Changes In Chromosome Number

Question 1

Aneuploidy

Answer 1

Individuals with chromosome number different from normal - excess of deficiency - can be associated with abnormalities

Question 2

Nondisjunciton

Answer 2

An error in cell division in which homologous chromosomes fail to separate and migrate to opposite poles; responsible for trisomy and monosomy

Question 3

Non disjunction and Down syndrome

Answer 3

Down’s syndrome (trisomy 21) - very common (about 1 out of every 800 births) – many physical
(including single palmer crease and simpler fingerprints), behavioural (more affectionate) and
physiological changes (including rapid ageing) – incidence on DS increases with mother’s age - can
also be associated with a translocation (14-21).

Question 4

Klinefelter’s and Turner’s syndrome

Answer 4

X chromosome inactivation means many faults in sex chromosome number are viable. Klinefelter’s
syndrome; XXY = male – often mild conditions have a number of female characteristics such as
breast development and female type pubic hair; XYY = male.

Turner’s syndrome; XO = female – associated with many developmental changes; XXX = female have
2 barr bodies

Question 5

Trisomy

Answer 5

Is generally lethal and results in the abortion of the zygote early in development. Edward’s
syndrome (trisomy 18) occurs in 1/6000 band results in heart abnormalities, kidney malformations
and other organ abnormalities

Question 6

Somatic aneuploidy

Answer 6

Drosophila (and finch) gynandromorphs; red eyed side is female and white eyed
side is male. Due to XX nondisjunction in early development.

Question 7

Haplodiploidy

Answer 7

Haplodiploidy sex determination in ants, bees and wasps (males are haploid n, females are diploid
2n).

Question 8

Polypoidisation

Answer 8

Changes in the number of chromosome sets; usually lethal in humans;
odd numbers of chromosomes are associated with infertility as cannot pair during meiosis

Question 9

Autopolyploid

Answer 9

Polyploid condition resulting from the duplication of one diploid set of chromosomes

Question 10

Allopolyploidy

Answer 10

Polypoid condition formed by the union of 2 or more distinct chromosome sets (i.e.
different species) with a subsequent doubling of chromosome number.

Question 11

Chromosome changes and agriculture

Answer 11

Most significant origin of crops was
about 10,000 years ago in the fertile crescent in the middle east.

Allopolyploidy is associated with
the origin of wheats and many other crops, Einkorn hybridised with another species to produce Emmer wheat. A further hybridisation resulted in today’s hexaploidy wheat.

Triticale is a recent Allopolyploidy of emmer wheat and rhy. Other polyploids include banana
(triploid and therefore sterile); maize (tetraploid) and strawberry (octaploid). Relatively few non-
plant polyploids including oysters.

Question 13

Polyploidy and cancer

Answer 13

Polyploidy is associated with some human cancers; adenocarcinoma cancerous cells have twice as much DNA as expected

Question 14

Drosophilia and chromosome changes

Answer 14

Hawaii is a chain of volcanos (newest island is about 5myo) and has a large density of Drosophila species.
Drosophila from different islands have different chromosome inversions and can be used to re-create their evolutionary history.

Question 15

Polyploidy and evolution

Answer 15

The genomes of different primates show there has been little change in the amount of DNA, but
many changes in its structures (inversions and translocations).

Human chromosome 2 is a fusion of chimp chromosome 2a and 2b.

You can see other human chromosome similarities with other organisms such as mice and even the pufferfish and sea anemones.

The polyploidisation of chromosome sets gives the raw information for evolution to work on.

Fish have had a number of ployploidisation events (salmon for example are hexaploidy) and may explain their diversity.