Title: Fundamentals of Genetics
1Fundamentals of Genetics
2Genetics
- 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.
3Gregor 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
5Mendels Experiments
- Started off with 2 pure plant groups for a
particular characteristic - P1 generation
- Cross pollinated these plant groups (sexual
reproduction) to produce the next generation of
plants - F1 generation
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7- 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!)
9Mendels 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
10Example Purple is dominant White is recessive
F1 generation all purple
F2 generation 75 purple 25 white
11The 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.
12The 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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14Molecular 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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169.2 Vocabulary
- Genotype the genetic makeup of the organism
(BB, Bb, bb) - Phenotype the physical appearance of the
organism (Black, white)
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18Genotype 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
19Genetic Probability
- The likelihood (probability) of offspring of
known parents can be determined by Punnett squares
203 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
21Monohybrid Cross
- A cross between individuals that involves one
pair of contrasting traits. - 1 characteristic
- 2 contrasting traits
22Dihybrid Cross
- A cross between individuals that involves 2 pairs
of contrasting traits. - 2 characteristics
- 4 contrasting traits
23How 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.
24The 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
25Complications!
- Incomplete Dominance and Codominance
- Incomplete Dominance occurs when the F1
offspring has a phenotype between that of the
parents. - neither allele is completely
- dominant
26Example) 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!
272) 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) !
28Codominance
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
Dominant
Dominant
Codominant
Recessive
32Complications Polygenic Inheritance and
Quantitative Characters
- One trait determined by multiple genes
- Ex) skin color at least 3 genes
33Complications Epistasis
- Expression of one gene depends on another
- Mouse coat color
- B - black coat
- b - brown coat
- C - pigment
- c - no pigment
34What 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.