Transcript Solving Genetics Problems

SOLVING GENETICS
PROBLEMS
Biology
Unit 6
Powerpoint #2 / Chapter 11
Mr. Velekei
Vocabulary
9. Phenotype
10.Genotype
11.Dominant
12.Recessive
13.Homozygous
14.Heterozygous
Unit 6: Genetics
PROBLEMS
Honors Biology
Unit 5
Powerpoint #1 / Chapter 11
Traits
• What are some of your traits?
• Where did they come from?
• Do you look like one of your parents, a
combination, or neither?
• Do certain traits “run” in your family?
Or pop up after skipping a generation
• What traits are common in our class?
why do you think that is?
Terminology
Gene: segment of DNA
that determines a trait
(protein)
Alleles: different forms
of a gene
(ex: Height: tall allele, or
short allele)
Chromosome # 12
Genotype vs. phenotype
• Difference between how an organism “looks” & its
genetics
• phenotype
• description of an organism’s trait
• the “physical”
• genotype
• description of an organism’s genetic makeup
X
P
Explain Mendel’s results using
…dominant & recessive
…phenotype & genotype
purple
F1
all purple
white
Notation
A capital letter represents the dominant allele.
A lower case letter represents the recessive
allele.
Example: Pea plant height –
Tall: T
Short: t
Remember…
•
Dominant: An allele that causes its
phenotype in a heterozygous genotype.
Examples: TT, Tt (Tall)
•
Recessive: An allele that causes a
phenotype only seen in a homozygous
genotype.
Example: tt (short)
Allele: A variety of a gene
• A gene for hair color could have the
B
allele: _______
for Brown hair or
b
_______
for Blonde hair
•
A gene for flower color could have
B
allele: ______for
blue flower or
b
________
for red flower
•
A gene for height could have the
alleles: _______
for tall or _______
for
T
t
short
Making crosses
• Can represent alleles as letters
• flower color alleles  P or p
• true-breeding purple-flower peas  PP
• true-breeding white-flower peas  pp
PP x pp
X
P
purple
F1
all purple
white
Pp
Solving Genetics Problems
Homozygous: organism with
two identical alleles for a trait
Heterozygous: organism with
two different alleles for a trait
Solving Genetics Problems
Homozygous dominant:
organism with two dominant
alleles
Homozygous recessive:
organism with two recessive
alleles
A
B
C
Plant A:
a. Phenotype:
b. Genotype:
D
E
F
G
H
A
B
C
Plant B:
a. Phenotype:
b. Genotype:
D
E
F
G
H
A
B
C
Plant C:
a. Phenotype:
b. Genotype:
D
E
F
G
H
Looking closer at Mendel’s work
P
true-breeding
purple-flower peas
X
true-breeding
white-flower peas
PP
pp
100%
purple-flower peas
F1
phenotype
genotype
100%
generation
(hybrids)
Pp Pp Pp Pp
self-pollinate
F2
75%
purple-flower peas
25%
white-flower peas
generation
?
?
?
?
3:1
Hybrid: offspring of crosses between parents
with different traits.
Example: Cross pollinate a true-breeding purple
flower and a true breeding white flower.
Seedlings=hybrid (even though they are purple)
X
=
Hybrid Cars
Gas + Electric
Solving Genetics Problems
We need a method to predict the
traits of the offspring, and we
have it, its called the
Punnett Square!
Solving Genetics Problems
Genetics Problems
Goal: to predict the traits of offspring
1.
Identify trait(s) and assign a letter to each (capital
letter for dominant, lower case letter for
recessive)
Solving Genetics Problems
Genetics Problems
Goal: to predict the traits of offspring
1.
Identify trait(s) and assign a letter to each (capital
letter for dominant, lower case letter for
recessive)
2.
Determine parents’ genotypes
Solving Genetics Problems
Genetics Problems
Goal: to predict the traits of offspring
1.
Identify trait(s) and assign a letter to each (capital
letter for dominant, lower case letter for
recessive)
2.
Determine parents’ genotypes
3.
Draw Punnett square and fill in
Solving Genetics Problems
Genetics Problems
Goal: to predict the traits of offspring
1.
Identify trait(s) and assign a letter to each (capital
letter for dominant, lower case letter for
recessive)
2.
Determine parents’ genotypes
3.
Draw Punnett square and fill in
4.
Determine the probabilities for offspring of each
genotype and phenotype
Solving Genetics Problems
Example:
In pea plants, the gene for tall height is dominant to
the gene for short height. A short pea plant is
cross pollinated with a true breeding tall pea
plant.
