BIOS E-1a Lecture 10 103111 annotated

BIOS E-1a Lecture 10 103111 annotated - Lecture 9:...

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Lecture 9: Mendelian Genetics, continued… Reading: Chapter 8 1
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2 Mendelian inheritance • Inheritance pattern of genes that segregate and assort independently • Simple Mendelian inheritance: one trait is completely dominant over the other • X-linked inheritance: pairs of dominant and recessive alleles found on the X chromosome
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3 Different types of Mendelian inheritance patterns and their molecular basis
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4 • In simple dominance, the recessive allele does not affect the phenotype of the heterozygote • A single copy of the dominant allele is sufficient to mask the recessive allele • Purple pigment, P – One P allele makes enough functional protein to provide a normal phenotype – In other cases, the heterozygote may make more than 50% of the normal amount of protein – up-regulated
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5
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Examples of recessive human genetic diseases
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7 • Incomplete dominance – Heterozygote has intermediate phenotype – Neither allele is dominant – Pink four-o’clocks • 50% of normal protein not enough to give red color – Phenylketonuria (PKU) • Heterozygotes appear phenotypically normal but heterozygotes have double the normal phenylalanine levels 1:2:1 ratio
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8 • Multiple alleles – 3 or more variants in a population – Phenotype depends on which 2 alleles are inherited – ABO blood types in humans • Type AB is codominance: expressing both alleles equally
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9 • Sex-influenced inheritance – Allele is dominant in one sex but recessive in the other – Pattern baldness • Baldness allele dominant in men but not women • Only a woman homozygous for baldness allele would be bald – Not X-linked Nonbald male Nonbald female Bald female Bald male I-2 I-1 II-1 II-8 II-7 II-6 II-5 II-4 II-3 II-2 III-1 III-10 III-9 III-8 III-7 III-6 III-5 III-2 III-3 III-4 IV-1 IV-2 IV-3 IV-4 IV-5 IV-6 IV-7 IV-8 IV-9 IV-10 IV-11 IV-12 IV-13 IV-14
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10 Role of environment • Norm of reaction: effects of environmental variation on a phenotype • Genetically identical plants grow to different heights in different temperatures • People with PKU can develop normally if given a diet free of phenylalanine – If their diet contains phenylalanine, they develop mental retardation, underdeveloped teeth and foul-smelling urine
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11 Norm of reaction
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12 Environmental influences on PKU within a family mutation in phenylalanine hydroxylase
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13 Probability • Chance that an event will have a particular outcome • For a single coin toss, chance of getting heads
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14 • Self-fertilization of a pea plant that was heterozygous for the height gene ( Tt ) • Punnett square predicted that one-fourth of the offspring would be dwarf
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15 Sample size • Accuracy of prediction depends on the number of events observed or sample size • Random sampling error: deviation between observed and expected outcome • Larger samples have smaller sampling errors • Humans have small families and observed data may be very different from expected outcome
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16 Product rule • Probability that two or more independent events
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BIOS E-1a Lecture 10 103111 annotated - Lecture 9:...

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