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AP Bio- Information 8: Chromosomal Abnormalities
Transcript of AP Bio- Information 8: Chromosomal Abnormalities
Make Sure You Can:
How it happens
In a non-disjunction event, chromosomes do not separate during anaphase.
This leads to gametes with irregular numbers of chromosomes.
This must happen in a germ-line cell to have an effect (why?)
Segments of chromosomes can also get altered during DNA replication.
There are four major types of chromosomal rearrangements
How do these alterations effect an organism?
involve individual extra/missing chromosomes
Usually result in early miscarriage
Down's Syndrome: Trisomy 21
Sex Chromosome "-somy" mutations
Three copies of chromosome 21
characteristic facial appearance.
varying levels of retardation
other varying effects
Are generally more tolerated by the organism. Don't result in miscarriage
Why would an extra 21 be tolerated by the organism?
Turner's Syndrome: Monosomy X
Associated with heart defects
Kleinfelter's Syndrome: XXY
Some "female" secondary sexual characteristics (e.g. over-developed breast tissue)
Multiple Y Chromosomes/Multiple X Chromosomes
Not a problem. Why?
The Y chromosome is the smallest human chromosome.
It contains very few genes.
It's major function is to direct testes formation early in development.
The X chromosome is pretty large.
It contains many genes.
BUT: Both males and females have to function with it (and males only get 1 copy).
X-inactivation: Early in development every X chromosome in a cell except for one is turned into an inactive "Barr body".
So multiple X chromosomes are not a problem
involve extra homologous sets of chromosomes.
Not usually tolerated in animals.
No rule about how a chromosomal rearrangement will affect an organism
Sometimes detrimental, sometimes silent.
A translocation in blood stem cells leads to CML leukemia
Map showing diseases associated with various translocations in the human genome:
How can genetic material be changed?
How do changes in the genetic material of an organism lead to changes in the traits of that organism?
Calico cats are always female!
Explain how the mutations that are discussed in this presentation arise.
Explain the causes and effects of all of the situations discussed in this presentation.