Chapter 14 Part II Chromosomes and Genes

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Chapter 14 Part II Chromosomes and Genes

• Incomplete dominance, codominance, multiple
  alleles, epistasis, polygenic inheritance, the
  chromosomal theory of inheritance, sex
  chromosomes, linked genes, and chromosomal
  mutations are covered in this chapter.

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12-1 Mendelism and the Genotype

• Incomplete Dominance and Codominance
• Incomplete Dominance offspring show traits
  intermediate between 2 parental phenotypes.
• Red x white pink
• One allele only partially dominant to partner

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• Codominance pattern of inheritance in which both
  alleles of a gene are expressed
• Ex A person with AB blood

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12-1 Mendelism and the Genotype

• Genes that interact
• More than one pair of genes may interact to
  produce the phenotype

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• Epistasis
• Epistasis absence of expected phenotype as a
  result of masking expression of one gene pair by
  the expression of another gene pair.
• Homozygous recessive masks effect of dominant
  allele at another locus.
• Ex albino animals (aa) for melanin production
  prevent expression of hair and eye color

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D. Pleiotropy
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D. Pleiotropy
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• Multiple Allele
• There may be more than 2 alleles for one locus,
  but each individual inherits only two alleles
• Ex Blood Type ABO gives 4 possible phenotypes
  A, B, AB, O

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• Polygenic Inheritance
• Polygenic Inheritance occurs when a trait is
  controlled by several diff. Allelic pairs at
  diff. loci
• Ex Seed color and skin color

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12-1 Mendelism and the Genotype

• Environment and Phenotype
• Both temperature and environment affect phenotype
• ex plants like primrose and animals like Siamese
  cats and Himalayan rabbits

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12-2 Mendelism and Chromosomes

• Chromosomal Theory of Inheritance
• Both chromos and alleles are paired in diploid
  cells
• Chromos and alleles of each pair separate during
  meiosis so gametes have 1/2.
• Chromos and alleles separate individually
  gametes contain all combinations.
• Fertilization restores diploid chromo and pairs
  alleles.

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• Sex Chromosomes
• Autosomes - non-sex chromos that are the same
  and kind in between sexes
• Sex Chromosomes determine if the individual is
  male or female
• Males produce X-containing or Y-containing
  gametes, males determine sex
• X-linked Gene is any gene located on X chromosome

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12-2 Mendelism and Chromosomes

• Sex-Linked Problems
• X-linked alleles are designed as superscript to X
  chromosome
• Heterozygous females are carriers they do not
  show the trait but can pass it on.
• Males are never carriers but express the one
  allele on the X chromosome
• One form of color-blindness is X-linked

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12-3 Chromosomal Mutations

• Changes in Chromo
• Monosomy indiv. only has one particular type of
  chromosome
• Trisomy
• Nondisjunction failure
• Polyploidy offspring end up with more than two
  complete sets of chromos.

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Changes in Chromosomal Structure

• Environmental Factors
• Inversion
• Translocation
• Deletion
• Duplication