Download Chapter 14 (Sep 28-30)

Chapter 14 Mendel and the Gene Idea
p 272-273 Ch 14 Genetics Problems (#1-17) – due Oct. 15th
p 291-292 Ch 15 Genetics Problems (#1-14) – due Oct. 15th
- I need to get the impression that you have worked out the problems &
not just copied the correct answer!!
Chapter 14 Mendel and the Gene Idea
1. What do you know about genetics?
- Mendel – Father of Genetics – peas
1
APPLICATION By crossing (mating) two true-breeding
varieties of an organism, scientists can study patterns of
inheritance. In this example, Mendel crossed pea plants
that varied in flower color.
TECHNIQUE
P generation
Removed stamens
from purple flower
2 Transferred sperm-
bearing pollen from
stamens of white
flower to eggbearing carpel of
purple flower
Parental
generation
(P)
3 Pollinated carpel
Stamens
Carpel (male)
(female)
matured into pod
4 Planted seeds
from pod
TECHNIQUE
RESULTS
When pollen from a white flower fertilizes
eggs of a purple flower, the first-generation hybrids all have purple
flowers. The result is the same for the reciprocal cross, the transfer
of pollen from purple flowers to white flowers.
F1 Generation
5 Examined
First
generation
offspring
(F1)
offspring:
all purple
flowers
Chapter 14 Mendel and the Gene Idea
EXPERIMENT True-breeding purple-flowered pea plants and
white-flowered pea plants were crossed (symbolized by ). The
resulting F1 hybrids were allowed to self-pollinate or were crosspollinated with other F1 hybrids. Flower color was then observed
in the F2 generation.

P Generation
(true-breeding
parents)
Purple
flowers
White
flowers
F1 Generation
(hybrids)
All plants had
purple flowers
RESULTS Both purple-flowered plants and whiteflowered plants appeared in the F2 generation. In Mendel’s
experiment, 705 plants had purple flowers, and 224 had white
flowers, a ratio of about 3 purple : 1 white.
F2 Generation
Chapter 14 Mendel and the Gene Idea
1. What do you know about genetics?
- Mendel – Father of Genetics – peas
- Allele – alternate form of a gene that gives different traits
- Dominant allele
- gives a visible trait with only 1 copy
- A
- Recessive allele
- gives a visible trait with 2 copies
- a
Allele for purple flowers
Locus for flower-color gene
Allele for white flowers
Homologous
pair of
chromosomes
Chapter 14 Mendel and the Gene Idea
1. What do you know about genetics?
- Mendel – Father of Genetics – peas
- Allele – alternate form of a gene that gives different traits
- Dominant allele
- gives a visible trait with only 1 copy
- A
- Recessive allele
- gives a visible trait with 2 copies
- a
- Homozygous
- 2 copies of the same allele
- AA or aa
- Heterozygous
- 1 copy of each allele
- Aa
- True breeders
- parents who mate & always yield the same genetic offspring
- AA x AA or aa x aa
Chapter 14 Mendel and the Gene Idea
1. What do you know about genetics?
- Mendel – Father of Genetics – peas
- Allele – alternate form of a gene that gives different traits
- Dominant allele
- Recessive allele
- Homozygous
- Heterozygous
- True breeders
- parents who mate & always yield the same genetic offspring
- AA x AA or aa x aa
- Monohybrid – organism that’s heterozygous for 1 gene of interest
- Dihybrid – organism that is heterozygous for 2 genes of interest
- Genotype – genetic make up of an organism (its alleles)
- Phenotype – physical traits exhibited – based on genotype
Figure 14.6 Phenotype versus genotype
Phenotype
Purple
3
Purple
Genotype
PP
(homozygous)
1
Pp
(heterozygous)
2
Pp
(heterozygous)
Purple
1
White
pp
(homozygous)
Ratio 3:1
Ratio 1:2:1
1
Chapter 14 Mendel and the Gene Idea
1. What do you know about genetics?
- Mendel – Father of Genetics – peas
- Allele – alternate form of a gene that gives different traits
- Dominant allele
- Recessive allele
- Homozygous
- Heterozygous
- True breeders
- parents who mate & always yield the same genetic offspring
- AA x AA or aa x aa
- Monohybrid – organism that’s heterozygous for 1 gene of interest
- Dihybrid – organism that is heterozygous for 2 genes of interest
- Genotype – genetic make up of an organism (its alleles)
- Phenotype – physical traits exhibited – based on genotype
- Law of Segregation – each allele in a pair segregates into a different
gamete during gamete formation (Anaphase I)
Figure 14.5 Mendel’s law of segregation
Each true-breeding plant of the
parental generation has identical
alleles, PP or pp.
Gametes (circles) each contain only
one allele for the flower-color gene.
In this case, every gamete produced
by one parent has the same allele.
Union of the parental gametes
produces F1 hybrids having a Pp
combination. Because the purpleflower allele is dominant, all
these hybrids have purple flowers.
When the hybrid plants produce
gametes, the two alleles segregate,
half the gametes receiving the P
allele and the other half the p allele.
P Generation

