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Human Genetics
Exploring the Human Genome
Human Chromosomes
 Let’s
Review:
– A diploid human cell contains 46
chromosomes
– A haploid gamete or sex cell has 23
chromosomes
– Chromosomes are a condensed form
of DNA that carries all of the
genetic information that makes up
that organism
Human Chromosomes




Scientists have been
analyzing our DNA to
see what makes us
human
They take pictures of
our DNA when it is
condensed into the
form of chromosomes
After that they group
the 23 pairs into
matched pairs
When chromosomes
are arranged like this it
is called karyotyping
(karyotype)
Human Chromosomes
 Of
the 46 chromosomes that make
up each of our cells two of them
are sex chromosomes
 It is our sex chromosomes that
determine whether or not we are
female or male
– Two X chromosomes and we are
female (XX)
– One X and one Y and we are male
(XY)
XY
Male
Sex
determination
X
XX
Female
X
Y
XX
Female
XY
Male
XX
Female
XY
Male
X
Human Chromosomes
The other 44
chromosomes are
known as autosomal
chromosomes or
autosomes
 This picture shows
what type of cell?
Sex cells or
autosomal cells?

Human Traits
 Humans
inherit genes according to
the principles that Mendel came up
with
 Both parents randomly assort their
genes into their sex cells and the two
sex cells are joined in fertilization
 Some traits are shown in the
phenotype of the offspring while other
traits are masked until further
generations
A Human Pedigree
A pedigree is a chart
that shows how
traits are passed
from one generation
to the next
 Spheres or circles
represent females
while boxes or
squares represent
males

Pedigrees illustrate inheritance

A half-shaded
circle or
square
represents a
carrier, a
heterozygous
individual.
Pedigrees illustrate inheritance

I
1
2
II
2
1
3
4
5
III
1
2
4
3
IV
1
2
3
4
5
A horizontal line
connecting a
circle and a
square indicates
that the
individuals are
parents, and a
vertical line
connects parents
with their
offspring.
Pedigrees illustrate inheritance

I
1
2
II
1
III
IV
1
2
1
3
2
4
4
3
2
5
3
4
5
Each horizontal
row of circles
and squares in
a pedigree
designates a
generation,
with the most
recent
generation
shown at the
bottom.
Pedigrees illustrate inheritance
I

1
2
II
1
3
2
4
5
III
?
1
2
4
3
IV
1
2
3
4
5
The
generations
are identified
in sequence by
Roman
numerals, and
each individual
is given an
Arabic number.
A Pedigree
Section 14-1
A circle
represents a
female.
A horizontal line
connecting a male and
female represents a
marriage.
A square
represents a
male.
A vertical line and a
bracket connect the
parents to their
children.
A half-shaded circle or
square indicates that a
person is a carrier of
the trait.
A completely shaded circle
or square indicates that a
person expresses the trait.
A circle or square that is not shaded
indicates that a person neither
expresses the trait nor is a carrier of the
trait. Some regular DUDE.
Human Traits
 It
can be quite difficult to trace an
actual trait through generations of a
family
 Some believe that you receive your
eyes from one parent and ears from
another
 Many traits, however, are considered
polygenic ; Meaning: a trait that is
controlled by many genes
Human Traits


The second reason
that it is difficult to
determine where you
receive your physical
characteristics from is
because only some of
your genes are
controlled by
inheritance
Many traits are
strongly influenced by
environmental, or nongenetic, factors
– Nutrition and exercise
– Habitat and lifestyle
In arctic foxes
temperature has an
effect on the expression of
coat color.
Human Blood Group Genes
 Why
is it important to know your
blood type?
– If you receive a transfusion of the
wrong blood type there is a very
strong chance that you will die
– Each person has a specific blood type
and can receive donor blood specific
to the type of blood that pumps
through their veins & arteries
Human Blood Group Genes

The ABO blood groups are the following:
– Type A , Type B , Type AB , and Type O
• There are three alleles for the ABO blood
group
•
IA ,
Phenotype
(Blood Type)
IB ,
Genotype
i
Antigen on
Red Blood Cell
Safe Transfusions
To
From
Human Blood Group Genes
 IA
and IB are codominant
This means:
 If you have both alleles you will
have Type AB blood
 If you have Type A or Type B with
the i allele you will express the
dominant trait of Type A or Type B
Phenotype
(Blood Type)
Genotype
Antigen on
Red Blood Cell
Safe Transfusions
To
From
Type A Blood
Type A blood is
the result of the
genotype IA IA or
IA i
 The surface of all
of the Type A
blood molecules is
the same
throughout the
body

