Changes to chromosome number Flashcards
(14 cards)
What is aneuploidy?
Individuals with chromosome number different from normal - excess or deficiency - associated with abnormalities such as Down’s syndrome.
What do trisomy and and monosomy mean and what causes them?
An additional or missing chromosome. Caused by nondisjunction: A cell division error which homologous chromosomes fail to separate and migrate to opposite poles, producing a diploid gamete and one with no chromosomes. When these are fertilised by haploid gametes, tri/monosomy occurs.
Trisomy generally lethal to zygote.
Describe down’s syndrome
Trisomy 21 in 1/800 births - many physical
(epicanthic eye fold, single palm crease and simpler fingerprints), behavioural (more affectionate) and
physiological changes (including rapid ageing, intestinal blockage, diminished muscle tone) – incidence on DS increases with mother’s age - can also be associated with a translocation (14-21).
What is Klinefelter’s syndrome?
XXY male, number of female characteristics like breast development, female pubic hair patterns, testicular atrophy, also tall stature. XYY simply produces a male.
What is Turner’s syndrome?
XO - female with developmental changes: poor breast development, aortic constriction, rudimentary ovaries and no menstruation, elbow deformity and more. XXX females simply have two barr bodies, protected by X-inactivation.
What is Edward’s syndrome?
Trisomy 18, low birth weight
ears in a low position on their head, cleft lip or palate, club foot , heart, kidney and spine problems and also with. breathing or digestion. Clenched fist, overlapping fingers. Most die before birth, 5% born survive a year.
How do gynandropmorph drosophila form?
first mitotic division of the cell (when the number of chromosomes doubles), there is a fault in the cell division which results in the loss of one of the X chromosomes. There are 3 left. One of the cell descendants becomes XX and is female
and the other cell becomes X0 and is male
Explain Haplodiploidy sex determination in ants, bees and wasps.
n = male, 2n = female. A queen will produce haploid (n) cells via meitosis. These alone can develop into n drone males, which can fertilise other haploid eggs to produce a 2n female, mostly maturing into sterile drones but when needed into another queen.
Define Polyploidisation
the creation of cells with 3 or more sets of chromosomes, usually lethal in humans as odd numbers of sets prevents proper pairing during mitosis. Autopolyploidy results from endoreduplication, while allopolyploidy also involves hybridisation.
What are the uses of polyploidisation.
Triploid – banana, ginger, seedless melon
Tetraploid – maize, cabbage, tobacco
Hexaploid – wheat, chrysanthemum
Octaploid – strawberry, sugar-cane
How does polyploidy arise in cancer cells?
Either by cell fusion, endomitosis, or abnormal mitosis in which two chromosome sets go to one pole. These larger cells with more DNA grow and divide quicker, turning malignant.
How is polyploidy linked to cancer?
Most cancers have chromosome abnormalities. E.g. adenocarcinoma is polyploid - DNA index 1.7
What do primate genomes show?
The genomes of different primates show there has been little change in the amount of DNA, but many changes in its structures (inversions and translocations). Human chromosome 2 is a fusion of chimp chromosome 2a and 2b. You can see other human synteny with other
organisms such as mice and even the pufferfish and sea anemones.
What is the relevance of fish diversity to chromosome rearrangement?
Several paleopolyploidisations might explain the vast body plan diversity in fish, as polyploidisation of chromosome sets gives the raw information for evolution to work on.
