Lecture 8- Chromosome mapping

Question 1

Knowing the exact location of a gene has what benefits?

Answer 1

• Can lead to screening
• Better diagnostic tests
• For gene therapy

Question 2

what are the three methods of determining the location of genes?

Answer 2

• somatic cell hybridisation
• In situ hybridisation
• Linkage analysis

Question 3

Describe somatic cell hybridisation?

Answer 3

A human and mouse cell are infused to form a hybrid cell, contains mouse and human chromosomes, it divides continuously.

The mouse chromosomes are stable and full number but human chromosomes are continuously lost to a point where there is only a single human chromosome left.

If we identify a specific protein made by humans then it must be made by a specific human chromosome which we can identify by its banding pattern; This method does not tell you where on the chromosome the gene resides.

Question 4

What is in-situ hybridisation?

Answer 4

This gives a precise gene location on chromosome.

• We must know the protein so we can figure out the amino acid and DNA code.
• Manufacture piece of the DNA code and make it radioactive = synthetic oligonucleotide so we can find out where it goes.
• Take dividing cells, so chromosomes are visible, ensure double stranded DNA is separated into single stranded and add synthetic oligonucleotide, which has same sequence as the gene we are looking for and will bind by hybridisation.

Question 5

what is a chromosome map?

Answer 5

shows a specific location of a gene

Question 6

What is Icthyosis and where is it mapped on the chromosome?

Answer 6

dry scaly fish/ reptile like skin on short arm (p)

Question 7

what three diseases have their gene on the short arm of the chromosome?

Answer 7

ichthyosis
albinism
retinoschisis

Question 8

what disease has its gene on the centromere of chromosome?

Answer 8

testicular feminisation-

inactive testiss

Question 9

what three diseases have their gene on the long arm (q) of the chromosome?

Answer 9

anaemia
lesch-nyhans syndrome
colour blindness (red/green sex-linked)

Question 10

what is retinoschisis?

Answer 10

Cyst in retina, causes detached retina after it splits

Question 11

where does meiosis occur

Answer 11

in sperm and egg

Question 12

what happens to chromosomes at meiosis?

Answer 12

chromosome number is halve

homologous pair up

genes exchanged by crossing over

Question 13

Describe what happens during crossing over in meiosis?

Answer 13

Outer threads of chromosomes remain same (big letters= A-B)

Inner threads of chromosomes break and rejoin such that A-b and a-B form- hence genes are REASSORTED.

Question 14

what is meant by recombinant?

Answer 14

when some sex cells have crossed over genes and not the original gene configuration.

Question 15

when are you able to see recombinants?

Answer 15

when genes are on either end of chromosomes then you will always see them; due to crossing over occurring between them.

Question 16

What is linkage analysis?

Answer 16

there is an unknown gene and a gene with a known location that is very close to the gene we have no clue about and isn’t separated from it due to recombination at meiosis. So we can then locate that gene by in-situ hybridisation, so we know the unknown disease gene will be next to it on chromosome.

Question 17

what is Huntington’s disease and where is it found?

Answer 17

Neurological condition resulting in dementia and unusual dance like movement of limbs

found on chromosome 4

Question 18

where are the following diseases found:

1- Alzhiemer's disease
2-PKU 
3-Lesch-Nyhan syndrome
4-Congenital cataract 
5-Aniridia
6-Retinoblastoma
7-Tay-sach's disease

Answer 18

21
12
X
1
2
13
15