1. UNIT 7 DAY 6
Pedigrees

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)

6. CHECK
What mode of
inheritance is this
showing???

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
Bbcarrier)
 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?