Pedigrees

• Pedigrees study how a trait is passed from one generation to the next.

• Infers genotypes of family members• Disorders can be carried on…

– Autosomes (22 pairs of chromosomes)– Sex Chromosomes (X or Y)– Number of Chromosomes (called N)

(either N > 46 > N)• Keep in mind: traits are influenced

heavily by non-genetic factors or environmental factors– Nutrition – Exercise– Toxins (mutagens)– Disease

Parts of a Pedigree

• Squares are males (XY)• Circles are females (XX)• Horizontal lines connect breeding

couples• Vertical lines connect parents to

children• Shading means the individual has the

trait• Half shading or a dot means they

carry the gene called a “carrier”• No shading means the individual does

not have the trait• A diagonal line means death.• Roman numerals show generations• Numbers assign an individual to a

generation– Example: What happened to II, 4?

Interpreting Pedigrees

• 1. Determine if the trait is dominant or recessive.– Every other

generation: It is recessive

– Every generation: It is Dominant

Interpreting Pedigrees

• 2. Determine if the trait is autosomal or sex linked.– Affects males and females equally:

Autosomal (Aa)– Affects one sex more than the

other: especially MALES! Sex-linked (XCXc or XcY)

• Typically sex-linked disorders or traits are carried on the X chromosome– Females tend to “carry” a trait and

affect their sons.– Females get the trait from an

affected father or carrier/affected mother

– Affected males got it from their mother and give it to their daughters to “carry.”

Recap on interpreting pedigrees1. Determine if it is dominant or recessive.2. Determine if it is autosomal or Sex-linked.3. Assign genotypes to affected (shaded) individuals first.

– If Autosomal then use two alleles to show inheritance. (AA, Aa or aa for example)

– In Sex-linked the shaded males will carry the gene (XcY) and be affected.

– In Sex-linked the females can be unaffected, affected or carriers and marked with a dot. (XCXc)

4. Assign remaining genotypes to unaffected individuals .– In Sex-linked the unshaded males will not carry the gene (XCY) and be

unaffected.

5. Double check your work, does the pedigree make sense?

Your Turn!

Is this dominant or recessive? Is this Autosomal or Sex-linked? Assign genotypes to the pedigree to show the inheritance pattern.

Check your work

Type of Inheritance? Autosomal dominant inheritance.

Sex-Related Punnet Squares• The genes for these traits are on the X chromosome,

because boys only receive one X chromosome they are more likely to inherit disorders passed to them from their mother who would be a carrier.– Humans have 22 pairs of autosomes and 1 pair of

sex chromosomes – Males are XY

• Males donate their Y chromosome to their sons only and their X chromosome to their daughters.

• They determine the sex of the child!

– Females are XX• Females donate either one of their X chromosomes to

their sons and daughters• Many times in women the other X chromosome coils

up and deactivates to become a Barr body.• Hemophilia and Colorblindness are sex linked traits, the

punnett square shows how a woman who is a carrier passes the trait to her son, but not her daughters.

– In what only case could you have a daughter with hemophilia and/or colorblindness?

– She inherits a recessive from her mother and her father!

Your Turn!• A mother whose

father had hemophilia marries a man without hemophilia.

• What is the probability they have children with the disorder?– Use H for normal and h

for hemophilia

Check your work• First you should figure out

the genotypes of the parents. If the mother had a father with hemophilia, then she is a carrier XHXh and the father is normal since he does not have hemophilia himself. XHY

• They have a 50% chance of having a boy with hemophilia; 0% chance for a daughter with hemophilia.

Your turn!

Is this dominant or recessive? Is this Autosomal or Sex-linked? Assign genotypes to the pedigree to show the inheritance pattern.

Check your work.

Type of Inheritance? Sex linked Recessive