Lecture 20 The effects of Mutations II

Question 1

Define the term Aneuploid

Answer 1

A diploid chromosome set that is missing one chromosome.

Question 2

Define a carrier

Answer 2

An individual who has one normal and one defective allele for a gene responsible for an inherited disease, but does not suffer from the disease because the effect of the defective allele is masked by the presence of the unmutated gene.

Question 3

Define haploinsufficiency

Answer 3

Situation where inactivation of one of a pair of gene results in a change in the phenotype of the mutant organism.

Question 4

Define monosomy

Answer 4

2n-1 , where one chromosome is missing from a pair in a diplpoid set.

Question 5

Explain what the Philadelphia Chromosome is

Answer 5

An abnormal chromosome resulting from a translocation between human chromosomes 9 and 22, a common cause of chronic myeloid leukemia.

Question 6

Define trisomy

Answer 6

This is where there are 3 copies of a chromosome in an otherwise diploid nucleus (2n+1)

Question 7

Explain the concept of haploinsufficiency (google definition)

Answer 7

The situation that occurs when one copy of a gene is inactivated and the remaining functional copy of the gene is not adequate to produce the normal phenotype. (so there is a change in the phenotype)

Question 8

How many genes are inactivated in haploinsufficiency

Answer 8

One copy out of the pair of alleles is inactivated.

Question 9

Explain how the Philadelphia chromosome arises

Answer 9

Occurs when chromosomes 9 and 22 break and exchange portions. This creates abnormally small chromosome 22.

Question 10

What do we mean by a diploid organism

Answer 10

• 2 copies of each chromosome

- 2 copies of each gene

Question 11

Which factor influences the shape of peas

Answer 11

Sucrose content.
Low sucrose causes the mature pea to stay round.
High sucrose causes mature peas to be wrinkled. Sucrose content is controlled by the SBE1 gene.

Question 12

Which gene converts sucrose into starch

Answer 12

SBE1 gene.

Question 13

Explain how wrinkled peas arise

Answer 13

• Pea shape depends on sucrose content
• SBE1 gene controls conversion of sucrose into starch.
• wrinkled peas have a defective SBE1 allele therefore cannot convert sucrose into starch.
• Results in high sucrose content, depletes water, results in wrinkly seeds.

Question 14

How many chromosomes in Pea cell

Answer 14

14 chromosomes (diploid number. Arises from 2 sets of 7.

Question 15

What are alternative forms of a gene called

Answer 15

Alleles

Question 16

Wrinkled peas is which type of inheritance

Answer 16

Recessive, as it requires two non functional copies of SBE1 alleles to produce the wrinkled phenotype.

Question 17

One functional and one non functional copy of SBE1 will result in which phenotype

Answer 17

Round pea phenotype.

Question 18

is cystic fibrosis recessive or dominant

Answer 18

Recessive

Question 19

What happens in haploinsufficient individuals

Answer 19

A mutation in just one gene/allele will cause disease.

Question 20

Give an example of a disease that shows haploinsufficiency

Answer 20

Alagille syndrome is an example of haploinsufficiency

Question 21

What does Alagille syndrome result in

Answer 21

Results in heart abnormalities and liver problems from abnormal bile ducts. Arises in deformed allele for the CD339 protein (JAG1) .

Question 22

What is the CD339 JAG1 protein involved in

Answer 22

it is inovolved in cell to cell signalling during embryo development.

Question 23

What arises when there is haploinsufficiency for the CD339 Jag 1 gene.

Answer 23

there is insufficient signalling protein (JAG 1)

Question 24

What is retinoblastoma

Answer 24

Cancer of the retina.

Question 25

Explain the pattern of diease w.r.t to sporadic retinoblastoma

Answer 25

Rare and occurs throughout the population

Question 26

Explain the pattern of disease w.r.t familial retinoblastoma

Answer 26

more common in afffected families. There is only one functional copy.

Question 27

Deletion of approx 500kb from the X chromosome results in which diseases

Answer 27

• Retinitis pigmentosa
• Chronic granulomatous disease
• Duchenne muscular dystrophy

Question 28

Downs syndroms arises due to …

Answer 28

Trisomy 21, there are three copies of chromosome 21

Question 29

Give an example of a condition due to monosomy, state which chromosome is missing.

Answer 29

Monosomy 7.
One copy of chromosome 7 is missing.
Leads to bone marrow failure, with a high risk of leukemia.

Question 30

Give an example of chromosome translocations

Answer 30

Occurs when part of one chromosome becomes attached to another chromosome.

Question 31

Give an example of a common chromosome translocation

Answer 31

Chromosome 9 and 22 have segments which break off and get exchanged. This forms the Philadelphia chromosome.

Question 32

Which region of chromosome 9 and chromosome 22 are broken off and exchanged

Answer 32

ABL region of chromosome 9

BCR region of chromosome 22.

Question 33

Which disease does the philadelphia chromosome cause

Answer 33

Leukemia

Question 34

Give an example of an inherited disease caused by large deletions

Answer 34

• Granutolmous
• Retinitis pigmentosa
• Duchenne muscular dystrophy

Question 35

State what has happened to the SBE1 gene in wrinkled peas

Answer 35

An extra piece of DNA has become inserted into the SBE1 gene, and as a resuly, no Starch Branching enzyme type 1 is made. (insertion mutation)

Question 36

Describe the effect that haploinsufficinecy has on the phenotype of an individual who has one mutant and one non mutant gene copy

Answer 36

Most eukaryotes are diploid, therefore a loss of function mutation might not result in a change of phenotype. The second copy of the gene is still active and