L14 - Numerical Chromosomal Abnormalities

Question 1

What is the difference between Mitosis and Meiosis?

Answer 1

Mitosis is the cell division process where somatic cells are produced (46 chromosomes)
Meiosis is the process whereby gametes are produced (23 chromosomes)

Question 2

What are sister chromatids?

Answer 2

they are 2 identical copies of a chromosome joined together by a centromere

Question 3

What happens in Prophase of Mitosis?

Answer 3

Cell spindle fibres form and move to opposite ends of the cells to forma web like structure across the cell.
chromosomes condense.

Question 4

What happens in Metaphase of Mitosis?

Answer 4

The web like structure arranges the chromosomes in a line in the middle

Question 5

What happens in Anaphase of Mitosis?

Answer 5

sister chromatids are pulled apart to opposite ends of the cell.

Question 6

What happens in Telophase of Mitosis?

Answer 6

A nuclear membrane forms around each set of chromosomes

they become less visible

Question 7

What may happen during errors in segregation of anaphase?

Answer 7

Both chromatids may go to one pole and not the other

Question 8

What is non-disjunction and what occurs as a result?

Answer 8

When Both chromatids may go to one pole and not the other. This results in daughter cells having too little or too many chromosomes

Question 9

Describe the normal human karyotype and the type of chromosomes that can be involved?

Answer 9

23 pairs of chromosomes
22 autosomes and 1 pair sex chromosomes (XX or XY)
chromosomes can be metacentric (p and q arms equal), submetacentric (p arm is shorter than q) or acrocentric (very small p arm and long q - p contains no unique DNA)

Question 10

What is meant by polyploid?

Answer 10

having chromosomes that are a multiple of the haploid number - 4n=92

Question 11

What is meant by Aneuploid?

Answer 11

Chromosome number which is not an exact multiple of a haploid number - due to extra or missing chromosomes

Question 12

How and when does genetic recombination occur

Answer 12

In metaphase 1 of Meiosis 1
homologous chromosomes align and form a bivalent structure - they are held together by the synaptonemal complex
chromosome crossover forms a structure called a chiasma. Breaking of sister chromatids on both homologous chromosomes, and the exchange of material

Question 13

State 3 Autosomal Aneuploidies?

Answer 13

trisomy 13 - patau’s
trisomy 18 - edwards
trisomy 21 - downs

Question 14

State 3 Sex chromosome Aneuploidies?

Answer 14

turners - lacking X chromosome female

Triple X syndrome - 3 X

Klinefelter’s - extra X male

Question 15

What is Mosaicism?

Answer 15

The presence of 2 or more genetically different cell lines derived from a single zygote

Question 16

What is Trisomy rescue/Anaphase lag?

Answer 16

cell recognises that it has the wrong number of chromosomes so it throws one copy out - it throws out at random - so we may be left with 2 maternal copies or normal contribution

This still only occurs in a proportion of cells so the individual is still mosaic