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Chapter 14: Mendel and the Gene Idea

Chapter 14: Mendel and the Gene Idea. Mendel’s Ideas based on Observations. Alternative alleles account for variations in inherited characteristics For each character, an organism inherits two alleles, one from each parent

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Chapter 14: Mendel and the Gene Idea

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  1. Chapter 14: Mendel and the Gene Idea

  2. Mendel’s Ideas based on Observations • Alternative alleles account for variations in inherited characteristics • For each character, an organism inherits two alleles, one from each parent • If two alleles differ, the dominant allele is expressed, the recessive allele has no effect • The two alleles segregate during gamete formation.

  3. Other common terms • Homozygous vs. heterozygous • Homozygous dominant • Homozygous recessive • Heterozygous • Genotype vs. phenotype • Phenotype is physical • Genotype describes collection of genes

  4. Solving problems (basics) • Read the problem • Write down the parents’ genotypes (if possible) • Punnet square • Answer the question

  5. Example: Having attached earlobes is recessive to free hanging. If a parent that is heterozygous has a child with a parent that has attached earlobes, what is the chance that their first child will have free-hanging earlobes?

  6. Test Cross • Done to determine the genotype of a dominant phenotype individual • Cross the individual with a homozygous recessive individual • Look at the ratio of the offspring • IQ 14.2

  7. Dihybrid Cross • Do IQ 14.3

  8. Using Probabilities • IQ 14.4, 14.5

  9. Extensions of Basic Mendian Genetics • Incomplete dominance • Heterozygotes have their own phenotype • Ex. Red X white snapdragons  PINK • Blended due to amount of pigment production being intermediate

  10. Codominance • Heterozygotes have both traits equally expressed (separate, distinguishable expression – not intermediate)

  11. Multiple Alleles • Most genes exist in more than two allelic forms • Ex. ABO blood groups, A and B show codominance, O is recessive • IQ 14.6

  12. Pleiotropy: • One gene affects an organism in many ways • Ex. Cystic fibrosis • Defective Cl- channel causes mucus to coat cells  poor absorption of nutrients, bronchitis, bacterial infections

  13. Epistasis • A gene at one locus affects the expression of a gene at another locus • Ex. Mouse color • Black is dominant to brown at one locus • At another gene, the dominant trait is for display of color. Any mouse homozygous recessive at this locus will be albino • IQ 14.7

  14. Polygenic inheritance • An additive affect of 2 or more genes on a single phenotypic character • Ex. Human skin color, affected by 3+ genes • Each dominant allele gives a “dose” of dark color • IQ 14.8

  15. Pedigree charts • Used to track inheritance patterns in humans • Males are squares, circles are females • Offspring listed in order of their birth • Shaded symbols have the trait being traced

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