Karotype Analysis

Question 1

What is a karyotype?

Answer 1

A visual representation of an individuals/ cells complete set of chromosomes

Question 2

How is a karyotype produced?

Answer 2

1. Collect a sample of cells- Blood for children & adults, amniotic fluid for foetal samples
2. Cells are cultured, arrested with colchicine during metaphase/ pro-metaphase
3. Cells are fixed and stained, with a d reveal reveal in light microscopy
4. C-some are rearranged and ordered into karyotype
5. A count and classification forms the text of the karyotype

Question 3

How are chromosomes classified?

Answer 3

Classification is based on the ratio of p to q arm length
The ratio defines the type of chromosome
1- Meta centric
1.5-2.5- Sb metacentric
2.5-10- Acrocentric
Telocentric- No p-arm at all, not found in human but can occur due to aberrations

Question 4

How are chromosomes identified?

Answer 4

Difficult to identify those in Group C, especially as they have similar positions of centromeres
So careful consideration of banding is considered
And there are modern techniques used that help

Question 5

Define polyploidy

Answer 5

More than 2 complete chromosome sets
Frequently found ini plants, but it’s rare in animals and normally lethal at birth but can be acquired in cancerous cells

Question 6

Define Aneuploidy and where does it originate from?

Answer 6

Presence of a abnormal number of chromosomes, originates from improper serration of chromosomes during cell division (non-disjunction)

Question 7

Define nondisjunction and what does it result in

Answer 7

Homologous c-some don’t separate during meiosis 1 OR sister chromatids do not separate during meiosis 2
Results in gametes being trisomic (2n +1) or monosomic (2n-1)

Question 8

What is the cause of Down Syndrome?

Answer 8

Trisomy 21 caused by a mistake in cell division, not inherited
Most likely to be caused by nondisjunction of chromosome 21 during egg/ sperm development
Produces the karyotypes 47, XX, +21 (females) and 47,XY, +21 (males0

Question 9

Give the 2 other types of Down syndrome

Answer 9

Mosaic- Mixture of normal and trisomy 21 cells, 1% of cases
Translocation- Robertsonian translocation occurs with chromosome 21, long arm of chromosome 21 is often used to the long arm of chromosome 14, 2-4% of cases

Question 10

What is a Robertsonian translocation?

Answer 10

Known as a balanced translocation
No info is lost

Question 11

What causes Edwards syndrome?

Answer 11

Trisomy 18
Produces the karyotype 47, XY, +18

Question 12

What causes Patau syndrome?

Answer 12

Caused by trisomy 13
Produces the karyotype 47, XY, +13

Question 13

Describe the Lyon hypothesis and Barr bodies

Answer 13

Lyonization was proposed by Mary Lyon in 1962, idea that in any given female cell only 1 X chromosome is active

Barr bodies were observed by Murray Llewelyn Barr in 1948, idea that the expression of genes is silenced by the packaging of the c-some into heterochromatin
Choice of which X chromosome is random and inactivation occurs in the embryonic cell

Question 14

What. is Klinefelter’s syndrome?

Answer 14

Occurs n males with an additional copy of X
Produces the karyotype 47, XXY
Causes sublet affects and most are unaware they have it
Barr bodies are present in cell, mating it possible for additional X c-some to occur
Multiple Barr bodes my result in intellectual disability

Question 15

What is XYY/ Jacobs syndrome?

Answer 15

Occur in males with an additional copy of Y
Produces the karyotype 47, YYX
Very few symptoms, most are unaware they have it

Question 16

What is Turner syndrome?

Answer 16

Occurs in females who have a single copy of X
Produces the karyotype 45, X/ 45, X0
No Barr bodies and this is the only viable human monosomy

Question 17

List and explain the different types of chromosome alterations

Answer 17

1. Deletion- genes have been lost, the functions of thee genes will be missing
2. Duplication- Info has been duplicated in a single chromosome
3. Inversion- Info ha been flipped and the flipping can disrupt the gene
4. Translocation- Portions of arms are swapping, can occur at both a regional and whole chromosome level to