For a long time, humans have selected the best plants and animals to breed
Why? Examples? Milk Cows
• 1947 - produced 4,997 lbs... of milk/year
• 1997 - produced 16,915 lbs.... of milk/year
Increasing the frequency of desired alleles in a population is the essence of genetic technology
Mating between closely related individuals
Why? Done to make sure that
breeds consistently exhibit a trait and to eliminate undesired trait • Creates purebred lines
Can be bad also • Can bring out harmful,
recessive alleles in a “family”
It can be beneficial to create hybrids
For example, disease-resistant plants crossed with plants that produce bigger fruit • Offspring get both qualities
Hybrids produced by crossing two purebred plants are often larger and stronger than their parents
1. Suppose you want to produce a plant that has red
flowers and speckled leaves. You have two offspring,
each having one of the desired traits. How would you
proceed?
2. Why is inbreeding rarely a problem among animals in
the wild?
3. Hybrid corn is produced that is resistant to bacterial
infection and is highly productive. What might have
been the phenotypes of its two parents?
4. How is selective breeding done?
5. What effect might selective breeding of plants and
animals have on the size of Earth’s human population?
Why?
Genetic engineering is a faster
and more reliable method for
increasing the frequency of an
allele in a population
This involves cutting - or cleaving
- DNA from one organism into
small fragments and inserting the
fragments into a host organism of
the same or a different species
Also called recombinant DNA
technology.
• Connecting, or recombining,
fragment of DNA from different
sources
Plants and animals that contain functional recombinant DNA from an organism of a different genus
• Ex: they grow a tobacco plant that glows from a gene in a firefly
3 steps:
• Isolate the foreign DNA fragment to be inserted
• Attach the DNA fragment to the carrier
• Transfer the DNA into the host organism
Bacterial proteins that have the ability to cut both strands of the DNA molecule at a specific sequence
Many enzyme cut in palindromes • Ex: a protein only cuts at AATT, it will cut the two
fragments at different points - not across from each other (called sticky ends) Called sticky ends because they want to bond with things due
to their “open” end
These sticky ends are beneficial, because if the same enzyme is used in both organisms, they will have identical ends and will bond with each other
A vector is the means by which DNA from another species can be carried into the host cell
If the plasmid and the DNA fragment were both cleaved with the same enzyme, they will stick together because they have “sticky ends”
A second enzyme helps this process
GSLC
E. coli has been modified to produce
an indigo dye to color blue jeans
Recombinant DNA has been used to
help production of cheese, laundry
detergent, paper production, sewage
treatment • Increase enzyme activity, stability
and specificity
Production of Human Growth Hormone to treat pituitary dwarfism
Insulin Production by bacterial plasmids
Antibodies, hormones, vaccines, enzymes, and hopefully more in the future
Mice reproduce quickly and have
chromosomes that are similar to humans’
The genome is known better
The roundworm Caenorhabditis elegans
and the fruit fly, Drosophila melanogaster
are also well understood • Used in transgenic studies
A transgenic sheep was produced that
contained the corrected human gene
for hemophilia
This human gene inserted into the
sheep produces the clotting protein in
the sheep’s milk • This protein can then be given to hemophilia
patients
Crops that stay fresh longer and are
more resistant to disease
Plants resistant to herbicide so weeds
can be killed easier
Higher product yields or higher in
vitamins
Peanuts and soybeans that don’t cause
allergic reactions
Dolly was the first animal cloned in 1997
Since then, goats, mice, cattle, pigs, etc. have been
cloned
Take DNA out of embryonic stem cells or zygote
(enucleation)
Insert new DNA (germ or somatic cell nuclear
transfer) with another pipette or electrical current
A way to artificially replicate DNA
DNA is heated and the strands separate
An enzyme isolated from a heat-loving bacterium is used to replicate the DNA when nucleotides are added (in a thermocycler)
• Makes millions of copies in less than a day
Why could this be helpful?
Animation
The gel is like firm gelatin • Molded with small wells at one end
• Has small holes in the gel (not visible)
DNA has a slight negative charge
A current is run through the gel and an
added buffer fluid • DNA will move towards the positive end
Smaller fragments fit through the holes
in the gel better and move farther
gslc
First, PCR is done to make millions of copies Separate the strands of DNA Cut them at certain places, put fluorescent tags on the
end of them by the different bases The fragments are separated according to size by a
process called gel electrophoresis
• Produces a pattern of fluorescent bands in the gel
Put the puzzle back together
Shows the sequence of DNA
PBS flash animation
Grunander’s mtDNA
How are transgenic organisms different from natural organisms of the same species?
