Week 12
Genetics I
Chapter 11 pages 189-201
Genetics II
Chapter 11 pages 202-209
EXAM III RESULTS
Total Students = 39
Total Pass= 15 (38.5%)
Total Fail= 24 (61.5%)
Class Average = 63
Top Score = 94
Low Score = 32
EXAM III GRADE DISTRIBUTION
9
8
8
8
7
7
6
6
5
5
Number of Students
4
3
3
2
2
1
0
90-100
80-89
A
B
70-79
C
60-69
D
50-59
F
40-49
F
30-39
F
TROUBLE SPOTS
Questions answered incorrectly:
#2 (61.5% (24/39))
#3 (41% (16/39))
#9 (46% (18/39))
#19 (67% (26/39))
#26 (47% (23/39))
#49 (69% (27/39))
#s 10 and 50 were well answered in general
#49 A. MEIOSIS
B. Pairing of homologous chromosomes
only occurs in meiosis crossing
over
Pairing of x-somes
HOMEWORK
Chapter 12 ALL including Self-tests
EXAM III Extra Credit- DUE MAY 10th
Aneuploidy
Euploidy= Correct number of chromosomes in a
species
Aneuploidy= A change in the number of
chromosomes due to nondisjuction
CHANGES IN CHROMOSOME
STRUCTURE
Changes in chromosome structures are mutations
X-somes can break due to radiation, organic
chemicals and viruses
End of chromosomes break and can go back
together improperly which leads to chromosomal
mutations:
Deletions
Duplications
Translocations
Inversions
Deletions
Inversions
Duplications
Translocations
DNA exists as chromatin or as a chromosome
DNA- Deoxyribonucleic Acid
A POLYMER of NUCLEOTIDES
How do we know that certain
complications will arise if genes
are added or deleted to portions
of chromosomes?
Through the Study of Genetics!
Genetics is the study of biologically inherited traits
Ex. How will the deletion of section ‘a’ affect
disease?
Genomics is the study of all of the genes in an
organism
Genetics and Genomics
‘Inherited traits are determined by the elements
of heredity that are transmitted from parent
to offspring in reproduction; these elements
of heredity are called genes.’
DNA is the molecule of heredity
Gregor Mendel, 1822-1884
Austrian Monk
Developed ‘Particulate
Theory of Inheretance’
By studying Pea Plants
in the 1860s
Combined Math and
Biology!
Used statistics and laws
of probability to study
biology
The Father of Genetics
Darwin 1809-1882
Mendel studied garden pea plants to understand the units of heredity
WHY?
At the time, the ‘Blending Concept of Inheritance’ was widely accepted
Blending Concept of Inheritance= an offspring’s genetic makeup is intermediate
to that of its parents
Ex. A cross between red and white flowers will only generate PINK flowers
Is this true?
NO!! Because…
Red, Pink and
White flowers
result in the 2nd
Generation!
Diverse forms could
not evolve if the
blending theory was
correct.
If we only had intermediate forms with
little variation, how could all of the
diversity we see have evolved?
•Confused both Mendel and Darwin
•Genes had not been discovered and would not be discovered until 1869 by
Friedrich Miescher
•The molecular makeup of genes was discovered, but the function of genes was
still not well understood.
•By 1900 it was understood that chromosome number is nearly constant in the
cells of any species.
•Seemed likely that chromosomes were carriers of genes.
How did Mendel and others come to the
conclusion that chromosomes were the
carriers of genes?
Through the study of phenotypes and crossings of pea
plants with various traits
PHENOTYPE
GENOTYPE
The set of an organism’s
observable properties resulting
from the interaction of the organisms
genotype with its environment
The genes present in a
particular organism or
cell
‘ATCCGCATTACG’
Mendel’s 7 Pea Plant Traits
P = Parental Generation
F1= First Generation
F2= Second Generation
1.
2.
3.
4.
Garden Pea Plant
Pisum sativum
5.
6.
7.
