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Human Genetic Variation
Basic terminology
What is a gene?
• A gene is a functional and physical unit of
heredity passed from parent to offspring.
• Genes are pieces of DNA, and most genes
contain information for making a specific
protein.
• Genes exist in 2 forms at each location on a
chromosome. These are called alleles.
• Alleles can be dominant or recessive.
What is DNA?
• DNA stands for Deoxyribonucleic Acid.
• It is the chemical in the nucleus of the cell
that carries the genetic instructions for
making living organisms.
Base Pairs
• Cytosine and Thymine = pyrimidines
• Adenine and Guanine = purines
• A purine always binds with a pyrimidine to
form a base pair.
• A base pair makes up one “rung” on the
DNA ladder (double-helix)
• Adenine-Thymine, Cytosine-Guanine
What is an amino acid?
• An amino acid is one of twenty different
kinds of small molecules that link together
in long chains to form proteins.
• Amino acids are referred to as the “building
blocks” of proteins.
20 amino acids
**you must memorize these**
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Alanine
Arginine
Asparagine
Aspartic acid
Cysteine
Glutamic acid
Glutamine
Glycine
Histidine
Isoleucine
Leucine
•Lysine
•Methionine
•Phenylalanine
•Proline
•Serine
•Threonine
•Tryptophan
•Tyrosine
•Valine
What is a chromosome?
• One of the threadlike “packages” composed of
proteins, genes, and other DNA in the nucleus of a
cell.
• Different kinds of organisms have different
numbers of chromosomes.
• Humans have 23 pairs of chromosomes, 46 total
chromosomes.
• 1 pair of sex chromosomes, 22 pairs of autosomal
chromosomes.
Contribution
• Each parent contributes 1 chromosome to
each pair, so children get ½ of their
chromosomes from their mother and ½ from
their father.
Put the following in order from
smallest to largest:
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Gene
Chromosome
Amino acid
DNA
Nucleus
Cell
Protein