Chapter 14
The Human Genome
Pg. 341
Section 14-1 Human Heredity
 In
order to learn more about
humans, scientists started looking at
our chromosomes.
– A Chromosome is tightly coiled DNA
that becomes visible under a
microscope during mitosis (cell
division).
Karyotypes
 Analyzing
chromosomes
– Photograph cells during mitosis (when
chromosomes are easy to see).
– Cut out the picture of the chromosomes
– Group them together in pairs.
– This picture of precisely
organized chromosomes
is called a karyotype.
Karyotypes
 Allows
us to see homologous
chromosomes, sex chromosomes,
and autosomes.
Humans
 Humans
have 46 chromosomes in a
typical body cell.
– Sperm cells have 23 and egg cells have 23 so
when they combine the fertilized egg has a
complete set of chromosomes.
 Sex
Chromosomes: determine a
persons gender (2).
– Females = XX
– Males = XY (the Y chromosome is much smaller than
an X)
 Autosomes:
all chromosomes except
the sex chromosomes (44)

http://en.wikipedia.org/wiki/List_of_organisms_by_chromosome_count
How to write it out!


Is this a girl or boy?
To write out their
karyotype scientists
use the following
method.
– Write the total # of
chromosomes.

46
– Write out the sex
chromosome
combination


XX or XY
This example is 46,XY
Try this one!
Did you get…
 47,
XX +21
– There were 47 chromosomes in this
karyotype.
– There were 2 X chromosomes making
this person a …….
– Now we need to indicate where the
extra chromosome was so we do that
with a + since it was extra and a 21 to
indicate where the extra chromosome
was found.
Boy or Girl?

Females carry two X chromosomes = XX
– This means that all human egg cells should
carry a single X chromosome (23,X)

Males carry one X and one Y = XY
– Half of all sperm cells should carry an X
chromosome (23, X)
– The other half should carry a Y chromosome
(23,Y)

These factors ensure that the just about
half of all offspring should be 46,XX and
half 46,XY.
– See Punnett Square on pg. 342.
Human Traits
 Pedigree
charts show relationships
within a family and are used to
determine if a trait is inherited rather
than a result of environmental
influences.
– Genetic counselors use pedigree charts
to infer genotypes of family members.
– Circles Represent females
– Squares Represent Males
 See
example on pg. 342
The Addiction Gene??

Biological differences that may make someone
more or less vulnerable to addiction.
– It may be harder for people with certain genes to quit once
they start or they may experience more severe withdrawal
symptoms if they try to quit.

Factors that make it harder to become addicted
also may be genetic.
– For example, an individual may feel sick from a drug that
makes other people feel good.

But someone's genetic makeup will never doom
them to inevitably become an addict. Remember,
environment makes up a large part of addiction
risk.
http://learn.genetics.utah.edu/content/addiction/
pi/
Genes and the Environment

Some human traits are almost impossible
to associate with single genes.
– Some traits are controlled by many genes.
 Eye
shape, ear shape, etc.
– Many traits are strongly influenced by
environmental factors including nutrition and
exercise.
 Good
nutrition has lead to an increase in height by
10cm since the 1800’s in Americans and British.
Human Genes
 Human
genome – the complete set
of our genetic information.
– Includes tens of thousands of genes.
– Difficult to do because of our long
generation times, complex life cycle,
and produce few offspring.
- Completed in early 2000’s
Human Genes
 Blood
Group Genes
– Human blood comes in a variety of
genetically determined blood groups
– A number of genes are responsible for
human blood groups
Human Genes
 Blood
Group Genes
– Best known blood groups are ABO and
the Rh
– Blood Groups are determined by
multiple alleles
Recessive Alleles
 Genetic
disorders have helped
scientists learn more about genes.
– Some disorders are autosomal
recessive.
– The presence of abnormal functioning
gene is revealed only when an abnormal
or nonfunctioning allele affects the
phenotype
 PKU,
Albinism, cystic fibrosis, etc.
Recessive Alleles
 Phenylketonuria
(PKU) – lack the
enzyme to break down phenylalanine
– Must have inherited the allele for the
trait from both parents
Dominant Alleles
 Expressed
even when the recessive
allele is present
 Achondroplasia (Dwarfism)
 Huntington's Disease (nervous
system disorder)
Codominant Alleles
 Sickle
cell disease – small change in
DNA of a single gene
 Common in African Americans
 Red Blood cells are bent and twisted
Sickle Cell
 Hemoglobin
– protein in red blood
cells that carries oxygen
 In sickle cell patients one DNA base
change makes an amino acid for
valine not glutamic acid (different
sequence of amino acids)
Section 14-2
Human Chromosomes

