Biology – Lecture 56
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Transcript of Biology – Lecture 56
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Biology – Lecture 56
Karyotypes
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Karyotype
• The number and appearance of chromosomes in the nucleus of a eukaryotic cell.
• The complete set of chromosomes in a species
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Human Karyotype
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What to Look For
• Karyotypes describe the number of chromosomes, and what they look like under a light microscope.
• Attention is paid to their length, the position of the centromeres, banding pattern, any differences between the sex chromosomes, and any other physical characteristics.
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How do they Look?
• The chromosomes are arranged in pairs, ordered by size and position of centromere for chromosomes of the same size.
• Sex Chromosomes are always last.
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Difference between Sex Chromosomes
• X chromosomes are significantly larger than Y chromosomes.
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Human karyotype
• The normal human karyotypes contain 22 pairs of autosomal chromosomes and one pair of sex chromosomes.
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Chromosome Pairs
• There are 2 chromosomes of each number – one from the mom and one from the dad.
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How a karyotype is made
• 1. Cells are blocked during mitosis.• 2. Chromosomes are taken from those cells
and stained (making dark bands). • 3. Pictures of the chromosomes are taken, cut
out and matched up according to size, banding pattern and centromere position.
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Interpreting a karyotype
• Look at:• 1. the total number of chromosomes• 2. the sex chromosomes• 3. any extra or missing autosomal
chromosomes
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Naming a Karyotype
• 1. Count the total number of Chromosomes• 2. Name the sex chromosomes• 3. If there are extra chromosomes, name the
placement of them after a + sign.
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Examples
• 47, XY, +18 indicates that the patient has 47 chromosomes, is a male, and has an extra autosomal chromosome 18.
• 46, XX is a female with a normal number of chromosomes
• 47, XXY is a patient with an extra sex chromosome.
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Normal Human Karyotype
• Females contain two X chromosomes and are denoted 46,XX;
• Males have both an X and a Y chromosome denoted 46,XY.
• Any variation from the standard karyotype may lead to developmental abnormalities.
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Developmental Abnormalities
• In trisomy there is an extra chromosome resulting in three copies of the same chromosome.
• In monosomy, there is a missing chromosome and the zygote will have one copy of that chromosome.
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How can cells end up with too many or too few chromosomes?
• Sometimes chromosomes are incorrectly distributed into the egg or sperm cells during meiosis. When this happens, one cell may get two copies of a particular chromosome, while another cell gets none.
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How Does it Cause Abnormalities?
• People who are born with an abnormal number of chromosomes often have genetic disorders because their cells contain too much or too little genetic information.
• Scientists can predict genetic disorders by looking for extra or missing chromosomes in a karyotype.
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Common AbnormalitiesChromosome abnormality
Syndrome name Effects on individual
X Turner’s ●sterile female●underdeveloped female characteristics●short stature●sometimes below normal intelligence
XXY Klinefelter’s ●sterile male●abnormal male characteristics●abnormally long arms and legs●below normal intelligence
Trisomy #21 Down’s ●low mental ability●short arms and legs●internal defects●distinct facial features
Trisomy #18 Edwards ●severe abnormalities●life expectancy about 10 weeks
Trisomy #13 Patans ●severe defects including small, non-functioning eyes●survive only a few weeks after birth
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Turner’s Syndrome
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Kleinfelter’s Syndrome
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Down’s Syndrome
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Edward’s Syndrome
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Practice an X-linked Pedigree
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Practice an Autosomal Pedigree