1.
Assign letters:
tall = T short = t
2.
Parents’ genotypes
True breeding tall: TT
True breeding short = tt
Solving Genetics Problems
3. Draw Punnett Square
Solving Genetics Problems
3. Draw Punnett Square
t
T
T
t
Solving Genetics Problems
3. Draw Punnett Square
t
t
T
Tt
Tt
T
Tt
Tt
Solving Genetics Problems
4. Calculate probabilities
TT = _____
Tt = ________
tt = _________
Tall = _________
Short = _________
t
t
T
Tt
Tt
T
Tt
Tt
Solving Genetics Problems
4. Calculate probabilities
10) TT = 0/4
Tt = 4/4
tt = 0/4
11) Tall = 4/4
Short = 0/4
t
t
T
Tt
Tt
T
Tt
Tt
Aaaaah,
phenotype & genotype
can have different
ratios
Punnett squares
Pp x Pp
F1
generation
(hybrids)
%
genotype
male / sperm
P
p
PP
25%
75%
female / eggs
Pp
P
PP
%
phenotype
50%
Pp
Pp
p
Pp
pp
pp
25%
1:2:1
25%
3:1
Genotypes
• Homozygous = same alleles = PP, pp
• Heterozygous = different alleles = Pp
homozygous
dominant
heterozygous
homozygous
recessive
Phenotype vs. genotype
• 2 organisms can have the same phenotype but have
different genotypes
purple
PP
purple
Pp heterozygous
homozygous dominant
How do you determine the
genotype of an individual with
with a dominant phenotype?
Can’t tell
by lookin’
at ya!
Test cross
• Breed the dominant phenotype —
the unknown genotype — with a homozygous
recessive (pp) to determine the identity of the
unknown allele
x
is it
PP or Pp?
pp
How does a Test cross work?
Am I
this?
Or am I
this?
x
PP
pp
x
Pp
p
p
P
Pp
Pp
P
Pp
Pp
P
Pp
Pp
p
pp
pp
100% purple
p
pp
p
50% purple:50% white or 1:1
P
Mendel’s 1st law of heredity
• Law of segregation
PP
P
• during meiosis, alleles segregate
• homologous chromosomes separate
• each allele for a trait is packaged into a separate
gamete
p
pp
p
P
Pp
p
Segregation of alleles and fertilization as chance events
Identify trait(s) and assign a letter to each (capital
letter for dominant, lower case letter for recessive.
Examples:
In guinea pigs, the gene for black fur is dominant to the
gene for white fur.
Determine parents’ genotypes.
Example:
In guinea pigs, the gene for black fur is
dominant to the gene for white fur. A white
guinea pig and a hybrid black guinea pig
produce 20 offspring. Find the probability of
offspring genotypes and phenotypes.
1. Black: ___White: ___
2. White guinea pig: ___
Hybrid black guinea pig: ___
Determine parents’ genotypes.
Example:
In guinea pigs, the gene for black fur is
dominant to the gene for white fur. A white
guinea pig and a hybrid black guinea pig
produce 20 offspring. Find the probability of
offspring genotypes and phenotypes.
1. Black: B White: b
2. White guinea pig: ___
Hybrid black guinea pig: ___
Determine parents’ genotypes.
Example:
In guinea pigs, the gene for black fur is
dominant to the gene for white fur. A white
guinea pig and a hybrid black guinea pig
produce 20 offspring. Find the probability of
offspring genotypes and phenotypes
1. Black: B White: b
2. White guinea pig: bb
Hybrid black guinea pig: ___
Determine parents’ genotypes.
Example:
In guinea pigs, the gene for black fur is
dominant to the gene for white fur. A white
guinea pig and a hybrid black guinea pig
produce 20 offspring. Find the probability of
offspring genotypes and phenotypes.
1. Black: B White: b
2. White guinea pig: bb
Hybrid black guinea pig: Bb
Solving Genetics Problems
4. Calculate probabilities
BB = 0/4
Bb = 2/4 (50%)
bb = 2/4 (50%)
How many of the babies will
Probably be Black =
10
How many of the babies will
Probably be White =
10
B
b
b
Bb
bb
b
Bb
bb
Tongue Rolling: Dominant
• If a mother can roll her tongue and a father can
not.
• What do we know about their genes?
Tongue Rolling: Dominant
• If a mother can roll her tongue and a
father can not.
• What do we know about their genes?
