Higher Eukaryotic Chromosomes

Question 1

What is meant by karyotype?

Answer 1

The number and visual appearance of the chromosomes in the cell nuclei

Question 2

True or False:
The number of chromosome is indicative of species’ complexity

Answer 2

False. Number of chromosome is uninformative. Think of it as two books with the same content but different number of chapters

Question 3

List the possible identifiers of a chromosome (3)

Answer 3

• Size
• Centromere position
• G-banding

Question 4

Explain how centromere position can be a possible identifier (3)

Answer 4

A chromosome can have its centromere in several different positions:
- Acrocentric -> close to one end
- Submetacentric -> off-centre
- Metacentric -> centrally located

Question 5

Explain what would be seen in Giemsa Staining

Answer 5

Giemsa staining is the staining of nucleic acids.
A-T will be seen as dark bands (gene poor)
G-C will be seen as light bands (gene rich)

Question 6

List the possible types of abnormalities

Answer 6

• Numerical, change in gene number
• Structural, change in gene position

Question 7

What is polyploidy?

Answer 7

The addition of one or more sets of chromosomes.
Ex. triploidy (3n = 69)
Humans too sensitive and often miscarriage occurs

Question 8

What is aneuploidy?

Answer 8

The loss or gain of one or more chromosomes

Question 9

What are possible structural changes that can occur?

Answer 9

• Deletion
• Duplication
• Inversion
• Translocation

Question 10

What are the causes of each abnormality?

Answer 10

• Aneuploidy, non-disjunction
• Structural Abnormalities, DNA breakages or non-allelic homologous recombination

Question 11

What is meant by inversion?

Answer 11

A chromosomal mutation consisting of the removal of a chromosome segment, its rotation through 180 degrees, and its reinsertion in the same location

Question 12

What are the types of inversions? (2)

Answer 12

• Paracentric - inversions flanking the centromere
• Pericentric - inversions encompassing the centromere

Question 13

What is meant by translocation?

Answer 13

The relocation of a chromosomal segment to a different position in the genome

Question 14

Explain the pairing and segregation of reciprocal translocation

Answer 14

Chromosomes form a cross-shaped pairing
1. Alternate (T1 + T2) or (N1 + N2): complete and viable

2. Adjacent (T1 + N2) or (N1 + T2): duplication and deletion of segements

Question 15

What is Robertsonian Translocation?

Answer 15

Centric fusion of acrocentric centromeres

Question 16

What is meant by synteny?

Answer 16

A situation in which genes are arranged in similar blocks in different species

Question 17

Explain the Eutherian Karyotype

Answer 17

The theory that chromosomes from different species have shared ancestry. The genome remains the same but is split and rearranged in different blocks

Question 18

What is the c-value paradox?

Answer 18

Genome size does not reflect complexity of an organism

Question 19

If genome size does not correlate to complexity, what does it correlate to?

Answer 19

Amount of DNA derived from transposable elements.

Genes are relatively constant components of genomes. Therefore the additional DNA in larger genomes are due to repeated DNA sequences

Question 20

What is the Cot Renaturation Curve used for?

Answer 20

It measures how much repetitive DNA is in a DNA sample using the principles of DNA reassociation kinetics

Question 21

What is the principles of DNA reassociation kinetics?

Answer 21

the rate at which a particular sequence reassociates is proportional to the number of times it is found in the genome

Question 22

Give examples of unique components of the genome (3)

Answer 22

• non-coding intervening sequences
• non-coding control sequences (promoters, enhancers etc)
• CpG islands

Question 23

Where are genes most often found?

Answer 23

Genes are unevenly distributed in the chromosome. Genes are more concentrated in areas of high G-C content

Question 24

What types of mutations can a duplicated gene acquire? (3)

Answer 24

1. Inactivating mutation: inactivated paralog is known as pseudogene (invisible to nat. sel.)
2. Alter activity of gene (neofunctionalisation)
3. Function divided between dupe, complement one another. Subfunctionalisation

Question 25

How is haemoglobin an example of repetitive sequences?

Answer 25

Genes for adult alpha chain in Chr 16 has a cluster of 5 repeated genes and beta chain in Chr 11 has cluster of 6 genes. However, gene families produce different proteins
Each cluster has pseudogenes

Question 26

Which types of transposable elements appear most often in the genome? (2)

Answer 26

Retrotransposons called Long Interspersed Elements (LINEs) and Short Interspersed Elements (SINEs)

Question 27

How are LINEs and SINEs so abundant?

Answer 27

SINEs and LINEs have integrated using reverse transcription
The DNA sequence transposes via RNA intermediate via copy and paste mechanism
LINEs are autonomous and encode own reverse transcriptase. SINEs use RTase produced by LINE

Question 28

What are VNTRs?

Answer 28

Short sequences repeated over and over in tandem

Variable Number Tandem Repeats

Question 29

What are the types of VNTR? (3)

Answer 29

Largest: Satellite (>100 bp) located in centromere area
Minisatellite (15-100bp)
Smallest: Microsatellite (<15bp). Located in telomere area

Question 30

What are the causes of VNTRs? (3)

Answer 30

1. Due to similarity, when lined up = unequal crossover
2. DNA replication slippage (re-replication or lost of replication)
3. DNA repair