Biology

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Biology

• Genetics Unit

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Gregor Mendel

• Considered the father of modern genetics
• He was an Austrian monk in the mid 1800s
• He did many experiments with pea plants

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Mendel Continued

• He discovered the basics for genetics as we know
  it today
• In the following slides, we will cover his major
  discoveries

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Dominant Traits

• In a pair of traits, this one always has an
  effect
• These traits get represented with a capital
  letter (B)

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Recessive Traits

• A trait that is only seen when two copies of the
  gene are present

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Alleles

• Different forms of the same trait or gene
• Examples would be blue and brown eyes, or
  hitchhikers and straight thumbs

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Homozygous

• A term describing an organism that has two of the
  same genes
• This could be two dominant traits (BB) or two
  recessive traits (bb)

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Heterozygous

• A term describing organisms that have two
  different genes for a trait.
• This means they have one dominant and one
  recessive trait (Bb)

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Genotype

• The genes that an organism has for a trait.
• For example, attached earlobes are a recessive
  trait, so a person with them must have two copies
  of that trait.
• Therefore, their genotype is ee.

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Phenotype

• This is the actual, physical trait that a person
  has.
• For example, if a person has the genes Ee for
  earlobe shape, their phenotype will be the
  dominant trait, which is free earlobes.

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Incomplete Dominance

• Sometimes, one trait does not dominate the other,
  and both the dominant and recessive traits are
  seen.

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Codominance

• With some traits, there can be more than one
  dominant allele.
• A good example is blood type. Type O is
  recessive, but types A and B are both dominant.

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Punnett Squares

• Punnett Squares are charts that are made in order
  to predict the results of two organisms
  reproducing.
• Usually only one or two traits are analyzed at a
  time.

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Single Trait Punnett Square

• The Problem Brown eyes are dominant and blue
  eyes are recessive. Cross a heterozygous woman
  with a homozygous recessive male.
• Step 1 define letters to represent the traits
• B brown b blue
• Step 2 write down Mom and Dads genotypes
• Mom Dad
• Bb bb

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Single Trait Punnett Square

• Now make the chart and put Mom and Dads genes on
  the chart.

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Single Trait Punnett Square

• Now, bring the genes across and down to determine
  the genes the possible offspring will have.

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Two Trait Punnett Square

• In this problem we will look at two traits at the
  same time.
• Problem make a Punnett Square using the
  following combinations of genes.
• Mom Dad
• AaBb AABb

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Two Trait Punnett Square

• Now, find the combinations of genes Mom and Dad
  can pass on.
• Mom - AaBb Dad - AABb
• AB AB
• Ab Ab
• aB AB
• ab Ab

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Two Trait Punnett Squares

• Now, take those traits and put them on a chart.

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Two Trait Punnett Squares

• Finally, fill in the boxes.

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Sex-Linked Punnett Squares

• These are traits that are only found on the X
  chromosome.
• Females have XX and males have XY
• The X chromosome is very large and the Y is very
  small. Because of this, there is not enough room
  on the Y for all of the genes on the X.

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Sex-Linked Punnett Squares

• The Problem Color blindness is a sex-linked
  recessive trait. Normal vision is dominant.
  Cross a heterozygous woman with a man who has
  normal vision.
• Step 1 assign letters to the trait
• B normal b color blind

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Sex-Linked Punnett Squares

• Step 2 add genes to Mom and Dads X chromosomes
• Mom Dad
• XBXb XBY

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Sex-Linked Punnett Squares

• Now, add Mom and Dads genes to the chart.

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Sex-Linked Punnett Squares

• Finally, fill in the squares on the chart.

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Pedigree Charts

• Pedigrees show the occurrence of specific genetic
  traits in a family.
• Each generation is designated by a Roman numeral
• Females are circles and males are squares
• When possible, the oldest person in a generation
  goes on the left. As you go to the right, the
  people should get younger.

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Pedigree Charts

• In the chart below, the man and woman are
  connected by a horizontal line. This means they
  are married.

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Pedigree Charts

• The vertical line dropping from the marriage line
  indicates children being born.

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Pedigree Charts

• Marriages in generation II are shown below. A
  first marriage is always shown to the left, the
  second to the right.

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Pedigree Charts

• Children are then added and generation III is
  formed. Note how twins are shown.

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Pedigree Charts

• People with the recessive trait are shaded and a
  key is added to explain the traits.

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Pedigree Charts

• Finally, genotypes are added to the chart.