Mendel’s Particulate Theory of
Inheritance
• Mendel used the scientific method to understand
inheritance in pea plants
• He created ‘pure’ or ‘true-breeding’ lines of plants
for specific traits (ex. Round or smooth seeds, purple
or white flowers…)
• He observed and tracked these phenotypes through
multiple generations of pea plants
• Based on his studies, he determined that hereditary
information is passed from parents to offspring in
the form of discrete “particles” (which we now refer
to as GENES)
Why study the Garden Pea Plant?
• Easy to cultivate
• Short generation time
• Can self pollinate
- Able to create ‘true-breeders’
• Can cross pollinate by hand
• Traits easy to observe
• Can observe dominant or
recessive characteristics
‘True-Breeding’
- Anther contain Sperm
- Ovules in ovary contain Eggs
- Pea plants are able to ‘selfpollinate’
- Therefore, offspring are identical
to the parents
- Mendel bred plants ‘true’ to ensure
the purity of each trait
Why secure the purity of each
trait?
• Had to ensure that the trait he was observing
was not confounded by other discrete
particles
• Ex. He had to make sure that a white colored
flower was truly white before making any
crosses
• His experiments would have failed because he
would have observed different outcomes each
generation
Cross-Pollination
After self pollinating
plants for several
generations to obtain
‘true-breeding’ plants
Mendel used the
anther from one truebred plant to
pollinate the Stigma
of another true-bred
plant= Cross Pollination
From plant A
onto the stigma
of plant B
Mendel’s Hypothesis
Hypothesis
Hereditary information is passed from parents
to offspring in the form of discrete “particles”
Mendel’s Observations (3:1, D:R)
Mendel’s Laws
Based on his observations of cross-pollination
studies:
1 LAW OF SEGREGATION
2 LAW OF INDEPENDENT ASSORTMENT
LAW OF SEGREGATION
Based on the hypothesis that if the blending
theory of inheritance were true, then a cross
should yield an “intermediate” phenotype in
comparison to the parents
Ex. Tall plant x Short plant = Medium plant
Mendel tested this by crossing plant varieties
that differed by only 1 single trait…
LAW OF SEGREGATION
Mendel performed ‘reciprocal’ crosses:
Dusted pollen of Tall plants onto Short plants
Dusted pollen of short plants onto Tall plants
All F1 resembled the TALL parent! NOT
intermediate!
Mendel allowed the F1s to self-pollinate  ¾ of
the F2 plants were Tall and ¼ of the F2 plants
were short!
ALL F1s were Tall
No intermediates observed!
ALL F1s would have had
the same genetic makeup
because the parents were
bred true.
ALL of the F1 generation plants would have had a Tt genotype
One T from parent 1 (bred true for TALL) and one t from parent 2
(bred true for SHORT)
What happens when you cross two F1 generation plants?
X
Gametes
A true-bred TALL plant gametes will only be T
A true-bred SHORT plant gametes will only be t
Gametes
THEREFORE, the ONLY resulting GENOTYPE for
the F1 generation is T t
F1 CROSS
X
The F1s are all
Tt, therefore when
Cross with each other
It is a ‘mono’(one type)
‘hybrid’ (Tt) cross
What will the GENOTYPES of the GAMETES look
like for this MONOHYBRID CROSS?
What will the GENOTYPES of the GAMETES
look like for this F1 MONOHYBRID
CROSS?
F1
F1
T
t
T
t
F1 GAMETES
F2 GENOTYPES
and PHENOTYPES
WHAT IS THE PHENOTYPIC RATIO OF TALL TO SHORT?
WHAT IS THE GENOTYPIC RATIO OF TALL TO SHORT?
