Chromosomal mutations. A mutation is a change in the DNA Generally, mutations are considered at the gene level, but some types of mutations involve addition, loss, or change of DNA at the chromosomal level. We basically consider two types of change: Change in chromosome number
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Definition: Autosomes vs. sex chromosomes
Risk of having a Down syndrome infant increases sharply with the mother’s age, especially older than 35.
Embryoid cultured in agar with nutrients and w/ plant hormones.
Cells differentiate into roots, stems, etc and become adult plant.
Seeds can be collected, and plant propagated.
Of the 15,000 pregnancies that ended in spontaneous abortions, 1275 of them were found to be triploids.
What percent is that?
What percent of all the pregnancies is that?
What percent of live births were triploids?
HINT: questions like this on the next exam?
Part of chromosome is doubled; visible in the banding pattern.
Duplication can increase gene dosage; this is usually harmful.
Duplications often caused by unequal crossing over:
Crossing over can also occur in the middle of a gene, causing partial color blindness.
A portion of the chromosome is flipped relative to the rest.
Most of the problems with inversion are due to complicated attempts by chromosomes to pair up properly during meiosis. See your text and next slide.
Duplications, deletions, and dicentric and acentric chromosomes can result from funny pairing and subsequent crossing over.
A piece of a chromosome winds up attached to another chromosome. Could be a swap (reciprocal) or not.
Translocations occur between non-homologous chromosomes!
Major problem is again pairing of chromosomes during meiosis, resulting in extra or missing pieces, leading to partial monosomies and trisomies.
Semi-sterility: only some gametes good
Piece of one chromosome breaks off, attaches to another chromosome. Creates partial trisomies, monosomies, which are generally fatal.Robertsonian translocation: fusion of chromosomes near the centromere. One animation shows two centromeres, the other shows none. Definition describes fusion of centromeres.
Cases of inherited Down syndrome involve translocation of part of Chromosome #21 to, typically, #14.