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Biology - Genetics > Evolution - Karyotypes > Flashcards

Evolution - Karyotypes Flashcards

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AP® Biology flashcards Biology 101 flashcards
1
Q

Karyotype

A

The number and visualisation of the set of chromosomes of individuals

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2
Q

How can karyotype be visualised?

A

Chromosome mapping

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3
Q

Chromosome Mapping

A

Hybridization with flurescent dyes label each chromosome a different colour

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4
Q

How are autosomes arranged in CM?

A

Longest to shortest(1 to 22)

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5
Q

Cytogenetic

A

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

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6
Q

Alternative way of staining chromosomes…

A

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

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7
Q

How are bands indicated in G-band staining?

A

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

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8
Q

How are bands arranged in G-band staining?

A

Numbered from centromere to telomere.

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9
Q

What would 1p34 indicate?

A

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

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10
Q

What are examples of genetic landmarks?

A

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

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11
Q

How are chromosomes obtained for chromosome mapping?

A

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

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12
Q

Types of chromosome based on centromere…

A

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

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13
Q

Acentric

A

Chromosomes without centromere, lost due to poor division.

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14
Q

Dicentric

A

Chromosomes containing two centromeres.

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15
Q

Why do majorty of chromosomes have single centromere?

A

Only ones reliably segregated in mitosis.

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16
Q

Dicentric segregation…

A

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

17
Q

Example of dicentrism?

A

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.

18
Q

Chromosomes in great apes?

A

48 chromosomes

19
Q

Gene dosage

A

Number of copies of a particular gene present in a genome

20
Q

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

A

Y chromosomes are heterochromatic with less genes.

21
Q

Dosage Compensation

A

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

22
Q

X-Inactivation

A

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

23
Q

Where does X-inactivation occur?

A

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

24
Q

Lyon Hypothesis

A

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

25
Q

Mosaicm

A

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

26
Q

What does mosaicsm result from?

A

X-Inactivation

27
Q

Why does mosaiscm occur?

A

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

28
Q

Pseudoautosomal Regions

A

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

29
Q

Where do pseudoautosomal regions exist?

A

Ends of short and long arms.

30
Q

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

A

They are indistinguishable and can undergo crossover.

31
Q

Function of centromeres…

A

Allow sister chromatid segregation

32
Q

Centromere structure…

A

Establish of alpha sattelites

33
Q

Alpha Sattelites

A

Tandemly repeat sequences at noram human chromosomes

34
Q

What causes X-Inactivation?

A

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

35
Q

What does Xist and Tsix do?q

A

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

36
Q

How is Xist/Tsix balance controlled?

A

DNA methylaiton

37
Q

How is a karyotype done?

A

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.

38
Q

Point of giemsa staining?

A

Seperates the chromosomes into bands allowing characterisation.

39
Q

What ways are chromosomes identified?

A

Length
Banding patterns
Centromere placement.

Biology - Genetics (14 decks)

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