3:1 TALL: SHORT
Dominant:Recessive
Monohybrid crosses ALWAYS result in a 3:1 ratio
The SHORT trait is masked by the TALL trait in
the F1 generation and is observed in the F2
generation
TALL is a dominant trait and SHORT is a recessive
trait
LAW OF SEGREGATION
1 Each individual has two factors for each trait
2 The factors ‘segregate’ during the formation
of gametes
3 Each gamete contains only one factor from
each pair of factors
4 Fertilization gives each new individual two
factors for each trait (haploiddiploid)
PAGE 192
Dominance
‘Tallness’ in pea plants is dominant to ‘shortness’
Tall =
T
Short=
t
If parent 1 = TT (tall plant) and parent 2 = tt (short plant)
ALL F1 generation plants will be Tt
Dominance
Genes occur at a particular ‘locus’ on a
chromosome
Alternative versions of the same gene are called
‘alleles’
The dominant allele masks the expression of the
recessive allele
Alleles= Alternative versions of the same gene
MOM
A gene occurs at a particular locus
DAD
If purple is dominant to white, the purple phenotype is observed,
but you are a carrier for white!
Remember: only 1 allele of each trait is in a gamete (meiosis!)
GENOTYPES
TT = Homozygous dominant
Tt = Heterozygous
tt = Homozygous recessive
Phenotypes
(Tall Plant)
(Tall Plant)
(Short Plant)
PUNNETT SQUARES
• Used to predict breeding outcomes
• Able to calculate probability of traits
Example:
Tt Tt
tt
tt
MENDEL’S LAW OF INDEPENDENT
ASSORTMENT
Mendel experimented with plants that differed
in 2 traits
The plants are hybrid in 2 ways therefore the
crosses between the F1 generation are
‘DIHYBRID CROSSES’
2 traits
Tall
Green pods
2 traits
short
Yellow pods
DiHybrid Cross Cont.’d
X
F1 GAMETES
?
?
Sperm
Eggs
DiHybrid Cross Cont.’d
X
TG
TG
Tg
Tg
tG
tG
tg
tg
F1 GAMETES
Sperm
Eggs
Mendel’s Dihybrid Cross
Hypothesis I
If the dominant factors always segregate
together (=TG) and the recessive factors
segregate together (=tg), then there would be
two phenotypes among the F2 plants ONLY,
tall plants (T) with green pods(G) and short
plants (t) with yellow pods (g)
Did Mendel observe this to be true?
NO!!!
Mendel’s Dihybrid Cross
Hypothesis II
If the four factors (T, G, t, g) segregate into the
F1 gametes independently, then there would
be four phenotypes among the F2 plants
Tall and green pods
Tall and yellow pods
Short and green pods
Short and yellow pods
Did Mendel observe this to be true? YES!!!!!
Mendel’s Dihybrid Cross
Observations 9:3:3:1
9:3:3:1
Dihybrid crosses always have this phenotypic ratio!!!
LAW OF INDEPENDENT
ASSORTMENT
1 Each pair of ‘factors’ segregates (assorts)
independently of the other pairs
2 All possible combinations of factors can occur
in the gametes
PAGE 194
Mendel and Meiosis
Homologous pairs of
chromosomes line up
randomly at the metaphase
plate
This allows for independent
segregation during gamete
formation
Probability
Wouldn’t it be nice to know the outcome of a
particular cross?
- Punnett squares enable us to calculate the
chance or probability of genotypes and
phenotypes of offspring
- How likely is it that an offspring will inherit a
specific set of two alleles, one from each
parent?
The Product Rule of Probability
What is the chance of offspring having:
EE
1/2
x
1/2
=
1/4
Ee
1/2
x
1/2
=
1/4
eE
1/2
x
1/2
=
1/4
ee
1/2
x
1/2
=
1/4
The Product Rule of Probability
In a monohybrid cross, we know that each
Child has a 25% (1/4) chance of having attached
Earlobes
The SUM Rule tells us that we can add together
all of the same phenotypic traits:
Ex. ¾ or 75% of the children will have unattached
Earlobes (¼ + ¼ + ¼ = 3/4)
Ratios
MONOHYBRID Crosses ALWAYS result in a:
3:1 ratio
3 Dominant: 1 Recessive trait
(Rr x Rr)
DIHYBRID Crosses ALWAYS result in a:
9:3:3:1 ratio
9 Dominant: 3 Dominant and Recessive: 3 Dominant
and Recessive :1 Recessive
(TtGg x TtGg)
YOUR TURN!
