2. TODAY’S PROBLEM
What information does a family tree show?
Answer what do you think in 1 – 2 sentences
3. REVIEW: WHAT ARE THE TYPES OF
CHROMOSOMES?
Autosomal: Karyotype picture
Chromosomes 1-22
Sex:
X and Y
chromosomes, determin
e whether a person is a
male or female
4. KP1: WHAT ARE GENETIC DISORDERS?
Genetic disorders are
diseases caused by mutations
in DNA in gametes
These disorders are passed
down from parent to child
Different disorders have
different modes of inheritance
5. KP2: WHAT ARE MODES OF INHERITANCE?
The way something is passed down from
parent to offspring
There are three main modes of inheritance
1. Autosomal dominant—only need one copy of
a gene to be affected
2. Autosomal recessive—need two copies of
the gene to be affected
3. Sex-linked recessive—gene is on the X
chromosome, need 2 copies to be affected
(UNLESS MALE—only need 1, b/c only have
1 X chromosome)
7. KP3: WHAT IS A PEDIGREE AND HOW
DO I INTERPRET IT?
A Pedigree is a chart or family
tree that traces the inheritance
of a trait.
Females are always
circles, males are always
squares
Half-shaded = carrier of gene
(but not affected)
Solid shaded = affected
Each horizontal line represents
a generation.
Children will always appear on
a line directly below their
parents.
8. CHECK
Circle a carrier
Square a male
Star an affected person
9. KP4: HOW CAN I USE A PEDIGREE TO
DETERMINE MODES OF INHERITANCE?
You can use clues in the pedigree to determine mode
of inheritance
1. If… Autosomal dominant
All generations affected, no carriers!
Equal number of males and females affected
2. If… Autosomal recessive
Generations are skipped
Equal number of males and females affected
3. If… Sex-linked recessive
Generations are skipped
Female carriers only
More males are affected
10. KP5: WHAT ARE THE STEPS TO SOLVE A
PEDIGREE PROBLEM?
Step 1: Are generations skipped?
Yes=recessive, No=dominant
Step 2: Are there carriers?
Yes=recessive, No=dominant
Step 3:
If ―Yes=recessive‖
Are more men affected?
Yes=sex-linked, No=autosomal
Are there only female carriers?
Yes=sex-linked, no=autosomal
11. KP6: HOW DO I PREDICT THE
GENOTYPE OF INDIVIDUALS IN A
PEDIGREE?
Determine mode of inheritance shown in pedigree
Determine genotype options (BB, bb, or
Bbcarrier)
Use children as clues
12. EXAMPLE
?
What is the mode of inheritance
?
What are my options?
Are generations skipped? SEX-LINKED
Are there carriers? RECESSIVE!
Are more men affected?
Are there only female carriers?