Transcript What Happens When Heredity Follows Different Rules?

A Look at Genetic Complexities
Chapter 12 Notes
The Exceptions to Mendel’s Rules
Section 12.2

At the end of this lesson, YOU will be able to:
◦ Distinguish between alleles for incomplete
dominance and codominance.
◦ Explain the patterns of multiple allelic and
polygenic inheritance.
◦ Analyze the pattern of sex-linked inheritance.
◦ Summarize how internal and external environments
affect gene expression.
dd
Heterozygous Chin Dimple
(male)
X
d
No Chin Dimple
(female)
Dd
D
d
d

His 4 conclusions were:
◦
◦
◦
◦
The
The
The
The
Rule of Unit Factors
Rule of Dominance
Law of Segregation
Law of Independent Assortment
http://www.pbs.org/wgbh/nova/orchid/images/amat_mendel.jpg


Sometimes,
patterns of
inheritance are not
as simple as
Mendel’s Rules
imply.
The exceptions to
Mendel’s Rules are
when nature uses a
different method of
determining traits.

The Law of
Independent
Assortment can be
broken when genes
are found close
together on the same
chromosome.
◦ The genes will appear
linked, or show up
together.
◦ The closer the genes
are to each other the
more they will be
inherited together.


Usually, a dominant
gene produces a
protein for the trait.
The recessive allele
either produces a
nonfunctional protein
or no protein at all.
◦ So we see the dominant
trait in hybrids because
it is the only trait
expressing a protein.
DNA
mRNA
mRNA
Protein

When heterozygous
individuals show an
intermediate
phenotype between
the two homozygous
phenotypes.
◦ Having one copy of a
gene does not produce
enough protein to
completely mask the
recessive allele.
http://www.miracosta.edu/home/rmooney/Mendelian%20genetics_files/slide0015_i
mage033.jpg

Snapdragons
◦ If you cross a red
flower and a white
flower, the resulting
hybrid will be pink.
 RR = red flower
 rr = white flower
 Rr = pink flower
◦ If you cross two pink
flowers (Rr), you get:
 25% Red Flowers
 50% Pink Flowers
 25% White Flowers
R
R
R
r
r r
Rr Rr
Rr Rr
R r
RR Rr
Rr rr

Hair
◦ Straight (HH)
◦ Wavy (Hh)
◦ Curly (hh)

When a
heterozygous
individual shows
the phenotypic
traits of both
alleles.
◦ Both alleles produce
a protein, which are
seen in the hybrids.
◦ The traits do not
blend!

Feather Color in
Chickens
◦ A black chicken
would be BB.
◦ A white chicken
would be WW.
◦ A hybrid, BW, would
have a checkered
appearance.
 Both white and black
pigments are seen in
the offspring.
B
B
W
BW
BW
W
BW
BW
B
B
BB
W
BW
W
BW
WW

Sickle Cell

When a trait is
controlled by more
than two alleles.
◦ Each individual only
owns two alleles, but
others in the
population may
possess different
types.

Fur Color in Rabbits
◦
◦
◦
◦
C = Dominant allele
ch = Himalayan fur
cch = Chinchilla fur
ca = Albino fur
C
ch
ca cch
cbcb- Bugs Bunny

Blood Types
◦ IA, IB, or i
IAIA or IAi
IBIB or IBi
IAIB
ii

When one trait is
controlled by more
than one gene.
◦ The genes may be on
the same or different
chromosomes.
◦ Both genes have a
single phenotypic
effect.

Coat Color in
Labrador Retrievers
◦ Controlled by two
different genes, the B
gene and the E gene.
◦ A dihybrid cross of two
black labs (BbEe x
BbEe) results in:




9 Black Pups
3 Chocolate Pups
3 Golden Pups
1 Golden Pup with a
brown nose and light
eyes.
http://www.oakhillkennel.com/library/color.html

Eye Color
◦ Brown Gene
◦ Green Gene

When traits are
determined by
several factors from
the genetic makeup
and the organism’s
environment.
◦ The genes only
represent the potential.
◦ Environmental
influences turn on the
genes at different
times and in different
amounts.

Temperature,
nutrition, light,
chemicals, and
infections can
influence gene
expression.
◦ Arctic Foxes have
coats that change
color due to
temperature.

