Topic 14: Chromosomes, Gene Carriers

Question 1

What is a chromosome?

Answer 1

Structures that pack DNA.

Question 2

What is the kinetochore?

Answer 2

A special attachment site of a chromatid by which it links to a spindle fibre.

Question 3

What are telomeres?

Answer 3

Normal terminal regions of a chromosome. Comprised of repetitive DNA strands which become shorter every time a cell divides.

Question 4

What is a karyotype?

Answer 4

Assists in the analysis of chromosomes present in cells. Organised according to international convention from cut out stained images of chromosomes photographed during metaphase of mitosis. Arrangement enables abnormalities in structure/number to be quickly identified.

Question 5

How are autosomes matched?

Answer 5

Banding pattern, centromere position, length, presence of satellites.

Question 6

What are matching autosomes called?

Answer 6

Homologues pairs, or homologues.

Question 7

What can occur due to mistakes in meiosis?

Answer 7

Changes in total number of chromosomes (aneuploidy) or chromosome structure/arrangement.

Question 8

What is aneuploidy?

Answer 8

Changes in total no. chromosomes, where chromosome no. is more or less than normal in diploid/haploid cell.

Question 9

What is non-disjunction?

Answer 9

Normal separation of homologous double stranded chromosomes doesn’t occur during Meiosis 1 (all chromosomes affected as half have +1 and half -1) or sister chromatids fail to separate during Meiosis 2 (half of gametes affected only). Results in more or less chromosomes in a gamete.

Question 10

What can non-disjunction of sister chromatids or chromosomes result in?

Answer 10

• lacks one member of homologous pair. Monosomy of autosomes results in non viable zygote
• gametes contain extra chromosome (trisomy)

Thus, gametes w/ wrong number of chromosomes fertilised = abnormal chromosome number = deleterious affects on development = syndrome.

Question 11

Name aneuploidy autosomal syndromes.

Answer 11

Down Syndrome: Trisomy-21

Edward Syndrome: Trisomy-18

Question 12

Name aneuploidy sex chromosomes syndromes.

Answer 12

Klinefelter syndrome: XXY

Turner syndrome: XO

Question 13

Describe deletion in toms of change to chromosomal structure or arrangement.

Answer 13

break occurs at 2 points on chromosome, middle piece falls out. Two ends rejoin forming chromosome deficient in some genes. CRI DU CHAT SYNDROME MISSING PART OF CHROMSOME 5

Question 14

Describe the effect of inversion in terms of chromosomal structure change

Answer 14

middle piece falls out, rotates 180° and then rejoins. Genes are in reverse order for this segment. No loss of genetic material.

Question 15

Describe translocation in terms of change to chromosome structure.

Answer 15

movement of group of genes between different chromosomes. Non homologous chromosomes swap genetic info. Some gametes consequentially receive extra genes and some deficient. EG DOWN SYNDROME 14 ATTACHES TO 21. PHILADELPHIA CHORMOSME RECIRPOCAL TRANSLOCATION RESUKTJNG IN CANCER.

Question 16

Describe duplication in terms of change to chromosomal structure.

Answer 16

segment lost from one chromosome added to its homologue. Thus, one will be deficient in genes while the other receive double the genes.

Question 17

Describe what process results in Down syndrome and how it may occur in MEIOSIS 1.

Answer 17

Non disjunction of homologous pair of chromosome-21 occurs during Meiosis I. At the end of Meiosis 1, one gamete has 22 chromosomes and the other has 24. After meiosis II, two gametes will have an extra chromosome 21. When fused with normal gamete, zygote will have 47 chromosomes. This results in trisomy-21 or Down syndrome. The other two gametes will have no chromosome 21s.

Question 18

Describe what process occurs in MEIOSIS II for resulting offspring to have Down syndrome.

Answer 18

Non disjunction of sister chromatids in Meiosis II. At the end of Meiosis, 2 gametes will have 1 chromosome-21, 1 will have no chromosome 21s and one will have an extra chromosome 21. If normal gamete fuses with this gamete, resulting offspring will be trisomy-21 resulting in Down syndrome.

Question 19

How are homologous chromosomes matched?

Answer 19

• same banding pattern
• same centromere position
• same length
• presence of satellites.

Question 20

What happens during Meiosis in hybrids?

Answer 20

• some/all of chromosomes do not pair up as cannot form homologous pair.
• segregate independently of other chromosomes
• viable gametes must contain a full set of chromosomes
• only occurs if all sheep chromosomes segregate to one side and all goat chromosomes segregate to other side.
• chance of this happening, very small
• gametes genetically unbalanced as do not contain full set of chromosomes
• gametes unviable, organism infertile.