1. ANNOUNCEMENTS Homework Quiz: Take out your HW
Take a sheet of scrap paper
Put your name and per. # on it
Content quiz on Fri - Pedigrees
Field Trip to the Field Museum next Monday!

2. Period 3 HW Quiz
Draw the proper shape with correct shading for the following:
Most genetic disorders follow (recessive or dominant) patterns of inheritance.
List 2 traits/diseases that follow simple recessive heredity.
Answer the following for Huntington's disease:
Pattern of inheritance
Symptoms of the disease

3. What is a pedigree?
It is a tool used to track information throughout generations
Determine inheritance pattern of diseases
Predict the risk of disease/trait in future offspring of a couple by determining genotypes
Trace familial lineage – similar to a family tree

4. A sample, advanced pedigree

5. What we will go over today:
How to read pedigrees
Basic patterns of inheritance
autosomal, recessive
autosomal, dominant
sex-linked (X-linked), recessive
Applying pedigree analysis - practice

6. Sample pedigree - Cystic fibrosis
Generations are designated
by Roman Numerals and
numbered from top to bottom.
Individuals in each generation
are given standard numbers
Starting from left to right.
female
male
affected individuals
What type of inheritance pattern does Cystic fibrosis follow?
What clues does the pedigree give you?

7. Only 2 individuals w/ trait
It is autosomal recessive.
What clues are there?
Shaded individuals with the trait are rarely seen on the pedigree.
Trait often skips generations (hidden in heterozygous carriers)
Trait affects males and females equally
Sometimes hard to determine, especially if not many individuals have the trait.
Only 2 individuals w/ trait
Parents do not exhibit
the trait

8. Autosomal recessive diseases in humans
Most common ones
Cystic fibrosis
Sickle cell anemia
Phenylketonuria (PKU)
Tay-Sachs disease
For each of these, overdominance (heterozygote superiority) has been suggested as a factor in maintaining the disease alleles at high frequency in some populations

9. Clues for identifying autosomal dominant pattern of inheritance
Trait is common in the pedigree
Trait is found in every generation
Affected individuals transmit the trait to about 1/2 of their children
Individuals of both sexes affected equally

10. ex. achondroplasia (a sketelal disorder causing dwarfism)
Autosomal dominant traits
There are few autosomal dominant human diseases (why?), but some rare traits have this inheritance pattern
ex. achondroplasia (a sketelal disorder causing dwarfism)

11. Clues for identifying X-linked recessive inheritance patterns
Trait is rare in pedigree
Trait skips generations
Affected fathers DO NOT pass to their sons
Why not?
Males are more often affected than females
Why?

12. ex. Hemophilia in European royalty
X-linked recessive traits
ex. Hemophilia in European royalty

13. Pedigree Analysis in real life
Remember:
dominant traits may be rare in population
recessive traits may be common in population
alleles may come into the pedigree from 2 sources
mutation happens
often traits are more complex
affected by environment & other genes

14. Once you know how to read a pedigree, then what?
Use the phenotypic information to determine genotypes of the individuals
When working on a pedigree, just write the alleles for the individuals as you figure them out.
Why do all this?
Helps to identify heterozygotes who may unknowingly have offspring at risk of a disease.
Rules for determining genotype:
Use pencil. Trust me.
Any individual w/ the recessive phenotype must be homozygous recessive.
An individual with homozygous recessive offspring must have 1 recessive allele.
Any individual with a homozygous recessive parent must have one recessive allele.
Don’t guess if you can’t determine both alleles. Simply write the allele you know and a “?” for the 2nd

15. What does the double line represent?
What is the pattern of inheritance?
What are IV-2’s odds of being a carrier?
Remember – determining genotypes will help!
Start with what you can quickly determine and
work your way around until you fill in the missing pieces.
What does the double line represent?
For these 2 individuals to have the trait when the parents do not,
will this be a dominant or recessive trait?

16. Make a punnett square w/ 2 heterozygous parents
Sample pedigree - cystic fibrosis
What can we say about the genotype of I-1 and I-2?
What can we say about the genotype of II-4 and II-5?
What is the chance that III-5 is a carrier?
Heterozygotes
Heterozygotes
Make a punnett square w/ 2 heterozygous parents
50% chance

17. III1 = XNY, III2 = XNXn, III3 = XNY
What is the inheritance pattern?
What is the genotype of III-1, III-2, and III-3?
Could IV-5 possibly pass the trait on to their son?
Sex-linked/X-linked
III1 = XNY, III2 = XNXn, III3 = XNY

18. III-1 has 12 kids with an unaffected wife
8 sons - 1 affected
4 daughters - 2 affected
Does he have reason to be concerned about paternity?