Di hybrid Crosses

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Di hybrid Crosses
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1. Di-hybrid Crosses

• Dihybrid crosses predict the probabilities of the
  combinations of two factors.
• Example An individual who is heterozygous for
  both brown eyes and brown hair has offspring with
  another individual who is heterozygous for both
  traits.
• Brown hair (H) is dominant to red (h)
• Brown eyes (E) are dominant to blue (e)

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g. Dihybrid Crosses
HE He hE he
HE
He
hE
he
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g. Dihybrid Crosses
HE He hE he
HE HHEE
He
hE
he
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g. Dihybrid Crosses
HE He hE he
HE HHEE HHEe
He
hE
he
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g. Dihybrid Crosses
HE He hE he
HE HHEE HHEe HhEE
He
hE
he
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g. Dihybrid Crosses
HE He hE he
HE HHEE HHEe HhEE HhEe
He
hE
he
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g. Dihybrid Crosses
HE He hE he
HE HHEE HHEe HhEE HhEe
He HHEe
hE
he
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g. Dihybrid Crosses
HE He hE he
HE HHEE HHEe HhEE HhEe
He HHEe HHee
hE
he
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g. Dihybrid Crosses
HE He hE he
HE HHEE HHEe HhEE HhEe
He HHEe HHee HhEe
hE
he
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g. Dihybrid Crosses
HE He hE he
HE HHEE HHEe HhEE HhEe
He HHEe HHee HhEe Hhee
hE
he
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g. Dihybrid Crosses
HE He hE he
HE HHEE HHEe HhEE HhEe
He HHEe HHee HhEe Hhee
hE HhEE
he
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g. Dihybrid Crosses
HE He hE he
HE HHEE HHEe HhEE HhEe
He HHEe HHee HhEe Hhee
hE HhEE HhEe
he
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g. Dihybrid Crosses
HE He hE he
HE HHEE HHEe HhEE HhEe
He HHEe HHee HhEe Hhee
hE HhEE HhEe hhEE
he
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g. Dihybrid Crosses
HE He hE he
HE HHEE HHEe HhEE HhEe
He HHEe HHee HhEe Hhee
hE HhEE HhEe hhEE hhEe
he
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g. Dihybrid Crosses
HE He hE he
HE HHEE HHEe HhEE HhEe
He HHEe HHee HhEe Hhee
hE HhEE HhEe hhEE hhEe
he HhEe
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g. Dihybrid Crosses
HE He hE he
HE HHEE HHEe HhEE HhEe
He HHEe HHee HhEe Hhee
hE HhEE HhEe hhEE hhEe
he HhEe Hhee
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g. Dihybrid Crosses
HE He hE he
HE HHEE HHEe HhEE HhEe
He HHEe HHee HhEe Hhee
hE HhEE HhEe hhEE hhEe
he HhEe Hhee hhEe
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g. Dihybrid Crosses
HE He hE he
HE HHEE HHEe HhEE HhEe
He HHEe HHee HhEe Hhee
hE HhEE HhEe hhEE hhEe
he HhEe Hhee hhEe hhee
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c. How many offspring have..

1. Dark hair and brown eyes? HxEx?
2. Dark hair and blue eyes? Hxee?
3. Red hair and brown eyes? hhEx?
4. Red hair and blue eyes? hhee?

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How many offspring have..

• Dark hair and brown eyes? HxEx?
• nine
• Dark hair and blue eyes? Hxee?
• Red hair and brown eyes? hhEx?
• Red hair and blue eyes? Hxee?

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How many offspring have..

• Dark hair and brown eyes? HxEx?
• nine
• Dark hair and blue eyes? Hxee?
• three
• Red hair and brown eyes? hhEx?
• Red hair and blue eyes? hhee?

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How many offspring have..

• Dark hair and brown eyes? HxEx?
• nine
• Dark hair and blue eyes? Hxee?
• three
• Red hair and brown eyes? hhEx?
• three
• Red hair and blue eyes? Hxee?

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How many offspring have..

• Dark hair and brown eyes? HxEx?
• nine
• Dark hair and blue eyes? Hxee?
• three
• Red hair and brown eyes? hhEx?
• three
• Red hair and blue eyes? Hxee?
• one

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2. Polygenic Inheritance
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F. Polygenic Inheritance

• Traits in which the phenotypes are determined by
  many genes contributing to the overall phenotype.
  Each gene is on a different location on the
  chromosome and may not even be on the same
  chromosome. The best way to recognize polygenic
  inheritance is when the phenotypes exhibit a wide
  range of expression or variation.
• Examples

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skin color
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Eye Color Hair Color
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d. Multiple Alleles Instead of having two forms
of an allele, there are more than two for one
gene.

• i. The best example for humans is blood. There 3
  alleles for blood types in humans A, B and O. A
  and B are co dominant while O is recessive.

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b. Multiple Alleles Blood Type

• Type A genotypes could be IAIA or IAi.
• Type B genotypes could be IBIB or IBi.
• Type AB genotype is IAIB
• Type O genotype is ii

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Practice

• A man who is heterozygous for type A blood
  marries a woman who is heterozygous for type B
  blood. Find the possible outcomes

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e. Sex linked traits

1. Sex linked traits Are genes located on the X
   chromosome. There is almost no information
   located on the Y chromosome.
2. Since males have only one X chromosome they show
   whatever allele is on the X chromosome,
   regardless of whether it is dominant or recessive.

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e. Sex linked traits

• iii. This is the only time that a single
  recessive allele is expressed.
• Two examples of sex-linked traits in humans are
  red/green colorblindness and hemophillia. (A
  recessive sex linked trait that keeps your blood
  from clotting.)

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Color Test
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Color Test
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Color Test
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Color Test
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Sex linked traits - Colorblindness

• If normal vision (N) is dominant to
  colorblindness (n) give the genotypes for each of
  the following
• A female carrier XNXn
• A homozygous dominant female XNXN
• Colorblind male XnY
• Colorblind female XnXn
• A male with normal vision XNY

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Sex linked traits

• Who does the male get the X chromosome from?
  Mother
• Who does a male inherit recessive sex linked
  traits from? Mother
• Who are colorblind more often, men or women?
  Men no information on Y to mask the recessive
  trait on X.

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Practice

• A female carrier has a child with a male with
  normal vision. What are the chances of
  colorblindness occuring in
• Son?
• Daughter?

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Practice

• A colorblind male has a child with a normal
  female. Fill out the cross.