Height, Intelligence, Cholesterol, Weight,
Mental Illness, etc.
Sex Determination and Sex-linked Traits
Section 12.2

Humans have a total
of 46 chromosomes,
or 23 pairs:
◦ 22 pairs of autosomes
◦ 1 pair of sex
chromosomes

Autosomes
◦ All of the
chromosomes that
determine the traits
other than sex.
◦ Come in different sizes
with different genes on
them.
◦ Pairs 1-22

Sex Chromosomes
◦ Determine the sex of
the individual.
◦ Pair 23
 In females, these
chromosomes match in
the form of XX.
 In males, these
chromosomes are
different, as in XY.

The combination of
sex chromosomes
decides if you are a
boy or a girl.
◦ A mother (XX) can only
supply eggs that have
an X chromosome.
◦ The father (XY) has
some sperm with a X
chromosome and some
with a Y chromosome.
X
X
X
XX
XX
Y
XY
XY
G- 50% XX; 50% XY
P- 50% female; 50% male

Genes that are
located on the sex
chromosomes.
◦ The X chromosome
contain many
important genes that
are necessary for
survival.
◦ The Y chromosome
contains the SRY
gene which
determines
maleness.


First observed in fruit
flies (Drosophila).
Fruit flies have either
red or white eyes.
◦ Thomas Hunt Morgan
noticed that all of the
white-eyed flies were
male.
◦ Therefore, eye-color in
flies is a sex-linked
trait.


Because the X
chromosome is much
larger than the Y,
most sex-linked
traits are on the X.
When writing the
alleles for these
traits, you must
include the
chromosomes that
the individual has:
Y
Y Chromosome
(no alleles)
R
X
X Chromosome
(red-eyed allele)
Xr
X Chromosome
(white-eyed allele)

Because males have
only one X
chromosome, they
are more likely to
get a single
defective copy.
XRY
◦ XRY- red-eyed male
◦ XrY- white-eyed male
r
XY


Because females
receive two X
chromosomes, they
are more likely to get
a dominant allele
that can cover the
effects of the
recessive trait.
A carrier female has
a recessive allele but
does not show the
trait (heterozygous)
R
R
X X
Homozygous Red-eyed
Female
R
r
X X
Carrier Female
XrXr
White-eyed female (rare)
Homozygous Red-eyed Female x White-eyed Male
XRXR
Xr
XR
XR
XR Xr
XR Xr
XrY
Y
XR Y
XR Y
G- 50% XRXr
50% XRY
P- 50% red-eyed female
50% red-eyed male
Heterozygous Red-eyed Female x Red-eyed Male
XRXr
XRY
XR
Y
XR
XR X R
XR Y
Xr
XR X r
Xr Y
G- 25% XRXR
25% XRXr
25% XRY
25% XrY
P- 50% red-eyed female
25% red-eyed male
25% white-eyed male
Understanding Pedigrees
Section 12.1

A graphic
representation of
traits inherited within
a family.
◦ Allows scientists to
trace the history of a
genetic disorder.
◦ Uses symbols to
represent individuals.
 Circles represent females
 Squares represent males
 If the symbol is shaded,
the individual is affected
by the trait.
Normal Female
Normal Male
Affected Female
Affected Male

Inherited traits can
be followed from
generation to
generation.
◦ Horizontal lines
connect two
individuals who have
mated.
II
◦ Vertical lines
represent the
offspring of a union.
I
Bb
Bb
1
2
Bb
bb
BB
Bb
1
2
3
4
5

Sex-Linked vs.
Autosomal
◦ If more males are
affected by a trait
than females, it is
probably sex-linked.
◦ If it affects males and
females equally, it is
probably autosomal.

Dominant vs.
Recessive
◦ If a trait skips a
generation, it is
recessive.
◦ If the trait is found in
each generation, it is
probably dominant.

Identifying
Genotypes
◦ If any males are
carriers, the trait is
autosomal.
◦ If a male has a sexlinked trait, his
mother was probably
a carrier.



Affects males and females equally.
Skips generations (appears in some
generations but not in others).
Males can be carriers


Affects males and females equally
Does not skip any generations.


