chromosomes Flashcards
(46 cards)
chromosome structure explained
consists of two identical strands called chromatids joined at the centromere
centromere divides the chromatids into short p and long q arms
telomeres at the tip
two different types of chromosome + definition
acrocentric- centromere is on one side
metacentric- centromere is in the middle
telomere function
maintain the structural integrity of chromosomes formed of highly conserved tandem repeat sequences
how is structure integrity maintained?
telomerase enzyme ensures replication, preventing the shortening of the DNA strand
what happens in cancers?
telomeres are over produced, preventing cell senesence
karyotype definition
a picture of a person’s chromosomes
G-banding explained
denature the proteins in the chromosome using trypsin, stain with Giemsa, a DNA binding dye which gives the chromosome a stripy pattern
active areas stain light
Other genetic techniques used to view chromosomes
FISH, Chromosome painting, CGH and array CGH
explain FISH
Uses DNA probe to anneal to its complementary target sequence where it is located on a metaphase spread
Used to detect chromosome abnormalities, such as Down’s syndrome
Three red dots shows that three probes bound to three chromosomes which signify Down’s syndrome
used when scientists are looking for a known sequence
explain chromosome painting
used when sequence is unknown
a mixture of probes specific for each chromosome are used, able to view translocations and identify which chromosomes they came from
CGH stands for
comparative genome hybridisation
explain CGH use
used when people do not look normal. try to detect regions of gene amplification or gene loss
Test DNA is labelled with green paint, normal DNA is labelled with red paint. Too much green shows gene amplification, too much red shows gene loss
Determination of the male sex
presence of Y chromosome leads to maleness regardless of the number of X chromosomes present
presence of SRY region on Y, the sex determining region, which encodes a transcription regulator
what happens if SRY gene is mutated?
XY female
SRY function
unregulated the gene transcription of genes involved in testis production from Wolffian ducts
testis Sertoli cells produce mullein inhibitory Factor, inhibiting female genitalia production
what happens if there is androgen insensitivity?
body does not react to testosterone, leading to an XY female despite SRY
Explain X-linked inactivation
Early in embryonic life, structurally abnormal X is preferentially inactivated, otherwise it is random.
Inactivation is not complete, some genes are known to escape inactivation
Inactivation is not permanent, reversed in development of germ cells
Barr body definition
inactivated X chromosome =, if an individual had 4 X chromosomes they would have 3 Barr bodies
abnormalities linked to X and Y
more Xs, more intellectually impaired
extra Y, more aggressive, increased criminal tendencies
2 different syndromes linked to sex chromosomes
Turner syndrome X
Klinefelter’s syndrome XXY
Explain Turner syndrome
intellectually normal, infertility, primary amenorrhoea, cardiac abnormalities and webbed neck
explain klinefelter’s
feminised male, moobs, fat around his and thighs, impaired IQ
three trisomies
Trisomy 21- Down’s
18- Edward’s
Patau- 13
explain nondisjunction of chromosomes
failure of separation of chromosomes during meiosis in gametes which results in cells with extra or less copies of a particular chromosome