Appearance:
Purple flower White flowers
Genetic makeup:
PP
pp
Gametes:
P
p
F1 Generation
Appearance:
Genetic makeup:
Gametes:
Purple flowers
Pp
Figure 14.5 Mendel’s law of segregation
Each true-breeding plant of the
parental generation has identical
alleles, PP or pp.
Gametes (circles) each contain only
one allele for the flower-color gene.
In this case, every gamete produced
by one parent has the same allele.
Union of the parental gametes
produces F1 hybrids having a Pp
combination. Because the purpleflower allele is dominant, all
these hybrids have purple flowers.
When the hybrid plants produce
gametes, the two alleles segregate,
half the gametes receiving the P
allele and the other half the p allele.
This box, a Punnett square, shows
all possible combinations of alleles
in offspring that result from an
F1  F1 (Pp  Pp) cross. Each square
represents an equally probable product
of fertilization. For example, the bottom
left box shows the genetic combination
resulting from a p egg fertilized by
a P sperm.
P Generation

Appearance:
Purple flower White flowers
Genetic makeup:
PP
pp
Gametes:
p
P
F1 Generation
Appearance:
Genetic makeup:
Gametes:
Purple flowers
Pp
1/
2
1/
P
p
F1 sperm
P
p
PP
Pp
F2 Generation
P
F1 eggs
p
pp
Pp
Random combination of the gametes
results in the 3:1 ratio that Mendel
observed in the F2 generation.
2
3
:1
Chapter 14 Mendel and the Gene Idea
1. What do you know about genetics?
- Mendel – Father of Genetics – peas
- Allele – alternate form of a gene that gives different traits
- Dominant allele
- Recessive allele
- Homozygous
- Heterozygous
- True breeders
- parents who mate & always yield the same genetic offspring
- AA x AA or aa x aa
- Monohybrid – organism that’s heterozygous for 1 gene of interest
- Dihybrid – organism that is heterozygous for 2 genes of interest
- Genotype – genetic make up of an organism (its alleles)
- Phenotype – physical traits exhibited – based on genotype
- Law of Segregation – each allele in a pair segregates into a different
gamete during gamete formation (Anaphase I)
- Testcross – breeding an organism of unknown genotype with a
homozygous recessive
Figure 14.7 The Testcross
APPLICATION An organism that exhibits a dominant trait,
such as purple flowers in pea plants, can be either homozygous for
the dominant allele or heterozygous. To determine the organism’s
genotype, geneticists can perform a testcross.

