Chromosomes

Question 1

What is chromatin?

Answer 1

nuclear DNA and associated proteins (e.g. histones)​

Question 2

Chromosomes aren’t the same length at the top or the bottom, what are these known as?

Answer 2

short=p arm
long=q arm

Question 3

What is the chromosomal make-up of any organism referred to as?

Answer 3

karyotype

Question 4

What is ploidy?

Answer 4

the number of sets of chromosomes in a cell, or in the cells of an organism.
Higher ploidy tends to mean larger cells therefore larger organisms.

Question 5

What are the other types of chromosomes and what makes them special?

Answer 5

B chromosomes (sometimes referred to as ‘supernumerary’) Germline Restricted Chromosomes and functioning ‘A’ chromosomes.​
These are often inherited in a non-Mendelian fashion

Question 6

Where are germline-restricted chromosome (GRC) found commonly?

Answer 6

They are widespread among songbirds

Question 7

Name a a haplodiploid species

Answer 7

some Hymenoptera (wasps and bees)
one sex has haploid cells and the other has diploid cells. The haploid sex develops from unfertilized eggs, the diploid from fertilized eggs.

Question 8

Variations in ploidy between species

Answer 8

ODD PLOIDY LEVELS ​
(Triploids 3n, penta-5n, hepta-7n…)​
-usually evolutionary ‘dead-end’ (but e.g. some lizards).
EVEN PLOIDY LEVELS​
(Tetraploids 4n, hexa- 6n, octa- 8n…) ​
-functioning although usually then isolated from ​PATERNAL STOCK

AUTOpolyploids formed through doubling​
ALLOpolyploids formed through hybridisation (U)

Particularly in plants, changes in ploidy and number of chromosomes is a common means of speciation.​

Question 9

Explain chromosomes (autosomes and gonosomes)

Answer 9

Chromosomes (=autosomes and gonosomes) are compact spools of DNA wound around proteins, histones, only seen during replication. Normally DNA exists as chromatin in cells. ​

Question 10

What is the chiasma?

Answer 10

Chiasma = point at which cross over occurs​