Chapter 14Mendel

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Chapter 14 Mendel The Gene Idea
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Mendelian genetics

• Character (heritable feature, i.e., fur color)
• Trait (variant for a character, i.e., brown)
• True-bred (all offspring of same
  variety)
• Hybridization (crossing of 2 different
  true-breds)
• P generation (parents)
• F1 generation (first filial generation)

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Leading to the Law of Segregation

• Alternative versions of genes (alleles) account
  for variations in inherited characteristics
• For each character, an organism inherits 2
  alleles, one from each parent
• If the two alleles differ, then one, the dominant
  allele, is fully expressed in the organisms
  appearance the other, the recessive allele, has
  no noticeable effect on the organisms appearance
• The alleles for each character segregate
  (separate) during gamete production (meiosis).
• Mendels Law of Segregation

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Genetic vocabulary.

• Punnett square predicts the results of a
  genetic cross between individuals of known
  genotype
• Homozygous pair of identical alleles for a
  character
• Heterozygous two different alleles for a gene
• Phenotype an organisms traits
• Genotype an organisms genetic makeup
• Testcross breeding of a recessive homozygote X
  dominate phenotype (but unknown genotype)

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The Law of Independent Assortment

• Law of Segregation involves 1 character. What
  about 2 (or more) characters?
• Monohybrid cross vs. dihybrid cross
• The two pairs of alleles segregate independently
  of each other.
• Mendels Law of Independent Assortment

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Mendelian inheritance reflects rule of probability

• Mendels laws of segregation and independent
  assortment reflect the same laws of probability
  that apply to tossing coins or rolling dice.
• We can use the rule of multiplication to
  determine the chance that two or more independent
  events will occur together in some specific
  combination
• The rule of addition also applies to genetic
  problems.
• Under the rule of addition, the probability of an
  event that can occur two or more different ways
  is the sum of the separate probabilities of those
  ways
• We can combine the rules of multiplication and
  addition to solve complex problems in Mendelian
  genetics.

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Non-single gene genetics, I

• Incomplete dominance appearance between the
  phenotypes of the 2 parents. Ex carnations
• Codominance two alleles affect the phenotype in
  separate, distinguishable ways.
  Ex Tay-Sachs disease

• Incomplete dominance in carnations red, pink,
  white

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Non-single gene genetics, II

• Multiple alleles more than 2 possible alleles
  for a gene. Ex human blood types

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Non-single gene genetics, III

• Pleiotropy genes with multiple phenotypic
  effect. Ex sickle-cell anemia

• Normal and sickle red blood cells

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Non-single gene genetics,IV

• Epistasis a gene at one locus (chromosomal
  location) affects the phenotypic expression of a
  gene at a second locus. Ex mice coat color

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Non-single gene genetics,V

• Polygenic Inheritance an additive effect of two
  or more genes on a single phenotypic character
  Ex human skin pigmentation and height

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Human disorders

• The family pedigree
• Recessive disorders
• Cystic fibrosis Tay-Sachs Sickle-cell
• Dominant disorders Huntingtons
• achondroplasia

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Human disorders

• Testing amniocentesis chorionic villus
  sampling (CVS)
• Examination of the fetus with ultrasound is
  another helpful technique