Transcript Fundamentals of Genetics

Fundamentals of
Genetics
Chapter 9
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.
Gregor Mendel
 Austrian monk &
science teacher in the
mid 1800’s
 Worked with pea
plants in his garden
 Studied 7
characteristics of peas
 Each characteristics had 2
different traits
EX) tall/short, purple/white
 Page 176
Mendel’s Experiments:
1. Started off with 2 pure plant groups for
a particular characteristic
1. P1 generation
2. Cross pollinated these plant groups
(sexual reproduction) to produce the
next generation of plants
1. F1 generation
3. When the seeds matured from the F1
generation, he counted & recorded the
traits of the offspring.
4. Then he allowed the F1 generation
plants self pollinate (sexual
reproduction with self) to produce the
next generation of plants
1. F2 generation
(notice that the predicted ratios & the
actual ratios are not exact!)
Mendel’s 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 3:1
(or a 75% to a 25%) ratio between the 2
traits
 Mendel named the second the recessive
factor
Example:
Purple is dominant
White is recessive
F1 generation:
all purple
F2 generation:
75% purple
25% white
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.
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.
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
 Recessive allele = lower case letter
(B)
(b)
9.2 Vocabulary:
 Genotype: the genetic makeup of the
organism (BB, Bb, bb)
 Phenotype: the physical appearance of
the organism (Black, white)
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
Genetic Probability
 The likelihood
(probability) of
offspring of
known parents
can be
determined by
Punnett squares
Punnett Squares: diagrams biologists use to
predict the probability that certain traits will be
inherited by offspring.
3 Types:
Monohybrid Cross – One characteristic
Dihybrid Cross – Two characteristics
Trihybrid Cross – Three characteristics
Monohybrid Cross
A cross between
individuals that
involves one pair
of contrasting
traits.
 1 characteristic
 2 contrasting traits
Dihybrid Cross
A cross between
individuals that involves
2 pairs of contrasting
traits.
• 2 characteristics
• 4 contrasting traits
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.
The results:
 If the flower is hybrid, the
offspring will be 50% red
and 50% white.
Result if flower is hybrid
 If the flower is pure, the
offspring will be all red.
Result if flower is pure
Complications!

Incomplete Dominance and Codominance
1) Incomplete Dominance: occurs when the
F1 offspring has a phenotype between
that of the parents.
 neither allele is completely
dominant
Example) Incomplete Dominance
 Four o’clock flowers
Q- What would
happen if you
crossed a red four
o’clock flower with a
white four o’clock
flower?
A- a pink flower!
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) !
Codominance
 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?
 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
Complications: Multiple alleles
 ABO blood groups
Dominant
Dominant
Codominant
Recessive
Complications: Polygenic Inheritance
and Quantitative Characters
 One trait
determined by
multiple genes
 Ex) skin color: at
least 3 genes
Complications: Epistasis
 Expression of one
gene depends on
another
 Mouse coat color:
 B - black coat
 b - brown coat
 C - pigment
 c - no pigment
What are my chances?
1. Obtain 2 pennies.
2. Flip each coin simultaneously 50 times.
Record the results of each set of flips.
3. Total the number of combinations of your
results:
__ Heads-Heads
__ Heads-Tails
__ Tails-Tails
4. Record your results on the board.
5. Calculate your percent chance of each
combination.
(# of combos)
50
6. Calculate the class average percent
chance of each combination.