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Human Genetics
Chapter 11
11-1 Basic Patterns in Human Inheritance
Objectives
1. Analyze genetic patterns to determine
dominant or recessive inheritance patterns
2. Summarize examples of dominant and
recessive disorders
3. Construct human pedigrees from genetic
information
Chapter 11
Complex Inheritance and Human Heredity
11.1 Basic Patterns of Human Inheritance
Recessive Genetic Disorders
 A recessive
trait is
expressed
when the
individual is
homozygous
recessive for
the trait.
Chapter 11
Complex Inheritance and Human Heredity
11.1 Basic Patterns of Human Inheritance
A dominant genetic disorder is expressed with
ONE dominant allele present
Chapter 11
Complex Inheritance and Human Heredity
11.1 Basic Patterns of Human Inheritance
Pedigrees
 A diagram that traces the inheritance of a
particular trait through several generations
Pedigrees can have the following
inheritance patterns:
Autosomal dominant
Autosomal recessive
X-Linked
A = the trait (a genetic
disease or
abnormality,
dominant)
a = normal (recessive)
Can we
determine the
Genotypes of all
the individuals?
What are the genotypes?
What is the inheritance
pattern?
A = the trait (a genetic
disease or
abnormality,
dominant)
a = normal (recessive)
What are the genotypes?
What is the inheritance
pattern?
What are the genotypes?
What is the inheritance
pattern?
What are the genotypes?
What is the inheritance
pattern?
11-2 Complex Patterns of Inheritance
Objectives
1. Distinguish between various complex
inheritance patterns
2. Analyze sex-linked and sex-limited inheritance
patterns
3. Explain how the environment can influence
the phenotype of an organism
Chapter 11
Complex Inheritance and Human Heredity
11.2 Complex Patterns of Inheritance
Incomplete Dominance
 The heterozygous phenotype is an intermediate
phenotype between the two homozygous
phenotypes.
• Coat color in mice is incompletely dominant.
Yellow and white-colored mice are
homozygous, while cream-colored mice are
heterozygous. If two cream-colored mice
mate, what phenotypic ratio can we expect of
their offspring? Show the Punnett Square?
In radishes, red and white are pure-breeding
colors, while hybrids are purple. If a red
radish is crossed with a white radish, what will
be the phenotype of the F2 generation
(assuming the F1 generation self-pollinates)?
Show the Punnett Square.
Chapter 11
Complex Inheritance and Human Heredity
11.2 Complex Patterns of Inheritance
Codominance
 Both alleles are expressed in the heterozygous
condition.
Chapter 11
Complex Inheritance and Human Heredity
11.2 Complex Patterns of Inheritance
Sickle-cell Disease – an example of codominance
Normal red blood cell
 Changes in hemoglobin
cause red blood cells to
change to a sickle shape.
 People who are
heterozygous for the trait
have both normal and
sickle-shaped cells.
Sickle cell
7766x
Sickle cell disease vs sickle
cell trait
-SCD, child inherits trait
from both parents
• stroke, acute chest
syndrome (a condition
that lowers the level of
oxygen in the blood),
organ damage, other
disabilities, and in some
cases premature death
-SCT, child inherits one trait
• Rarely, extreme
conditions such as severe
dehydration and highintensity physical activity
can lead to serious health
issues, including sudden
death
In shorthorn cattle, when a red bull (RR) is
crossed with a white cow (WW), all the
offspring are roan—a spotted, red and white
or milky red color. What offspring are
expected from mating a roan bull and a roan
cow? Show the Punnett Square
Chapter 11
Complex Inheritance and Human Heredity
11.2 Complex Patterns of Inheritance
Multiple Alleles
 Blood groups in
humans
 ABO blood groups
have three forms of
alleles.
 AB are codominant
to each other also!
Pretend that Brad Pitt is homozygous for the
type B allele, and Angelina Jolie is type “O.”
What are all the possible blood types of their
babies
Two parents think their baby was switched at the
hospital. Its 1968, so DNA fingerprinting
technology does not exist yet. The mother has
blood type “O,” the father has blood type “AB,”
and the baby has blood type “B.”
–
–
–
–
Mother’s genotype: _______
Father’s genotype: _______
Baby’s genotype: ______ or ________
Punnett square showing all possible genotypes for
children produced by this couple
– Was the baby switched?
