Incomplete Dominance, Multiple Alleles, and Sexlinked Traits

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Incomplete Dominance, Multiple Alleles, and
Sex-linked Traits
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Incomplete Dominance

• One of the principles
• 1900 Karl Correns (German Biologist)
• Some gene pairs are neither dominant nor
  recessive
• For example the 4 oclock flower cross
• a red and white flower
• RR x WW
• offspring are all pink
• For example a palomino
• cross a purebred chestnut brown horse with a
  purebred creamy white horse
• BB x WW
• Offspring are all pale golden brown with
  white mane and tail

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Multiple Alleles

• Some of your traits are not so easily determined
• For example skin color
• These are determined by more than one gene
• Remember..each form of a gene is called an
  allele
• Skin color is determined by 3 or more
  alleles.this is called multiple alleles

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Blood Types/Groups

• Page 119
• Blood groups are determined by multiple alleles
• 4 types of Blood
• A alleles are AA or AO
• B alleles are BB or BO
• AB alleles are AB
• O alleles are OO
• A and B types are co-dominant and O is
  recessive

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Let us Practice

• Male is A blood type
• Female is B blood type
• What will the offspring be?

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Sex-linked traits

• Page 121
• One pair of chromosomes determines whether the
  offspring is male or female
• Male is XY (half of the reproductive cells will
  be x and half Y)
• Female XX (all the reproductive cells will be X)
• The larger chromosome is the X and the smaller
  chromosome is the Y
• Every time these are crossed, the offspring have
  a 50 chance of being a boy and a 50 chance of
  being a girl
• Why does the male determine the sex?

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Sex-linked Traits

• Some traits are more common to one sex
• Examples Color Blindness
• Hemophilia
• These are traits controlled by genes on one or
  the other sex chromosome
• The above examples are both on the X chromosome
• Controlled by a recessive allele

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Let us discuss some examples

• Let us try these