In Pea Plants, yellow seed color (Y) is dominant
over green seed color (y).
When two heterozygous plants are crossed,
what percentage of plants would have yellow
seeds? ¾ or 75%
What percentage would have green seeds?
¼ or 25%
YOUR TURN!
In humans, pointed eyebrows (B) are dominant
over smooth eyebrows (b). Mary’s father has
pointed eyebrows, but she and her mother
have smooth eyebrows. What is the genotype
of the father?
Mary’s father can’t have a BB genotype otherwise all of the offspring
would have pointed eyebrows. He can’t be bb otherwise he would have
smooth eyebrows. He MUST have a Bb genotype in order for Mary
to have smooth eyebrows.
Testcrosses
Testcrosses are performed in order to figure out
the genotype underlying a particular
phenotype
Mendel performed test crosses of F1 individuals
with “true-bred” individuals to figure out the
laws of segregation (that alleles segregate
independently during gamete formation)
Testcrosses
One-trait test cross:
Individual w/ Dominant phenotype is
heterozygous
Individual w/ Dominant phenotype is
homozygous
Testcrosses
Two trait test-crosses:
Individual w/ dominant phenotype is crossed
with one having the recessive phenotype
Is the fly on the left heterozygous or homozygous for wing and body color?
WE HAVE NO IDEA SO WE MUST TESTCROSS TO DETERMINE THE GENOTYPE!!
For fruit flies (Drosophila melanogaster) we know:
L = long wings
l = short (vestigial) wings
G=gray bodies
g =black bodies
What are the genotypes for these flies?
The black fly with short wings MUST be llgg
If these are the offspring between the
homozygous recessive (black/short
wings) and the gray body with long
wings, what was the gray/long fly’s
genotype?
llgg
x
?
=
What is the genotype for the gray/long fly?
For fruit flies (Drosophila melanogaster) we know:
L = long wings
l = short (vestigial) wings
If Dominant for both traits=
LLGG
If Heterozygous for both traits =
LlGg
G=gray bodies
g =black bodies
llgg
If Dominant Homozygous:
LLGG
x
llgg
Gametes
Gametes
LG
LG
LG
LG
lg
lg
lg
lg
Punnett Square
X
lg
lg
lg
lg
LG
LlGg
LlGg
LlGg
LlGg
LG
LlGg
LlGg
LlGg
LlGg
LG
LlGg
LlGg
LlGg
LlGg
LG
LlGg
LlGg
LlGg
LlGg
ALL of the flies would have the same phenotype
if the gray/long fly had a LG genotype!!
We know these are the offspring
and they are not all gray with long
wings!!! So…..
If Dominant Homozygous:
LlGg
x
llgg
Gametes
Gametes
LG
Lg
lG
lg
lg
lg
lg
lg
Punnett Square
lg
lg
lg
lg
LG
LlGg
LlGg
LlGg
LlGg
Lg
Llgg
Llgg
Llgg
Llgg
25%=Long/Black
lG
llGg
llGg
llGg
llGg
25%=Short/Gray
lg
llgg
llgg
llgg
llgg
25%=Short/Black
X
25%= LlGg, 25%= Llgg, 25%= llGg, 25%= llgg
25%=Long/Gray
MUST be heterozygous for both traits!!
This is the only way a homozygous recessive
fly could have been produced!