Mother: _______
RR or Rr
Father: _______
rr only
2) B. If you know that they have 2 children, one that
can roll and one that can not. Will that give you
more info about the parent’s genotypes?
R
Yes!
c. Draw a punnett
square:
r
r
Rr
rr
r
Rr
rr
Tongue Rolling: Dominant
d. Which people in the family would be considered
hybrids?
Mom and the child that can roll
their tongue
e. Are their any genotypes that this mother and
father can not produce in their offspring? Why or
why not?
Yes, they can not produce a Homozygous
Dominant (RR) child because the father
only has recessive genes (r) to pass on
Humans can have unattached earlobes (picture A) or attached
earlobes (picture B). Attached earlobes are dominant. Use the
letter ‘E’ to complete the following questions.
Ear Lobes
Humans can have unattached earlobes (picture A) or attached
earlobes (picture B). Attached earlobes are dominant. Use the
letter ‘E’ to complete the following questions.
1) A mother is homozygous dominant
for ear type and a father is
heterozygous:
EE
a) What is the mother’s genotype? ______
Ee
Father’s genotype? ____
b) What are their phenotypes?
Mother: ___________
Attached
Father: _________
Attached
1) A mother is homozygous dominant for ear
type and a father is heterozygous:
• Draw a punnett square:
E
e
E
EE
Ee
E
EE
Ee
1) A mother is homozygous dominant for
ear type and a father is heterozygous:
d: What are the chances
they will have children
that are:
Homozygous Dominant:
E
____
50%
Heterozygous:
____
E
50%
Homozygous Recessive:
____
0%
E
e
EE
Ee
EE
Ee
DIHYBRID (2 FACTOR)
CROSSES
+
INCOMPLETE AND CODOMINANCE
Monohybrid cross
• Some of Mendel’s experiments followed the
inheritance of single characters
• flower color
• seed color
• monohybrid crosses
Dihybrid (2 factor) cross
• Other of Mendel’s experiments
followed the inheritance of 2
different characters
• seed color and seed shape
• dihybrid (2 factor) crosses
Mendel
was working out
many of the
genetic rules!
Dihybrid cross
P
true-breeding
yellow, round peas
Y = yellow
R = round
true-breeding
green, wrinkled peas
x
YYRR
yyrr
y = green
r = wrinkled
yellow, round peas
F1
100%
generation
(hybrids)
YyRr
self-pollinate
F2
generation
9:3:3:1
9/16
yellow
round
peas
3/16
green
round
peas
3/16
yellow
wrinkled
peas
1/16
green
wrinkled
peas
What’s going on here?
• If genes are on different chromosomes…
• how do they assort in the gametes?
• together or independently?
YyRr
YR
yr
Is it this?
Or this?
YR
Which system
explains the
data?
YyRr
Yr
yR
yr
YyRr
Is this the way it works?
YR
YyRr x YyRr
yr
or
YyRr
YR Yr
yR
yr
9/16
yellow
round
YR
yr
YR
yr
YYRR
YyRr
YyRr
yyrr
3/16
green
round
3/16
yellow
wrinkled
1/16
green
wrinkled
YyRr
Dihybrid cross
YR
YyRr x YyRr
YR
Yr
yR
yr
yr
YR YYRR YYRr YyRR YyRr
Yr
YYrr
YyRr
Yyrr
yR YyRR YyRr
yyRR
yyRr
yr
YYRr
YyRr
Yyrr
yyRr
yyrr
or
YyRr
YR Yr
yR
yr
9/16
yellow
round
3/16
green
round
3/16
yellow
wrinkled
1/16
green
wrinkled
The laws of probability govern Mendelian
inheritance
• Rule of Multiplication:
• probability that 2+ independent events will occur
together in a specific combination  multiply
probabilities of each event
• Ex. 1: probability of throwing 2 sixes
• 1/6 x 1/6 = 1/36
• Ex. 2: probability of having 5 boys in a row
• ½ x ½ x ½ x ½ x ½ = 1/32
The laws of probability govern Mendelian inheritance
• Rule of Addition:
• Probability that 2+ mutually exclusive events will
occur  add together individual probabilities
• Ex. 1: chances of throwing a die that will land on 4 or 5?
