Download Chapter 4 - Modern GENETICS

Chapter 4 - Modern GENETICS
Cells and Heredity Textbook
Gregor Mendel did a lot to initiate and progress
the Genetics--study of heredity.
• What organisms did Mendel study?
He studied pea plants.
Why were traits in pea plants (like tallness)easy to
study? These traits were clearly defined—like tall and short,
green or yellow, wrinkled or smooth. There is often
a definite dominant and definite recessive trait.
A Single gene with 2 alleles controls a trait.
• REVIEW of TRAITS:
One of the most important principles that governs life is inheritance
of genes. There are over 200 traits that are transmitted from
generation to generation in humans.
The physical traits are those that are expressed and what makes
every individual an 'individual'. These genes reside on specific
segments of the DNA. Each gene is grouped to form a chromosome
and each chromosome is found in the nucleus of the cell. There are
two copies of each gene present in an individual's body with the
exception of sex cells.
It is generally believed that the dominant alleles are the most
common traits observed in a population. However, this is not a
complete fact. Many times the alleles may be dominant, but the
allele for expression of a trait may be recessive. Thus, many times
the dominant trait is not expressed in an individual. Let me explain
this inheritance pattern in the following examples.
Now , we are going to look at:
• “Mendelian” traits in humans.
• Many of these traits have been
claimed to be controlled by ONE
gene with just 2 alleles. As we
continue to learn more, some
scientists disagree.
As you can see….
• Traits like hitchhikers thumb, mid-digit
hair, cleft-chin, curly hair, handedness,
etc are examples of…
– “Mendelian Inheritance”
– What is mendelian inheritance???
Traits are controlled by a single gene with 2 alleles, and
one alleles is generally dominant over the other.
HOWEVER……
• There are a variety of inheritance patterns for
the many traits that humans have.
• Right now , brainstorm traits that are more
complicated than “Mendelian traits”
Ex: height, skin color, eye color, hair
color, metabolism, body build, etc.
Some Inheritance Patterns
–1. Single gene with 2 alleles
–2. Single Gene with multiple alleles
–3. Traits controlled by many genes
–4. Sex – linked genes
Single Genes with Multiple
Alleles
• These genes have 3 or more forms (alleles).
• Humans can only carry 2 of them
• Ex: Blood
– Alleles:
• IA, IB, I
• IA and IB are codominant
– Blood Types
• A, B, AB, O
Traits controlled by many genes
• At least 4 different genes control height
• 3 or more genes control skin color
• Sex Chromosomes carry genes that determine
whether a person is male or female, and some other
traits.
– XX = female
• All female sex cells have an X chromosome
– XY = male
• Half of the male sex cells have an X chromosome and half have a Y
chromosome
Sex Linked Genes
• These genes are carried from parent to
offspring on the sex chromosomes.
• Sex-linked traits
– Ex: red/green colorblindness
– Occur more often in males.
• If there is a sex-linked trait controlled by a
recessive allele,
– If a guy gets it, he will have the trait because he
only has one X chromosome.
– If a girl gets it, there’s a good chance her other X
chromosome will be normal and she will not
express the trait.
Ex: Colorblindness
• It’s a trait controlled by a recessive allele on
the X chromosomes
– Carrier = a person who has one recessive allele for
a trait and one dominant allele. They do not have
the trait.
Effect of Environment
• Many of a person’s characteristics are
determined by an interaction between genes
and the environment
– Ex: bad dietaffects height
– Ex: hair dye
DO NOW
• Pg 117 Discover Activity
Human Genetic Disorders
• Genetic Disorder = abnormal condition that a
person inherits through genes or
chromosomes
– Caused by
• mutations in DNA
• Change in overall structure of chromosomes
• Change in number of chromosomes
Genetic Disorders
•
•
•
•
Cystic Fibrosis
Sickle-cell disease
Hemophilia
Down syndrome
Cystic Fibrosis
Body produces too thick
of mucus in lungs and
intestines
Mucus fill the lungs so
the person has trouble
breathing
The disease is carried on
a recessive allele
The recessive allele has
a mutation with 3 bases
missing from the DNA
Sickle-Cell Disease
Red blood cells has a special
protein that carries oxygen—
called hemoglobin
The sickle-cell allele is
codominant. A person with
one normal and one sicklecell allele will produce half
normal and half sickled blood
cells.
People with this disease have
abnormal hemoglobin, so
their red blood cells have
abnormal shapes that clog
blood vessels and can’t carry
oxygen well.
Hemophilia
A person’s blood clots
slowly or not at all.
They are at danger for
internal bleeding from
small bumps and
bruises.
It occurs on the
recessive allele of the X
chromosome
It’s a sex-linked disorder
Down Syndrome
A person with this
has an extra copy
of chromosome 21
in their cells.
Why does this
happen?
Chromosomes fail
to separate
properly in meiosis.
Pedigrees
• A chart or “family tree” use to track witch
members of a family have a particular trait
Which trait do you think is
dominant? Which is recessive?
Managing Genetic Disorders
• Doctors use tools such as karyotypes to help
diagnose genetic disorders.
• People with genetic disorders are helped
through medical care, education, job training,
and other methods
What’s a Karyotype??
• It’s a picture of all the chromosomes in a cell.
Chromosomes are arranged in pairs.
• They can reveal whether a person has the correct
number of chromosomes.
Sec 3 - ADVANCES IN GENETICS
• Genetic Techniques to produce organisms
with desirable traits:
– 1. Selective Breeding
– 2. Cloning
– 3. Genetic Engineering
1. Selective Breeding
HISTORY:
• In Mexico thousands of years ago, Mexican farmers
saved seeds from the healthiest corn plants each year.
Then, in the spring, they planted those seeds. After a
while, plants produced better corn and crops were
improved.
SELECTIVE BREEDING
Inbreeding
Crossing 2 individuals that
have similar characteristics.
Inbred organisms have alleles
very similar to those of their
parents.
• Ex: Take male and female turkeys
that are both plump and both grow
quickly. Their offspring will too.
• THE BAD: these organisms are
genetically very similar and often
inherit alleles that lead to genetic
disorders
SELECTIVE BREEDING
Hybridization
• Cross 2 genetically different organisms so that
the offspring will have the best traits from
both.
– Ex: cross a McIntosh apple with a Red Delicious to
get Empire.
•
2.
Cloning
Clone = organism that has exactly the same genes as the organism from which it
was produced
– PLANTS:
– African violet, just cut a stem from one plant and put it in soil.
– ANIMALS:
– Sheep and pigs have been cloned
3. Genetic Engineering
• Genes from one organism are transferred into
the DNA of another organism.
make medicines
improve crops
Genetic Engineeringin Bacteria
• Pg 126
Genetic Engineering…
• Scientists take human genes and insert them
into cells of cows so that they start to produce
a human protein in their milk. This protein is
needed by people with hemophilia.
Genetic Engineering……
• Scientists insert genes into the cells of plants
like tomatoes and rice so that they will survive
despite cold temperatures or poor soil.
Gene Therapy- A Thing of the
Future
• Inserting copies of a gene DIRECTLY into a
person’s cells.
Concerns about Genetic
Engineering
•
•
•
•
•
•
What are long-term effects?
Are they safe?
Are genetically engineered crops okay to eat?
Will these crops harm the environment?
Will these foods cause health problems?
Scientists are needed to study these concerns!
Learning about Human
Genetics
• THE HUMAN GENOME PROJECT
– Genome = ALL the DNA in one cell of an organism
– Scientists are trying to identify the DNA sequence
of every single gene
– Chromosome 1 was completed in 2006. yay.
• DNA FINGERPRINTING