GENO- numerical chromosomal abnormalities

Question 1

outline the process of mitosis

Answer 1

prophase- chromosomes condense and become visible - 2 sister chromatids joined in the centre - spindle fibres form and move to opposite ends of the cell

metaphase- sister chromatids line up in the middle of the cell

anaphase- sister chromatids are separated and pulled to opposite ends of the cell

telophase- nuclear membrane forms around each of the separated chromosomes and they unravel and become less condensed

cytokinesis - cytoplasm divides forming 2 identical daughter cells

Question 2

outline the process of meiosis

Answer 2

gamete cell division

meiosis 1-

prophase- chromosome replication
metaphase line up on middle plate as 23 ambivalence
telophase - pairs of chromatids are pulled to opposite ends of the cells and made into two separate daughter cells

meiosis 2
sister chromatids are then separated and then 4 daughter cells are formed each with 23 chromosomes

Question 3

describe a normal human karyotype

Answer 3

23 pairs of chromosomes
22 autosomes
1 sex chromosomes

Question 4

define metacentric

Answer 4

p and q arms are the same length

joined by centromere in middle

Question 5

define submetacentric

Answer 5

p arm is shorter than the q arm

Question 6

define acrocentric

Answer 6

long q arms small p arms

p contains no DNA

Question 7

define haploid

Answer 7

one set of chromosomes - normal gamete

Question 8

define diploid

Answer 8

cell contains two sets of chromosomes (46 in a normal human)

Question 9

define polyploid

Answer 9

multiple of the haploid number (4n - 92)

Question 10

define aneuploidy

Answer 10

chromosome number which is not an exact haploid number - due to extra / missing chromosomes - trisomy, monosomy

Question 11

explain non-disjunction

Answer 11

when both chromatids go to one pole and none to the other resulting in daughter cells who have too many or too few chromosomes

Question 12

what does non-disjunction mean for an individual in meiosis

Answer 12

resulting gametes are chromosomally unbalanced - resulting foetus will have too many or too few chromosomes

Question 13

where does most non-disjunction occur and why

Answer 13

occurrs in women as meiosis 1 is longer - therefore aneuploidy is increased with age

Question 14

why is independent assortment important

Answer 14

leads to genetic variation which is really important

Question 15

define mosaicism

Answer 15

the presence of two or more genetically different cell lines derived from a single zygote

Question 16

what is trisomy rescue

Answer 16

recognises trisomy so throws out one copy of the chromosome - this is random and can have various consequences

Question 17

what is the clinical relevance of mosaicism

Answer 17

mosaic phenotype is thought to be less severe

difficult to assess - proportions, tissues / organs affected