Hrincevich_CH_12_student_outline

Hrincevich_CH_12_student_outline - Patterns of Inheritance...

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Unformatted text preview: Patterns of Inheritance Chapter 12 How are Traits Controlled? Many traits in humans are NOT controlled by one gene, but by MANY genes Eye color, height, hair color, etc. Several traits in humans that are controlled by ONE gene, makes it easy to determine your phenotype and possibly your genotype The presence or absence of these traits does not express anything meaningful. You are not a freak if you have/lack these traits! X Examples of single gene control we looked at before 10 20 30 40 50 60 70 80 90 widows peak ear lobes tongue roller digit hair hand crossing DOM rec yes no free attached yes no yes no left on top right on top Do any of these not follow what you would have expected? Single Gene Variation Dominant allele vs. recessive allele Earlobes EE or Ee was free/unattached phenotype (homozygous dominant or heterozygous) ee was attached phenotype (homozygous recessive) Easy way to examine particular traits Many diseases (>10,000) are due to single genes Early Ideas about Heredity People knew that sperm and eggs transmitted information about traits Blending theory Problem: Would expect variation to disappear Variation in traits persists Gregor Mendel (1822-1884) Monk in a monastery in late 1800s Strong background in plant breeding and mathematics Experimentation with pea plant inheritance took place in the monastery garden Found indirect but observable evidence of how parents transmit genes to offspring The Secrets of Mendels Success Important aspects of pea plants Pea flowers have male structures that produce pollen (male gametes) by meiosis Pea flowers have female structures that produce ovules (female gametes) by meiosis Pea flower petals enclose both male and female flower parts and prevent entry of pollen from another pea plant intact pea flower flower dissected to show reproductive structures Cross Fertilization of Parents cross-fertilize pollen pollen Parental generation (P) True-breeding, purple-flowered plant True-breeding white-flowered plant First generation (F 1 ) All purple- flowered plants SUMMARY: Tracking Generations Parental generation P 1 First-generation offspring F 1 Second-generation offspring F 2 Self-Fertilization of F 1 plants self-fertilize Genes Units of information about specific traits Passed from parents to offspring Each has a specific location (locus) on a chromosome Alleles Alternative molecular forms of a gene Arise by mutation Dominant allele masks a recessive allele that is paired with it Genetic Symbolism Often use letter initials for alleles - capital letter represents DOMINANT trait- lower case letter represents recessive trait If purple flower is dominant to white - R represents allele for purple- r represents allele for white Allele Combinations Homozygous having two identical alleles at a locus RR or rr Heterozygous having two different alleles at a locus Rr Genetic Terms A pair of homologous chromosomes A gene locus A pair of alleles Three pairs of genes...
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Hrincevich_CH_12_student_outline - Patterns of Inheritance...

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