How are sticky ends important in making recombinant DNA?
How does gel electrophoresis separate fragments of DNA?
What is a restriction enzyme? What is PCR? Explain two ways in which recombinant bacteria
are used for human applications. Many scientists consider engineering to be
simply an efficient method of selective breeding. Explain.
In 1990, scientists in the U.S. organized the Human Genome Project (HGP)
• An international effort to completely map and sequence the human genome
Approximately 20,000 - 25,000 genes on 46 chromosomes
In February, 2001, the HGP published its working draft of the 3 billion base pairs in most human cells
Video
Probably the biggest application so far has been the identification of genetic disorders
Predicted that you will be able to sequence your DNA for about $1000 in the next decade
Do you want to know what you’ve got?
Can be done prenatal • Take cells from
amniotic fluid and look for deviations
• Increase abortions?
The insertion of normal genes into human
cells to correct genetic disorders
Have been used for SCID (severe
combined immunodeficiency syndrome),
cystic fibrosis, sickle-cell anemia,
hemophilia and others.
Scientists are hopeful his will help treat
cancer, heart disease, AIDS and many
other things.
Cystic Fibrosis Case Study
Gene Therapy for
Breast Cancer
Genes are separated by segments of
noncoding DNA (“junk DNA”) • These segments produce distinct combinations of
patterns unique to each individual
What are the uses?
Small DNA sample obtained
Clone samples with PCR
Cut into fragments Separated by gel
electrophoresis Chances of two
identical matches are infinitesimally small
Virtual Lab The Romanovs
An undifferentiated cell • Doesn’t have a specific function yet
Will eventually become differentiated • It will get a specific function and then can only
do certain things
GSLC site
What is the Human Genome Project?
Compare a linkage map and a
sequencing map.
What is the goal of gene therapy?
Explain why DNA fingerprinting can be
used as evidence in law enforcement.
Describe some possible benefits of the
Human Genome Project
A pedigree is a graphic representation of the genetic inheritance of ONE trait
• Generally used to study historical inheritance – make inferences
Symbols
• Circle - female
• Square - male
• Shaded in - shows the trait
• Half shaded in - is a carrier, heterozygous individual that does not show the trait
• Each horizontal row is a generation - represented by roman numerals
• Parents are connected horizontally
• Children are connected to parents with a vertical line
PTC
Most genetic disorders are recessive
Cystic Fibrosis 1/25 white Americans is
a carrier 1/2500 white Americans
inherits the disorder Defective protein in the
plasma membrane • Formation and
accumulation of thick mucus in the lungs and digestive tract
Tay-Sachs Disease
Results in the absence of an enzyme that normally
breaks down a lipid produced and stored in the central
nervous system(CNS)
• The lipid accumulates
Common among Ashkanazic Jews - Eastern Europe
Blue stained areas are swollen neurons
Phenylketonuria (PKU) Absence of an enzyme that
converts the amino acid, phenyalanine, to tyrosine.
Phenylalanine accumulates and damages the CNS (in milk, diet foods) • Can also damage a heterozygous
fetus with blood from homozygous recessive mother
Common in those with ancestry from Norway, Sweden, or Iceland
Cleft chin, widow’s
peak, unattached
earlobes,
hitchhiker’s thumb
(back more than 30
degrees), almond-
shaped eyes, thick
lips, mid-digital hair
Huntington’s Disease Breakdown of certain areas of the brain Usually, dominant disorders like this
disappear, because it kills before the individual can reproduce
In this disease, onset happens between 30 and 50
1. What do these symbols represent in a pedigree:
square, circle, unshaded circle, shaded square,
horizontal line, vertical line?
2. Describe a genetic disorder that is inherited as a
recessive trait.
3. How are the cause and onset of symptoms of
Huntington’s disease different from those of PKU
and Tay-Sachs disease?
4. Describe one trait that you inherited by simple
dominance. Will you pass it on to your offspring?
5. Suppose that a child with unattached earlobes has
a mother with attached earlobes. Can a man with
attached earlobes be the child’s father?
There are 22 pairs
of homologous
chromosomes
called autosomes
The 23rd pair of
chromosomes are
called the sex
chromosomes
Male XY
Female XX
The inheritance pattern of a trait is controlled by two or more genes • Skin color, height, corn cob length
• Genes may be on the same chromosome or different chromosomes
• Each gene may have two or more alleles
Each allele represented by an uppercase letter contributes a small, but equal, portion to the trait being expressed • The result is that phenotypes show a continuous
range of variability
back
Hypothetical Example Stem length in a plant is
controlled by 3 different genes: A, B, D. • Each gene is on a different
chromosome and has two alleles (A & a, B & b, D & d)
• Each plant will have 6 alleles for stem length
• Each tall allele contributes 2 cm (4 cm base minimum)
What would a plant with a genotype of AaBbDd look like?
