Mendelian Genetics

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Mendelian Genetics
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Gregor MendelThe Father of Genetics
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Gene

• A discrete unit of hereditary information
  consisting of a specific nucleotide sequence in
  DNA (or RNA in some viruses)

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Alleles

• Alleles are alternate forms of a gene.
• Examples tall and short for plant height or
  purple or white for flower color.
• Every trait has at least two alleles- one from
  each parent.
• The location of an allele on a chromosome is
  known as its locus (loci plural form).

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Genotype

• The letters that represent (symbolize) the trait
  being investigated. The genetic make-up of an
  organism.
• Examples Bb, BB, bb

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Phenotype

• The actual representation of the genes. The
  Physical appearance or traits in an organism
  resulting from its genetic makeup (what you see).
  
• Examples tall, purple flower or white flower,
  blond hair, freckles, etc.

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Dominant

• The allele that is fully expressed in an organism
  (observed).
• Represented by capital letters.
• Tall T

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Recessive

• The allele that is masked by the dominant
  allele.
• Represented by lower case letters.
• Short t

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Homozygous

• When both alleles (letters) are the same.
• BB Homozygous Dominant
• bb Homozygous recessive

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Heterozygous

• When the alleles (letters) are different.
• One upper case letter and one that is lower case.
• Bb Heterozygous

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Example Problem

• Round R
• wrinkled r
• If a plant has round seeds, do we know what its
  genotype is?
• It could be RR or Rr
• If a plant has wrinkled seeds, do we know what
  its genotype is?
• Yes, it is rr.

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Punnett Square

• A method for finding predicted outcomes and
  probabilities for offspring from any cross.
• A chart for predicting the traits of offspring.

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Some more terms

• P-generation is the parental generation.
• The p-generation produce the F1 generation.
• The F1 generation crossed with itself produces
  the F2 generation.

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Example Problem
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• In foxes, red coat color is determined by the
  dominant gene R silver-black coat is determined
  by the recessive gene r. A homozygous (pure) red
  male is crossed with a silver-black female. (The
  P generation).

1.What is the genotype of the female?
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What are the genotype percentages of their
offspring?

• Firstmake a Punnett square for showing your work

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Example Problem
R
R
r
Rr
Rr
r
Rr
Rr
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Assignment

• Section 32-3

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Assignment

• 33-4 33-5

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1
1 point
B Brown b blue
B
b
b
bb
Bb
b
bb
Bb
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1
1 point

• 1/2 or 50 chance of blue-eyed.
• 1/2 or 50 chance of Brown-eyed.

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2
1 point
T Tall t short
T
t
t
tt
Tt
t
tt
Tt
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2 What fraction of offspring would be tall?
1 point

• 1/2 or 50 would be Tall.

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1 point
W White w black
3
W
w
W
Ww
WW
w
ww
Ww
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3a What fraction of the offspring will be white?
1 point

• 3/4 or 75 will be white.

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3b What fraction of the offspring will be black?
1 point

• 1/4 or 25 will be black.

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3c What fraction of each genotype will you get?
1 point

• 1/4 or 25 will be WW
• 1/2 or 50 will be Ww
• 1/4 or 25 will be ww.

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3d What fraction of each phenotype will you get?
1 point

• 3/4 or 75 will be White.
• 1/4 or 25 will be black.

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1 point
RR Red WW White RW Roan
4
R
R
W
RW
RW
W
RW
RW
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4 Give the fraction of each color of offspring?
1 point

• 1/1 or 100 will be Roan - RW.

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1 point
5
RR Red WW White RW Roan
R
W
W
WW
RW
W
WW
RW
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5 Give the fraction of each color of offspring?
1 point

• 1/2 or 50 will be Roan - RW.
• 1/2 or 50 will be White - WW.

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1 point
G Green g red
1a
G
g
G
Gg
GG
g
gg
Gg
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1a Give the fraction of each genotype of
offspring?
1 point

• 1/4 or 25 will be GG.
• 1/2 or 50 will be Gg.
• 1/4 or 25 will be gg.

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1 point
G Green g red
1b
G
g
g
gg
Gg
g
gg
Gg
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1b Give the fraction of each genotype of
offspring?
1 point

• 1/2 or 50 will be Gg.
• 1/2 or 50 will be gg.

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2a What is the fraction of each phenotype?
1 point

• 3/4 or 75 will be Green.
• 1/4 or 25 will be red.

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2b What is the fraction of each phenotype.
1 point

• 1/2 or 50 will be Green
• 1/2 or 50 will be red.

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3
b
b
B
Bb
Bb
1 point
b
bb
bb

• The mother had to be heterozygous or Bb since the
  couple had a blue eyed child.

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4
1 point

• There would be a 50 chance that the 2nd child
  from the couple would have a brown eyes.

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5
2 points
The couple had two spotted and two white kittens.

• Spotted S
• white s
• Mother ss since she is white.
• Fathers Genotype would be Ss.
• Fathers Phenotype would be Spotted

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6
5 points

• Man has blue eyes - bb.
• G-Ma has blue eyes - bb.
• Woman has brown eyes - Bb.
• 50 of children would be Bb. (Brown)
• 50 of children would be bb. (Blue)

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Please put a score on top of their paper.

• Put the number correct out of 28

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Punnett Squares

• Why are punnett squares useful?
• We can use a punnett square to predict the
  probable genotypes and phenotypes for offspring
  from a genetic cross.
• Genotype What is inside the genes, the make-up.
• Phenotype The outward expression of the genes.