Download Ch. 12 .1 12.2 Human Genetics Notes

CH. 12 HUMAN GENETICS
Pp 248
GENOME: 12.1
An organism’s complete set of genetic material.
 Fits into the nucleus- compact packing of DNA
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DNA wraps around proteins called histones.
 Tight helical, supercoil.
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Human Genome Project
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Government funded
Joint venture with industry
Sequenced human genome
Computer database
Completed 2000
CHROMOSOME DISORDERS 12.2
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Normal human karytoype (picture of a person’s
chromosomes)- 46, in 23 pairs.
Nondisjuction- unequal separation of chromosomes
into gametes during meiosis.
anaphase of meiosis I or II
 results in gametes with abnormal numbers of
chromosomes.
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Example- Trisomy - an extra chromosome
Worse in Meiosis I- all gametes have abnormal numbers of
chromosomes.
 In meiosis II- two normal gametes and two abnormal
gametes.
 See figure 12-4- pg 251.
 Most embryos with abnormal chromosome numbersmiscarriage.
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Figure 12-4
Nondisjunction in meiosis I results in all the gametes having abnormal numbers of chromosomes.
Nondisjunction in meiosis II results in two normal gametes and two abnormal gametes. (Note that for
simplicity only two pairs of homologous chromosomes are shown rather than all 23 pairs.)
TRISOMY 21
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Down’s syndromeExtra #21 chromosome.
 Embryos survive.
 Symptoms
Facial features Forehead, slanted eyes
 Shorter height
 Heart defects
 * Degrees of mental disability
 Impaired immune system
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Increases with age of mother
Hypothesis- lag in meiosis-may cause errors of
nondisjunction
CHROMOSOME STRUCTURE CHANGES
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Duplication – repeat of part of the chromosome.
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Delection- part of chromosome is lost.
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Very severe- loss of genes that code for proteins.
Inversion- chromosome part is reversed.
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Not always fatal- developmental abnormalities.
Least severe- since all genes are present.
Translocation- a chromosome part attaches to
another chromosome.
See figure 12-6 pg 252
Figure 12-6
Changes to a chromosome's structure may lead to various human disorders. Part of the chromosome
may be duplicated, deleted, inverted, or translocated to another chromosome.
JUMPING GENES:
Transposons
 Different from chromosome structure changes.
 One gene can move from one place to another in a
chromosome.
 Can disrupt another gene and its protein.
 Found in all organisms including humans.
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Provides diversity
 Example- color in corn- spotted corn.
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Discovered by Barbara McClintock.