Chapters 13 & 14

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-”

O+ 38%

A+ 34%

B+ 9%

O- 7%

A- 6%

AB+ 3%

B- 2%

AB- 1%

A karyotype, a chart of chromosome pairs

during metaphase, is used to detect these

disorders

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.