Affects males more than females.
Skips generations.
◦ Must use the chromosomes (XY or XX)
Are males affected more frequently that females?
NO
Autosomal Disorder
A- normal
a - albino
Does the disorder skip generations?
YES
Recessive Disorder
(P1)
Autosomal Recessive
Are males affected more frequently that females?
YES
Sex-Linked Disorder
Does the disorder skip generations?
YES
+ = normal
Recessive Disorder
H = hemophilia
Sex-Linked Recessive
Genetic Trait: ACHOO
(Sneezes in response to light)
A
#1- Is this trait sexlinked or autosomal?
B
#2- Is this trait dominant
or recessive?
#3- What is the genotype
of individual A?
C
#4- What is the genotype
of individual B?
#5- What is the genotype
of individual C?
#6- What is the genotype
of individual D?
D

A picture of an
individuals
chromosomes.
◦ Homologous
chromosomes are
paired up.
◦ Pairs are arranged by
size.
◦ Karyotypes can help
diagnose
chromosomal
disorders.

When arranging the
chromosomes:
◦ Autosomal
Chromosomes are
placed in order by
size.
◦ The Sex
Chromosomes are
pair 23.

What to look for:
◦ The Sex
Chromosomes:
 Male (XY) or Female (XX)
 Is there an odd number
(XXY, XYY, XO, XXX)
◦ The Autosomes
 Are there two or three
chromosomes for pair
21?
 Trisomy 21  Down
Syndrome
Number of Autosomes:
44
Number of Sex-Chromosomes:
1
Karyotype:
45 (X)
Phenotype:
FemaleTurner Syndrome
Number of Autosomes:
44
Number of Sex-Chromosomes:
3
Karyotype:
47 (XYY)
Phenotype:
Male
Jacob’s Syndrome
Number of Autosomes:
44
Number of Sex-Chromosomes:
3
Karyotype:
47 (XXY)
Phenotype:
Male
Klinefelter Syndrome
Understanding Blood Types

Your body produces
antibodies that attack
any foreign objects
within you.
◦ Usually, this fights
bacteria, viruses, or
fungi.

All of your cells have
antigens on their
surface.
◦ Antigens are cellular
nametags.
◦ Your body makes
antibodies to fight off
anything without your
particular antigen.


Your special
antigens are made
by your DNA.
The antigens found
on the red blood
cells determine
your blood type.
◦
◦
◦
◦
Type
Type
Type
Type
A
B
AB
O
Genotype
IAIA or IAi
Antigens
A antigens
Antibodies
Anti-B
antibodies
Genotype
IBIB or IBi
Antigens
B antigens
Antibodies
Anti-A
antibodies
Genotype
I AI B
Antigens
A antigens and
B antigens
Antibodies
No Antibodies
Genotype
ii
Antigens
No antigens
Antibodies
Anti-A and
Anti-B
antibodies

Another antigen on
the surface of the
RBC, is the Rhesus
Factor.
◦ Named after it was
discovered in Rhesus
Monkeys


People who have the
Rh factor are
positive.
People without the
Rh factor are
negative.
Commonly, a
AntiAntiA
B rh
person’s blood type
combines their ABO
type and Rh factor. Type A+
AntiRh
AntiB
AntiRh
AntiB
AntiRh
Type ABAntiA
rh
AntiA
rh
◦ Type A neg.
◦ Type O pos.
rh


A person cannot
receive any blood that
contains an antigen
that they posses the
antibody for.
◦ Type A individuals
produce anti-B
antibodies.
◦ Giving that person type B
blood can have
dangerous effects.
◦ The anti-B antibodies will
cause the Type B blood to
stick together.
 This is called clumping.

The Universal
Recipient
◦ Produces no antibodies
◦ Can receive all types of
blood
◦ Type AB+

The Universal Donor
◦ RBC’s have no
antigens.
◦ Can give blood to
anyone
◦ Type O-
A
A
I I
Type A
x
B
B
I I
Type B
B
I
B
I
IA
A
B
I I
A
B
I I
G: 100% IAIB
A
I
A
B
I I
A
B
I I
P: 100% AB
Type AB x
IAIB
Type O
ii
i
i
IA
A
I i
A
I i
G: 50% IAi
B
I
B
I i
B
I i
P: 50% Type A
50% IBi
50% Type B
Hospital Mix-Up
On a busy night at the Plainsboro Hospital, three families
delivered three healthy baby boys. Unfortunately, the babies
became mixed up during a rush and no one knows which baby
belongs to which family. The nurses were able to take blood
samples from each parent and each baby. Use your knowledge
of blood type genetics to figure out which baby belongs to each
family.
Parent
Blood Type
Baby
Blood Type
Mr. Robinson
AB
Baby #1
O
Mrs. Robinson
B
Baby #2
AB
Mr. Jones
O
Baby #3
A
Ms. Jones
AB
Mr. Jackson
B
Ms. Jackson
B
Baby #1 belongs to the Jacksons
Baby #2 belongs to the Robinsons
Baby #3 belongs to the Jones

