genetics lecture 9 Flashcards
what polyploidy
Three or more sets of the same chromosomes
what causes polyploidy
when meiosis goes wrong
what is polyploidy common in/
common in plants but rare in most animals, it causes sterility in plants and is used by breeders to produce seedless fruits.
Aneuploidy
An increase or decrease of the number of individual chromosomes
Nullisomy
The loss of both numbers of homologous pair of chromosomes.
Monosomy
The loss of a single chromosome
Trisomy
The gain of a single chromosome
Tetrasomy
The gain of 2 homologous chromosomes
How does aneuploidy occur?
Caused by two homologous chromosomes not separating during meiosis. This is called a non-disjunctional event.
One daughter cell has both chromosomes, while the other has none when fertilised, either 2n +1 = trisomy or 2n-1 = monosomy.
what causes down syndrome
Down’s syndrome is usually caused by trisomy of chromosome 21.
Klinefelter’s syndrome male
xxx
Trisomy X female
XXX
Jacob’s syndrome male
XYY
Turner syndrome female
XO
Detection of Barr Bodies
to determine sex chromosome abnormalities
what should a female barr body have normal
A normal female (XX) should have a single Barr body whereas a female with three X chromosomes will have 2 Barr bodies.
what causes turner sydrome
Usually caused by a non-disjunction event
A pair of sex chromosomes does not separate during formation of either egg or sperm
what happens when an abnoraml egg unites with a nomral sperm to form embryo (turner sydnrome)
It ends up lacking a sex chromosome i.e. X instead of XX, hence the offspring is X0
what are the results of jacobs syndrome
extra Y chromosome
slightly taller than average
more active
normal intelligence, slight learning disabilities
delayed emotional immaturity
normal sexual development
Trisomy X (metafemale) outcome
Tall stature
Small head (microcephaly)
Vertical skin folds that may cover the inner corners of your eyes
Weak muscle tone
