chromosomal mutations - lecture 10

Question 1

What types of chromosome rearrangements are there?

Answer 1

• duplication
• deletion
• inversion
• translocation

Question 2

Which is the more common duplication , intra -chromosomal vs inter - chromosomal duplications?

Answer 2

intra chromosomal

Question 3

What is a Tandem duplication?

Answer 3

Duplicated region is immediately adjacent to the original segment

Question 4

what is a displaced duplication?

Answer 4

Duplicated segment some distance from the original segment

Question 5

What is a reverse duplication?

Answer 5

When the duplicate is inverted

Question 6

What happens to an individual heterozygous for duplication?

Answer 6

Has one normal chromosome and one abnormal one .

Question 7

What happens to the added gene in an individual heterozygous?

Answer 7

The duplicated chromosome loops out during pairing in prophase 1.

Question 8

What is one problem with chromosomal deletions?

Answer 8

• Heterozygous conditions may produce imbalanced gene products

Question 9

What is the second problem with chromosomal deletions?

Answer 9

• Some genes must be present in two copies for normal function

Question 10

What happens in an paracentric inversion?

Answer 10

centromere unaffected

Question 11

What happens in an pericentric inversion?

Answer 11

centromere affected

Question 12

What happens to chromosomes when a heterozygote has one normal chromosome and one chromosome with a deletion?

Answer 12

In prophase 1 , the normal chromosome must loop out for the homologous sequences of the chromosome to align

Question 13

The mechanism of a paracentric chromosome mutation

Answer 13

• one wild type chromosome and one with a paracentric inversion
• In prophase 1 an inversion loops form , resulting in a chromosome that lacks a centromere
• This part is lost

Question 14

What are the resulting games from paracentric meiosis?

Answer 14

• 1 normal gamete
• 2 nonviable recombinant gametes
• 1 non- recombinant gamut with a paracentric inversion

Question 15

What is the mechanism for pericentric meiosis?

Answer 15

Crossing over occurs and produces chromatids which have too many copies of one gene , and not enough of others

Question 16

Results of pericentric meiosis

Answer 16

• 1 normal recombinant gamete
• 2 non viable recombinant gametes
• 1 non recombinant gamete with pericentric inversion

Question 17

What is translocation?

Answer 17

movement of genetic material between non -homologous chromosomes

Question 18

What is a non. - reciprocal translocation?

Answer 18

Genetic material not transferred between both chromosomes ( less common)

Question 19

What is a Robertsonian Translocation?

Answer 19

A Robertsonian translocation is when the long arms of two chromosomes with centromeres towards the ends (= acrocentric) become joined to a common centromere generating one big chromosome with a centromere near the middle (=metacentric)

Question 20

nullisomy

Answer 20

Loss of homologous par (2n-2)

Question 21

monosomy

Answer 21

loss of a single chromosome (2n-1)

Question 22

trisomy

Answer 22

gain of a single chromosome(2n +1)

Question 23

tetrasomy

Answer 23

gain of homologous pair (2n +2)

Question 24

How can aneuploidy arise?

Answer 24

• if a centromere is deleted - spindle fibres cannot attach. no division.
• Robertsonian translation
• non - disjunction

Question 25

How would reduced cohesion lead to improper segregation?

Answer 25

if sister chromatids not attached properly in prophase , no crossover , crossover needed for proper segregation

Question 26

How many Down syndrome people have trisomy 21

Answer 26

95% of all Down syndrome patients have trisomy 21. 91% of these are random nondisjunction in egg rather than sperm.

Question 27

What are the percentage of people who owe Down syndrome to Robertsonian translocation?

Answer 27

4%

Question 28

The incidence of Aneuploidy and maternal age

Answer 28

increases drastically with maternal age

Question 29

Is polyploidy more common in animals or plants?

Answer 29

more common plants

Question 30

What does autoplolyploidy mean?

Answer 30

Accidents of meiosis/ mitosis that produce extra sets of chromosomes, all derived from a single species

Question 31

What does allopolyploidy?

Answer 31

arises from hybridisation between two species, resulting polyploid carries chromosomes from two or more species

Question 32

Which is more common? tandem or displaced duplication?

Answer 32

Tandem duplication more common

Question 33

What is an example of chromosomal deletion?

Answer 33

reduced eye size

Question 34

What percentage of the human genome is duplicated?

Answer 34

4%

Question 35

Why do gene inversions affect fitness?

Answer 35

• gene split in middle
• position effects
• disrupted meiosis

Question 36

What are the Robertsonian translocations fitness effects?

Answer 36

• cuts within genes
• position effects
• loss of genes , due to the small fragment