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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!. Period 3 HW Quiz. Draw the proper shape with correct shading for the following:

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  • 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!

Period 3 hw quiz
Period 3 HW Quiz

  • Draw the proper shape with correct shading for the following:

  • Most genetic disorders follow (recessiveor 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

What is a pedigree
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


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




affected individuals

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.

What type of inheritance pattern does Cystic fibrosis follow?

What clues does the pedigree give you?


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


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


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


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)


Clues for identifying X-linked recessive inheritance


  • 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?


X-linked recessive traits

ex. Hemophilia in European royalty


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

Once you know how to read a pedigree then what
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


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?


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?



Make a punnett square w/ 2 heterozygous parents

50% chance


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?




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?