Non-Mendelian and
Pedigrees
Elston Eusores, MBio
Incomplete Vs. Co-dominance
• Codominance - A form of inheritance in which both
alleles are equally shown.
• Incomplete dominance - A form of inheritance in which
the heterozygous alleles are both expressed, resulting in
a combined phenotype.
– Most commonly found in plants.
• A red and a white allele gives pink. If it were
codominance, you would see the red and white colors.
Human Genetics: Karyotypes
46 TOTAL
23
homologous
pairs
46 TOTAL
Chromosomes
23
homologous
pairs
What is the difference between an Autosome and a Sexchromosome?
• Autosomes are the first 22
homologous pairs of human
chromosomes that do not
influence the sex of an
individual.
• Sex Chromosomes are the
23rd pair of chromosomes
that determine the sex of an
individual.
Autosomal Traits
• Genes located on Autosomes control
Autosomal traits and disorders.
2 Types of Traits:
• Autosomal Dominant
• Autosomal Recessive
Autosomal Recessive Traits
• In order to express the trait, two recessive alleles
must be present.
• What would be the genotype of an individual with an
autosomal recessive trait? (A = dominant)
– aa
• What would be the genotype of an individual
without the autosomal recessive trait?
– AA or Aa
– Aa – called a Carrier because they carry the
recessive allele and can pass it on to offspring, but
they do not express the trait.
Albinism
Defect of melanin production that results in little or
no color in the skin, hair, and eyes
Albinism
Albinism
How does
it
happen?
Affected
Genotype:
aa
Cystic Fibrosis
Disease that causes the
body to produce unusually
thick, sticky mucus that:
•Clogs the lungs and leads
to lung infections
• Obstructs the pancreas
• Stops natural enzymes
from helping the body
break down and absorb
food
How does
it
happen?
Affected
Genotype:
cc
Sickle Cell Anemia
Caused by an abnormal
hemoglobin shape which
causes the red blood
cells to have a crescent
shape.
Red blood cells carry oxygen.
How does
it
happen?
Affected
Genotype:
ss
Tay–Sachs disease
• Symptoms:
– a build up of lipids in the brain
– Seizures
– blindness
• Mainly occurs in Jewish people
Tay-Sachs Disease
PKU (phenylketournia)
• symptoms;
– cannot break down the specific amino acid (phenylalanine found in
foods like milk)
– results in brain damage
• Mainly occurs in people of European descent
Autosomal Dominant Traits
• If dominant allele is present on the autosome, then the individual will
express the trait.
• What would be the genotype of an individual with an autosomal
dominant trait?
– AA and Aa (Heterozygotes are affected)
• What would be the genotype of an individual without the autosomal
dominant trait?
– aa
Huntington’s Disease
Causes the break down of
brain cells, (neurons) in
certain areas of the brain.
Causes uncontrolled
movements, loss of
intellectual faculties, and
emotional disturbance.
How does
it
happen?
Affected
Genotype:
HH or Hh
Progeria
• Drastic premature aging, rare, die by age 13.
Symptoms include limited growth, alopecia,
small face and jaw, wrinkled skin,
atherosclerosis, and cardiovascular problems
but mental development not affected.
Sex-Linked Traits
• Sex-linked traits are produced by genes only on the X
chromosome.
– They can be Dominant or Recessive.
• What would be the genotypes of a male and female that have a
Sex-linked Dominant trait and do not express the trait?
• Expresses Trait:
Male - XA Y
Female - XA XA or XA Xa
• No Expression:
Male - Xa Y
Female - Xa Xa
• What would be the genotypes of a male and female that have a
Sex-linked Recessive trait and do not express the trait?
• Expresses Trait:
Male - Xa Y
Female - Xa Xa
• No Expression:
Male - XA Y
Female - XA XA or XA Xa
(Carrier)
• Most Sex-linked traits are Recessive!
Color Blindness
Inability to see colors in the normal way
How does it
happen?
Affected
Genotypes:
XbXb
XbY
Hemophilia
Inability of the blood to clot properly
How does it
happen?
Affected
Genotypes:
XhXh
XhY
Pedigree Analysis
• A pedigree shows the relationship between parents and children over
the generations and how a trait is passed down from one generation to
the next.
How to Construct a Pedigree?
• A Pedigree is a visual showing the pattern of
inheritance for a trait. (Family tree)
•
•
•
•
Symbols and Rules:
Male =
Female =
Affected =
Unaffected =
Carrier =
Link parents together with a line and then
make a vertical line to connect to offspring.
Autosomal Dominant Pedigree
• Draw a Pedigree showing a cross between
Heterozygous parents that have 2 boys and 2
girls. (Show all possibilities)
Genotypes of Affected and Unaffected:
• AA and Aa = Affected aa = Unaffected
Aa
aa
Aa
Aa
Aa
AA
Autosomal Recessive Pedigree
• Draw a Pedigree showing a cross between
Heterozygous parents that have 2 boys and 2
girls. (Show all possibilities)
Genotypes of Affected and Unaffected:
• AA=Unaffected Aa=Carrier, Unaffected
aa=Affected
Aa
aa
Aa
Aa
Aa
AA
Sex-Linked Recessive Pedigree
• Draw a Pedigree showing a cross between a normal
male and a Carrier Female.
• Genotypes of Parents:
• Male = Xh Y Female = XH Xh
XRY
XRY
XR
Xr
XrY
XRXR
XRXr