Lecture 2

Question 1

What are telomeres and what are their function?

Answer 1

They are repeated sequences of DNA bases at the end of chromosomes that serve to protect the chromosome.

Question 2

What is a centromere?

Answer 2

Repetitive sequence that links sister chromatids.

Question 3

What happens at each stage of mitosis?

Answer 3

G2- loosely coiled chromosomes that have been replicated

Prophase- spindle fibres appear and chromosomes condense

Prometaphase- spindle fibres attach and chromosomes condense

Metaphase- chromosomes align on metaphase plate

Anaphase- sister chromatids pulled to opposite ends of cell

Telophase- nuclear membrane reforms and spindle fibres break down. Chromosomes decondense.

Cytokinesis- cytoplasm divides and two identical daughter cells are obtained

Question 4

What are homologous chromosomes?

Answer 4

Two chromosomes that have the same DNA sequence and the same genes in the same locations but may be different variants which are called alleles. Eg alleles for eye colour.

Sister chromatids on the other hand have identical genes and the same alleles.

Question 5

What is recombination in meiosis?

Answer 5

Crossing over of genetic material between non sister chromatids eg the chromatids of the other chromosome.
Crossing over sites called chiasmata.

Question 6

What is a tetrad?

Answer 6

Two sets of two sister chromatids. The two sets are known as bivalent forms as they come from the same chromosome pair.

Question 7

Can you describe meiosis?

Answer 7

Go back to lecture if not.

Question 8

What are the consequences of meiosis?

Answer 8

Maintain constant chromosome number

Generation of genetic diversity through random assortment and crossing over

Question 9

Why is it more likely that you will get problems with offspring if you have them when you are older?

Answer 9

Meiosis 2 for example only happens upon fertilisation by the egg. If this happens later in life there is a higher chance that mistakes will occur.

Question 10

Can you describe the processes of oogenesis and spermatogenesis?

Answer 10

Yes/no

Question 11

When in mitosis do the homologous pairs of chromosomes line up?

Answer 11

They don’t, this only occurs in meiosis

Question 12

Which phase of cell cycle or chromosomes replicated?

Answer 12

S phase

Question 13

What is the function of the sry gene on the Y chromosome?

Answer 13

It determines sex

Question 14

What is non disjunction?

Answer 14

Failure of homologous chromosomes or sister chromatids to separate properly during meiosis or mitosis

Question 15

What is a metaphase spread?

Answer 15

When cycle stopped in metaphase and chromosomes looked at to see banding patterns etc

Question 16

What is a karyotype?

Answer 16

Number and type of chromosomes in a cell. Total number of chromosomes in a species

Question 17

What is trisomy 21?

Answer 17

3 number 21 chromosomes which will result in Down’s syndrome

Question 18

What is G0

Answer 18

Time in cell when nothing mitosis related is happening

Question 19

What is aneuploidy

Answer 19

Abnormal chromosomes number

Question 20

What is mosaicism?

Answer 20

Presence of two or more different cell lines in the body.

If non disjunction occurs at first post zygotes cell division then more cells will be affected if it happens later down the line. This is because later you would have a line of normal cells and a line of affected cells.