Transcript Human Genetics: Dominant & Recessive Trait

Human Genetics:
Dominant & Recessive Traits
Human Genetics:
Dominant & Recessive Traits
The physical characteristics below are common
genetic traits inherited from one generation to the
next:



Free vs. Attached Earlobes
Straight vs. Curved Thumbs
Bent vs. Straight Pinky
Review the following slides that contain:


Definition and images of each genetic trait
Identification of the Dominant / Recessive trait
Allele: An alternate form of a gene.
Alleles occur at loci on chromosomes


Dominant: Only one allele
at a locus is expressed. The
other (recessive gene) is
suppressed.
Recessive: An allele that is
suppressed in the presence
of a dominant gene. If the
two recessive alleles occur
at a locus, then the trait is
expressed
Free vs. Attached Earlobes
Free earlobes (dominant trait)
hang below the point of
attachment to the head.
Attached ear lobes (recessive
trait) are attached directly to the
side of the head.
Straight vs. Curved Thumbs
Straight thumbs (dominant
trait) can be seen as nearly a
straight line and may contain a
slight arch when viewed from
the side as in the illustrations.
Curved thumbs (recessive
trait) can be seen as part of a
circle.
Bent vs. Straight Pinky
Bent pinky (dominant trait)
vs. Straight pinky (recessive
trait):
1.
Hold your hands together as if
you are covering your face.
2.
If the tips of the pinkies (or
baby fingers) point away from
one another, the pinkies are bent
(dominant trait).
Tongue rolling
People with the
DOMINANT allele can roll
their tongues into a tube
shape.
People with 2 recessive
versions are non-rollers
Tongue rolling
People with the
DOMINANT allele can roll
their tongues into a tube
shape.
People with 2 recessive
versions are non-rollers
Thumb Crossing
In a relaxed interlocking of the fingers, left
thumb over right results from having 1 or 2
copies of the dominant version of the gene.
People with 2 recessive places right thumb
over left
Mid Digit Hair
People lacking hair in the
middle segments of the
finger have 2 recessive
versions of the gene
Not Everything is Genetic
100%
Environmental
Struck by lightning
Infection
Weight
Hair Colour
Cancer
Diabetes
Height
100%
Genetic
Sex, Down syndrome, achondroplasia
Co-dominant




The alleles for curly hair and
straight hair are examples of
alleles for a trait that are
codominant.
Individuals with curly hair are
homozygous for curly hair
alleles.
Individuals with straight hair
are homozygous for straight
hair alleles.
Individuals who are
heterozygous, with one of each
allele have wavy hair, which is
a blend of the expressions of the
curly and straight hair alleles.
Codominant Continued



In codominance, neither phenotype is
completely dominant. Instead, the
heterozygous individual expresses
both phenotypes.
A common example is the ABO
blood group system. The gene for
blood types has three alleles: A, B,
and O type .
O type is recessive to both A and B.
The A and B alleles are codominant
with each other. When a person has
both an A and a B allele, the person
has type AB blood.
Karotype
X-linked recessive




Many more males than
females show the disorder.
All the daughters of an
affected male are
“carriers”.
None of the sons of an
affected male show the
disorder or are carriers.
e.g., hemophilia
X-linked
X-linked dominant



Affected males pass the disorder to all
daughters but to none of their sons.
Affected heterozygous females married
to unaffected males pass the condition
to half their sons and daughters
e.g. fragile X syndrome
X-linked Dominant