Chromosome structure

Question 1

length of chromosome complement

Answer 1

less than half a mm

Question 2

package of DNA into chromosomes

Answer 2

primary coiling of DNA double helix
secondary coiling around spherical histone beads, forming nucleosomes
tertiary coiling of nucleosomes to form chromatin fibres
chromatin fibres form long loops on scaffold of non-histone acidic proteins
further wound into tight coil - chromosome
solenoid

Question 3

non-coding regions

Answer 3

mostly heterochromatic and centromeric

Question 4

highest gene density

Answer 4

subtelomeric regions

Question 5

gene rich chromosome

Answer 5

19 and 22

Question 6

gene poor chromosomes

Answer 6

4 and 18

Question 7

unique single copy genes

Answer 7

code for polypeptides involved in cellular functions e.g. enzymes, hormones, receptors, structural and regulatory proteins

Question 8

multigene families

Answer 8

similar functions (genes) - arise through gene duplication events with evolutionary divergence
some found physically close, in clusters e.g. alpha and beta globin genes on 16 and 11.
some widely dispersed, e.g. HOX homeobox family
2 types: classic gene families and gene superfamilies

Question 9

classic gene families

Answer 9

high degree of sequence homology
copies of genes coding for ribosomal RNAs, clustered as tandem arrays at nucleolar organising regions on short arms of 5 acrocentric chromosomes
different transfer RNA gene families, multiple clusters across genome

Question 10

gene superfamilies

Answer 10

limited sequence homology
functionally related, similar structural domains
HLA (human leukocyte antigen) on 6
T-cell receptor genes - structural homology w/ immunoglobin (Ig) genes