Transcript attached / unattached earlobes

• 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
DOMINANT
STRAIGHT PINKIES
RECESSIVE
CLEFT CHIN
CLEFT
NO CLEFT
DOMINANT
RECESSIVE
SECOND TOES
LONGER SECOND TOE
DOMINANT
SHORTER SECOND TOE
RECESSIVE
NUMBER OF FINGERS
SIX FINGERS:
POLYDACTYLY
DOMINANT!!!!
FIVE FINGERS
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
ENDED RELATIONSHIP
MALE
PREGNANCY
UNIDENTIFIED SEX
ADOPTED IN TO THE FAMILY
AFFECTED
CARRIER
ADOPTED OUT OF THE FAMILY
RELATIONSHIP
PARENTS AND
CHILDREN
(one boy, one girl) in order
of birth
Generations
FRATERNAL TWINS
IDENTICAL TWINS
DECEASED
ADOPTED BY ONE FAMILY
MEMBER FROM ANOTHER
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 trait
While 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,
aa
keep in mind that the pedigree may not be
possible for a dominant trait; it may not be
possible to write the genotypes.
A?
Is it possible that the pedigree here is for
an autosomal dominant trait? NO!
aa
aa
Write the genotypes in the symbol for each person
in the pedigree below assuming that it is for a
dominant trait.
Is it possible that this pedigree is for an autosomal
dominant trait? YES!
What can you conclude from these two examples
about the parents of a child that has a dominant
characteristic?
aa
A?
A?
aa
One parent must also
carry the dominant trait.
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.
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?
A?
A?
aa
aa
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
Is it possible that the pedigree below is for an
autosomal recessive trait?
NO!
aa
aa
A?
Assuming that the pedigree below is for a recessive
trait, write the genotype in the symbol for each
person.
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?
aa
aa
aa
YES!
aa
aa
aa
All children will
be affected!
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.
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.
Aa
Aa
aa
A?
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.
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!
aa
Aa
Notice that two generations were aa
skipped in this instance!
A?
Aa
Aa
A?
Aa
Aa
A?
A?
aa
A?
Determine if the pedigree below can be for a trait
that is X-linked recessive. Use the following
designations:
Start by filling in the
XA = normal
individuals that you absolutely
Xa = the trait
know the genotypes for.
Y = Y chromosome
Can this pedigree possible show
a sex-X-linked recessive disorder?
a a
A
XX
X Y
NO!
XAY
Write the genotype within the symbol for each
person in the pedigree below.
Is it possible that this pedigree is for an X-linked
recessive trait
YES!
XaXa
XAY
XaY
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
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?
NO!
XAY
XAXa
XaXa
XAY
XaXa
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
Is it possible that this pedigree
is for an X-linked recessive
trait?
What genotypes are you
absolutely sure of?
XaY
Can you know what the
female’s genotype is?
YES!
Which parent did the son get the Xa gene from?
XAXa
XaY
XaY
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.
XaXa
XaY
XaXa
First, fill in the known genotypes.
Can these parents produce this
offspring, if the trait is sex-Xlinked?
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.
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.
For this pedigree, tell if the trait can be autosomal
dominant, autosomal recessive, or X-linked
recessive.
Sex-X-Linked?
Possible. #1 could be a carrier,
and pass the disorder on to her
her son
Autosomal
recessive?
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.
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
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.