When crossing a heterozygous for two trait
Individual w/ an individual recessive for both
Traits the ratio is always:
1:1:1:1
Mendel’s Laws and Human Genetic
Disorders
Two types of human genetic disorders:
1 Autosomal (x-somes other than X or Y)
– Recessive
– Dominant
2 X-linked (x-somes that are X or Y)
Autosomal Patterns of Inheritance
Autosomal Dominant
Individual with AA or Aa HAS the disorder
a = recessive
Autosomal Recessive
Invididual with aa HAS the disorder
A= dominant
Pedigrees
Pedigrees are used to track patterns of
inheritance of a particular condition and to
determine dominance or recessiveness
For Example:
= MALE
= FEMALE
= A UNION
= A CHILD
Pedigrees
-The shaded/colored shapes do not indicate
whether the person is dominant or recessive
-Only indicates that the person is affected
Pedigrees
In these pedigrees, which is autosomal
dominant and which is autosomal recessive?
= MALE
= FEMALE
I Only the Child is affected
II Only the Parents are affected
Aa
Aa
aa
Autosomal recessive
HAS disorder
Autosomal RECESSIVE
 Most affected children have unaffected parents
 Heterozygotes (Aa)have an unaffected phenotype
 Two affected parents will always have affected children
 Close relatives who reproduce are more likely to have affected
children
 Both males and females are affected with equal frequency
Aa
Aa
aa
Autosomal DOMINANT
 Affected children will usually have an unaffected parent
 Heterozygotes (Aa) ARE affected
 Two affected parents can produce an unaffected child
 Two unaffected parents will not have affected children
 Both males and females are affected with equal frequency
Carriers
In Pattern I, the parents are Carriers for the condition, but they do not exhibit the
condition themselves
Is this pattern Autosomal
Dominant or Recessive?
*The double line indicates inbreeding/breeding
Between closely related individuals
(Inbreeding increased frequency of obtaining
the disorder
Is this pattern Autosomal
Dominant or Recessive?
Note that BOTH heterozygotes HAVE the
condition
Autosomal Recessive Disorders
1 Methemoglobinemia
2 Cystic Fibrosis
3 Nieman-Pick Disease
Methemoglobinemia
An accumulation of methemoglobin in the blood
causing the blood to appear blue instead of
red  skin appears blue in color
Hemoglobin
Methemoglobin
Those affected lack enzyme diaphorase that converts
Methemoglobin back to hemoglobin
(enzyme is coded for in gene on x-some 22)
Autosomal RECESSIVE trait
Cystic Fibrosis (CF)
• Most common lethal genetic disease among
Caucasians in the US (1/20=carrier, 1/2000
newborns has the disease)
• Caused by a defective chloride ion channel
(protein channel) located in the cell
membrane
• Cl- ions fail to pass through the channel which
in turn does not allow Na+ or water to pass
• Lack of water leads to thick mucus in the
bronchial tubes and pancreatic ducts
Cystic Fibrosis (CF)
Life expectancy is usually into the teens and twenties,
but some people can live as many as 35 years with
the disease
Gene therapy is currently being researched to
correct the defective gene that produces the
faulty protein
CFTR= Cystic Fibrosis
Transmembrane Conductance
Regulator
The CFTR gene
is located on
Chromosome 7
Summers of 1998 and 1999
Studied Cystic Fibrosis by researching the effect of various toxins
on the regulation of Chloride secretion in dogfish shark rectal
glands in Mount Desert Island Biological Laboratories in
Mount Desert Island, Maine
Performed dogfish shark rectal gland perfusions
Squalus acanthias
Nieman-Pick Disease
 Caused by defective versions of the same gene located on
chromosome 11
 Normally, Gene codes for enzyme, sphingomyelinase which
breaks down sphingomyelin (a lipid)
 Without proper functioning enzyme, lipid droplets
accumulate in the cells of the liver, lymph nodes and spleen
