Chromosome Numbers Flashcards
(27 cards)
Aneuploidy
Results from the loss or gain of one or more chromosomes
Aneuploids
Have not exact multiple of haploid chromosome number (n)
Monosomic
One chromosome from the diploid number (2n-1)
Trisomic
Has one chromosome in addition to the diploid set (2n+1)
Tetrasomic
Has four copies of a particular chromosome (2n+2)
Autosomal Aneuploidy
Where organism is missing one of the autosomal chromosomes, generally lethal in large chromosomes
Somatic aneuploidy
Abnormal gene dosage, where trisomies of larger chromosomes are spontaneously aborted in pregnancy (excessive amounts of certain proteins), Trisomy 21 is well tolerated, Trisomy 13 and 18 have short life expectancy
X inactivation
In many mammals, all but one X chromosome is repressed into a Barr body, preventing the use of the genes on that chromosome
- Results in mosaic expression
What causes colour blindness?
Having the recessive opsin gene on the X-chromosome
- 8% of males, 0.5% of females
Kleinfelter Syndrome
When a human has two X chromosomes and one Y chromosome
1 in 500 males
- some genes expressed twice as much
Consequences of Aneuploidy
Monosomic: 1/2 gametes have no X chromosome, not viable
Trisomic: 1/2 gametes will have two X chromosomes
How does Turner’s syndrome occur?
Mitotic nondisjunction: where the set of sister chromatids do not separate properly
Chromosome loss: where one chromosome is not “grabbed” during anaphase
Gynandromorph
Equal parts male and female tissue
Drosophila bilateral gynandromorph
Literally half of the fly is female, half is male, you can draw a line
Results from loss of X during FIRST mitotic division
Asymmetrical gynandromorph
Patches of male and female phenotype, but not perfectly bilateral
Results from the loss of X chromosome in second or third mitotic division
Turner syndrome human females
Mosaics, carry both XX and XO cells
Chimera
Where two fertilized zygotes fuse together and form one organism with two different genomes in one
Euploids
Contain complete sets of chromosomes (2n)
Polyploids
Have three or more sets of chromosomes (3n, 4n, etc)
Monoploids
Have only one complete set of chromosomes (1n)
Haplodiploidy in ants, bees and wasps
Unfertilized eggs (haploid) -> males
Fertilized eggs (diploid) -> females
Parthenogenesis
Reproduction without fertilization
Parthenogenesis: Komodo dragon
Female produces haploid gametes, which double. ZZ (male) offspring possible, WW is lethal
Triploids
Three sets of chromosomes, usually sterile, example: seedless watermelon