TECHNIQUE In a testcross, the individual with the
unknown genotype is crossed with a homozygous individual
expressing the recessive trait (white flowers in this example).
By observing the phenotypes of the offspring resulting from this
cross, we can deduce the genotype of the purple-flowered
parent.
Dominant phenotype,
unknown genotype:
PP or Pp?
Recessive phenotype,
known genotype:
pp
If PP,
then all offspring
purple:
If Pp,
then 2 offspring purple
and 1⁄2 offspring white:
p
1⁄
p
p
p
Pp
Pp
pp
pp
RESULTS
P
P
Pp
Pp
P
p
Pp
Pp
Chapter 14 Mendel and the Gene Idea
1. What do you know about genetics?
- Mendel – Father of Genetics – peas
- Allele – alternate form of a gene that gives different traits
- Dominant allele
- Recessive allele
- Homozygous
- Heterozygous
- True breeders
- parents who mate & always yield the same genetic offspring
- AA x AA or aa x aa
- Monohybrid – organism that’s heterozygous for 1 gene of interest
- Dihybrid – organism that is heterozygous for 2 genes of interest
- Genotype – genetic make up of an organism (its alleles)
- Phenotype – physical traits exhibited – based on genotype
- Law of Segregation – each allele in a pair segregates into a different
gamete during gamete formation (Anaphase I)
- Testcross – breeding an organism of unknown genotype with a
homozygous recessive
- Law of Independent Assortment – each pair of alleles separates
independently during gamete formation when genes for 2 traits are on
different homologous chromosomes (Metaphase I)
Figure 14.8 Do the alleles for seed color and seed shape sort
into gametes dependently (together) or independently?
EXPERIMENT Two true-breeding pea plants—
one with yellow-round seeds and the other with
green-wrinkled seeds—were crossed, producing
dihybrid F1 plants. Self-pollination of the F1 dihybrids,
which are heterozygous for both characters,
produced the F2 generation. The two hypotheses
predict different phenotypic ratios. Note that yellow
color (Y) and round shape (R) are dominant.
P Generation
YYRR
yyrr
Gametes
YR
F1 Generation

yr
YyRr
Hypothesis of
independent
assortment
Hypothesis of
dependent
assortment
RESULTS
Sperm
1⁄
4
Sperm
1⁄
2
F2 Generation
(predicted
offspring)
Eggs
1⁄
2 YR
1⁄
2
YR
YYRR
1⁄
2
1⁄
4
yR
1⁄
4
YyRr
yyrr
1⁄
4
YR
1⁄
4
Yr
1⁄
4
yR
1⁄
4
yr
YYRR
YYRr
YyRR
YyRr
YYRr
YYrr
YyRr
Yyrr
YyRR
YyRr
yyRR
yyRr
YyRr
Yyrr
yyRr
1⁄
4
Phenotypic ratio 3:1
9⁄
16
3⁄
16
3⁄
16
yyrr
1⁄
16
Phenotypic ratio 9:3:3:1
315
108
yr
yr
3⁄
4
CONCLUSION The results support the hypothesis of
independent assortment. The alleles for seed color and seed
shape sort into gametes independently of each other.
Yr
Eggs
yr
YyRr
YR
1⁄
4
101
32
Phenotypic ratio approximately 9:3:3:1
Chapter 14 Mendel and the Gene Idea
1. What do you know about genetics? Terms to know…
2. How does genetics reflect probabilities? Rr

- 0 = never will happen
Segregation of
- 1 = always happens
alleles into eggs
- Consider a coin….
- Probability of heads = 0.5
Sperm
- Probability of tails = 0.5
3. What is the rule of multiplication?
1⁄
1⁄
r
R
2
2
- prob. of RR offspring from
Rr x Rr
R
R
- R (½ ) x R (½) = ¼
r
R
1⁄
R
2
- Prob. of rr offspring from
1⁄
1⁄
4
4
Rr x Rr
Eggs
- r (½) x r (½) = ¼
r
r
4. What is the rule of addition?
R
r
1⁄
r
2
- Prob. of Rr offspring from
1⁄
1⁄
4
4
Rr x Rr
- R (½) x r (½) = ¼ (1st parent gives R)
- R (½) x r (½) = ¼ (2nd parent gives R)
- ¼ + ¼ = ½ Rr offspring
- Only when Rr x Rr make Rr
Rr
Segregation of
alleles into sperm
Let’s practice…..
PpYyRr x Ppyyrr
1.
2.
3.
4.
5.
ppyyRr = ?
ppYyrr = ?
Ppyyrr = ?
PPyyrr = ?
ppyyrr = ?
1/16
1/16
1/8
1/16
1/16
¼ · ½ · ½ = 1/16
¼ · ½ · ½ · = 1/16
½ · ½ · ½ = 1/8
¼ · ½ · ½ = 1/16
¼ · ½ · ½ = 1/16
Chapter 14 Mendel and the Gene Idea
1.
2.
3.
4.
5.
What do you know about genetics? Terms to know…
How does genetics reflect probabilities?
What is the rule of multiplication?
What is the rule of addition?
P Generation
What is incomplete dominance?
Red
CRCR
- Heterozygous phenotype is in
between the 2 homozygous
Gametes
phenotypes
- snapdragons
- 1:2:1 for phenotype = genotype
White
CWCW

