Tuesday, March 22, 2011

Materials: Journal, Pen/Pencil, TextbookTurn In: n/aWarm-Up: Complete the Pedigree Symbols HandoutHomework: Finish Pedigree Handout. Due Thursday

Pedigrees

Pedigrees• Found in your book on pages 342-343.• A pedigree is a chart which shows the

relationships within a family. • Pedigrees are used to:

– study how the traits are passed from one generation to the next.

– inferring genotypes (carriers)• Pedigrees are based on the individual’s

phenotype. • So if someone has the trait being studied

they are “phenotypically affected.”

Pedigrees• How to read a pedigree…

– Square = male or– Circle = female or– Shaded means “Phenotypically Affected”

or– Un-shaded means “Phenotypically Unaffected”

or• A line connecting a male and a female

represents a marriage.• A line coming off of a male and a female

represents their offspring.

Pedigrees• How to read a pedigree…

–Sometimes the pedigree will show half filled shapes. This indicates a carrier.

–What is a carrier?

Traits continued• Sex-linked trait- gene on allele is located

only on the X or Y chromosome.– If sex-linked, the effects are usually seen only

in males.– Most sex-linked genes are carried on the X

chromosome and recessive

• Females: Only express the recessive condition if she inherits two recessive alleles.

• Thus chances of inheriting or exhibiting a sex-linked condition are significantly less.

Traits continued

• Dominant or Recessive?

– Gene is autosomal dominant = every individual with the condition will have a parent with the condition.

– Gene is recessive = an individual with the condition can have one, two, or neither parent exhibit the condition.

Traits continued• Heterozygous or homozygous?

– Individuals with autosomal traits are homozygous dominant or heterozygous = phenotype will show dominant allele

– Individuals that are homozygous recessive = phenotype will show the recessive allele.

– Two people who are heterozygous carriers of a recessive mutation will not show the mutation

• Can produce children who are homozygous for the recessive allele.

Pedigrees• Practice…

– How many children did this first couple have?

I.

II.

III.

1 2

1 2 3 4

21

Pedigrees• Practice… – How many children did this first couple have?

–THREE

Pedigrees• Practice…

– How many grandchildren did this first couple have?

Pedigrees• Practice… – How many grandchildren did this first couple have?

–TWO

Pedigrees• Practice…

– How many people in this family are affected?

Pedigrees• Practice… – How many people in this family are affected?

– THREE

Pedigrees• Practice… – How many people can you be certain are carrying

the trait?

Pedigrees• Practice… – How many people can you be certain are carrying the trait?

–FOUR

?

Pedigrees• Practice…

– If the allele for this trait is the letter “e”, assign a genotype to all of the individuals you are sure of.

Pedigrees• Practice…

– If the allele for this trait is the letter “e”, assign a genotype to all of the individuals you are sure of.

ee

ee

ee

Ee

Ee Ee Ee

Pedigrees• Practice…

– So which individual is the only one we can not be sure of?

Ee orEE

Pedigrees• Practice… – What genotype is individual #14?

?

Pedigrees• Practice… – What genotype is individual #14?

Start by labeling what you know for sure.

aa

aa

aa aa aa aa

?

Pedigrees• Practice… – What genotype is individual #14?

Move on to the carriers.

aa

aa

aa aa aa aa

Aa

AaAa

Aa

Aa Aa

?

Pedigrees• Practice… – What genotype is individual #14?

Do you know anything else?

aa

aa

aa aa aa aa

Aa

AaAa

Aa

Aa Aa

?

Pedigrees• Practice… – What genotype is individual #14?

Do you know anything else?

aa

aa

aa aa aa aa

Aa

AaAa

A?Aa

Aa Aa

?

Pedigrees• Practice… – What genotype is individual #14?

What must individual #14 be?

aa

aa

aa aa aa aa

Aa

AaAa

A?Aa

Aa Aa

?

?

Pedigrees• Practice… – What genotype is individual #14?

Do a Punnett Square and the only result is aa.

aa

aa

aa aa aa aa

Aa

AaAa

A?Aa

Aa Aa

aa

You didn’t have to go through it all to get that answer, but it was good practice.

Pedigrees• Practice…–Label each individual with a number and

a genotype (use the letter H).

Pedigrees• Practice…

– If individual #10 marries a carrier, what is the probability that their second child will not show the trait?

#10

Pedigrees• Practice…

– If individual #10 marries a carrier, what is the probability that their second child will not show the trait?

Hh h

hHh Hhhh hh

There is a 50% (or 1 in 2) chance that their second child will not show the trait.

Your turn…

Pedigrees• Assign a number and a genotype to each

individual. Use whatever letter you would like.

Pedigrees• If #6 married a carrier, what is the

probability their first child will be affected?

#6