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Fundamentals of Genetics

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Title: Fundamentals of Genetics


1
Fundamentals of Genetics
  • Chapter 9

2
Genetics
  • The field of biology dedicated to understanding
    how characteristics are transmitted from parent
    to offspring.
  • Studied by Gregor Mendel
  • Heredity- the transmission of characteristics
    from parents to offspring.

3
Gregor Mendel
  • Austrian monk science teacher in the mid 1800s
  • Worked with pea plants in his garden
  • Studied 7 characteristics of peas

4
  • Each characteristics had 2 different traits
  • EX) tall/short, purple/white
  • Page 176

5
Mendels Experiments
  1. Started off with 2 pure plant groups for a
    particular characteristic
  2. P1 generation
  3. Cross pollinated these plant groups (sexual
    reproduction) to produce the next generation of
    plants
  4. F1 generation

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  • When the seeds matured from the F1 generation, he
    counted recorded the traits of the offspring.
  • Then he allowed the F1 generation plants self
    pollinate (sexual reproduction with self) to
    produce the next generation of plants
  • F2 generation

8
(notice that the predicted ratios the actual
ratios are not exact!)
9
Mendels Results
  • The F1 generation always showed only 1 of the 2
    traits for the characteristic
  • Mendel named this the dominant factor
  • The F2 generation always showed a 31 (or a 75
    to a 25) ratio between the 2 traits
  • Mendel named the second the recessive factor

10
Example Purple is dominant White is recessive
F1 generation all purple
F2 generation 75 purple 25 white
11
The Law of Segregation
  • Mendel stated that a pair of factors is
    segregated, or separated, during the formation of
    gametes.
  • So, What does this mean?
  • Each egg and sperm receives only one factor from
    each parent.

12
The Law of Independent Assortment
  • Mendel also stated that factors for different
    characteristics are distributed to gametes
    independently.
  • So, What does this mean?
  • The factors for different characteristics are not
    connected.

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14
Molecular Genetics
  • The study of the structure function of
    chromosomes genes
  • Allele alternate form of a gene
  • Mendel called them factors
  • Abbreviations
  • Dominant allele capital letter (B)
  • Recessive allele lower case letter (b)

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16
9.2 Vocabulary
  • Genotype the genetic makeup of the organism
    (BB, Bb, bb)
  • Phenotype the physical appearance of the
    organism (Black, white)

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18
Genotype Vocabulary
  • Homozygous same genes
  • When the organism has the same alleles for the
    characteristic
  • BB homozygous dominant
  • bb homozygous recessive
  • Heterozygous different genes
  • When the organism has different alleles for the
    characteristic
  • Bb

19
Genetic Probability
  • The likelihood (probability) of offspring of
    known parents can be determined by Punnett squares

20
3 Types
Punnett Squares diagrams biologists use to
predict the probability that certain traits will
be inherited by offspring.
  • Monohybrid Cross One characteristic
  • Dihybrid Cross Two characteristics
  • Trihybrid Cross Three characteristics

21
Monohybrid Cross
  • A cross between individuals that involves one
    pair of contrasting traits.
  • 1 characteristic
  • 2 contrasting traits

22
Dihybrid Cross
  • A cross between individuals that involves 2 pairs
    of contrasting traits.
  • 2 characteristics
  • 4 contrasting traits

23
How do you find an unknown genotype?
  • Testcross
  • Example) Is the red flower a pure (RR) or hybrid
    (Rr) ?
  • Cross the unknown flower with a pure recessive
    flower (rr).
  • This will allow the recessives to show up in the
    next generation.

24
The results
  • If the flower is hybrid, the offspring will be
    50 red and 50 white.
  • If the flower is pure, the offspring will be all
    red.

Result if flower is hybrid
Result if flower is pure
25
Complications!
  • Incomplete Dominance and Codominance
  • Incomplete Dominance occurs when the F1
    offspring has a phenotype between that of the
    parents.
  • neither allele is completely
  • dominant

26
Example) Incomplete Dominance
  • Four oclock flowers
  • Q- What would happen if you crossed a red four
    oclock flower with a white four oclock flower?
  • A- a pink flower!

27
2) Codominance
  • Occurs when both alleles are expressed in a
    heterozygous offspring.
  • Neither allele is dominant or recessive
  • Q- What would happen if you crossed a horse with
    a white coat with a horse with a red coat?
  • A- A horse with a roan coat (both red and white
    hairs) !

28
Codominance
29
  • Question
  • In rabbits, the allele for black coat color (B)
    is dominant over the allele for brown coat color
    (b). Predict the results of a cross between a
    rabbit homozygous for black coat color and a
    rabbit homozygous for brown coat color.
  • What is the genotypic ratio?
  • What is the phenotypic ratio?

30
  • Brown hair color is dominant over blond hair, and
    brown eyes are dominant over blue eyes.
  • Q- If 2 heterozygous parents for both traits
    mate, what is the phenotypic ratio of their
    offspring?
  • __________ Brown hair, Brown eyes
  • __________ Brown hair, Blue eyes
  • __________ Blond hair, Brown eyes
  • __________ Blond hair, Blue eyes

31
Complications Multiple alleles
  • ABO blood groups

Dominant
Dominant
Codominant
Recessive
32
Complications Polygenic Inheritance and
Quantitative Characters
  • One trait determined by multiple genes
  • Ex) skin color at least 3 genes

33
Complications Epistasis
  • Expression of one gene depends on another
  • Mouse coat color
  • B - black coat
  • b - brown coat
  • C - pigment
  • c - no pigment

34
What are my chances?
  • Obtain 2 pennies.
  • Flip each coin simultaneously 50 times. Record
    the results of each set of flips.
  • Total the number of combinations of your results
  • __ Heads-Heads
  • __ Heads-Tails
  • __ Tails-Tails

35
  • Record your results on the board.
  • Calculate your percent chance of each
    combination.
  • ( of combos)
  • 50
  • Calculate the class average percent chance of
    each combination.
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