A population will follow a normal curve. back
The study of the changes in
phenotype of gene expression
caused by something other
than the DNA
• May be passed on
Deals with certain genes being
turned on or off in an
individual
• Cell memory – cells “remember”
which genes were turned on or
off through changes to the
chromatin proteins
May be one reason we can
have so few genes
Genetics only determine
potential
External Environmental
Influences
• Temperature, nutrition, light,
chemicals and infectious
agents can all influence gene
expression (arctic fox, siamese cat)
Internal Environmental
Influences • Hormones, age
1. How is gender determined in humans? Explain the chromosome difference.
2. The color of wheat grains shows variability between red and white with multiple phenotypes. What is the inheritance pattern?
3. What is epigenetics? 4. Why do more men go bald than women? 5. Armadillos always have four offspring that have
identical genetic makeups. Suppose that, within a litter, each young armadillo is found to have a different phenotype for a particular trait. How could you explain this?
An example of codominance in humans
Common in African Americans and Americans with ancestry near the Mediterranean Sea
Homozygous – hemoglobin differs from normal by 1 amino acid
• Changes the shape of the red blood cells (rbc)
• Slow blood flow, block small vessels, and result in tissue damage and pain
Heterozygous – produce both normal and
sickle hemoglobin (codominance)
• Enough that they don’t have major health
problems
• Show sickle-cell related disorders when oxygen
isn’t readily available
There are three alleles for the gene, “I” • IA, IB, and i
IA,IA (AA) or IA, i (AO) – blood type A IB, IB (BB) or IB, i (BO) – blood type B IA, IB (AB) – codominance, blood type AB ii (OO) – blood type O There are different molecules that are
produced on the surface of the rbc – represented by A and B
Your immune system fights against blood cells with different molecules
So who can donate blood to whom? IA, i x IB, i – What will be produced?
Separate gene from
ABO blood type
Simple heredity - “Rh+”
is dominant over “Rh-”
If an antiserum
agglutinates your red
cells, you are “Rh+” If it
doesn't, you are “Rh-”
Trisomy 21
The only autosomal
trisomy in which
affected individuals
survive to adulthood
• Occurs about 1 in 700
births
• A group of symptoms,
including some degree of
mental retardation, results
from trisomy 21
XO – Turner’s Syndrome
XXY – Klinefelter Syndrome
XXX – Trisomy X Syndrome
XYY Syndrome
Most of these individuals have some
degree of mental retardation and might
be infertile
Written a bit different because they are located on
the X or Y chromosomes (mostly X)
Red-Green Color Blindness
• Recessive allele on the X chromosome
• Females: XRXr does not have it, XrXr does
• Males – XrY has it, XRY does not
Why are there more color blind males than females?
Hemophilia
Recessive disease
that prevents the
blood’s ability to clot
In males – 1 in
10,000
In females – 1 in
100,000,000
Why the difference?
Both polygenic
traits
What was polygenic
inheritance?
How will this work
for skin?
How will this work
for eye color?
Human eye color, like skin color, is determined by polygenic inheritance. You can detect several shades of eye color, especially if you look closely at the iris with a magnifying glass. Often, the pigment is deposited so that light reflects from the eye, causing the iris to appear blue, green, gray, or hazel (brown-green). In actuality, the pigment may be yellowish or brown, but not blue.
Procedure: • 1. Observe the patterns and colors of pigments in the eyes of 5 classmates.
• 2. Use crayons to make drawings of the 5 irises.
• 3. Describe your observations.
Analysis
• 1. Observe How many different pigments were you able to detect in each eye?
• 2. Critique From your data, do you suspect that eye color might not be inherited by simple Mendelian rules? Explain.
• 3. Analyze Suppose that two people have brown eyes. They have two children with brown eyes, one with blue eyes, and one with green eyes. What pattern might this suggest?
1. Describe how a zygote with trisomy 21 is likely to occur during fertilization.
2. In addition to revealing chromosome abnormalities, what other information about an individual would a karyotype show?
3. What would the genotypes of parents have to be for them to have a color-blind daughter?
4. Describe a genetic trait in humans that is inherited as codominance. Describe the phenotypes of the two homozygotes and that of the heterozygote. Why is this trait an example of codominance?
5. A man is accused of fathering two children, one with type O blood and another with type A blood. The mother of the children has type B blood. The man has type AB blood. Could he be the father of both children? Explain your answer.
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