 Type A= lipid droplet buildup in brain neurological disorders
 Type B= milder form, protein has some function
 Children present with persistant jaundice, feeding difficulties,
enlarged abdomen, pronounced mental retardation
Autosomal Dominant Disorders
1 Osteogenesis Imperfecta
2 Hereditary Spherocytosis
Osteogenesis Imperfecta
• Autosomal dominant disorder
• Caused by mutations in 2 genes needed to
synthesize type I collagen
• Defective collagen I is produced
• Results in weak, brittle bones
• Defective collagen can combine with
normal collagen and can cause structural defects
• Incidence=1/5,000 live births
• Treated with drugs
Hereditary Spherocytosis
• Autosomal dominant genetic blood disorder
• Caused by defective copy of ankyrin-1 gene found on
x-some 8
• Leads to defective protein normally responsible for
the structure and shape maintenance of red blood
cells (RBCs)
• RBCs become spherical and burst
easily due to osmotic stress
• Incidence = 1/5,000
• Some cases (25%) are spontaneous mutations and
are not inherited by either parent
Mendel’s Laws and Human Genetic
Disorders
Two types of human genetic disorders:
1 Autosomal (x-somes other than X or Y)
– Recessive
– Dominant
2 X-linked (x-somes that are X or Y)
X-Linked Inheritance
• Refers to genes that are carried on the X chromosome
• Chromosome theory of inheritance (Thomas Hunt Morgan,
1900s)- specific alleles correspond specifically with the X
chromosome
• The Y chromosome lacks these alleles
• Males always receive an X-linked recessive mutant allele from
the female parent, therefore sex linked recessive traits appear
more frequently in males
• Males can not be carriers for X-linked traits
• Males express whatever allele is present on the xchromosome and are therefore ‘hemizygous’ for X-linked
traits
Morgan’s Observations
Used fruit flies (Drosophila melanogaster) b/c
they have the same chromosome pattern as
humans.
White eyes only
Observed in
Males!
Males can only
Inherit the recessive
Allele from the
Female parent
Note: the allele is now
associated with the
X chromosome
The F1s will all have red eyes because the female is XR homozygous dominant!
What will the F1 gametes look like?
XR
Y
XR
Xr
The F1 Cross
Result of F1 cross
is that only 1
male has white
eyes
Females will only have
white eyes when they
receive a recessive
allele from both parents
Human X-linked Recessive
Disorders
1 Color Blindness
2 Hemophilia
3 Muscular Dystrophy
4 Adrenoleukodystrophy
5 Menkes Syndrome
Color Blindness
• 3 classes of cone cells in the retina of the
human eye and each contains either:
1. Blue-sensitive pigment proteins
2. Red-sensitive pigment proteins
3. Green-sensitive pigment proteins
Red and green sensitive pigment proteins are on the
X-chromosome
Blue-sensitive pigment proteins are autosomal
Usuallly passes from grandfather to grandson
through a carrier daughter
X-linked Recessive Pedigree
8% of Caucasian males have
red-green colorblindness
Bright Green= tan
Olive green= brown
Reds= reddish brown
Some only see yellow, blue, black
white and gray
Hemophilia
1/10,000 males is a hemophiliac
Two types:
Hemophilia A- due to absence/minimal
presence of clotting factor VIII
Hemophilia B- due to absence of clotting factor
IX
Hemophiliacs lack the ability to clot blood or
they clot blood very slowly
Hemophilia: a Royal Pain
Queen Victoria
Queen of England (and Ireland)
b.1819- d.1901
9 children
Hemophilia “A Royal Disease”
Other Types of Inheritance
1 Multiple Allelic Traits
2 Incomplete Dominance and Incomplete
Penetrance
3 Pleiotropic Effects
4 Polygenic Inheritance
Multiple Allelic Traits
When traits are controlled by multiple alleles,
the gene exists in several allelic forms
Ex. Human blood types are A B O
There are 3 possible alleles that determine the
blood type BUT….
