Chromosome Variations & Sex Determination

Question 1

What is a karyotype?

Answer 1

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

Question 2

What are euploid organisms?

Answer 2

organisms with multiples of basic chromosome set

chromsome number can vary among closely related species

Question 3

What are polyploids?

Answer 3

organisms with 2+ chromosome sets

can be triploid, tetraploid, pentaploid

Question 4

What is a monoploid?

Answer 4

individual from typically diploid species that has only one set of chromosomes
usually lethal

Question 5

Where is polylpoidy common?

Answer 5

plants
less common in animals
frog tolerate polyploidy well

Question 6

What are aneuploid organisms?

Answer 6

individuals whose chromosome number different by one or a small number of chromosomes

2n+1 = triatomic
e.g. downs syndrome

Question 7

How do cells have abnormal chromosome numbers?

Answer 7

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

Question 8

what is the phenotypic effect of monosomies?

Answer 8

humans die in eutro
monosomy for X causes Turners Syndrome

Question 9

What is the phenotypic effect of trisomies?

Answer 9

many are lethal
trisomy 21 causes downs syndrome
XXY karyotype causes Klienfelter syndrome

Question 10

What are chromosome duplications?

Answer 10

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

Question 11

What are chromosome deletions?

Answer 11

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

Question 12

What are CNVs?

Answer 12

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

Question 13

What is it when chromosomes have mixed up pieces?

Answer 13

inversions and translocations

Question 14

How do you create an inversion?

Answer 14

segment of chromosome cut out
flipped
reinserted into chromosome in opposite orientation

balanced rearrangements
don’t involve gain or loss of any genetic material

Question 15

How do you create a translocation?

Answer 15

rearrangement involving part of one chromosome
broken off
reattached to different chromosome

reciprocal = switched with another chromosome
robertsonian = fusion, without switch

Question 16

What is the CML?

Answer 16

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

Question 17

What is chromosomal sex determination?

Answer 17

XY determination system
males are XY
females are XX

presence of Y determines maleness

Question 18

what is the Y chromosome?

Answer 18

sex chromosome that determines maleness
inheritance from father to son

Question 19

what is the X chromosome?

Answer 19

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’

Question 20

What is epigenetics with reference to X chromosome?

Answer 20

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

Question 21

What is the sex determination system?

Answer 21

XY sex determination system
X-linked recessive traits can be deduced from certain clues

Question 22

What are the XY determination clues?

Answer 22

1. more males than females express the trait
2. characteristic often skips a generation
3. if female expresses, all her offspring will also express