Lecture_18_DulaiS09_HumanGenetics

Lecture_18_DulaiS09_HumanGenetics - Genetics: Principles of...

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1 Genetics: Principles of inheritance Human Genetics Chapter 12
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2 Revision •W h a t i s pleiotropy ? Pleiotropic gene - a gene that affects more than one phenotype • In one example the gene that causes yellowing of the coat in mice also affects viability and is termed a pleiotropic gene.
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3 Human genetic make-up is determined by genes carried on 46 chromosomes (the diploid number) Male Gamete (Father) n (23) Female Gamete (Mother) n (23) Fertilization ZYGOTE 2 n (46)
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4 Human Life Cycle
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5 A karyotype is an image of chromosomes ( at metaphase at metaphase ) arranged by size and shape and aligned by their centromeres. The human genome consists of 22 pairs of autosomes (non-sex chromosomes) and 1 pair of sex chromosomes (XX or or XY) For each pair, one chromosome was inherited from the mother, and the other chromosome was inherited from the father. Remember, each pair of chromosomes is a pair of homologous chromosomes, which carry genes that code for the same traits (although not necessarily the same alleles)
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6 Chromosomes are easiest to see and identify at their most condensed form (metaphase). Scientists do not try to find cells at metaphase in Scientists do not try to find cells at metaphase in a human body! a human body! a. A sample of cells is mixed with a chemical that stimulates mitotic division: cells divide until cell division is stopped (by colchicine) at metaphase b. The culture is subjected to centrifugation (heavier cells are at the bottom of the tube) c. Isotonic solution is replaced by a hypotonic solution: cells swell and chromosomes move apart d. Cells are mounted on a microscope slide and stained e. A photograph of the chromosomes of a cell is cut of and organized
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7 In a multicellular organism, cells are often in different stages of the cell cycle
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8 Most human traits arise from complex gene interactions However, many traits can be traced to autosomal dominant or autosomal recessive alleles that are inherited in simple Mendelian patterns Some of those alleles cause genetic disorders or abnormalities. Some of those alleles cause genetic disorders or abnormalities. A genetic abnormality is an uncommon version of a trait, e.g., polydactyly : • Unusual number of toes or fingers • Does not cause any health problems • View of trait as disfiguring is subjective A genetic disorder is an inherited condition that causes mild to severe medical problems
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9 Autosomal dominant Non-sex chromosomal location & just one copy of the gene causes trait
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10 Autosomal dominant disorders & abnormalities require only one parent to be a carrier Traits usually appear in every generation
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11 e.g. Huntington’s disease results from having nucleotide (CAG) repeats in a particular gene
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This note was uploaded on 11/18/2010 for the course SS 101 taught by Professor Denver during the Spring '10 term at Alabama.

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Lecture_18_DulaiS09_HumanGenetics - Genetics: Principles of...

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