3. Karyograms

Question 1

How many chromosomes do prokaryotes have? How many do eukaryotes have? What do they do?

Answer 1

• pro: 1

- eu: different chromosomes that carry genes

Question 2

How many chromosomes in humans? What do they do?

Answer 2

23 different chromosome types each of which carries a different group of genes

Question 3

Define ‘homologous’ in terms of chromosomes.

Answer 3

chromosomes of one particular type - same genes in same sequence, but different alleles of those genes

Question 4

Define ‘alleles’

Answer 4

different forms of a gene

Question 5

The number of chromosomes is a…..species

Answer 5

• characteristic feature of members of a species

Question 6

When quoting numbers of chromosomes a species has, what number is usually quoted?

Answer 6

the diploid number - how many chromosomes are present in normal body cells

Question 7

Give 5 examples and diploid chromosome number.

Answer 7

Homo sapiens (humans) - 46
Pan troglodytes (chimpanzee) - 48
Canis familiaris (dog) - 78
Oryza sativa (rice) - 24
Parascaris equorum (horse threadworm) - 4

Question 8

What sort of nucleus do most plant and animal cells have? What do some cells have?

Answer 8

• diploid nucleus - nucleus contains pairs of homologous chromosomes
• haploid nucleus - only has one chromosome of each type

Question 9

Name two cells that have haploid nucleus’?

Answer 9

gametes such as sperm and egg cells of humans

Question 10

How is a diploid nucleus cell formed by two gametes?

Answer 10

gametes such as sperm and egg cells fuse together during fertilisation and produce one diploid cell - a zygote

Question 11

Which pair of chromosomes determines your sex in humans? How?

Answer 11

the 23rd pair:

• two types of sex chromosome: X and Y
• XX: female
• XY: male

Question 12

Define ‘karyotype’.

Answer 12

the number and type of chromosomes present in a cell or organism

Question 13

What is a karyogram?

Answer 13

• a photograph or diagram in which the chromosomes of an organism are shown in homologous pairs of decreasing length

Question 14

Why are karyograms useful (general)? Give two examples of when a karyogram might be prepared.

Answer 14

so the chromosomes of an individual can be studied:

a) deducing the sex of an individual
b) diagnosing conditions due to chromosome abnormalities
- normal karyotypes: pair of each chromosome type including a pair of sex cells
- more or less than 2 of each pair = chromosome abnormality
- Down Syndrome: three of chromosome 21
- (males only) Klinefelter Syndrome: XXY (extra X)