Download Chapter 4: Modern Genetics

Modern Genetics
Human Inheritance
A. Traits Controlled by Single Genes
1. traits are controlled by 2 alleles
on a single gene
2. these traits have 2 distinctly
different phenotypes
3. ex: widow’s peak, dimples
Section 1: Human Inheritance
B. Multiple Alleles
1. some traits are controlled by a single
gene with more than one allele
2. because chromosomes exist in pairs, a
person can carry only 2 of these alleles
3. ex: blood types
Blood Types
Section 1: Human Inheritance
C. Traits Controlled by Many Genes
1. some human traits show a large
number of phenotypes because the traits
are controlled by many genes. The genes
act together as a group to produce a
single trait
2. ex: at least 4 genes control height, at
least 3 genes control skin color
Human Inheritance
D. The Effect of the Environment
1. effects of genes can be altered by the
environment
2. ex: height can be affected by diet
Human Inheritance
Male or Female?
1. one of the 23 pairs of chromosomes is called
the sex chromosomes
2. sex chromosomes are the only chromosomes
that don’t always match (as in males) – Y is
much smaller than X
3. eggs and sperm cells can each have only one
chromosome; females always contribute an X,
while males may contribute an X or a Y
4. XX = female XY = male
Human Inheritance
F. Sex-Linked Genes
1. alleles are passed from parent to child on sex
chromosomes
2. because females have 2 matching X chromosomes, a
dominant allele on one can mask a recessive allele
on the other
3. in males any allele on the X chromosome – even a
recessive one – will produce a trait
4. ex: color-blindness
5. carrier = person who has one recessive allele for a
trait and one dominant one. doesn’t have trait but
can pass it on
Human Genetic Disorders
1. genetic disorders are abnormal
conditions that a person inherits through
genes or chromosomes
2. are caused by mutations or changes in a
person’s DNA
Cystic Fibrosis
• carried on a recessive allele
• causes body to produce a
thick mucus in lungs and
intestine
• no cure
Cystic fibrosis website
C
c
C
CC
Cc
c
Cc
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Carriers!
Sickle-Cell Disease
• carried on a codominant allele
• prominent in Africans
• causes body to produce an abnormal form
of hemoglobin
• red blood cells become sickle shaped and
do not carry oxygen as well
• no cure – treatments available
• Sickle-Cell Website
sickle cell
Hemophilia
• carried on a recessive allele on the X
chromosome
• causes blood to clot slowly or not at all
• can be treated with clotting protein
• Hemophilia website
Human Inheritance
Pedigrees
1. a chart or family tree that tracks which
members of a family have a particular trait
The Walker Family Tree
James Henry
Dennis
Eden
Molly
Nancy
Clark
Steven
Brent
Sharum
Andrea
Neil
Sharum
Emily
Christine Marie
“Judy”
Brent
April
Joyce
Brent
Lisa
Steven
Rick
Down Syndrome
• caused by an extra copy of chromosome
21
• causes distinctive appearance and usually
some mental retardation
Down Syndrome Website
Diagnosing Genetic Disorders
• amniocentesis = fluid containing baby’s
cells is removed and analyzed
• karyotype = a picture of the chromosomes
arranged in pairs
• Karyotype website
The Blue Fugates
the methemoglobinemia gene
Genetic Counseling
• Doctors use karyotypes,
pedigrees and Punnett squares to
help couples understand their
chances of having a child with a
particular genetic disorder
Section 3: Advances in Genetics
• For thousands of years people have tried
to produce plants and animals with
desirable traits
Selective Breeding
the process of selecting a few organisms to serve as
parents of the next generation
Inbreeding
• crossing two individuals that have identical
or similar sets of alleles
• reduces an offspring’s chances of
inheriting new allele combinations
• increases the probability that organisms
may inherit alleles that lead to genetic
disorders
INBREEDING
(Mating of
closely related
individuals)
Pros
Cons
Produces uniform
or predictable
offspring.
Hidden (recessive)
genes show up and
can be eliminated.
Individuals will
"breed true" and
are "pure."
Doubles up good
genes.
Eliminates
unwanted traits.
Doubles up on faults and
weaknesses.
Progressive loss of vigor and
immune response.
Increased reproductive
failures, fewer offspring.
Emphasis on appearance
means accidental loss of
"good" genes for other
attributes.
Genetically impoverished
individuals.
Hybridization
• breeders cross two genetically different
individuals
• hybrid organisms that result are bred to
have the best traits of both parents
Mom & Dad
California Schnoodles
Cloning
• A clone is an organism that is genetically
identical to the organism from which it was
produced
1. Cloning Plants
a. cutting
2. Cloning Animals
a. much more difficult (Dolly)
Cloning
Genetic Engineering
Defined: genes from one organism are transferred into
the DNA of another; also called gene-splicing
1. Genetic Engineering in Bacteria
a. segments of human DNA can be spliced into
bacterial chromosomes. the bacteria then produce
human hormones
2. Genetic Engineering in Other Organisms
a. genes from one organism can be inserted into
another to achieve desired traits
3. Gene Therapy
a. inserting working copies of a gene directly into
cells in an attempt to correct a genetic disorder
Genetic Engineering
First human somatic gene therapy – On
September 14, 1990, the first human gene therapy
experiment was conducted on four year-old
Ashanti Desilva who suffered from ADA deficiency.
•Dr. W. French Anderson performed the
experimental therapy by infusing white blood cells
(with the correct genetic composition) into Ashanti
to correct her immunodeficiency.
•While the therapy did not yield a complete cure, it
did help correct the deficiency so that Ashanti only
takes small, weekly doses of the traditional PEGADA drug.
First gene therapy death – In September
1999, 18 year-old Jesse Gelsinger was the
first reported death to be directly caused by
gene therapy treatment.
Jesse suffered from OTC disease (ornithine
transcarboxylase deficiency), a liver
disorder that results in poisonous levels of
ammonia build-up in the body.
His disorder was being controlled through
diet and medication. Although he was
healthy and full of life, he chose to
participate in the gene therapy study
because of his desire to help others with
same disease.
Four days after starting treatment, he died
of multiple organ failure.
His death is thought to be a result of a
severe immune response to the adenovirus
carrier (the vector used to carry the altered
genes to his liver).
DNA Fingerprinting
• no two people, except identical twins, have
the same DNA
• DNA in blood, skin, saliva, hair, etc can be
used to solve crimes
Who Did It?
The 1st DNA
Fingerprint!
The Human Genome Project
genome = all the DNA in one cell of an
organism
• the main goal of the human genome
project is to identify the DNA sequence of
every gene in the human genome and
discover what the genes do
Are They Real???