Transcript Human Chromosomes

Ch. 14 The Human
Genome
Ch. 14 Outline
 14-1: Human Heredity
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Human Chromosomes
Human Traits
Human Genes
From Gene to Molecule
Ch. 14 Outline
 14-2: Human Chromosomes
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Human Genes and Chromosomes
Sex-linked Genes
X-Chromosome Inactivation
Chromosomal Disorders
 14-3: Human Molecular Genetics
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Human DNA Analysis
The Human Genome Project
Gene Therapy
Ethical Issues in Human Genetics
Human Chromosomes
 Karyotypes:
 A Picture of chromosomes arranged in rows is a
karyotype
Human Chromosomes
 Humans have 23 pairs (46 total) chromosomes.
 Two of the 46 chromosomes are called sex
chromosome because they determine an
individual’s sex.
 In Human’s:
Female – two copies of large X chromosome
Male – one X and one small Y chromosome
Karyotype
Human Chromsomes
 Autosomes: the remaining 44
chromosomes. They do not determine the
sex of the organism.
 All Human egg cells carry a single X
chromosome.
 Half of all sperm cells carry an X
chromosome and half carry the Y.
 This ensures that about half of the
zygotes will be female XX and half will
be male XY.
Human Traits
Biologists must identify an inherited
trait controlled by a single gene
Must establish that the trait is
actually inherited and not the result
of environmental influences
Human Traits
They study how the trait is passed
from one generation to the next
Scientists use a pedigree chart to
help study how a trait is passed
from one generation to the next.
 Pedigree: a chart that shows the
relationships within a family.
How to read a pedigree
A circle represents a
female.
A horizontal line
connecting a male and
female represents a
marriage.
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 square represents
a male.
A vertical line and a
bracket connect the
parents to their
children.
A circle or square
that is not shaded
indicates that a
person neither
expresses the trait
nor is a carrier of
the trait.
Pedigrees
These Charts are used to infer the
genotypes of family members.
They can reveal if traits are sex-linked,
dominant or recessive.
Using a Pedigree
 A human geneticist determined the pedigree
shown in the diagram with filled symbols showing
the affected individuals. How is this pattern of
inheritance described?
Using a Pedigree
 Below is a pedigree for an inherited lung
disease. Provide the genotypes of each of the
individuals marked with lower case letters.
Using a Pedigree
 Below is a pedigree for an inherited brain
disease. Provide the genotypes of each of the
individuals marked with lower case letters.
Brain Disease
Human Genes
 Biologists were able to identify genes that directly
control a single human trait. Some of the very first
genes to be identified were those that controlled
blood type.
 Blood Group Genes
Knowing a person’s blood group is important
during transfusions.
 Two blood groups:
Rh groups
ABO groups
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The Rh Blood Group
 The Rh blood group is determined by a
single gene with two alleles: Positive and
negative
 Rh+ is dominant to Rh The Rh factor is named after the Rhesus
Monkey where the factor was first isolated
 Very important for females to know
during pregnancies.
ABO Blood Groups
 There are three alleles for the ABO Blood Group:
 IA, IB,
I
 “i” is the recessive allele. ii  type O blood
 IAIB are codominant  type AB blood
 IAIA or IAi  type A Blood
 IBIB or IBi  type B Blood
ABO Blood Groups
Phenotype
(Blood Type
Genotype
Antigen on
Red Blood Cell
Safe Transfusions
To
From
Antigens and Blood
Disorders in Humans
 Genetic Disorders may be caused by:
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Recessive Alleles
 Ex.
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CF, PKU, Tay-Sachs
Dominant Alleles
 Huntington’s
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Disease
Codominant Alleles
 Sickle
Cell Anemia
Concept Map
Autosomol
Disorders
caused
by
Recessive
alleles
Dominant
alleles
include
Galactosemia
Albinism
Cystic
fibrosis
Phenylketonuria
Tay-Sachs
disease
Codominant
alleles
include
include
Huntington’s
disease
Sickle cell
disease
Achondroplasia
Hypercholesterolemia
Sex-Linked Genes
 Sex-linked genes: Genes Located on the sex
chromosomes
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Many genes are located on the X chromosome
Males have just one X chromosome. Thus, all X
linked alleles are expressed in males, even if they
are recessive.
