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Inheritance: Mendelian Genetics. I. Gregor Mendel (1865) A. Before Mendel B. Mendel’s experimental approach II. Genetic terms 1. genes 2. gene pair 3. alleles 4. homozygous/heterozygous 5. dominant/recessive 6. homozygous dominant and recessive/heterozygous

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Inheritance: Mendelian Genetics

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Inheritance mendelian genetics l.jpg

Inheritance: Mendelian Genetics

I. Gregor Mendel (1865)

A. Before Mendel

B. Mendel’s experimental approach

II. Genetic terms

1. genes

2. gene pair

3. alleles

4. homozygous/heterozygous

5. dominant/recessive

6. homozygous dominant and recessive/heterozygous

7. genotype/phenotype

III. Genetic crosses

A. Monohybrid crosses

B. Dihybrid crosses

IV. Mendel's discoveries

A. Principle of segregation

B. Principle of independent assortment

C. Genes are particles


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Darwin and Mendel

A. Before Mendel

The blending theory (paradigm)

Inheritance of acquired characteristics

  • statistics

  • amateur

  • inductive leap


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B. Mendel’s experimental approach

Hermaphrodite

Perfect flowers

Genetic barriers

pollen

egg


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Pea plant traits


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Pure breeding lines

Breed true


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  • Why was Mendel’s experimental findings ignored during

  • his lifetime?

  • He was an amateur

  • There was a problem with inductive leaps

  • The dominant paradigm was opposed to his findings

  • He used statistics

  • All of the above


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II. Genetic terms

1. genes/ loci

2. gene pair = homologues

3. alleles

4. homozygous/heterozygous

5. dominant/recessive

6. homozygous dominant and recessive/heterozygous

7. genotype/phenotype


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Human traits

Hand folding


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III. Genetic crosses

Punnett Square


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III. Genetic crosses


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Red coat in foxes is a dominant trait; white is the

recessive trait. If a red fox whose mother had a

white coat is bred to a white fox, what will be the

probable percentage of red kits (baby foxes)?

a. 25%b. 50%c. 75%d. 100%


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Monohybrid cross: genetic disorders and lethal genes


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  • Tay-Sachs is a lethal disorder resulting in death by the

  • age of 4. A couple who are normal have a child with Tay-

  • Sachs. Which of the following is true of the parents?

  • One parent is homozygous dominant and the other is

  • homozygous recessive

  • b. both parents are heterozygous

  • c. both parents are homozygous dominant

  • d. both parents are homozygous recessive


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Sickle cell trait: recessive disorder


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Sickle cell trait: recessive disorder

Homozygous dominant = normal, not malaria resistant

Heterozygous = malaria resistant

Homozygous recessive = sickle cell anemia


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Huntington’s disease: dominant disorder

CAGCAGCAG

Normal, 26 times

HD, 40 to >100 times

Manifests after age 40

Why is dominant lethality less common than recessive?


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Dwarfism: dominant trait

Homozygous dominant = lethal

Heterozygous = dwarf

Homozygous recessive = normal height

Hardy-Weinburg rule


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If two achondroplasic dwarfs have children, what fraction of the children would be expected to be dwarfs like their parents?

a. 1/4 b. 1/2c. 2/3 d. 3/4

  • What determines how common a trait is in a population?

  • it’s frequency

  • Dominance

  • Selection

  • Chance


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B. Dihybrid crosses: Human traits

Dark hair dominant to light hair

Curly hair incompletely dominant to straight hair

Brown eyes dominant to blue

Dimples dominant to no dimples


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In humans, a widow's peak is dominant and a straight hairline is

recessive. Dimples are dominant and no dimples are recessive. A male

who is heterozygous for both widow's peak and dimples has a child with

a woman who has a straight hairline and no dimples.

What is the phenotype ratio of children can they produce?

a. 3: 1b. 2:2c. 1:1:1:1 d. 4:0


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IV. Mendel’s discoveries

A. Principle of segregation

Sexually reproducing diploid

organisms have 2 alleles of

each gene.

These 2 alleles segregate from

each other to form gametes

that contain only 1 allele of

each gene.


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B. Principle of independent assortment

Different genes on different chromosomes segregate into gametes independently of each other.


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C. Genes are particles


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V. Eugenics

Social Darwinism

Francis Galton

Positive Eugenics


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Eugenics


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Eugenics


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Eugenics today?

IVF/ PGD

Gene “therapy”


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The end


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