Mendelian%20Patterns%20of%20Inheritance

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Mendelian Patterns of Inheritance

• Chapter 11

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Heredity

• Heredity- passing of traits from parent to
  offspring
• Traits- characteristics that are inherited
• hair color, height, blood type, susceptibility to
  a certain disease (diabetes, depression, obesity,
  breast cancer)
• Genetics- the study of heredity

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Gregor Mendel

• Austrian monk who formulated fundamental laws of
  heredity in early 1860s
• Studied science and mathematics at University of
  Vienna
• Conducted breeding experiments with the garden
  pea (Pisum sativum)
• Gathered and documented mathematical data from
  his experiments

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Mendels Experiments

• Garden Pea
• Easy to cultivate
• Short generation time
• Cross-pollination by hand

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Mendels Experiments
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Self-Pollination

• Involves having
• the pollen (male
• sperm) be directly
• deposited on the
• female section of
• the flower

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Cross- Pollination

• Requires the
• removal of the male
• stamen (makes
• pollen) on 1st flower
• and transferring the
• pollen from a
• different flower
• to the first one

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Blending Inheritance

• Prior to Mendel, most breeders believed parents
  of contrasting appearance always produce
  offspring of intermediate appearance
• No knowledge of cells/chromosomes
• Based on the idea that offspring have traits of
  both parents
• Reappearance of traits attributed to genetic
  instability

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Mendels Experiments

• Studied mathematical trends in breeding patterns
• Looked at simple discrete traits
• Mendels experiments helped him formulate the
  particulate theory of inheritance
• Inheritance involves reshuffling of genes from
  generation to generation

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One-Trait Inheritance

• Mendel performed cross-breeding experiments
  between true-breeding plants
• True-breeding parents with a certain trait
  consistently pass that trait to every offspring
  (homozygous)
• Chose varieties that differed in only one trait
  (monohybrid cross)

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Results of Mendels cross of true breeding short
with a true breeding tall pea plant
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Mendel saw the same results in different traits
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One-Trait Inheritance

• Performed reciprocal crosses individuals
  pollinate one another
• Parental generation P
• First generation offspring F1
• Second generation offspring F2
• Formulated law of segregation

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Law of Segregation

• Each individual has two factors for each trait
• The factors segregate during gamete formation
• Each gamete contains only one factor from each
  pair of factors
• Fertilization gives each new individual two
  factors for each trait

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Law of Segregation

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Mendels Monohybrid Cross
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Mendels Monohybrid Cross
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Alleles on homologous chromosomes

• These alternative forms of a gene that code for a
  trait are called alleles. There are 2 alleles
  for each trait 1 allele for a trait is from mom
  and 1 allele is from dad.

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Homologous Chromosomes
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Principle of Dominance

• Dominant allele (capital letter) masks the
  expression of the recessive allele (lower-case)
• Alleles occur on a homologous pair of chromosomes
  at a particular gene locus (location of gene on
  the chromosome)
• Homozygous identical alleles (TT, tt)
• Heterozygous different alleles (Tt)

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Genotype Vs. Phenotype

• Genotype
• Refers to the alleles an individual receives at
  fertilization
• If alleles are identical, genotype is homozygous
• If alleles are different, genotype is
  heterozygous
• Phenotype
• Refers to the physical appearance of the
  individual

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Practice

• In humans, the ability to taste the bitterness
  of PTC paper is dominant (T) to not being able to
  taste the bitterness of PTC paper (t).

GENOTYPE GENOTYPE IN SCIENCE TERMS PHENOTYPE



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Punnett Square

• All possible genotypes of sperm are lined up on
  one axis, and all possible genotypes of eggs are
  lined up on the other axis
• Every possible combination of alleles (zygote
  genotypes) placed within the squares

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Formative Assessment

• Get your clickers!

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Alternate forms of a gene are called

1. Chromosomes
2. Alleles
3. Gametes
4. Heterozygotes

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Only one ________ allele is needed in order for
that trait to be expressed in the phenotype.

1. Recessive
2. Dominant
3. Heterozygous
4. Homozygous

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Which of the following genotypes is homozygous
recessive?

1. RR
2. Rr
3. rr

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The genotype TT is

1. Homozygous recessive
2. Homozygous dominant
3. Heterozygous

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Which of the following genotypes is heterozygous?

1. BB
2. Bb
3. bb

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Brown eyes (B) are dominant over blue eyes (b).
Mr. Mallin has blue eyes. What is his genotype?

1. BB
2. Bb
3. bb

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Brown eyes (B) are dominant over blue eyes (b).
Channing Tatum has brown eyes. What is his
genotype?

1. BB
2. Bb
3. bb
4. BB or Bb

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Brown eyes (B) are dominant over blue eyes (b).
Assume Mr. Ward is homozygous dominant for brown
eyes. What is his sons phenotype?

1. Brown eyes
2. Blue eyes
3. Bb
4. BB

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Free earlobes (E) are dominant over attached
earlobes (e). Ms. Palmeris phenotype is free
earlobes and her genotype is heterozygous (Ee).
Which of these statements is true?

1. Both of her parents have attached ear lobes
2. At least one of her parents has free earlobes
3. Both of her parents are homozygous recessive

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If a persons genotype is EE, what percentage of
their gametes (produced by meiosis) would contain
the recessive allele?

1. 100
2. 50
3. 25
4. 0

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The previous question is a direct application of
which of Mendels laws?

1. Law of independent assortment
2. Law of Homozygous Dominance
3. Law of Segregation
4. Principle of Dominance

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Testcross

• A monohybrid testcross is used to determine if an
  individual with the dominant phenotype is
  homozygous dominant or heterozygous for a
  particular trait
• Individuals with recessive phenotype always have
  the homozygous recessive genotype
• However, Individuals with dominant phenotype have
  indeterminate genotype
• May be homozygous dominant, or
• Heterozygous

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Testcross
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Dihybrid Cross
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Dihybrid Cross
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Two-Trait Testcross

• A two-trait testcross is used to determine if an
  individual is homozygous dominant or heterozygous
  for either of the two traits

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Two-Trait Testcross
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Law of Independent Assortment

• Pairs of alleles for different traits separate
  independently of one another during gamete
  formation (meiosis).
• In other words the inheritance of one trait has
  no influence on the inheritance of another trait.

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