Bentzen 10 - Chromosome Variations

Question 1

What are chromosome variations (mutations)?

Answer 1

Permanent chromosmal changes that can be passed on to offspring if they occur in cells that will become gametes.

Question 2

What are two general types of chromosome variations (mutations)?

Answer 2

1. Chromosomal rearrangement - changes in the structure of individual chromosomes
2. Variation in chromosome numbers - changes in the number of chromosomes. One or more individual chromosomes are added or deleted (includes aneuploids and polyploids)

Question 3

How many autosomes do humans have?

Answer 3

22

Question 4

How many sex chromosomes do humans have?

Answer 4

1

Question 5

What does a metacentric chromosome look like?

Answer 5

Equal length of the chromosome arms extending from the centromere

Question 6

What does submetacentric chromosome look like?

Answer 6

There is a short arm and a long arm

Question 7

What does an acrocentric chromosome look like?

Answer 7

Stubby arms and long arms

Question 8

What does a telocentric chromosome look like?

Answer 8

Two arms extending from the centromere

Question 9

What are chromosome rearrangements?

Answer 9

When a length of the chromosome is duplicated or something else happens to it. There is no change in ploidy level

Question 10

What is aneuploidy?

Answer 10

Also known as trisomy. Where there is ONE extra chromosome added

Question 11

What is polyploidy?

Answer 11

Also known as autotriploid, where there are multiple numbers of chromosomes made, eg. 3n=9

Question 12

What is the genetic reason for the Cri du Chat syndrome?

Answer 12

A deleted region of chromosome 5

Question 13

What is the genetic reason for Down Syndrome?

Answer 13

Trisomy (aneuploidy) of chromosome 21

Question 14

What are four types of chromosome rearrangements?

Answer 14

Duplication (length in chromosome duplicated)

Inversion (Where a sequence in chromosome inverts)

Deletion (Where a sequence in a chromosome is deleted)

Reciprocal Translocation (where a sequence in a chromosome is switched with another chromosome)

Question 15

How are chromosome rearrangements made?

Answer 15

They are a consequence of repair mechanisms gone wrong after double-stranded DNA breaks

Question 16

At what part of a cell’s life cycle can deletion loops be detected?

Answer 16

During meiosis

Question 17

How can you detect chromosome deletions?

Answer 17

There is a formation of a deletion loop during pairing of homologs in prophase I, in prophase I, the normal chromosome must loop out for the homologous sequences of the chromosomes to align.

Question 18

What is a consequence of chromosome deletions?

Answer 18

The genes that are deleted will not be deleted on the homologous chromosome so that the other genes will be expressed no matter what (in terms of recession or dominance).

Will lead to more mutant traits expressed (rather than the wild type)

Question 19

What is a tandem chromosomal duplication?

Answer 19

It is the simplest type of duplication where the two segments are adjacent to one another.

Question 20

What are the effects of duplication of a segment of a chromosome?

Answer 20

There is no loss of genetic information.
Usually viable, but bad effects from abnormal gene dosage can occur.
Important in evolution

Question 21

What generates chromosomal duplications and deletions?

Answer 21

Unequal crossing over of misaligned chromosomes generates duplications and deletions

Question 22

How can you detect tandem duplications in chromosomes?

Answer 22

During alignment of homologous chromosomes in prophase I of meiosis a duplicated chromosome forms a loop

Question 23

What does more copies of Bar gene region in Drosophilia lead to?

Answer 23

Fewer eye facets. A consequence of duplication

Question 24

What is it called in duplication where both copies of a gene remain the same after duplication?

Answer 24

redundancy

Question 25

What is it called where only one duplicated gene becomes inactive?

Answer 25

Pseudogene

Question 26

What is it called where one duplicated gene acquires a new function?

Answer 26

Neofunctionalization (important in evolution, often tandem to the original duplicated gene)

Question 27

What causes inversions in chromosomes?

Answer 27

2 breaks on a chromosome

Question 28

What is the consequence of inversion in chromosomes?

Answer 28

Gametes are usually viable because genetic information is not lost or gained, but viability changes if crossing over occurs!

Question 29

What is pericentric inversion?

Answer 29

Where inversion of the chromosome involves the centromere

Question 30

What is paracentric inversion?

Answer 30

Where inversion in the chromosome does not involve the centromere (just somewhere in the arms)

Question 31

What is the position effect from chromosome inversions?

Answer 31

It is where new location of genes on the chromosome alters gene expression in some cells (gene is silenced in some but not in others, leading to 'patchy' phenotype)

Question 32

What is the consequence of crossing over after inversion in a chromosome?

Answer 32

Crossing over outside of inverted region: viable gametes Crossing over inside inverted region: some nonviable gametes Inverted chromosomes forms an inversion loop

Question 33

What is a dicentric chromatid?

Answer 33

Where there are two centromeres attached by chromatid from crossing over in paracentric inverted chromosomes (no centromere involved). The link between the chromatids is called the dicentric bridge. Dicentric = two centromeres

Question 34

What is a acentric chromatid?

Answer 34

A chromatid with no centromere, can happen when dicentric bridge is formed as a consequence of crossing over in paracentric inverted chromosomes.

Question 35

What is the consequence of recombination in paracentric inversion chromosomes?

Answer 35

It will produce non-viable gametes because they are missing some genes

Question 36

What is the consequence of recombination and pericentric inversion in chromosomes?

Answer 36

Recombinant gametes are nonviable because genes are missing or present in too many copies

Question 37

What is reciprocal translocation?

Answer 37

Echange of genetic material between nonhomologous chromosomes also in prophase I of meiosis there is a pairing configuration between the two heterozygous chromosomes (they make a + shape)

Question 38

What is a consequence of reciprocal translocation?

Answer 38

Creation of a gene fusion or hybrid gene. Can lead to protein produced with improper functions, leading to cancer

Question 39

How can reciprocal translocation be detected?

Answer 39

In a karyotype using chromosome painting to show different coloured chromosome pieces in one chromosome (which should all be one colour)

Question 40

What are three different ways that reciprocal translocated chromosomes may segregate in anaphase? Which one produces viable gametes?

Answer 40

Alternate segregation (Where the two normal copies separate from the translocated copies) Adjacent-1 segregation (where the T1 and N2 separate from T2 and N1) Adjacent-2 Segregation (where the T1 and N1 segregate form T2 and N2 - rare) Only alternate segregation produces viable gametes

Question 41

What is Robertsonian translocation?

Answer 41

The fusion of two chromosomes, leading to the loss of genetic information. Two acrocentric chromosomes form break point which subsequently fuse leading to a metacentric chromosome and a chromosome fragment (which is lost due to a failure to segregate).

Question 42

What are three ways that chromosomes can separate in Robersonian Translocation?

Answer 42

Adjacent-1 segregation (common and unbalanced, two fused with fragment, and two fused no fragment) Adjacent-2 Segregation (Rare, unbalanced, two fused with long fragment, two non fused) Alternate segregation (common and balanced, two fused and two normal)

Question 43

How does Robsertsonian translocation provide evidence for evolution?

Answer 43

Humans have 2n=46 chromosomes and great apes hae 2n=48 chromosomes. Logically there must be two fused chromosomes in humans and there is, it is human chromosome 2, which is seperated in two for the great apes.

Question 44

Are copy number variations (CNV) common in the human genome? How big are they?

Answer 44

Yes. Thousands of base pairs. The average person has 1000 and most have no observable effects, but some are associated with deseases such as osteoporosis, autism and schizophrenia