Lecture 28: Variation in Chromosome Number: Aneuploidy and Polyploidy

Aneuploidy

The number of chromosome in an interphase somatic cell is not an exact multiple of the haploid number

• ex) Humans are 2n = 46 so haploid number is 23

Monosomic

2n-1=7

Nullisomic

2n-2=6

Double Monosomic

2n-1-1=6

Trisomic

2n+1=9

Tetrasomic

2n+2=10

Double Tetrasomic

2n+1+1=10

Polyploidy

more then 2 “sets” of chromosomes

Haploid

1 of every chromosome

Diploid

2 of every chromosome

Triploid

3 of every chromosome

Tetraploid

4 of every chromosome

Polypoid

more than 2 copies of haploid genome

Autopolyploidy

extra sets of chromosomes are identical to normal chromosome set (all sets are from the same species)

Allopolyploidy

combination of sets of chromosomes from 2 species

Amphidiploids

are allopolyploids that behave as diploids which happens when the resulting hybrid ends up with exactly 2 copies of every chromosome type

ex) Triticale

ex) Wheat: where triticale is an allotetraploid, wheat is described as an allohexaploid since there are three diploid genomes that make up the wheat genome.

Allotriploid

(AAB) - third is not homologous, cannot form a trivalent

Autotriploid

(AA)

Autotetraploid

(AAAA)

Allotetraploid

(AABB)

Turner Syndrome

have an XO chromosome composition

Klinefelter Syndrome

have an XXY chromosome composition

Nondisjunction

in meiosis (cell division) there is the improper separation of chromosomes

ex) Turner Syndrome and Klinefelter Syndrome which are also examples of aneuploidy