GENETICS ESSENTIAL QUESTIONS: What is genetics? What did ...

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14 déc. 2012 (il y a 9 années et 1 mois)

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GENETICS

ESSENTIAL QUESTIONS:

What is genetics? What did Gregor
Mendel’s experiments discover about variations?


Genetics
-
science of heredity

Heredity
-

study of the way in
which traits are passed on from
parents to offspring


Traits
-
characteristics. Exs. Hair
and eye color.

History of Genetics:



In 1857, Gregor Mendel,
an Austrian monk
conducted 8 years of
experiments on pea plants.
As a result of his
experiments, a set of basic
principles of heredity was
established. Mendel is
known as the founder of
genetics.


Mendel proposed that
characteristics were
inherited as result of the
transmission of
hereditary

factors

(genes).

Genes

Genes
-
1. Composed of
DNA.


2. Located at
permanent locations
on chromosomes


3. Each
chromosome may
contain 100’s of
genes.

Essential Question: What is an allele?


Allele
-

pair of genes
that carry the same
trait and are found at
the same location on
pairs of
homologous
chromosomes


Alleles

ESSENTIAL QUESTIONS:

What are dominant and
recessive alleles? How does the allele affect the
phenotype of an individual?


Gregor Mendel


Crossed tall pea plants with short pea
plants (
parental

generation
).


All the offspring (
first filial generation
-
F
1
)
were tall.


Later crossed F
1

generation and
discovered ¾ tall and ¼ short 9
produced over 1000 plants).


Used 7 contrasting traits.

Pea

Characteristitics

Based on Mendel’s work, scientists have
come up with the
Law of Dominance.

Law of Dominance
-

The allele that
appears or shows up in an individual
with two different alleles. Ex.

ESSENTIAL QUESTIONS:

What are
dominant and recessive alleles? How does the
allele affect the phenotype of an individual?


Basics of Genetics:


Dominate Allele
-
a
. The allele that is
expressed (shown) in an allelic pair


b. Expressed by a capital
letter.


Recessive Allele
-

a. The gene that is
present but not expressed in an allelic
pair. Ex. Tt


b. Expressed by a lower
case letter.

Essential Question: What is a genotype and a
phenotype?

Genotype
-
genetic makeup

Phenotype
-
physical
appearance

Homozygous (
pure
)
-
two
alleles for the same trait
are the same. Exs. TT, tt

Heterozygous (
hybrid
)
-
two
alleles for the same trait
are different. Ex. Tt

ESSENTIAL QUESTION:

What is incomplete dominance
and Co
-
dominance?


Incomplete Dominance
-

a. There
are no dominant and recessive
alleles


b. There
is a blending of traits.

Roan Cow

Co
-
Dominance
-
a. Involves
the expression of two
dominant alleles.


b. Results
in expression of both
alleles in a
heterozygous
individual.


Others examples
include:
Blood groups
and Sickle Cell Anemia

ESSENTIAL QUESTIONS:

What are sex
-
linked traits?
What are some diseases associated with sex
-
linked traits?


Sex
-
Linked
-
Traits
-
a.
Defective portion of the
gene is found “
linked”

(on) the
X

chromosome.
b. Exs.
Color blindness,
Hemophilia, Duchene
Muscular Dystrophy
(disease that slowly
destroys the muscles).

ESSENTIAL QUESTIONS:
What are sex
-
linked traits? What
are some diseases associated with sex
-
linked traits?

Genetically Related Diseases


Phenylketonuria (PKU)
-
a
. Recessive disorder


Absence of the enzyme that converts
phenylalanine

tyrosine (A.A.)



Accumulation of phenylalanine causes mental
retardation


Testing at birth and then the limit amount of
phenylalanine.

Punnet Square

Sickle
-
Cell Anemia:

a. Caused by a mutation of a gene that
controls synthesis of hemoglobin (one
amino acid is substituted for another at
one point in the hemoglobin molecule).


b. Mutant gene is recessive


c. Pain, weakness, and anemia


d. Heterozygous for sickle cell makes an
individual resistant to malaria.

Sickle
-
Cell Anemia

Sex
-
Linkage

Tay
-
Sachs
-
a. Recessive
gene


b. Results in
the absence of an
enzyme that breaks
down lipids .Lipids are
produced and stored it
the CNS.


c. Blindness,
paralysis and death by
the age of 3.

Cystic Fibrosis (CF))
-
a. Recessive gene (3
missing nucleotides).


b. Most common
genetic disorder in White Americans.


1/25 carry recessive gene, 1/2000
children have CF.


C. Formation and accumulation of
thick mucus in the lungs and in the
digestive system.

ESSENTIAL QUESTIONS
: What is a karyotype ? What is
its role in genetic screening?




IV. Techniques for
Detecting Genetics
Defects:

Amniocentesis
-
amniotic
fluid is withdrawn during
pregnancy and examined
for the presence of
certain substances.

Essential Question: What is the process of
amniocentesis?

Karyotyping:


Karyotype
-

a. Enlarged
photograph of the pair so
homologous chromosome
(during mitosis).


b. Shows abnormal
chromosomes or abnormal
chromosome number.


c
. Down’s Syndrome

can be identified by this
technique.


Down’s Syndrome


Down’s syndrome


Essential Questions: What is a pedigree chart? How can is
be used to detect the probability of a trait or a disease
?

Screening
-
a. Analysis of body fluids (blood,
urine) to detect presence of certain enzymes
of cellular products.

Pedigree Charts
-
a
. Chart used to trace the
occurrence of a disease or trait in past
generations.


b. Based on this chart,
prediction can be made about the
probabilities

of this trait appearing in the
future generations.


c. Uses symbols:

Pedigree Chart


Pedigree

Square
-
male

Circle
-
female

Half shaded symbol
-
carrier

Fully shaded symbol
-
has the disease



ESSENTIAL QUESTIONS
: What is genetic engineering?
What is gene splicing? What is recombinant DNA? How
will the field of genetic engineering affect the future of
medicine?


Genetic Engineering:


Biotechnology
-
a. application of technology
to biological science.


b. Includes
selective

breeding

and
genetic engineering
.

Selective breeding
-

a. Process that produces
domestic animals and
varieties of plants with
traits that are desirable.

b. Exs.: Animals with less
fat, fruits and
vegetables that are
larger, sweeter, and
hardier.

Genetic Engineering
-

a.
New technology that alters the genetic
code.

b.

Removing genes from an organism and
adding them to the genes of different
organism.


Resulting in a changed genetic code.


Transgenic
Organisms
-

organisms that
contains foreign DNA.
Ex. Glowing tobacco
plant

Recombinant DNA


Tools of Genetic Engineering:

Restriction Enzymes
-
enzymes that cut DNA in
very specific places


A large number of restriction enzymes cut the
two strands of DNA molecules at slightly
different places. Short, single
-
stranded leftover
pieces of DNA remain are the cut ends. These
DNA fragments are said to have “
sticky ends

because of their unpaired bases.

Gene Splicing
-
adding

or gluing pieces of DNA
from an organism to another of the sticky ends.

Vectors


a. Organisms that move the recombinant DNA from one
organism to another organism.

Bacteria
-

a. contains a circular piece of DNA called
a
plasmid
.

b. By splicing a foreign gene into a plasmid. A scientist
can transport the gene to a new bacterial cell.

c. This technique and vectors are used to produce
insulin, tomatoes that don’t become overripe.

Genetic Engineering

Gene Therapy

Gene Therapy
-

a.
Giving normal
genes to a person
in order to treat a
genetic disorder.
Ex. Parkinson’s


b. Not very successful.
How do we turn off
the genes?

Turning on Genes