Topic 15: Chromosomal Changes

Question 1

What are the four types of chromosomal rearrangements

Answer 1

1. Duplication
2. Deletion
3. Inversion
4. Translation
   Slide 5*

Question 2

Duplication and deletion are… Inversion and translation are…

Answer 2

Addition or loss of genetic material
Movement of genetic material within the genome

Question 3

How do chromosomal rearrangements occur? (3)

Answer 3

1. Unequal crossing over (duplication and deletion)
2. Double strand break repair (deletions, inversions, translocation)
3. Transposable elements causing rearrangement

Question 4

What is unequal crossing over

Answer 4

Mis-alignment during prophase 1 plus crossing over in the mis aligned region
Usually due to repetitive regions

Question 5

Example of unequal crossing over

Answer 5

Red-green colourblindness: genes for red and green opsin are very similar and can mis align easily during prophase 1

Question 6

Example of double stranded break repair causing rearrangement

Answer 6

Robertsonian translocation
Tiny chromosome fragmet is often lost

Question 7

What is tandem duplication

Answer 7

Duplicated segments are adjacent

Question 8

What are displaced duplications

Answer 8

Duplicated segments are located distantly on the same chr or diff chr (intra or inter chromosomal)

Question 9

Types of duplications

Answer 9

1. Tandem duplication
2. Displaced duplication
3. Reverse duplication

Question 10

What is reverse duplication

Answer 10

Duplicated segments are inverted relative to each other
e.g. E F F E

Question 11

What are the effects of duplication

Answer 11

1. Problems with homologous pairing during meiosis
   -> Causes duplicated region to loop out during pairing
2. Problems with gene dosage (alter phenotypic results)

Question 12

How does gene duplication play a role in evolution

Answer 12

Many genes have essential roles in metabolism, development, physiology, etc
Gene needs to do its function, if there are duplicates one can be mutated while other is functioning. Mutant can become a new kind of gene

Question 13

Effects of deletions

Answer 13

Phenotypic effects depend on what genes were located on deleted DNA
Many deletions = recessive lethal alleles

Question 14

Individuals that are heterozygous for a deletion have three possible results:

Answer 14

1. Gene dosage imbalance (essentially hemizygous)
2. Recessive alleles on the WT homolog will be expressed (pseudodominance)
3. Haploinsufficiency (one remaining copy is not enough)

Question 15

E.g. of haploinsufficiency in deletion

Answer 15

Notch gene in fruit flies

Question 16

Types of inversions

Answer 16

1. Paracentric inversions = next to the centromere, centromere does not move
2. Pericentric inversions = around the centromere, centromere moves
   Slide 16

Question 17

Types of translocations

Answer 17

Nonreciprocal translocation: one-way movement of genetic material from one chr to diff nonhomologous chr

Reciprocal translocation: two-way swap of genetic material btw nonhomologous chr

Question 18

Diff btw translocation and crossing over

Answer 18

Translocation = movement of genetical material btw nonhomologous chr
Crossing over = homologous chr

Question 19

Effects of inversion and translocation

Answer 19

Do not result in gain or loss of genetic material, but:
1. Can break genes into pieces = usually non functional or altered expression
2. Position dependent regulation is altered

Question 20

What is the position effect

Answer 20

When the location of a gene on a chr contributes to gene expression
e.g. euchromatin vs heterochromatin

Question 21

Example of the position effect

Answer 21

White locus in flies
W= red eyes, W- = white eyes
Inversion mutation leads to movement from euchromatin to heterochromatin = downregulation = red and white spotted eye

Question 22

Animations for meiotic complications

Answer 22

Are on eclass