CR
CW
Pink
CRCW
F1 Generation
Gametes
Eggs
F2 Generation
1⁄
2
1⁄
2
CR
1⁄
2
CR
1⁄
2
CW
1⁄
2
CW Sperm
CR
CR CR CR CW
1⁄
2
Cw
CR CW CW CW
Chapter 14 Mendel and the Gene Idea
1.
2.
3.
4.
5.
6.
What do you know about genetics? Terms to know…
How does genetics reflect probabilities?
What is the rule of multiplication?
What is the rule of addition?
What is incomplete dominance?
What is codominance?
- Heterozygous phenotype shows both alleles being expressed
- Both alleles can be detected
- Blood typing – glycoprotein on RBC
- Blood typing also shows
multiple alleles (more than 2
allelic variations at a gene locus)
Chapter 14 Mendel and the Gene Idea
Tay-Sachs disease – brain cells cannot metabolize a certain lipid because of an
enzyme deficiency
Phenotype seen - dd (homozygous recessive)
- consider Dd
- appear normal – 1 copy sufficient
- biochemically – incomplete dominance – less enzyme activity
can be detected….in between DD and dd
- molecularly – codominant – both normal enzyme & mutant
enzyme can be detected
Chapter 14 Mendel and the Gene Idea
What do you know about genetics? Terms to know…
How does genetics reflect probabilities?
What is the rule of multiplication?
What is the rule of addition?
What is incomplete dominance?
What is codominance?
What is pleiotropy?
- 1 gene with multiple effects/phenotypes
- Sickle cell allele
- RBC form a sickle shape (“C”) when oxygen deprived causing blood
flow problems leading to fatigue, pain, brain damage, etc.
8. What is epistasis?
- Gene at 1 locus alters the phenotypic expression of a gene at a 2nd locus
1.
2.
3.
4.
5.
6.
7.
Figure 14.11 An example of epistasis
B = black coat
b = brown coat
C = pigment
c = no pigment
In order to have color,
the cells must have
pigment.

BbCc
BbCc
Sperm
1⁄
BC
4
1⁄
4
bC
1⁄
4
1⁄
Bc
4
bc
Eggs
1⁄
1⁄
4
BC
BBCC
BbCC
BBCc
BbCc
4
bC
BbCC
bbCC
BbCc
bbCc
1⁄
1⁄
4
Bc
BBCc
BbCc
BBcc
4
bc
BbCc
bbCc
Bbcc
9⁄
16
3⁄
16
Bbcc
bbcc
4⁄
16
Chapter 14 Mendel and the Gene Idea
1.
2.
3.
4.
5.
6.
7.
8.
9.
What do you know about genetics? Terms to know…
How does genetics reflect probabilities?
What is the rule of multiplication?
What is the rule of addition?
What is incomplete dominance?
What is codominance?
What is pleiotropy?
What is epistasis?
What is polygenic inheritance?
- An additive effect of 2 or more genes on a single phenotype
- Opposite of pleiotropy
- Skin pigmentation
Figure 14.12 A simplified model for polygenic inheritance of skin color
Skin pigmentation controlled by 3 separate genes

