theme 3- CB18 Meiosis

Question 1

Describe Karyotypes?

Answer 1

the number and visual appearance of the chromosomes in the cell nuclei of an organism or species.

Question 2

What are karyotypes used for?

Answer 2

studied after Amniocentesis and chorionic villus sampling of a foetus to detect aneuploidies (differences in chromosome number).
to see if a person has “healthy” chromosomes number
Identification of disease/syndromes

Question 3

How do you prepare a karyotype?

Answer 3

1) Place blood sample in cell culture for 3 days
2) Add colchcine ( a drug that arrests cells in metaphase by inhibiting spindle formation) and hypertonic saline
3) prepare slide and stain
4) Analyze “metaphase spread”

Question 4

What are the 3 ways of staining chromosomes and their main functions?

Answer 4

1) trypsin and Giemsa staining, produces banding pattern- identify individual chromosomes by pattern and sizes
2) chromosome “painting” using labelled DNA probes- identification of chromosomes by their colour and size
3) Fluorescence In-Situ Hybridization- shows 2 colours, one for each of the 2 chosen pairs, allowing for translocation of non-homologous chromosomes to be shown e.g. 9:22

Question 5

1) What does NIPD stand for?
2) what is it used for?
3) What other conditions can be caused by aneuploides?

Answer 5

1) non-invasive prenatal diagnosis
2) analyse maternal peripheral blood to look for foetal aneuploidies, primarily to diagnosis down’s syndrom
3) other rarer syndrome e.g.Edwards syndrome (trisomy 18), Patau syndrome (trisomy 13), Turner syndrome

Question 6

Describe the chromosomes in diploid cells?

Answer 6

22 homologous somatic chromosomes, one paternal one maternal

2 sex chromosomes

Question 7

Why is meiosis necessary?

Answer 7

1) Introduce genetic diversity

2) Produces haploid gametes that allow fusion to form a diploid zygote

Question 8

How is genetic diversity introduced during meiosis?

Answer 8

1) Independent segregation of homologous chromosomes

2) recombination of chromosomes ( equivalent sections of homologous chromosomes are exchanged)

Question 9

When do you call DNA chromatids?

Answer 9

After the chromosome has replicated in prophase it is made up of 2 chromatids, they r sister chromatids if they r from the same chromosome,

Question 10

1)Describe recombination events:
When does it happen?
2)Why is it needed?

Answer 10

1) Exchange of fragments of maternal and paternal homologous chromatids • During the first meiotic division
2) genetic diversity, gives species competitive advantage so has a evolutionary significance

Question 11

What is the difference chromosomal mutation and genetic mutation?

Answer 11

1) Chromosomal mutation is not inherited but “acquired”, gene mutation is inherited. IN GENERAL (don’t argue)
2) Chromosome mutation is where either the number (numerical abnormality) or the structure of chromosomes is changed. Gene mutation is a change in the base sequence so is a much smaller change

Question 12

What are the 2 types of numerical abnormalities of chromosomes?

Answer 12

• Aneuploidy: Loss or gain of one or more chromosomes

- Polyploidy: Addition of one or more complete haploid complements

Question 13

Give 2 examples of 2 types of Aneuploidy:

Answer 13

1) Trisomy e.g. Down’s syndrome, chromosome 21

2) Monosomy e.g. Turner’s syndrome (lack of an X or Y chromosome)

Question 14

Give an example of a type of Polyploidy: what does it lead to?

Answer 14

Triploidy: 69 chromosomes = spontaneous miscarriage

Question 15

Syndrome disorders caused by trisomy often include the symptoms:

Answer 15

• craniofacial disorders
• developmental disorders e.g 15-20% of Down’s have severe cardiac abnormalities
• syndromes caused by the effect of gene “dose” (the number of copies of a particular gene present in a genome) e.g. Alzheimer’s susceptibility gene (APP) is more likely to be expressed if it is on chromosome 21

Question 16

non-dysjunction in meiosis is…

Answer 16

when the chromosomes don’t separate properly either metaphase 1 or 2 during meiosis. metaphase 2 is better as half will still be okay

Question 17

What causes numerical abnormalities in chromosomes?

Answer 17

1) absence of recombination of chromosomes increases the risk as usually even a single exchange helps to facilitate proper alignment of homologous
chromosomes, therefore without it homologous chromosomes are at risk for malsegregation
during MI.
2) more common in female gametogenesis
3) Increased risk as age increases.

Question 18

How can chronic myeloid leukemia be identified?

Answer 18

Fluorescences in-situ hybridisation will colour chromosome 9 red and 22 green, there is clearly a swap between chromosome 9 and 22

Question 19

What is cytogenetics?

Answer 19

analysing karyotypes

Question 20

What causes structural abnormalities in chromosomes?

Answer 20

Chromosome breakage followed by reunion in a new configuration, this is a translocation-transfer if material from one chromosome to another.

Question 21

What is haematological malignancy?

Answer 21

cancers of the blood and lymphatic vessels

Question 22

What is Chronic myeloid leukaemia (CML) ?

Answer 22

People who have CML make too many granulocytes, a type of white blood cell. These are not fully developed and fill the bone marrow so that it can’t make healthy blood cells.

Question 23

What causes Chronic myeloid leukaemia (CML)?

Answer 23

when a gene from one chromosome ) wrongly attaches to a gene on another chromosome. In 90 per cent of cases this is a 9:22 translocation. This means that 2 genes that should be completely separate become attached. This altered gene is a derivative of chromosome 22 and is called the Philadelphia chromosome = chimeric gene is expressed which is associated with the transformation in leukaemia ( helps cause leukaemia), transforma

Question 24

Define chimeric gene:

Answer 24

form through the combination of portions of two or more coding sequences to produce new genes

Question 25

What is the p and q regions of the chromosome?

Answer 25

The p region is represented in the shorter arm of the chromosome (p is for petit, French for small) while the q region is in the larger arm (chosen as next letter in alphabet after p).

Question 26

What does 15q12 mean?

Answer 26

In chromosome 15 in the q region (longer arm), the band labelled 12 has had some of its bases deleted.