Download - The Human Genome Chapter 14
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The Human Genome
Chapter 14
Donna HowellBiology IBlacksburg High School
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Chromosomes
• All human beings have 46 chromosomes: 23 from the egg, and 23 from the sperm.
• Two of those chromosomes are called sex chromosomes: the X and the Y.
• The other 44 are called autosomes.
• Females’ chromosomes are XX, and males’ chromosomes are XY.
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Karyotype
• Scientists can take pictures of a cell’s chromosomes, and cut them out.
• When they sort them out by chromosome number, they have created a karyotype.
Human female karyotype
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Pedigree
• A pedigree is a chart that shows the relationships within a family, and allows us to infer genotypes we may not know.
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Genes and the Environment
• Some traits are not totally controlled by our genes; the environment contributes to some, such as height.
• Mostly due to genes, but also dependent on nutrition.
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Blood Group Genes
• Some of the first genes to be discovered were the human blood type genes.
• There are 4 types of blood: A, B, AB and O.
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Recessive Alleles
• Some genetic disorders are caused by recessive alleles.
• Examples: albinism, cystic fibrosis, Tay-Sachs disease.
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Dominant Alleles
• Some genetic disorders are caused by dominant alleles.
• Examples: Huntington disease, Dwarfism
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Co-Dominant Alleles
• Some genetic disorders are caused by co-dominant alleles – both alleles contribute to the disease.
• Examples: sickle cell disease
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From Gene to Molecule
• Sometimes, deletions in DNA can cause diseases.
• One example is cystic fibrosis.
• Three bases are deleted in the DNA, causing an amino acid to not be produced.
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From Gene to Molecule
• Another example is sickle cell disease.
• One base in DNA is changed, causing valine to be produced instead of glutamic acid.
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Sex-linked Genes
• Because X and Y chromosomes are different, some genes reside on one and not the other.
• These are called sex-linked genes.
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Sex-linked Genes
• One example is colorblindness.
• This gene is located on the X chromosome.
• Because males only have one X, all colorblindness shows up in males, even if it is recessive.
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Chromosomal Disorders
• Sometimes the cell makes errors when undergoing meiosis.
• One common error is nondisjunction.
• Causes abnormal number of chromosomes in gametes.
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Nondisjunction
• One example is Down syndrome.
• When a chromosome fails to separate during meiosis, cells may have an extra chromosome.
• Called trisomy.
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Sex Chromosome Disorders
• Disorders can also happen in the X and Y chromosomes.
• In females, nondisjunction causes Turner’s Syndrome; in males, it causes Klinefelter’s syndrome.
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Turner’s Syndrome
• Woman only inherits one X chromosome.
• Unable to reproduce – are sterile.
• Sex organs do not develop at puberty.
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Klinefelter’s Syndrome
• Man has two X chromosomes and a Y chromosome.
• Unable to reproduce – sterile.
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DNA Testing
• Human DNA can be tested to find out a person’s genotype.
• This can be used for family planning purposes.
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DNA Fingerprinting
• A process where DNA from two or more sources can be matched.
• Remember the Gene Machine? That was DNA fingerprinting!
• Used for crimes, paternity, etc.
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Human Genome Project
• In 1990, the Human Genome Project began.
• This was an attempt to analyze the complete human DNA sequence.
• Completed in 2000.
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Gene Therapy
• Information about our genes can be used to replace an absent or faulty gene with a normal, working gene.
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The End