AaBbCc
AaBbCc
aabbcc Aabbcc AaBbcc AaBbCc AABbCc AABBCc AABBCC
20⁄
64
15⁄
6⁄
64
64
1⁄
64
Chapter 14 Mendel and the Gene Idea
1. What do you know about genetics? Terms to know…
2. How does genetics reflect probabilities?
3. What is the rule of multiplication?
4. What is the rule of addition?
5. What is incomplete dominance?
6. What is codominance?
7. What is pleiotropy?
8. What is epistasis?
9. What is polygenic inheritance?
10. Can the environment influence phenotype?
- Plants – leaf shape, size, greenness – depend on wind, sunlight, rain
nutrition – Figure 50.9
- Us – height, weight – depend on exercise & nutrition
- Hydrangea color depends
on soil acidity
- Multifactorial – many factors,
genetic & environmental
influence phenotype
Figure 14.14 Pedigree analysis
Pedigree analysis - follows specific traits over generations of a family
Ww
ww
Ww ww ww Ww
WW
or
Ww
ww
Ww
Ww
ww
First generation
(grandparents)
Second generation
(parents plus aunts
and uncles)
(a) Dominant trait (widow’s peak)
FF or Ff
Ff
ff
Third
generation
(two sisters)
ww
Widow’s peak
Ff
No Widow’s peak
Attached earlobe
ff
ff
Ff
Ff
Ff
ff
ff
FF
or
Ff
Free earlobe
(b) Recessive trait (attached earlobe)
Chapter 14 Mendel and the Gene Idea
1. What do you know about genetics? Terms to know…
2. How does genetics reflect probabilities?
3. What is the rule of multiplication?
4. What is the rule of addition?
5. What is incomplete dominance?
6. What is codominance?
7. What is pleiotropy?
8. What is epistasis?
9. What is polygenic inheritance?
10. Can the environment influence phenotype?
11. What are some recessively inherited human disorders?
- Only seen as dd, Dd are considered carriers
- Cystic fibrosis – caused by a defect in a Cl- channel protein in lungs
which leads to a mucus build up due to an increase in Cl- concentration
- 1 in 2500 Caucasians of European descent
- 1 in 25 (4%) carriers
- Sickle-cell disease
Chapter 14 Mendel and the Gene Idea
1. What do you know about genetics? Terms to know…
2. How does genetics reflect probabilities?
3. What is the rule of multiplication?
4. What is the rule of addition?
5. What is incomplete dominance?
6. What is codominance?
7. What is pleiotropy?
8. What is epistasis?
9. What is polygenic inheritance?
10. Can the environment influence phenotype?
11. What are some recessively inherited human disorders?
12. What are some dominantly inherited disorders?
- Achondroplasia
- form of dwarfism
- 1 in 25,000
- Huntington’s disease
- degenerative disease of the nervous system
- lethal dominant
- phenotype visible between 35 – 45 yrs old
- 1 in 10,000
Chapter 14 Mendel and the Gene Idea
1. What do you know about genetics? Terms to know…
2. How does genetics reflect probabilities?
3. What is the rule of multiplication?
4. What is the rule of addition?
5. What is incomplete dominance?
6. What is codominance?
7. What is pleiotropy?
8. What is epistasis?
9. What is polygenic inheritance?
10. Can the environment influence phenotype?
11. What are some recessively inherited human disorders?
12. What are some dominantly inherited alleles?
13. How do doctors test for genetic anomalies?
- amniocentesis
- chorionic villus sampling (CVS)
Figure 14.17 Testing a fetus for genetic disorders
(b) Chorionic villus sampling (CVS)
(a) Amniocentesis
Amniotic
fluid
withdrawn
A sample of chorionic villus
tissue can be taken as early
as the 8th to 10th week of
pregnancy.
A sample of
amniotic fluid can
be taken starting at
the 14th to 16th
week of pregnancy.
Fetus
Fetus
Suction tube
Inserted through
cervix
Centrifugation
Placenta
Placenta
Uterus
Chorionic viIIi
Cervix
Fluid
Fetal
cells
Fetal
cells
Biochemical tests can be
Performed immediately on
the amniotic fluid or later
on the cultured cells.
Fetal cells must be cultured
for several weeks to obtain
sufficient numbers for
karyotyping.
Biochemical
tests
Several
weeks
Several
hours
Karyotyping
Karyotyping and biochemical
tests can be performed on
the fetal cells immediately,
providing results within a day
or so.