Evolution - Karyotypes

Question 1

Karyotype

Answer 1

The number and visualisation of the set of chromosomes of individuals

Question 2

How can karyotype be visualised?

Answer 2

Chromosome mapping

Question 3

Chromosome Mapping

Answer 3

Hybridization with flurescent dyes label each chromosome a different colour

Question 4

How are autosomes arranged in CM?

Answer 4

Longest to shortest(1 to 22)

Question 5

Cytogenetic

Answer 5

The study of inheritance in relation to structure/function of chromosomes

Question 6

Alternative way of staining chromosomes…

Answer 6

Giemsa reagant exhibit G-bands specific to each pair of homologs.

Question 7

How are bands indicated in G-band staining?

Answer 7

G-bands replicated in S phase. being gene poor and R bands with are gene rich.

Question 8

How are bands arranged in G-band staining?

Answer 8

Numbered from centromere to telomere.

Question 9

What would 1p34 indicate?

Answer 9

First chromosome, on the short arm and 34th band.

Question 10

What are examples of genetic landmarks?

Answer 10

Rhesus is 1p34
ABO blood-group is 9q34
Red-green color blindness at Xq28

Question 11

How are chromosomes obtained for chromosome mapping?

Answer 11

Microdissection followed by PCR amplification, then labelling with fluoresnce, made to hybridize with complement strands, observed under confocal microscope.

Question 12

Types of chromosome based on centromere…

Answer 12

Metacentric (In the middle)
Submetacentric (Off-centred)
Acrocentric (Localised to one end)

Question 13

Acentric

Answer 13

Chromosomes without centromere, lost due to poor division.

Question 14

Dicentric

Answer 14

Chromosomes containing two centromeres.

Question 15

Why do majorty of chromosomes have single centromere?

Answer 15

Only ones reliably segregated in mitosis.

Question 16

Dicentric segregation…

Answer 16

Bridge between each daughter cell, breaking leaving broken chromosome in either cell

Question 17

Example of dicentrism?

Answer 17

Human chromosome 2, derived from chimps where there’s two medium-sized acrocentric chromosomes, G-bands indicate chromo 2 formed by telomeric fusion between the short arms.

Question 18

Chromosomes in great apes?

Answer 18

48 chromosomes

Question 19

Gene dosage

Answer 19

Number of copies of a particular gene present in a genome

Question 20

Why is gene dosage a problem in sex-determination in chromosomes?

Answer 20

Y chromosomes are heterochromatic with less genes.

Question 21

Dosage Compensation

Answer 21

An evolved mechanism either increasing male X chromosome activity or decreases female X chromosome activity

Question 22

X-Inactivation

Answer 22

This is inactivation of a random X chromosome in early embryo development.

Question 23

Where does X-inactivation occur?

Answer 23

At the XIC site near centromere on the long-arm.

Question 24

Lyon Hypothesis

Answer 24

This results in equalisation of number of active copies of X-linked genes, both having same active x-chromosomes

Question 25

Mosaicm

Answer 25

The presence of DNA alteration in only some of the bodys cells

Question 26

What does mosaicsm result from?

Answer 26

X-Inactivation

Question 27

Why does mosaiscm occur?

Answer 27

Because in each cell, X-inactivation can occur in either chromosome, if heterozygous for enzyme A or B, progeny produce half and half of the alleles

Question 28

Pseudoautosomal Regions

Answer 28

This is the resembelence of functional genes in Y and X chromosomes

Question 29

Where do pseudoautosomal regions exist?

Answer 29

Ends of short and long arms.

Question 30

Why aren't Y nor X linked despite pseudoautosomal regions?

Answer 30

They are indistinguishable and can undergo crossover.

Question 31

Function of centromeres...

Answer 31

Allow sister chromatid segregation

Question 32

Centromere structure...

Answer 32

Establish of alpha sattelites

Question 33

Alpha Sattelites

Answer 33

Tandemly repeat sequences at noram human chromosomes

Question 34

What causes X-Inactivation?

Answer 34

Expression of the Xist/Tsix genes and differential regulation of active/inactivity

Question 35

What does Xist and Tsix do?q

Answer 35

Sist silences/inactivates one X chromosome whilst Tsix preveents Xist accumulation.

Question 36

How is Xist/Tsix balance controlled?

Answer 36

DNA methylaiton

Question 37

How is a karyotype done?

Answer 37

Taken blood for nucleated white blood cells Mitotic stimulation by phytohaemagglutinin. Incubation Condensed chromosomes frozen in metaphase mitosis by colcemia Tube centrifugation then cell lysis by hypotonic solution. Giemsa staining.

Question 38

Point of giemsa staining?

Answer 38

Seperates the chromosomes into bands allowing characterisation.

Question 39

What ways are chromosomes identified?

Answer 39

Length Banding patterns Centromere placement.