Transcript ppt lesson incomplete dominance codominance

Beyond Mendelian
Inheritance
INCOMPLETE DOMINANCE
-NEITHER ALLELE IS COMPLETELY DOMINANT
OVER THE OTHER
-THE HETEROZYGOUS PHENOTYPE IS
A BLENDING OF THE TWO
HOMOZYGOUS PHENOTYPES
Red flower = RR
Pink flower = Rr
White flower = rr
A trait exhibits incomplete dominance is the pitch of human
male voices:
-Lowest pitch (LL) and highest pitch (ll), but the intermediate
range baritones are (Ll)
Guess the
genotypes:
______
______
Sample problem:
Red snapdragon flowers (R) are incompletely
dominant to white snapdragon flowers (r).
A heterozygous flower is crossed with a white flower.
What is the genotypic and phenotypic ratios of the
offspring?
CODOMINANCE
-BOTH THE DOMINANT ALLELES ARE
EXPRESSED IN THE HETEROZYGOUS
INDIVIDUAL.
-USE 2 DIFFERENT CAPITAL LETTERS TO
RERESENT THE DOMINANT ALLELES
Cattle:
A homozygous
red bull and a
homozygous
white cow will
produce a
heterozygous
roan (spotted)
offspring
Red cow ______
White cow ______
Roan cow ______
Sample problem:
Red and white coat color are co-dominant in cattle.
Two heterozygous cows are crossed. What is the
genotypic and phenotypic ratio of the offspring?
MULTIPLE ALLELES
Several dominant alleles and/or recessive
alleles can be combined to create multiple
phenotypes.
Blood Type
In human blood, type A blood and type B blood
are codominant. However, there is a recessive
allele for type O.
Type A and B show regular dominance over this
recessive allele. Thus, the only way to be type
O is to be homozygous recessive.
BLOOD TYPE
Type A
Type B
Type AB
Type O
CAN RECEIVE FROM:
CAN DONATE TO:
Sample Problem #1:
Adam Sandler is homozygous for type A blood.
Megan Fox is heterozygous for type B. If they have
kids what will be the genotypic and phenotypic ratios
of the possible kids?
Human Blood Genotypes and
Phenotypes
Phenotype
• 1.
• 2.
• 3.
• 4.
Genotype(s)
Sample Problem #2:
Jimmy Fallon has type O blood. Jennifer
Aniston has type AB blood. If they have kids
what will be the genotypic and phenotypic ratios
of the possible kids?
Sample Problem #3:
Channing Tatum has type A blood. Ms. Palmeri
has type B blood. They have a baby with type O
blood. How is this possible? Show your work!
Polygenic Traits
• Most of your traits are controlled by the
interaction of many genes.
• Multiple genes working together produce a
continuous distribution in a “Bell Shape”
curve of degrees.
Examples of Polygenic Traits
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•
•
•
•
•
•
Body Type
Height
Skin Color
Hair color
Eye color
Intelligence
We often see the
famous “Bell Curve”
Individual genes of a
polygenic trait follow
Mendel's laws but
together do not
produce Mendelian
ratios.
Recent studies show …
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•
•
•
•
•
Hypertension
Diabetes
Cancers
Allergies
Cardiovascular diseases
Behavioral traits (alcoholism and phobias)
…..have some genetic link but also
environmental explanation.
Genetic Diseases
Autosomal Dominant, Autosomal
Recessive, and Sex-Linked
Autosomes =
first 22 pairs
ofchromosomes
Sex
Chromosomes =
23rd pair of
chromosmes (X
and Y)
Autosomal Dominant
• Autosomal dominant is one of several ways that
a trait or disorder can be passed down through
families.
• Caused by the presence of a dominant
allele.
• If a disease is autosomal dominant, it means you
only need to get the abnormal gene from one
parent in order for you to inherit the disease.
One of the parents may often have the disease.
Huntington’s Disease
• a neurodegenerative genetic disorder that
affects muscle coordination and leads to cognitive
decline and psychiatric problems
• It typically becomes noticeable in mid-adult life.
• HD is the most common genetic cause of
abnormal involuntary writhing movements
HH or Hh = Huntington’s disease
hh= normal
Neurofibromatosis
• a genetic disorder characterized by a number of remarkable skin
findings including multiple cafe au lait (coffee with milk) spots,
multiple benign tumors on the skin, thick and misshapen
nerves, and freckles in the armpit and groin.
• The cafe au lait spots increase in number and size with age.
