Transcript Inheritance of Traits: Pedigrees and Genetic Disorders

INHERITANCE OF TRAITS:
PEDIGREES AND GENETIC
DISORDERS
Pedigree definition
 Pedigree: a family history that shows how
a trait is inherited over several generations
 Pedigrees are usually used when parents
want to know if they are carriers of a
particular disorder
Making a Pedigree
 Female
 Male
 Married Couple
 Siblings
Filled in symbols
indicate
individual is
affected with a
disorder
How do you read a pedigree chart?
• A shape that is not shaded indicates that
the person does NOT have the trait.
• A shape that is half-shaded indicates
that the person is a “carrier” (has 1
allele).
• A shape that is completely-shaded
indicates that the person has the trait
Example of a Pedigree
Grandparents
Grandparents
Parents
Aunts, Uncles
Aunts, Uncles
Brother
You
Do any disorders run in this family??
Interpreting a Pedigree
 What can you tell from a pedigree?
 Whether a family has an autosomal or sex-linked disease
or disorder
 Autosomal disorder: 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?
 Whether a disorder is dominant or recessive
Is this disorder 1) autosomal or
sex linked, 2) dominant or
recessive?
Grandparents
Grandparents
Parents
Aunts, Uncles
Aunts, Uncles
Brother
You
Sex Linked! (in this case
allele is recessive and
located on the X
chromosome)
Is this disorder 1) autosomal or
sex linked, 2) dominant or
recessive?
Grandparents
Grandparents
Parents
Aunts, Uncles
Aunts, Uncles
Autosomal dominant!
Brother
You
Is this disorder 1) autosomal or
sex linked, 2) dominant or
recessive?
Grandparents
Grandparents
Parents
Aunts, Uncles
Aunts, Uncles
Autosomal recessive!
Brother
You
More Practice
 http://highered.mheducation.com/sites/0072
485949/student_view0/chapter3/interactive_
activity.html
 Sex Chromosomes: one of the two
chromosomes that determine an individual’s
sex (XX=female, XY=male)
 Autosomal Chromosomes: chromosome that
is not a sex chromosome
 Sex-linked gene: gene located on a sex
chromosome
Common Genetic Disorders
 Color blindness
 Sickle cell anemia
 Cystic Fibrosis
 Hemophilia
 Huntington’s Disease
For more info, go to: http://www.ncbi.nlm.nih.gov/pubmedhealth/
Color Blindness
 Deficiency to
perceive colors
 Problem with color-
sensing pigments in
certain nerve cells
of the eye
 About 1 in 10 men
have some form of
color blindness.
 Sex-linked disorder
Sickle Cell Anemia
 Disorder where abnormal
hemoglobin (a protein
inside red blood cells) is
produced and warps red
blood cells
 Sickle cells deliver less
oxygen to body’s tissues and
can get stuck in small blood
vessels
 Tends to be seen in people
of African or Mediterranean
descent
 Recessive trait
Cystic Fibrosis
 Life threatening, causes thick mucus to build up in
various areas of the body (lungs, digestive tract,
etc).
 Tends to run in Caucasians, of Northern/Central
European descent
(1 in 29 Americans
carry the allele)
 Recessive, autosomal disease
 Average life span in US
for people with CF is 37,
death usually caused by
lung complications
Hemophilia
 Bleeding disorder, where it takes a long time for
blood to clot (body lacks proteins involved in
clotting)
 Treatment
involves
injection with
missing clotting
protein
 Sex-linked
(carried on the X
chromosome)
Huntington’s Disease
 Deterioration of brain
tissue, usually begins
between age 30 and 40.
 No cure, but have
medications to cope
with symptoms
 People usually die 15-20
years after onset of
degeneration
 Autosomal, dominant
Chromosomal Disorders
 Nondisjunction: error in meiosis in which the
homologous chromosomes fail to separate
properly
 If nondisjunction occurs during meiosis,
gametes with an abnormal number of
chromosomes may result, leading to a
disorder of chromosome numbers.
 Examples of nondisjunction:
 Trisomy: three copies of a chromosome
 Trisomy 21: Down Syndrome (characterized by mild
to severe mental retardation)
 Turner’s Syndrome: Nondisjunction of the X
chromosomes. Females usually only inherits one X
chromosome. Women are sterile.
 Klinefelter’s Syndrome: males inherit an extra X
chromosome. Males are sterile.
Karyotype
 A karyotype shows the complete diploid set
of chromosomes grouped together in pairs,
arranged in order of decreasing size.