Chapter 11
Complex Inheritance and Human Heredity
11.2 Complex Patterns of Inheritance
Sex Determination
 Sex chromosomes
determine an individual’s
gender.
 Humans have 2 sex
chromosomes.
 The other 22 pairs of
chromosomes are called
autosomes
 SO who determines the
sex of a child??????
Chapter 11
Complex Inheritance and Human Heredity
11.2 Complex Patterns of Inheritance
Sex-Linked Traits
 Genes located on the X chromosome
 Red-green color blindness
 Hemophilia
In fruit flies, the gene for white eyes is sex-linked
recessive. (R) is red and (r) is white. Cross a
white-eyed female with a normal red-eyed
male
Hemophilia
In humans, hemophilia is a sex-linked recessive trait. If a female
who is a carrier for hemophilia marries a male with normal
blood clotting, answer the following questions
•
•
•
•
•
What fraction of the female children will have hemophilia?
What fraction of the female children will be carriers?
What fraction of the male children will have normal blood clotting?
What fraction of the male children will be carriers?
What fraction of the male children will have hemophilia?
Chapter 11
Complex Inheritance and Human Heredity
11.2 Complex Patterns of Inheritance
Polygenic Traits
 Polygenic traits arise from the interaction of
multiple pairs of genes.
 Skin color, height, eye color, fingerprint
patterns
Chapter 11
Complex Inheritance and Human Heredity
11.2 Complex Patterns of Inheritance
Environmental Influences
 Environmental factors
 Diet and exercise
 Sunlight and water
 Temperature
• video
11-3 Chromosomes and Human
Heredity
Objectives
1. Distinguish normal karyotypes from those
with abnormal numbers of chromosomes
2. Define and describe the role of telomeres
3. Relate the effect of nondisjunction to Down
Syndrome and other abnormal chromosomes
numbers
Chapter 11
Complex Inheritance and Human Heredity
11.3 Chromosomes and Human Heredity
Karyotype Studies
 Karyotype—micrograph in which the pairs of
homologous chromosomes are arranged in
decreasing size.
Chapter 11
Complex Inheritance and Human Heredity
11.3 Chromosomes and Human Heredity
Nondisjunction
 Cell division during which sister chromatids
fail to separate properly
 Ex. Disease-Down syndrome
Chromosomes Don’t Separate Properly during
Meiosis
Chromosome mutations
• Chromosome mutations- changes in the
structure of a chromosome or the loss of a
chromosome. Often occur during cell division.
– Deletion- loss of a piece of a chromosome due to
breakage. Information carried by the missing piece
is lost.
– Inversion- a chromosomal segment breaks off and
reattaches in the reverse orientation on the same
chromosome.
Chromosome mutations cont.
– Translocation- a chromosomal segment breaks off
and attaches to another, non-homologous
chromosome.
Patterns of Inheritance
– Monosomy- and individual is missing one of a pair
of particular chromosomes (the total number
would be 45 for humans)
Nondisjunction Also Can Change the
Number of Sex Chromosomes
• Turner syndrome
– Missing an X chromosome; XO
– Female; webbed neck; no secondary
sexual traits at puberty; sterile; may
age prematurely
• XXX females
– May develop normally or may have developmental
delays
– 1 out 1000 females have it
In Downs Syndrome There Are Three
Copies of Chromosome 21
Nondisjunction Also Can Change the
Number of Sex Chromosomes
Trisomy- an individual has 3 of a particular chromosome. (total number would be 47
for humans)
• Down syndrome- extra chromosome at number 21- individual has mental
deficiencies, folded skin above the eyes, weak muscles
•
Klinefelter syndrome (XXY)
•
XYY condition
•
•
•
– Low fertility; mental retardation; small testes; sparse body hair; enlarged breasts
– Testosterone injections may reverse the phenotype
– intellectual disability, distinctive facial features, skeletal abnormalities, poor coordination, and
severe problems with speech
Some develop normally
increased risk of learning disabilities and delayed development of speech and language skills.
Delayed development of motor skills (such as sitting and walking), weak muscle tone
(hypotonia), hand tremors or other involuntary movements (motor tics), and behavioral and
emotional difficulties are also possible
Some develop autistic spectrum disorders, which are developmental conditions that affect
communication and social interaction.
Turner Syndrome
Kleinfelter’s Syndrome