 Sex-linked disorders are caused by genes on the
X or Y chromosome
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Colorblindness, Hemophilia
Sex-Linked Genes : Pedigree for Color Blindness
X-Chromosome Inactivation
 Females have two X chromosomes but males
only have one. How do females cells “adjust”
to having an extra X if males can survive with
just one?
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One of the X chromosomes in female cells are
randomly switched off. Those are called Barr
bodies.
Chromosomal Disorders
 Nondisjunction: failure of chromosomes to
separate correctly in meiosis
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This leads to an abnormal number of chromosomes in
gametes
Down Syndrome (3 copies of chromosome 21 
“trisomy”)
 Ex:
Nondisjunction
Homologous
chromosomes
fail to separate
Meiosis I:
Nondisjunction
Meiosis II
Nondisjunction can occur with autosomes or sex
Chromosomes during meiosis
Chromosomal Nondisjunction Disorders
Down Syndrome Down Syndrome
1 in 31,000 births
46 chromosomes
XY=97%
XX=3%
Trisomy 21
1 in 1,250 births
47 chromosomes
XY or XX
#21 Trisomy
Nondisjunction
Down Syndrome
Short, broad hands
Stubby fingers
Rough skin
Impotency in males
Mentally impaired
Small round face
Protruding tongue
Short lifespan
Patau’s Trisomy Syndrome
1 in 14,000 births
47 chromosomes
XY or XX
#13 Trisomy
Nondisjunction
Patau’s Trisomy Syndrome
Small head
Small or missing eyes
Heart defects
Extra fingers
Abnormal genitalia
Mentally impaired
Cleft palate
Most die a few weeks
after birth
Edward’s Trisomy Syndrome
1 in 4,400 births
47 chromosomes
XX =80%
XY=20%
#18 Trisomy
Nondisjunction
Edward’s
Trisomy Syndrome
Small head
Mentally impaired
Internal organ abnormalities
90% die before 5 months of
age
Turners Syndrome
1 in 5,000 births
45 chromosomes
X only
#23 Monosomy
Nondisjunction
Turners Syndrome
96-98% do not survive to birth
No menstruation
No breast development
No hips (curve)
Broad shoulders and neck
Jacob’s Syndrome
1 in 1,800 births
47
chromosomes
XYY only
#23 Trisomy
Nondisjunction
Jacob’s Syndrome
?
Normal physically
Normal mentally
Increase in testosterone
More aggressive
Normal lifespan
Kleinfelter Syndrome
1 in 1,100 births
47 chromosomes
XXY only
#23 Trisomy
Nondisjunction
Kleinfelter Syndrome
Scarce beard
Longer fingers and arms
Sterile
Delicate skin
Low mental ability
Normal lifespan
Triple X Syndrome
1 in 2,500 births
47 chromosomes
XXX only
#23 Trisomy
Nondisjunction
Triple X Syndrome
Normally physically
Normal mentally
Tall
Fertile
Short lifespan
The Human Genome Project
 A research project to sequence (identify in order)
all the bases in Human DNA ~3.2 BILLION pairs!
 Some discoveries:
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A large amount of DNA does not code for
proteins
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Humans only have 30,000-40,000 genes
(scientists expected 100,000)
The Human Genome Project
Website
 http://www.genome.gov/
 Really interesting Information about the Human
Genome Project. It might help you understand
stuff better.
 EDUCATE YOURSELF!
Gene Therapy
 Information about the human genome might be
used to cure genetic disorders though the use of
gene therapy.
 Gene therapy: the process of changing a gene
that causes a genetic disorder
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It replaces the faulty gene with a normal, working
gene
Ethical Issues
 If Human cells can be manipulated to cure
disease, should biologists try to engineer
people with specific traits?
 What will happen to the human species if
we design our own bodies?
 Should we clone humans?