Chromosome Variations & Sex Determination Flashcards
What is a karyotype?
individuals complete set of chromosomes
also an image of chromosomes isolated from individual cell in metaphase
may be used to look for abnormalities in chromosome structure & order
What are euploid organisms?
organisms with multiples of basic chromosome set
chromsome number can vary among closely related species
What are polyploids?
organisms with 2+ chromosome sets
can be triploid, tetraploid, pentaploid
What is a monoploid?
individual from typically diploid species that has only one set of chromosomes
usually lethal
Where is polylpoidy common?
plants
less common in animals
frog tolerate polyploidy well
What are aneuploid organisms?
individuals whose chromosome number different by one or a small number of chromosomes
2n+1 = triatomic
e.g. downs syndrome
How do cells have abnormal chromosome numbers?
chromosomes aren’t evenly distributed in mitosis or meiosis
so gametes are evenly distributed
can result in n+1 and n-1; when crossed with normal gamete all offspring abnormal
risk of non-disjunction increases with maternal age
what is the phenotypic effect of monosomies?
humans die in eutro
monosomy for X causes Turners Syndrome
What is the phenotypic effect of trisomies?
many are lethal
trisomy 21 causes downs syndrome
XXY karyotype causes Klienfelter syndrome
What are chromosome duplications?
duplications of individual chromsomes
play important part in evolution of genome
happens in cell division
once duplicated, can add genetic info and can evolve to change function
adds opportunity for advantageous mutations to arise
What are chromosome deletions?
loss of a part of a chromosome arm
can be small only covering one arm of the gene
can be large missing big enough to be visualised on karyotype
What are CNVs?
Copy number variations
chromosome have extra or missing pieces on one
associated with several disorders
can be identified as they have half of the genetic sequencing
What is it when chromosomes have mixed up pieces?
inversions and translocations
How do you create an inversion?
segment of chromosome cut out
flipped
reinserted into chromosome in opposite orientation
balanced rearrangements
don’t involve gain or loss of any genetic material
How do you create a translocation?
rearrangement involving part of one chromosome
broken off
reattached to different chromosome
reciprocal = switched with another chromosome
robertsonian = fusion, without switch
What is the CML?
a specific gene abnormality in CML cancer cells
reciprocal translocation occurs
created fusion gene- translocation event
this codes for a hybrid protein that is always turned on
cell uncontrollably divides
What is chromosomal sex determination?
XY determination system
males are XY
females are XX
presence of Y determines maleness
what is the Y chromosome?
sex chromosome that determines maleness
inheritance from father to son
what is the X chromosome?
sex chromosome that are larger than Y
results in X linked traits
- red-green colour vision deficiency
- haemophilia
if recessive mutation in X chromosome then it is expressed in males as there is no copy to ‘back it up’
What is epigenetics with reference to X chromosome?
in females, one X chromosome epigenetically inactivated early in development
seen as highly condensed Barr body
female body is mosaic for genes on X chromosome
What is the sex determination system?
XY sex determination system
X-linked recessive traits can be deduced from certain clues
What are the XY determination clues?
- more males than females express the trait
- characteristic often skips a generation
- if female expresses, all her offspring will also express
