Less common must have both recessive alleles in

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Less common; must have both recessive alleles in genotype to express the phenotype o Examples: albinism, sickle cell anemia (a blood disorder), etc. - Some genetic disorders are caused by dominant alleles o A dominant disease can be transmitted to offspring if at least 1 parent suffers from the disease o e.g. Huntington’s disease (slow, progressive deterioration of the brain) Disease does not begin until adulthood (post-reproductive years) so the genetic disease is passed on o Other diseases that may be caused in adulthood by dominant alleles may be Alzheimer’s & some types of breast cancer Chapter 11: DNA structure: 3 nucleotide components, 4 bases, complimentary bases, shape DNA is a type of nucleic acid (biological molecule) made up of chains of nucleotides There are 3 components of a nucleotide:
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A phosphate group A monosaccharide (simple sugar ) A base A nucleotide can have 1 of 4 bases Adenine: A Guanine: G Thymine: T Cytosine: C The secrets of DNA function are found in the 3D structure of DNA DNA = a double helix Double = two nucleotide strands connect together (like a ladder) Helix = the nucleotide strands are then twisted like a corkscrew or circular staircase - The nucleotide bases (A, T, G, C) stick out from the backbone (making up the “rungs” of the “ladder”) o The bases are bonded together, holding each strand together, through hydrogen bonds (weak) The bases pair in a precise combination: complimentary base pairs A always bonds to T Via 2 hydrogen bonds G always bonds to C Via 3 hydrogen bonds DNA replication - Replication of DNA is a critical for cells- review: - All cells come from pre-existing cells - Cells reproduce by dividing in half - Each of two daughter cells gets an exact copy of the parent cell’s genetic information - Duplication of the parent cell DNA is called DNA replication o 3 ingredients for DNA replication: o The parental DNA strands o Free nucleotides o A variety of enzymes that unwind the parental DNA double helix & synthesize new DNA strands o DNA replication begins with enzymes, called DNA helicases , that pull apart the parental DNA o “Unzip” the double helix (step 2 below) by breaking the hydrogen bonds between bases o A 2 nd strand of new DNA is synthesized along each separated strand by DNA polymerases (step 3) o = enzymes that pair free nucleotides with their complimentary nucleotides Mutations: 5 types - DNA repair enzymes “proofread” each new daughter strand & replace mismatched nucleotides
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- Sometimes proofreading fails: mutations - Mutations = changes in the sequence of bases - Mutations range from changes in single nucleotides to movements of large pieces of chromosomes - Mutations have varying effects on function o 1. Point mutations- mutations —also called nucleotide substitutions involve changes to individual nucleotides in the DNA sequence (1 base) e.g. an A is swapped (substituted) for a T o 2. Insertion- occur when 1 or more new nucleotides are inserted into the DNA double helix o 3. Deletion- occur when 1 or more nucleotides are
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