer 40

Paracentric or pericentric inverisons