Almost every human cell contains more
than 6 billion base pairs of DNA.
– All of our DNA is packaged into 46
chromosomes.
 Genes
make up a small part of your
chromosomes. Only 2% of the DNA in your
chromosomes functions as genes, which
make proteins, that give us our traits.
– Genes located close on the same chromosome
are usually passed on together.
Chromosomes 21 and 22
Smallest human autosomes.
 These were the first two chromosomes to
be sequenced.
 Chromosome 22

– Contains around 545 genes
– Very important to human health.
– Contains long stretches of repetitive DNA that
do not code for proteins.
 Unstable

sites that can easily rearrange
Chromosome 21 is similar, also having
many regions with no genes.
Chromosome 21 Sequence
Chromosome 22
Sex Linked Genes

Genes located on both the sex
chromosomes (X and Y). These are called
sex-linked genes.
– More than 100 genetic disorders have been
mapped to the X chromosome.
 Males
have just one X chromosome. Thus ALL Xlinked alleles are expressed in males, even if they are
recessive.
– Color blindness, hemophilia, muscular dystrophy, etc.
– Three genes associated with color vision are located on
the X chromosome
– The Y chromosome is much smaller and carries
only a few genes.
X
Chromosome
 Contains around
1,000 genes!
– Learning disabilities
– Colorblindness pg.350
– Hemophilia
– Muscular Dystrophy
– Etc…
X-Chromosome Inactivation
Females = XX
Males = XY
 If one X is enough in males why do
females need 2?
 In
female cells, one X chromosome is
randomly switched off.
 This turned off chromosome turns into a
dark spot in the nucleus called a Barr body.
– A condensed x chromosome that is inactive
Cat Coat Color
 In
cats, a gene that controls coat
color is on the X chromosome.
– One X may have an allele for orange spots, the
other X may have an allele for black spots.
XoXb
– Females can be calico because in some parts
of their body the Xo is activated and
in other areas the Xb is activated.
– Males can only have spots of
one color.
Chromosomal Disorders

During meiosis, errors can happen.
– The most common error is called nondisjunction. Nondisjunction is when pairs of
chromosomes fail to separate during meiosis
(sex cell formation) which causes an abnormal
number of chromosomes in a sex cell.
– If fertilized, a child may be born with a
chromosomal disorder.
– http://www.biostudio.com/d_%20Meiotic%20N
ondisjunction%20Meiosis%20I.htm
Down’s Syndrome
Trisomy means three bodies.
“Trisomy 21” means that a person has 3 number 21
chromosomes. This gives a person Down Syndrome.
In the US 1 out of 800 babies has Downs.
 Symptoms

– Mental retardation
– Increased susceptibility to diseases.
– Higher incidence of birth defects.
Sex Chromosome Disorders
 Turner’s
Syndrome: only 1 X
– Sterile females (don’t go through puberty)
– Affects 1 in 2,500 girls
– Short stature 4’7
– Webbed neck
– Abnormal bone development
Klinefelter’s Syndrome
 In
Males they have XXY (or XXXY)
– Sterile
– Affects physical, language and social
development.
– Taller, less muscle, less facial hair,
breasts all due to low testosterone.
No X
 There
have been no reported
instances of babies born without an
X Chromosome
– X chromosome contains genes vital for
the survival and development of an
embryo
Videos
 Williams
Syndrome
 Turners
 Achondroplasia
 PKU
 Amish
 Children
of Glass
Project time
 Look
at a chromosome map and
select a genetic disorder we can find
in its genes.

http://www.ornl.gov/sci/techresources/Human_Genome/posters/chromosome/choos
er.shtml
 You
will be making an informational
presentation or brochure about this
disorder or a chromosomal disorder
of your choice.
Genetics Unit Review
 What are genes?
 http://www.watchknow.org/Video.aspx?VideoID=
3775&CategoryID=1138
 What are SNP’s?
 http://www.watchknow.org/Video.aspx?VideoID=
7256&CategoryID=1138
 Where

do your genes come from?
http://www.watchknow.org/Video.aspx?VideoID=
7255&CategoryID=1138