• Through a family tree, you can identify the relationships among your cousins, aunts, uncles, grandparents, and great-grandparents.Something to remember as we go through this list of

heritable traits…dominant does not necessarily mean “predominant” in a population.

ATTACHED / UNATTACHED EARLOBES

DOMINANT RECESSIVE

ROLLING YOUR TONGUE

DOMINANT RECESSIVE

WIDOW’S PEAK

WIDOW’S PEAK STRAIGHT HAIRLINE

DOMINANT RECESSIVE

HITCHHIKER’S THUMB

STRAIGHT THUMB HITCHHIKER’S THUMB

DOMINANT RECESSIVE

PINKIES

BENT PINKIES STRAIGHT PINKIES

DOMINANT RECESSIVE

CLEFT CHIN

NO CLEFTCLEFT

DOMINANT RECESSIVE

SECOND TOES

LONGER SECOND TOE SHORTER SECOND TOE

DOMINANT RECESSIVE

NUMBER OF FINGERS

SIX FINGERS: POLYDACTYLY FIVE FINGERS

DOMINANT!!!! RECESSIVE

A pedigree can be used as a graphic representation of genetic inheritance patterns. It is a tool used by genetic counselors to help trace disorders which are inherited in families.

FEMALE

MALE

UNIDENTIFIED SEX

AFFECTED

CARRIER

RELATIONSHIP

PARENTS AND CHILDREN

(one boy, one girl) in order of birth

FRATERNAL TWINS

IDENTICAL TWINS

DECEASED

ENDED RELATIONSHIP

PREGNANCY

ADOPTED IN TO THE FAMILY

ADOPTED OUT OF THE FAMILY

ADOPTED BY ONE FAMILY MEMBER FROM ANOTHER

Generations

The pedigree below shows a genetic disease or abnormality. How can we determine if it is dominant or recessive, autosomal or sex linked? If the trait is dominant, we would use the following designations:A = the trait a = normal If the trait is recessive, we would use the following designations:A = normal a = the traitWhile we know the phenotypes of the individuals, we don’t know the genotypes of the three unaffected individuals.

Assume for the moment that the trait is dominant (we don't know yet). The pedigree shows that three of the individuals have the recessive phenotype and one individual has the dominant phenotype.

Write the genotype of the affected individual in her symbol in the pedigree below.

To do this, simply make up the allele in question…pretend the allele “A” codes for the disease, as on the previous slide. Since you don’t know if she is heterozygous, or homozygous, simply put a ? For the second allele.

If possible, write the genotype of the three recessive individuals in their symbols. As you attempt to write the genotypes, keep in mind that the pedigree may not be possible for a dominant trait; it may not be possible to write the genotypes.

Is it possible that the pedigree here is for an autosomal dominant trait?

A?

aa aa

aaNO!

Write the genotypes in the symbol for each person in the pedigree below assuming that it is for a dominant trait. 

A?

A?aa

aa

Is it possible that this pedigree is for an autosomal dominant trait?

What can you conclude from these two examples about the parents of a child that has a dominant characteristic?

One parent must also carry the dominant trait.

YES!

What must the genotypes of the affected individuals be in this pedigree? Aa

Determine if the pedigree below can be for a trait that is autosomal dominant. Use "A" and "a" as you did for the previous pedigrees.

A?A?

aaaa

Is it possible that this pedigree is for an autosomal dominant trait? In conclusion, can two individuals that have an autosomal dominant trait have unaffected children?

YES!

Assuming that the trait is recessive, write the genotype of each individual in the symbol (use the same symbolic designations as before)A = normal

a = the trait

aa aa

A?

Is it possible that the pedigree below is for an autosomal recessive trait?

NO!

Assuming that the pedigree below is for a recessive trait, write the genotype in the symbol for each person.

aaaa

aaaaaaaa

Is it possible that this pedigree is for an autosomal recessive trait? If a trait is autosomal recessive, what can you conclude about the children if both parents are affected? 

All children will be affected!

YES!

Determine if the pedigree below can be for a trait that is autosomal recessive.

Using the same alleles as previously, volunteer to show proof either way.

aa

Aa Aa

A?