• 1/6 + 1/6 = 1/3
Mendel’s 2nd law of heredity
• Law of independent assortment
• different loci (genes) separate into gametes
independently
• non-homologous chromosomes align independently
• classes of gametes produced in equal amounts
yellow
green
• YR = Yr = yR = yr
• only true for genes on separate chromosomes or
on same chromosome but so far apart that crossing over
happens frequently
round
wrinkled
YyRr
Yr
Yr
1
yR
:
yR
1
YR
:
YR
1
yr
:
yr
1
Review: Mendel’s laws of heredity
• Law of segregation
• monohybrid cross
• single trait
• each allele segregates into separate gametes
• established by Metaphase 1
• Law of independent assortment
• dihybrid (or more) cross
• 2 or more traits
• genes on separate chromosomes
assort into gametes independently
EXCEPTION
 linked genes
Beyond Mendel’s Laws
of Inheritance
Vocabulary
15. Co-dominance
16. Incomplete dominance
17. Probability
Extending Mendelian genetics
• Mendel worked with a simple system
• peas are genetically simple
• most traits are controlled by a single gene
• each gene has only 2 alleles, 1 of which
is completely dominant to the other
• The relationship between
genotype & phenotype
is rarely that simple
Incomplete dominance
• Heterozygote shows an intermediate,
blended phenotype
• example:
• RR = red flowers RR
• rr = white flowers WW
• Rr = pink flowers RW
• make 50% less color
RR
RW
WW
Incomplete dominance
P
true-breeding
red flowers
true-breeding
white flowers
X
100% pink flowers
F1
100%
generation
(hybrids)
self-pollinate
25%
red
F2
generation
50%
pink
25%
white
It’s like
flipping 2
pennies!
1:2:1
Fill in the Punnett Square
Genotypes
Phenotypes
B
B
Bb
Bb
b Bb
Bb
b
What percentages will the F1 be:
•
•
•
•
•
•
BB: _______%
0
Bb: ________%
100
bb: ________%
0
Black:_________%
0
White:_________%
0
Hybrid: ________%
100
BB: ________%
Bb: ________%
bb: ________%
Black:_______%
B
b
B
b
BB
Bb
Bb
bb
BB: 25%
Bb: 50%
bb: 25%
Black: 25%
B
b
B
b
BB
Bb
Bb
bb
definitions
• Co-dominance:
Both alleles are
dominant and
contribute to the
phenotype of a
heterozygous
individual
Solve the following crosses:
Co-Dominance
3. In Cows the trait for coat (fur)
color is expressed by FR for Red
fur and FW for white fur. The
hybrid of the two is called a Roan
color (FRFW)
a) Describe what you think the Roan cow’s
fur will look like:
Co-dominance
2. FR= Red Fur
FW= White Fur
• What do you think a FRFW cow will look like:
____________________
Red and White spots
• If the mother cow is homozygous red for fur
RFR
F
color. What is her genotype: _____
Red Fur
Phenotype?________________
• If the dad is homozygous white for fur color.
FWFW
What is his genotype: _____
White Fur
Phenotype?________________
• What percentage of the offspring will be
100%
FRFW: ______________
Fill in the Punnett Square
Genotypes
W
F
R
F
R
F
R
W
F F
R
W
F F
Phenotypes
W
F
R
W
F F
R
W
F F
Solve the following crosses:
Co-Dominance
In mushrooms there is a gene for
Purple Spots (SP) and a gene for Green
spots (SG). Cross a Homozygous
purple with a Homozygous Green.
a) What do you think their offspring will look
like? Genotype? Phenotype?
b) What will the genotype and phenotype
percentages be in the F2 when you cross
two from the F1 generation.
Phenotypes & Genotypes
S P SP
SGSG
100 % SPSG
b) F1 x F1
P
S
SPSP= 25%
G
S
SPSG= 50%
SGSG=25%
Green Spots = 25%
G & P Spots = 50%
Purple Spots = 25%
SP
G
S
SPSP
SPSG
P
G
S S
G
G
S S
Pleiotropy
• Most genes are pleiotropic
• one gene affects more than one phenotypic character
• 1 gene affects more than 1 trait
• dwarfism (achondroplasia)
• gigantism (acromegaly)
Acromegaly: André the Giant
Epistasis
• One gene completely masks another gene
• coat color in mice = 2 separate genes
• C,c:
B_C_
bbC_
_ _cc
pigment (C) or
no pigment (c)
• B,b:
more pigment (black=B)
or less (brown=b)
• cc = albino,
no matter B allele
• 9:3:3:1 becomes 9:3:4
Polygenic inheritance
• Some phenotypes determined by additive effects of 2
or more genes on a single character
• phenotypes on a continuum
• human traits
• skin color
• height
• weight
• intelligence
• behaviors