Chromosomes

Question 1

Diploid

Answer 1

• 46 chromosomes in human cells
• 23 inherited from each parent
• 22 pairs of autosomes and 2 sex chromosomes

Question 2

Sex chromosomes

Answer 2

-X and Y
-not homologous but different in size and shape
Male= XY
Women =XX
-haploid cells- chromosomes are not doubled

Question 3

Centromere

Answer 3

• divides the chromosome into a short arm and a long arm
• short arm= P
• long arm=Q

Question 4

Metacentric chromosome

Answer 4

• has centromere right in the middle

- p and q arms are of equal length

Question 5

Acrocentric chromosome

Answer 5

-centromere is placed at one end and so arms are not of equal length

Question 6

Telocentric

Answer 6

• Centromere is at the tale of the chromosomes

- not seen in humans

Question 7

Holocentric chromosomes

Answer 7

• entire length of the chromosome acts a the centromere

- not seen in humans

Question 8

Aneuploidy

Answer 8

-when there are different chromosome numbers to the normal diploid status
.e.g trisomy 21, trisomy 18, monosomy of Turners
-very rarely there are more than 2 copies of the entire chromosome set and have a chromosome number of 69-triploidy and tetraploidy result in spontaneous abortion

Question 9

Non-disjunction

Answer 9

-chromosome or chromatids fail to separate in meiosis and so one gamete received two copies of that chromosome and one with no copies
-this can result in an extra chromosome- trisonomic
or no chromosome- monosomic
-only individuals with trisomy 13, 18 and 21 survive to birth and most children with trisomy 13 and 18 die in childhood

Question 10

Mosaic

Answer 10

• sometimes non-disjunction can occur during mitosis immediately after two gametes have fued
• this leads to the formation of 2 cell lineages each with a different chromosomal makeup
• this occurs more frequently with the sex chromosomes and results in ‘mosaic’ individual
• mosaics have milder malformations