12-4 Beyond Medelian Genetics

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12-4 Beyond Medelian Genetics
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• Alleles are the possible options for a trait.

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Summary of Mendels Principles

• 1. The inheritance of traits is determined by
  genes which are passed from parent to offspring.

2. When 2 or more alleles for a gene exist, some
alleles may be dominant and other alleles may be
recessive. (_______________________)
3. Genes are segregated from each other when
gametes are formed. (____________________)
4. The alleles for different genes usually
segregate independently of one another.
(__________________________________)
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Exceptions to Mendels Principles

• Not all genes show simple patterns of dominant
  and recessive alleles.
• The majority of genes have more than 2 alleles
• Traits are sometimes controlled by more than one
  gene.

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Exceptions to Mendels Principles

• Incomplete Dominance one allele is not
  completely dominant over another. There is an
  appearance of a 3rd phenotype. Heterozygous
  phenotypes show up somewhere in between. Example
  snapdragon flowers
• Red Flowers x White flowers Pink Flowers
• RR rr Rr

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Exceptions to Mendels Principles

• Codominance both alleles contribute to the
  phenotype of the organism. The offspring have a
  phenotype that expresses both alleles equally.
• Examples
• Chickens
• Black feathers x white feathers
  speckled
• black and white

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Blue roan Red roan
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Exceptions to Mendels Principles

• Multiple Alleles genes that have more than 2
  alleles for a specific trait
• Examples
• Rabbit fur color has 4 different alleles
• C full color
• Cch chinchilla
• Ch himalayan
• c albino no color

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Rabbit Fur Colors
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Exceptions to Mendels Principles

• Multiple Alleles continue
• Examples The alleles IA and IB are always
  expressed they are codominant. Both IA and IB
  are dominant to i.

Genotypes Phenotypes
IA IA or IA i A
IB IB or IB i B
IA IB AB
i i O
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Exceptions to Mendels Principles

• Polygenic Traits traits controlled by 2 or more
  genes. The genes can be on the same chromosome
  or on different chromosomes. In polygenic
  inheritance, all heterozygotes are intermediate
  in phenotype.
• Examples
• Eye color in fruit flies 3 genes
• Skin color in humans there are three or four
  genes involved in the inheritance of skin color
  in humans

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Linkage

• Linkage Some genes that are close on the same
  chromosomes are less likely to be separated
  during crossing-over.
• i.e. they end up getting shuffled together most
  of the time.
• Example red hair and
• freckles.

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Sex Linked

• Traits that can only be passed to males or
  females.
• The gene can be found on the X or Y chromosome.
• Example color blindness
• Can be found on the X chromosome because females
  have two, males only have one chance for a good
  color vision gene.

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