what is a karyotype? karyotype: picture of an individuals chromosomes arranged in homologous pairs....
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What is a Karyotype?
Karyotype: picture of an individual’s chromosomes arranged in homologous pairs.
Chromosomes are usually extracted during METAPHASE of a cell. Why?
You can form a karyotype from any cell that is going through metaphase.
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You can identify the gender of the person by looking at the sex chromosomes on the karyotype.
XX Female
XY Male
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Doctors can also run tests on fetuses to check for chromosomal errors.
This test is called an amniocentesis.
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What happens when things go wrong with the chromosomes?
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Nondisjunction
When homologous chromosomes or sister chromatids fail to separate during meiosis.
-Can occur in anaphase I or II;
Resulting in gametes with abnormal # of chromosomes.
It is not fully understood why nondisjunction occurs. *usually occurs in women over 40
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Nondisjunction
• Example of nondisjunction:
Trisomy-21 an error most likely during meiosis I, causing 3 of the 21st chromosome.
Commonly known as: Down’s Syndrome
Symptoms: characteristic facial features, below average height, heart defects, impaired immune system, varying degrees of mental disability.
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Other forms of NondisjunctionTrisomy-13: (Patau Syndrome)
Due to an extra chromosome on
The 13th chromosome.
1 in 10,000 of children born.
There are varying degrees.
Symptoms: cleft lip, clenched
fist, close set eyes, mental
Retardation, etc.
More than 80% die in the first year.
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Klinefelter’s Syndrome: (XXY Male)
When a male has an extra X chromosome in most of their cells.
Most common symptom is infertility.
Most do not know they have it until puberty.
Have less testosterone, so lack some male features.
**caused by nondisjunction
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Turner Syndrome: (Monosomy-X)
Found in females that do not have the normal XX in their cells. They only have one.
1 in 2000 live births.
Symptoms: swollen hands and feet, lack female features after puberty, wide, webbed neck, flat/broad chest, drooping eyes, infertility.
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Damaged ChromosomesChromosomes can also be damaged and cause problems.
There are 4 types of changes that can occur to chromosomes and cause varying problems to the body.
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Duplication: when part of the chromosome is repeated. Not always fatal but can cause some developmental abnormalities.
Deletion: when part of the chromosome is lost.
Inversion: reversing a section of the original chromosome. (not as harmful)
Translocation: when a section of one chromosome attaches to a NONhomologous chromosome.
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Jumping GENESTransposons: where a section/gene of a chromosome “jumps” to another chromosome. Disrupting the genes.
Barbara McClintock discovered these in the 1940s with variations of corn. She received the Nobel Prize in 1983 for her pioneering work!