Codominance

Multiple Alleles

Polygenic
◦ Both A and B are
dominant.
◦ In a hybrid (AB) both
types of antigen will be
present.
◦ The ABO blood group
has three alleles that
produce four
phenotypes.
◦ Two genes control
blood type: ABO and Rh
factor
When Genetics Goes Wrong

Inheritance
◦ Autosomal Recessive
◦ Chromosome #7

Symptoms
◦ Abnormally thick
mucous clogs pores
in lungs, liver,
pancreas.
Gene Therapy is a hopeful
avenue of treatment for those
with cystic fibrosis.
Here’s how it works:
1. Insert a working copy of the
gene into a virus.
2. Load the virus into an
inhaler.
3. Have the patient breath in
the virus with the working
copy.
4. The virus then injects its
DNA and the working CF
gene into the patient’s cells
What would be one potential
downside to using gene
therapy?

Inheritance
◦ Autosomal Recessive
◦ Chromosome # 12

Symptoms
◦ Victims are unable to
metabolize
phenylalanine
properly.
◦ Leads to mental
retardation.
All babies are tested for PKU in the first few days.
How would being diagnosed with PKU
affect your life?

Inheritance
◦ Autosomal
Codominant
◦ Chromosome # 11

Symptoms
◦ Defective hemoglobin
becomes sickleshaped
◦ Pain crises result
when, cells clog
blood vessels.
http://www.ehponline.org/docs/2004/112-6/bloodcells.jpg
AA
Normal RBC/
Susceptible to Malaria
AS
Normal RBC and Sickle
Cells/
Resistant to Malaria
SS
Sickle Cells/
Resistant to Malaria
If sickle-cell is so
bad, why has the
gene not been taken
out of the genome?

Inheritance
◦ Autosomal Dominant
◦ Chromosome # 4

Symptoms
◦ Progressive
neurological disorder.
◦ Nerve cells begin to
deteriorate resulting in
a loss of coordination.
◦ Begins in late 40’s or
early 50’s.
Huntington’s Disease is autosomal dominant.
If one of your parents have it, you have a 50%
chance of inheriting this progressive disorder.
Question #1
Genetic testing can determine if you have
inherited the dominant allele or not. If
one of your parent’s had it, would you
want to know if you have the disease or
not?
Question #2
Should the results of genetic testing be
given to employers by insurance
companies? Is having the trait cause for
firing somebody, even if they have not
shown any symptoms?
h
h
Hh
Hh
H
hh
hh
h

Inheritance
◦ Sex-linked Recessive
◦ X Chromosome

Symptoms
◦ Unable to distinguish
between red and
green colors.
How would colorblindness affect
the way you see the world?
Tritanopia
Deuteranopia
Protanopia
Normal Vision

Inheritance
◦ Sex-linked Recessive
◦ X Chromosome

Symptoms
◦ Unable to clot
properly because of
missing Factor VII.
◦ Seen in the Royal
family of Britain

Inheritance

Symptoms
◦ Chromosomal
Nondisjunction
◦ Trisomy 21
◦ Mild mental
retardation
◦ Simian Crease,
Epicanthal fold,
shorter limbs, poor
muscle tone,
protruding tongue
Women over the age of 35
increase the chances of a DS
child up to 1 in 378 (over 45
is 1 in 30).
An amniocentesis extracts
some fetal cells to prepare a
karyotype.
If you found out that your
child would be born with
Trisomy 21 (Down
Syndrome), would you
support terminating the
pregnancy?

Polygenic Traits
◦ Eye Color- 2 genes
◦ Skin Color- 3 genes

Multifactorial
◦ Height
◦ Cholesterol
◦ Behavioral Traits