Complex
Inheritance and
Human Heredity
Chapter 11
• We inherit traits from
our parents, we get half
of our genes from mom,
and half from dad
• Alleles are either
recessive (lowercase) or
dominant (uppercase)
• Homozygous recessive,
homozygous dominant,
heterozygous
Let’s review!
• Autosome/Autosomal: Any chromosome other than the
sex chromosomes (X & Y). Chromosomes designated
1-22.
• Carrier: An individual who is heterozygous for a
recessive disorder
• Pedigree: A diagram that traces the inheritance of a
particular trait through several generations of the same
family
New Words!
BASIC PATTERNS OF
INHERITANCE
Genetic Disorders
• An abnormal condition that a person inherits through
their genes
• Can be caused by either changes in DNA, or an extra or
missing chromosome
• Genetic disorders can be recessive or dominant
Genetic Disorders
• Two recessive alleles,
one from each parent
• If an individual is
heterozygous, they are
a carrier (this means
they could pass it on
even if they don’t have
it!)
• BB – Normal
• Bb – okay, but a carrier
• bb – disease
• Often skips a
generation
Recessive Disorders
• Affects cell membrane
protein, water cannot diffuse
from cells
• the body produces an
abnormally thick mucus in
the lungs
• Chromosome 7
• Medication, strict diet,
enzyme replacement
• Death is usually caused by lung
complications
Cystic Fibrosis
• Absence of enzyme that breaks
down fatty substances
• Chromosome 15
• Buildup of fatty acids in brain
• Cherry red spot on back of eye
• Causes deafness, blindness,
severe retardation, and death
usually by age 4
• Most carriers choose to avoid
birth because there is no cure
Tay-Sachs
• Caused by altered
genes, resulting in the
absence of the skin
pigment melanin in
hair and eyes
• White hair
• Very pale skin
• Pink pupils
Albinism
• Recessive genetic disorder characterized by the inability
of the body to digest galactose.
• People with this disorder should avoid milk products
Galactosemia
The mutation for cataracts (c) occurs on a gene represented by the
letter E. Owls that are homozygous for the mutation (EcEc) exhibit
cataracts. Owls that are homozygous for normal eyes are EE and
owls that are carriers of the mutation but do not exhibit cataracts
are EEc.
What percentage of the offspring in a cross between parents with
the genotypes EE and EcEc will exhibit cataracts?
A. 0%
B. 25%
C. 50%
D. 75%
OGT
• Caused by dominant
alleles
• Those who do not
have the disorder are
homozygous
recessive.
• BB – have disease
• Bb – have disease
• bb – normal
Dominant Disorders
• Affects the nervous system
• Deterioration of brain
tissue, usually begins
between age 30 and 40
• Chromosome 4
• No cure, but have
medications to cope with
symptoms
• People usually die 15-20
years after onset of
degeneration
Huntington’s Disease
• causes small body size
and limbs that are
comparatively short,
most common type of
dwarfism
• Chromosome 4
• 75% born to parents of
average size
• When this happens it is
due to a gene mutation
Achondroplasia
GENETIC DISORDERS
To Test or Not to Test?
• You will need one worksheet and one index card
• Find the rest of your family based on the number on your
cards
• Complete the worksheet as a group and be prepared to
discuss your answers as a class
Choosing Thomas
PEDIGREES
• A diagram that traces the inheritance of a particular trait
through several generations of the same family
• Allows us to use family trees and affected individuals to
predict the risk of disease in future offspring
Pedigrees
• Male:
• Mating:
• Female:
• Siblings:
• Affected Individual:
• Divorced/Separated:
• Carrier:
• Deceased:
Symbols
• Individuals are in birth order from left to right (oldest at
left, youngest on right)
• Individuals are numbered
• Generations are numbered with roman numerals
• When referring to an individual, use the generation
number and then the individual number
• II-4
Example of a Pedigree
Grandparents
Grandparents
I
Parents
II
Aunts, Uncles
Aunts, Uncles
III
Brother
You
Do any disorders run in this family??
• Whether a family has an autosomal or sex-linked disease or disorder
• If the trait is dominant or recessive
• Autosomal: appears in both sexes equally
• Sex-linked disorder: allele is located only on the X or Y chromosome.
Most sex-linked genes are on the X chromosome and are recessive
• So who would have an X-linked disorder more often, boys or girls?
What can you tell from a
pedigree?
COMPLEX PATTERNS OF
INHERITANCE
• Basic patterns of inheritance involve…
• The passing of dominant or recessive traits
• Disorders that are recessive require:
• 2 recessive alleles, 1 from mom, 1 from dad
• A normal person who carries the gene could pass it on
• Disorders that are dominant require:
• 2 dominant alleles, 1 from mom, 1 from dad OR
• 1 dominant allele (heterozygous)
• There are no carriers for these disorders, you either have it
or you don’t!
Let’s Review!
• These disorders are autosomal
• Chromosomes 1-22
• Geneticists use a diagram called a pedigree to trace
familial traits and predict the inheritance of the trait in
future offspring
Let’s Review!
• Sometimes the laws
and principles of
genetics established
by Gregor Mendel do
not always explain the
inheritance patterns
seen in an organism.
• Neither allele is
completely dominant
nor completely
recessive
• Heterozygous
phenotype is a blend of
the two homozygous
phenotypes
• a mix in physical
appearance between the
dominant and the
recessive
Incomplete Dominance
• Both alleles are
completely expressed
in the heterozygous
condition.