The A B O blood type is controlled by a single
gene pair
Alleles determine the presence or absence of antigens
on red blood cells
IA = A antigen on red blood cells
IB = B antigen on red blood cells
i = Neither A nor B antigen on red blood cells
Possible phenotypes or genotypes:
Phenotype
Genotype
A
IAIA, IAi
B
IBIB, IBi
AB
IAIB
O
ii
CODOMINANCE
Inheritance of blood types in humans is an
example of Codominance
Both IA and IB are fully expressed
in the presence of the other
A person who is IAIB will have blood type AB
IA is not dominant over IB
IB is not dominant over IA
IA and IB are dominant over ii
AO
AO
AA
AA
BO
BB
AB
Universal
Recipient
OO
Universal
Donor
Incomplete Dominance and
Incomplete Penetrance
Incomplete Dominance:
When the heterozygote (Aa) exhibits an
intermediate phenotype
Incomplete Penetrance:
When the dominant allele in a heterozygote
does not lead to the dominant phenotype
The dominant allele may not always determine
the phenotype
Incomplete Dominance
R1 = allele for red pigment
R2 = allele for no pigment
Incomplete Penetrance
Ex. Polydactyly (extra digits on
hands, feet or both)
Is inherited as autosomal dominant
BUT, not all individuals exhibit the trait who
Inherit the dominant allele
Other genes may influence the appearance of
the trait
Pleiotropic Effects
Occurs when a single mutant gene affects two or more
distinct, unrelated traits
Ex. Sickle-cell disease
Results from a mutation in gene coding for hemoglobin
polypeptide
Mutation causes change in 1 amino acid in the
hemoglobin polypeptide
Causes RBCs to be sickle-shaped
-Slows blood flow -Decreased O2 carrying
capacity
-Clogs blood vessels
-Resistant to Malaria!
-Cells have shorter life span -Severe Anemia
Polygenic Inheritance
The expression of a trait is controlled by two or more sets of
alleles at different loci on different chromosomes =polygenes
(each allele contributes to the phenotype)
Dominant alleles have a quantitative effect on the phenotype=
they are additive
This leads to ‘multifactorial traits’continuous variation in
phenotypes and genotypes
Ex. To what degree does a gene contribute to a trait? How much
is due to Environment?
The study of this kind of inheritance= Quantitative Genetics
(estimates of heritability- I did this by breeding fish!!)
Doiminant pairs of genes
Multiple outcomes due to several pairs of
genes controlling a trait
Individual genes of a polygenic trait follow
Mendel's laws, but together do not
produce Mendelian ratios =bell shaped
curve
Orange shading represents environmental
influence
WHAT KIND OF HUMAN TRAITS EXHIBIT
POLYGENIC/MULTIFACTORIAL
INHERITANCE?
WHAT KIND OF HUMAN TRAITS EXHIBIT
POLYGENIC/MULTIFACTORIAL
INHERITANCE?
QUANTITATIVE TRAITS:
• Skin color (allele frequencies are the best indicator of shared
heritage in a population, therefore, skin color alone does not
effectively indicate a person's ethnic and genetic background,
sun exposure is an environmental factor)
• Height (varies continuously in a bell shape distribution, Diet
and health are environmental factors)
• Hair color (little environmental influence)
• Body Mass (Diet and health are environmental factors)
• Finger print patterns (environmental influence possible
during gestation)
• Eye color (little environmental influence, five human eye
colors, interact additively)
HAIR COLOR
– Hair color is controlled by alleles on chromosomes
3, 6, 10, and 18.
– The more dominant alleles that appear in the
genotype, the darker the hair.
Pepper Color
Gene 1: R= red
r= yellow
Gene 2: Y= absence of chlorophyll (no green)
y= presence of chlorophyll (green)
Pepper Color
Genotypes:
Phenotypes:
R-/Y- : (red/no chlorophyll)
R-/yy : (red/chlorophyll)
rr/Y- : (yellow/no chlorophyll)
rr/yy : (yellow/chlorophyll)
Red
Brown/orange
Yellow
Green
“-” Indicates that genotype could be hetero or homozygous
Pepper Color
• Try crossing a brown pepper (RRyy) with a
yellow pepper (rrYY).
• Which trait will your offspring (F1 generation)
produce?
• What traits are produced when you cross two
of the peppers found in the F1 generation?
THIS WEEK IN YOUR LAB
DNA Fingerprinting:
Individual 1 2 3 4 5 6 7 8 9 10
Restriction Fragment Length
Polymorphisms (RFLPs)