Both parents are unaffected, but they produced an affected offspring, so they must be heterozygous for the condition. The only genotype we can be unsure of is the male child in this pedigree.

He may be homozygous dominant, or heterozygous. Either way, he does not have the autosomal recessive illness.

Determine if the pedigree below can be for a trait that is autosomal recessive.

aa

aa

aa

A?

Aa

Aa Aa

A?

Aa Aa A?

A?

A?

Start by filling in the individuals you absolutely know the genotypes of.What other genotypes can you be absolutely sure of?Then fill in the ones you partially know, but can’t be sure if they’re heterozygous, or homozygous dominant.Is it possible that this pedigree is for an autosomal recessive trait?

YES!Notice that two generations were skipped in this instance!

Determine if the pedigree below can be for a trait that is X-linked recessive. Use the following designations:

XA = normalXa = the trait Y = Y chromosome

Start by filling in the individuals that you absolutely know the genotypes for.

XaXa XAY

XAY

Can this pedigree possible show a sex-X-linked recessive disorder?

NO!

Write the genotype within the symbol for each person in the pedigree below.

XaXa XAY

XaY

Is it possible that this pedigree is for an X-linked recessive trait YES!

Write the genotype in the symbol for each person in the pedigree below.

XaXa XAY

XAXa

Is it possible that this pedigree is for an X-linked recessive trait?

YES!Write the genotype in the symbol for each person in the pedigree below.

Is it possible that this pedigree is for an X-linked recessive trait?

XaXa XAY

XaXa

NO!What conclusions can you make based on the results of these pedigree crosses?

Affected mothers will always pass their X-linked condition on to their sons, but only if the father is also affected, will their daughters inherit the X-linked recessive condition. Carrier mothers have the ability to pass the condition on to their sons, but may only pass the allele on to their daughters, making them “carriers”.

Determine if the pedigree below can be for a trait that is X-linked recessive. We will continue to use the designations "XA and Xa".

XAXa XaY

XaY

Is it possible that this pedigree is for an X-linked recessive trait?

YES!

What genotypes are you absolutely sure of?Can you know what the female’s genotype is?

Which parent did the son get the Xa gene from?

XaY

XaY

XAXa

Males ALWAYS get their X chromosome from their mothers. The Y chromosome is ONLY donated by their fathers…so only mothers can pass sex-X-linked conditions on to their sons.

Fathers will not pass their affected X allele on to their sons, only their daughters. The chance of a female getting the X-linked recessive condition depends upon BOTH parents donating a recessive X to her. It is for that reason that males are more commonly affected by sex-X-linked conditions than females.

Determine if the pedigree below can be for a trait that is X-linked recessive.

First, fill in the known genotypes.XaXa XaY

Can these parents produce this offspring, if the trait is sex-X-linked?

XaXa NO!In this particular cross, the female can only receive the Xa allele from mom, and the Xa allele from dad, so she MUST be affected.

For this pedigree, tell if the trait can be autosomal dominant, autosomal recessive, or X-linked recessive.

Autosomal Dominant?

#9 is impossible, because he would have to have gotten the dominant trait from one of his parents, and neither of them have it.

Autosomal recessive?

Possible

Sex-X-Linked?

Possible. #1 could be a carrier, and pass the disorder on to her her son

For this pedigree, tell if the trait can be autosomal dominant, autosomal recessive, or X-linked recessive. If the pedigree cannot fit a mode of inheritance, tell why.  Autosomal dominant?

Possible

Sex-X-Linked?

Impossible. 7 and 8 would only produce recessive children

Autosomal recessive?

Impossible, because 11 and 12 are not possible, as 7 and 8 would only produce recessive children.

Contrary to popular belief, inbreeding does not result in "monstrous" offspring. Marrying and mating with close relatives, as often occurred in royal families did increase the chances that recessive harmful alleles (like hemophilia) would be inherited. Inbreeding has caused many breeds of dogs to have harmful genetic traits. Dalmatians are often deaf, and other dog breeds have high frequencies of epilepsy, blindness, and hip dysplasia. It is true, that mutts are often hardier and have less health problems than the pure breeds.