• Sickle Cell
Codominance
• Abnormal hemoglobin causes a person’s red blood cells
to be sickle shaped
• The shape causes clots and blockages, they also carry less
oxygen
• The allele for the disease is codominant with the normal
allele (heterozygous)
• People who are heterozygous for sickle cell also have a
higher resistance to malaria
Sickle Cell Anemia
• rr – all sickle shaped
cells
• Rr– mixture of both
• RR– normal shaped
cells
Sickle Cell
Codominant or Incomplete?
• Sometimes, there are 3 or 4 alleles that code for a single
trait
• Blood Groups
• This doesn’t mean a person has more than 2 alleles for
the trait, just that more than 2 exist in the population
• 1 gene, more than 2 alleles
Multiple Alleles
• 3 forms of the allele
• IA – type A
• IB – type B
• i – type O
• i is recessive to IA and IB
• IA and IB are codominant
• IAIB – type AB
Blood Groups
Heterozygous
• IAi – type A
• IBi – Type B
• IAIB – type AB
Blood Groups
Homozygous
• IAIA – Type A
• IBIB – Type B
• ii – Type O
A scientist uses a microscope to examine two slides of living
bacteria. Each slide contains a different type of bacteria. While the
cells on the first slide are moving rapidly, the cells on the second
slide are stationary.
Based on these observations, the cells on the second slide most
likely have no
A. nucleus
B. flagella
C. chloroplasts
D. mitochondria
OGT
• Genes that are found on the X
chromosome
• Expressed more in males
because they only have one X
chromosome (XY) compared
to females (XX)
Sex-Linked Traits
• Recessive sex-linked
disorder
• Takes a long time for blood
to clot (body lacks proteins
involved in clotting)
• Very rare in females
because she would need to
have both X chromosomes
with the recessive trait.
Hemophilia
Patricia is a healthy carrier of hemophilia and Sam
is completely healthy. Complete the Punnett square
below.
• Mom’s genotype:
• Dad’s genotype:
• What is the probability of getting:
•
•
•
•
Daughter with hemophilia?
Son with hemophilia?
Carrier?
Healthy child?
• Recessive X-linked trait
• Male only needs one copy
of this allele in order to be
colorblind.
• Female would need to have
two copies of the recessive
allele.
• It is very rare to find a color
blind female.
• Mothers pass this to their
sons
• Father pass it to their
daughters
Red-Green Colorblindness
Judy is homozygous recessive for colorblindness
and Dennis is healthy. Complete their Punnett
square below.
• Mom’s genotype:
• Dad’s genotype:
• What is the probability of getting:
•
•
•
•
Colorblind daughter?
Color blind son?
Carrier?
Heterozygous child?
Baldness is X-linked Recessive
Grandpa bald = XbY
X
Grandma = XBXB
Daughter = XBXb marries Male = XBY
Sons?
50% XB(normal)
50% Xb(bald)
This is why men should
look to their mom’s dad
for probability of baldness.
But beware grandma could
be a carrier too!
Baldness
At 25°C, water has a density of 1.0 g/mL and vegetable oil has a
density of 0.90 g/mL.
How would a substance with a density of 0.95 g/mL behave when
placed in both oil and water?
A. a decrease in air quality.
B. a decrease in biodiversity.
C. an increase in deciduous tree species.
D. an increase in nighttime temperatures.
OGT
What’s
different?
• Cell division during which sister chromatids fail to separate
properly
• If this occurs during Meiosis I or II then the resulting
gametes will not have the correct number of chromosomes
• Nondisjunction occurs in both autosomes (body cells) and
in gametes
• Trisomic: one extra chromosome (only 3 trisomies that
result in survival after birth)
• Monosomic: one missing chromosome (usually lethal,
except in Turner’s Syndrome)
Nondisjunction
• Chromosome 21
• Trisomy
• Can be moderate or severe
• Short stature, heart
defects, and mental
disability
• Correlated with mother’s
age, can be from
nondisjunction of father’s
chromosome 21
Down Syndrome
Autosomal
• Patau Syndrome: Trisomy 13
• serious eye, brain, circulatory
defects as well as cleft palate.
1:5000 live births. Children rarely
live more than a few months
• Edwards’s Syndrome: Trisomy
18
• almost every organ system
affected 1:10,000 live births.
Children with full Trisomy 18
generally do not live more than a
few months.
Sex Chromosomes
• Klinefelter Syndrome: XXY
• Male sex organs; unusually small
testes, sterile. Breast enlargement
and other feminine body
characteristics. Normal intelligence.
• Trisomy X: XXX
• 1:1000 live births - healthy and
fertile - usually cannot be
distinguished from normal female
• Monosomy X: Turner’s Syndrome
Other Examples
• 1:5000 live births; the only viable
monosomy in humans - women
with Turner's have only 45
chromosomes!!! XO individuals are
genetically female, however, they do
not mature sexually during puberty
and are sterile. Short stature and
normal intelligence. (98% of these
fetuses die before birth)
• The environment can
have an influence on
how genes are
expressed
•
•
•
•
•
Toxic agents
Diet and exercise
Sunlight and water
Temperature
Medications
• Conditions can cause a
gene to shut down or
turn on
I got the “fat” gene.
Environmental Factors
• Karyotype: an image
that shows homologous
chromosomes arranged
in decreasing size
• Telomere: caps on the
ends of chromosomes,
have a protective
function
Additional Vocabulary
• BBC: The Ghost in Your Genes
• Epistasis: When the one gene hides the effects of another
gene
• Epigenetics
Epistasis
A driver traveling from the coniferous region to the tundra region
would most likely observe
A. sink in both oil and water
B. sink in oil and float on water
C. float on oil and sink in water
D. float on both oil and water
OGT