Download evidence from genetics

EVIDENCE FROM
GENETICS
Can you answer this?
 Which represents a monohybrid cross
between a homozygous recessive and a
heterozygote?
 A) Tt x Tt
 B) ttmm x TtMm
 C) tt x Tt
 D) ttmm x TTMM
Can you answer this?
In rats, black fur is dominant over white.
If a white rat is crossed with a
heterozygous black rat, what is the
likely % of the offspring that will be
white?
A) 0%
B) 25%
C) 50%
D) 75%
And can you answer this?
Which of the following pairs
of crosses results in
the same phenotypic
ratios?
A) Aa x Aa and AA x aa
B) AA x aa and AA x Aa
C) AA x Aa and Aa x aa
D) None of the above
EVIDENCE FROM
GENETICS
 Deduction: If the hypothesis of
evolution is correct, then we should
see evidence of this in genetics
 Background:
Gregor Mendel (1822-1884
Experiments with the garden pea.
His paper in 1866 established the
field of genetics.
MENDEL’S GARDEN
Mendel at work
Mendel at work
Mendel’s Traits
Monohybrid Crosses
(=Breeding experiments involving one trait)
 Pea plants
 P Tall x Tall
 F1
All Tall
Short x Short
All Short
Monohybrid Crosses
(=Breeding experiments involving one trait)
 Pea plants
 P Tall x Tall
 F1
 F2
Short x Short
All Tall
All Short
All Tall
The tall trait is dominant
Monohybrid Crosses
(=Breeding experiments involving one trait)
 Pea plants
 P Tall x Tall
 F1
Short x Short
All Tall
All Short
All Tall
 F2
F2 x F2
Monohybrid Crosses
(=Breeding experiments involving one trait)
 Pea plants
 P Tall x Tall
 F1
Short x Short
All Tall
All Short
All Tall
 F2
 F3
F2
x F2
75% Tall, 25% Short
MENDEL’S TRAITS




5474/1850=
6022/2001=
882/299=
428/152=
2.96
3.01
2.95
2.82
 705/224=
3.15
 651/207=
3.14
 787/277=
2.84
MENDEL’S TRAITS




5474/1850=
6022/2001=
882/299=
428/152=
2.96
3.01
2.95
2.82
 705/224=
3.15
 651/207=
3.14
 787/277=
2.84
Mendel analyzes the data
Traits passed in the gametes
Pollen (sperm) & eggs
Note: ¾ Tall= TT, Tt, tT
¼ Short= tt
3:1 Phenotypic Ratio
Terms and Principles
 Dominant (e.g. Tall)
 Recessive (e.g. Short)
 Phenotype (visible characteristics)
 Genotype (genetic characteristics)
 Particulate theory of inheritance=
2 particles (factors) determine a trait
Using a Punnett Square
Alleles= Alternative forms of the same
gene (T or t)
Suppose Tt X Tt
T
t
T
TT
Tt
t
Tt
tt
Using a Punnett Square
Eggs
T
Tall
t
T
TT
Tt
t
Tt
tt
Tall
Pollen
Tall
Short
Using a Punnett Square
Homozygous condition= both alleles are alike (TT or tt)
T
t
T
TT
Tt
t
Tt
tt
Using a Punnett Square
Heterozygous condition= both alleles are different (Tt)
T
t
T
TT
Tt
t
Tt
tt
Clicker Question

A)
B)
Blue eyes (b) are recessive to brown (B).
Suppose 2 parents had 11 children: 6 with blue
and 5 with brown. Which of these statements is
most likely to be right?
Both parents had blue eyes.
One parent had blue & the other was homozygous
dominant
C) Both parents had brown eyes.
D) One parent had blue & the other was heterozygous
E) Both parents were heterozygous.
Dihybrid Crosses
(=Breeding experiments involving two traits)
P
F1
Round (R)
Yellow (Y)
or
or
RRYY
x
Wrinkled (r) seeds
Green (y) seeds
RrYy
Round Yellow
rryy
Genotype
Phenotype
Dihybrid Cross
RrYy x RrYy
Dihybrid Cross
RrYy x RrYy
Dihybrid Cross
RrYy x RrYy
Dihybrid Cross
RrYy x RrYy
Clicker Question
What belongs in the red square?





A)
B)
C
D)
E)
RRYY
RrYY
rrYy
rrYY
rryy
Dihybrid Cross
RrYy x RrYy
Clicker Question:
How many wrinkled green seeds will there
be out of 16 possibilities?





A) All 16
B) 9 out of 16
C) 50%
D) 3 0ut of 16
E) 1 out of 16
Clicker Question:
How many wrinkled green seeds will there
be out of 16 possibilities?





A) All 16
B) 9 out of 16
C) 50%
D) 3 0ut of 16
E) 1 out of 16
Dihybrid Cross
RrYy x RrYy
9:
Round
Yellow
3:
Round
Green
3:
Wrinkled
Yellow
1
Wrinkled
Green
Principle of
Independent Assortment
= Factors (genes) sort independently of
one another.
i.e. all possible combinations of Y and y
and R and r occur
BUT
What if
RY are linked together &
ry are linked together ?
Non Independent Assortment
Can you answer this?
 Which represents a monohybrid cross
between a homozygous recessive and a
heterozygote?
 A) Tt x Tt
 B) ttmm x TtMm
 C) tt x Tt
 D) ttmm x TTMM
Can you answer this?
In rats, black fur is dominant over white.
If a white rat is crossed with a
heterozygous black rat, what is the
likely % of the offspring that will be
white?
A) 0%
B) 25%
C) 50%
D) 75%
And can you answer this?
Which of the following pairs
of crosses results in
the same phenotypic
ratios?
A) Aa x Aa and AA x aa
B) AA x aa and AA x Aa
C) AA x Aa and Aa x aa
D) None of the above
According to J.K. Rowling wizards & witches can
be born from pure bloods or muggles. Suppose the
wizard/witch trait is recessive (m)
and the muggle trait is dominant (M)

A)
B)
C)
D)
E)
Hermione is a witch born
of muggle parents. If her
parents had another child
what are the chances that
that one also would be a
wizard or witch?
0%
25%
50%
75%
100%