• increased risk of scoliosis, optic gliomas (benign tumors on the
optic nerve), epilepsy, and learning disability
• inherited in an autosomal dominant manner and is due to
mutation of the NF1 gene (in chromosome band 17q11) that
encodes a protein called neurofibromin.
• Half of cases are due to new mutations in the NF1 gene.
Prenatal testing is available. Also called von Recklinghausen
disease.
NN or Nn = Neurofibromatosis
nn= normal
Autosomal Recessive
• Caused by inheriting 2 recessive alleles.
• An autosomal recessive disorder means two
copies of an abnormal gene must be present in
order for the disease or trait to develop (aa).
• A person who is heterozygous (Aa) is considered
a “carrier” of the gene.
Albinism
• a defect of melanin production
that results in little or no color
(pigment) in the skin, hair, and
eyes.
AA = normal
Aa = carrier
aa = albino
Tay-Sach’s Disease
• Deadly disease of the nervous system
• body lacks a protein that helps break down a
chemical found in nerve tissue
• Without this protein, the chemical build up in cells,
especially nerve cells in the brain.
• Symptoms appear at 3-6 months old
• Death in early childhood 3-5 years old
• Common among the Ashkenazi Jewish population
• About 1 in every 27 members of the Ashkenazi
Jewish population carries the Tay-Sachs gene
TT= normal
Tt= carrier
tt= Tay Sach’s
Cystic Fibrosis
• Causes thick, sticky mucus to build up in the lungs,
digestive tract, and other areas of the body.
• It is one of the most common chronic lung diseases in
children and young adults.
• An estimated 1 in 29 Caucasian Americans have the
CF gene.
• The disease is the most common, deadly, inherited
disorder affecting Caucasians in the United States. It's
more common among those of Northern or Central
European descent.
• Most children with CF are diagnosed by age 2.
• A small number, however, are not diagnosed until
age 18 or older. These patients usually have a milder
form of the disease and live until their mid- 30’s.
CC= normal
Cc= carrier
cc= cystic fibrosis
Sample Problem #1.Albinism is a recessive
disorder. Mr. Ward is and his wife are both heterozygous,
making them carriers of the albinism gene. What’s the
chance their next child will be albino?
A. 50%
B. 25%
C. 0%
D. 75%
0%
75
%
0%
0%
0%
25
%
50
%
0%
Sample Problem #2. Tay Sach’s is a recessive disorder. A
normal person marries a carrier of Tay Sach’s disease.
What is the percent chance of them having a child that is
a carrier?
A. 0%
B. 25%
C. 50%
D. 75%
0%
75
%
0%
50
%
0%
25
%
0%
0%
Huntington’s disease is autosomal dominant.
Olivia Wilde has Huntington’s disease. What is her
genotype?
A. HH
B. Hh
C. Hh
D. HH or Hh
0%
HH
or
Hh
0%
Hh
0%
Hh
HH
0%
Sex-Linked Inheritance
• Follows Mendel’s principle of
dominance however the genes that are
located on the X chromosome
• Sex chromosomes (X and Y)
• Female = XX Male = XY
XH = dominant allele
Xh = recessive allele
Because the allele is located on the X
chromosome, sex-linked genetic disorders
are more common in males!
Sex-Linked Recessive
Disorders
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Hemophilia
Duchenne’s Muscular Dystrophy
Red-Green Colorblindness
Male Pattern Baldness
Sex-Linked Example
Hemophilia (Xh)is a sex linked recessive
disorder.
Female Genotypes
Phenotype
1.
1.
2.
2.
3.
3.
Male Genotypes
Phenotype
1.
1.
2.
2.
Sample Problem #1
Hemophilia is a sex-linked recessive condition.
Beyonce is a carrier of hemophilia and Jay-Z is
normal. What are the chances of them having a
child with hemophilia?
Sex Linked Formative
Jimmy Fallon is colorblind and Tina Fey is a
carrier. What are the chances of them having
a color blind child? Circle the color blind
children.
Xb
Y
XbY
X
XBXb
50% Chance of colorblindness
XB
XBXb
XBY
Genotypes
Xb
XbXb
XbY
Phenotypes
XBXb , XbXb , XBY , XbY
1 Colorblind : 1 Normal Vision
Sample Problem #3
Will Smith is normal for male-pattern baldness,
but Jada Pinkett Smith is a carrier. What are
the chances of their daughter, Willow, being a
carrier? Is it possible for their son, Jaden, to
have inherited male pattern baldness?
Sex-Linked Dominant
Disorders
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Fragile X Syndrome
Rett Syndrome
Charcot–Marie–Tooth disease
Vitamin D resistance Rickets