Type B Blood


Type B blood is
the result of
IB IB or IB i
All of the blood
in a Type B
person has the
same surface
Type AB Blood


The only way to
have Type AB
blood is to have
the alleles IA IB
Because it has
both surfaces it
can accept donor
blood from all
blood types
Human Blood Group Genes
 The
i allele is recessive
This means:
 If it is with any other allele it will
be masked
 If someone has both ii they will
have Type O blood
Phenotype
(Blood Type)
Genotype
Antigen on
Red Blood Cell
Safe Transfusions
To
From
Type O Blood


With two
recessive alleles ii
you have the
Blood Type O
Type O blood has
a smooth surface
and because of
that it is a
universal donor
Human Blood Group Genes
 Blood
transfusions are specific
Type AB is the universal acceptor
 Type AB can ONLY donate to
another Type AB !!
Type O is the universal donor
 Type O can ONLY accept another
Type O blood type
Phenotype
(Blood Type)
Genotype
Antigen on
Red Blood Cell
Safe Transfusions
To
From
Human Blood Group Genes
 Human
blood is governed by another
gene as well
 The Rh Blood group only has two
alleles
– Rh+ is dominant
 Rh+
/ Rh+
OR
Rh+ / Rh- is positive
– Rh- is recessive
 ONLY
Rh- / Rh- is a negative blood type
Human Blood Group Genes
 When
a doctor refers to your
blood type he or she will use
both groups
 For
example: you may have
Type O negative blood
Autosomal Disorders
 There
are three types of
autosomal disorders in humans:
– Disorders caused by:
Recessive alleles
Dominant
alleles
Codominant
alleles
Recessive Autosomal
Disorders


Albinism – is the
lack of the
pigment melanin
in the skin, hair,
and eyes
In this chart it
shows that you
must have both
(aa) recessive
alleles to be
“albino”
Recessive Autosomal Disorders
People with PKU
(phenylketonuria)
lack the enzyme
needed to break
down phenylalanine
 Phenylalanine is
found in milk and
many other foods
 PKU is carried by a
recessive allele
found on
chromosome 12

Simple Dominant Traits

A cleft chin,
widow’s peak
hairline,
hitchhiker’s
thumb, almond
shaped eyes, thick
lips, and the
presence of hair
on the middle
section of your
fingers all are
examples of
dominant traits.
Dominant Autosomal Disorders
Huntington’s


disease
Huntington’s disease is a lethal
genetic disorder caused by a rare
dominant allele.
It results in a breakdown of certain
areas of the brain.
Huntington’s disease
Ordinarily, a dominant allele with such
severe effects would result in death before
the affected individual could have children
and pass the allele on to the next
generation.
 But because the onset of Huntington’s
disease usually occurs between the ages
of 30 and 50, an individual may already
have had children before knowing whether
he or she is affected.

Typical Pedigree of Huntington’s
Disease
I
1
2
II
2
1
4
3
5
III
1
2
3
4
5
Incomplete Dominance
Appearance of a third phenotype


When inheritance follows a pattern of
dominance, heterozygous and homozygous
dominant individuals both have the same
phenotype.
When traits are inherited in an incomplete
dominance pattern, however, the
phenotype of heterozygous individuals is
intermediate between those of the two
homozygotes.
Incomplete Dominance



For example, if a homozygous red-flowered
snapdragon plant (RR) is crossed with a
homozygous white-flowered snapdragon
plant (R′ R′), all of the F1 offspring will have
pink flowers.
The new phenotype occurs because the
flowers contain enzymes that control
pigment production.
The R allele codes for an enzyme that
produces a red pigment. The R’ allele
codes for a defective enzyme that makes
no pigment.
Incomplete
dominance:
Appearance of
a third
phenotype
Red
All
pink
Red
(RR)
White
(R’R’)
White
Pink
(RR’)
Pink
(RR’)
All pink flowers
1 red: 2 pink: 1 white
Incomplete dominance:
Appearance of a third phenotype
 Because
the heterozygote has
only one copy of the R allele, its
flowers appear pink because
they produce only half the
amount of red pigment that red
homozygote flowers produce.
Because the heterozygote
has only one copy of the R
allele, its flowers appear
Red
pink because they produce
only half the amount of red
pigment that red
All
homozygote flowers
pink
produce.
Red
(RR)
White
(R’R’)
White
Pink
(RR’)
Pink
(RR’)
All pink flowers
1 red: 2 pink: 1 white
Human Genes & Chromosomes
Genes are located on chromosomes and
each chromosome in the human genome
is a different size
 On each chromosome can be hundreds or
even thousands of genes

Locating Genes
Gene Sequence
Promoter
Start
signal
Gene
Stop
signal