Download Unit A - Topic 3.0 Notes

3.0 DNA is the inherited
material responsible for
variation
• Captive breeding programs enable
scientists to control populations of
species at risk of extinction.
• Using modern technology, geneticists and
staff from zoos around the world can
analyze the genetic code of the species
they are trying to save and use it to
introduce variation that will help the
species survive when the environment
changes.
• Eg.Bengal tiger
Selective Breeding in Dogs
Selective breeding, or breeding organisms for specific features or
behaviors, has been done for thousands of years.
The Great Pyrenees (#2) is one of the oldest-known dog breeds,
bred several thousand years ago to protect sheep herds from
wolves(#1) and bears. The dachshund (#3) was bred about 600
years ago to hunt badgers in their underground dens. The toy
poodle (#4), a product of the mid-twentieth century, was bred to
provide dog lovers with the intelligence and sensitivity of the large
poodle in a much smaller form.
http://www.dailymotion.com/video/xwq3rs_evolution-in-action-the-silver-foxexperiment_shortfilms
3.1 DNA - Transmitter of
Genetic Code
Characteristics are passed on from one
generation to another through the genetic
code of the parents.
DNA is the genetic code or “blueprint” for
all life.
All living organisms contain DNA in the
nucleus of their cells.
Deoxyribonucleic acid (DNA) is the
inherited material responsible for variation.
DNA and the Genetic Code
1869: DNA is first identified
1944: Canadian scientist Oswald Avery
confirms that DNA is in fact responsible for
genetic inheritance and asks the question,
“how can the blueprint for so many different
organisms be passed on by what seems to be
the exact same molecule?”
James Watson and Francis Crick
unraveled the structure of DNA,
revealing how the same chemical
building blocks can carry a wide range
of instructions.
Every DNA molecule contains exactly
the same chemicals.
DNA is like a ladder twisted into a
spiral.
The sides of the ladder are the same in
all DNA molecules.
The rungs are what make the variations.
Each rung pairs up two of the following
chemicals: guanine (G), cytosine (C),
adenine (A), and thymine (T).
The arrangement of these four chemicals
creates the code that the cells are able
to interpret. This is the genetic code of
the organism.
Q: Which chemicals always pair up together?
A:
Chromosomes
DNA contains all the instructions for
an organism's characteristics.
If the DNA from a single human body
cell were stretched out it would be
about 2m long!
To fit all that DNA into a single cell it
is arranged in compact packages called
chromosomes.
In plants and animals, chromosomes are
stored in the cell nucleus.
Every human cell contains 46
chromosomes,containing all the instructions
for making a human.
In each cell, 23 chromosomes came from their
mother’s egg cell, and 23 came from their
father’s sperm cell.
Not all organisms have the same number of
chromosomes ( A dog cell has 78, cats have 38,
so dog cells have 39 pairs, cats have 19 pairs).
Not all chromosomes from species to species
are the same, which accounts for the
different characteristics between species.
Sex Chromosomes
The 23rd pair of chromosomes are called sex
chromosomes because they carry information
about sexual characteristics and determine
sex of the individual.
If the 23rd pair is XX you are female and if
it is XY you are male.
Genes
A single gene is an uninterrupted segment of
DNA containing coded instructions for a
particular trait.
Genes are located on the chromosomes.
Each chromosome has many genes.
Genes come in pairs (one from each parent).
Both genes in a pair carry instructions for the
same trait (eg. hair color, height . . .)
Gene pairs occupy matching locations on the
two chromosomes.
DNA code may not be exactly the same in both
locations. eg. the parents may have different
eye colors.
Q: How many genes does the DNA found in the
46 chromosomes of each human cell contain?
(p. 39)
Offspring inherit genes from both parents.
Different forms of a gene are called alleles
(eg. straight hairline or widow’s peak hairline)
The ultimate combination of the chromosome
pair is what makes variation possible.
Two chromosome pairs.
Different alleles are
marked with uppercase
or lowercase letters.
OK, let’s get this straight. . .
DNA is packaged into chromosomes
Each chromosome contains many genes
Genes are coded instructions for
specific traits
Different variations of the same gene
are called alleles
Much of what we know today about genes comes from
research done on fruit flies.
Do Check and Reflect p.45 #1-4, and 8
Read the info BIT on p.46
Q: what did scientists believe about reproduction
until the 1600’s?
3.2 Cell Division
A. Cell Division and Asexual Reproduction
Asexual reproduction involves only one parent.
All of the offspring are genetically identical
to the parent.
In single celled organisms, binary fission
enables the parent cell to split its contents
equally between the two new cells.
Prior to division the parent cell duplicates its
DNA. When the split takes place each new cell
receives a complete exact copy of the parent’s
DNA.
Binary Fission in Single Cellular Organisms
We will look at two types of cell
division in multicellular organisms:
Mitosis and Meiosis
1. Mitosis
During mitosis a cell divides into 2 daughter
cells, each containing the same number of
chromosomes as the parent cell.
Q: parent cell - 46 chr; 2 daughter cells Before division, DNA is replicated (doubled)
and then the cell divides.
Mitosis occurs during growth and tissue repair.
Mitosis Animation
A More Detailed Look at Mitosis
2. Meiosis
A type of cell division that produces four
daughter cells, each with only half the DNA
of the parent cell.
Q: parent- 46 chr; 4 daughtersThis process involves two cell divisions.
Meiosis occurs to produce gametes (sex cells)
for sexual reproduction.
Q: male gametes =
female gametes =
Meiosis Animation
Meiosis
Comparison: Mitosis vs. Meiosis
B. Cell Division and Sexual Reproduction
in Plants and Animals
Sexual reproduction involves joining the
gametes of two individual organisms.
Offspring produced contain genes from both
parents, and are therefore genetically
different from either parent.
Half the DNA is from one parent and half from
the other parent, resulting in a unique
offspring.
During sexual reproduction, specialized sex
cells (gametes) unite to form a zygote, which
develops into the new organism.
Gametes contain only half the number of
chromosomes that other cells from the
organism contain
That way when male and female gametes
unite, the offspring has the correct number
of chromosomes
Q: human gametes have ____chromosomes.
Do “Give it a Try” p.48
And Check and Reflect p.48 #1-4,6, and 7
3.3 Patterns of Inheritance
Long before the science of genetics, people
tried to produce organisms with only the most
preferred traits by allowing only the
organisms with the most desirable traits to
reproduce. (artificial selection)
This method was not always successful, but
through time (trial and error), this practice
of controlled breeding provided scientists
with the information to detect certain basic
patterns of inheritance.
Gregor Mendel
Gregor Mendel was an Augustinian monk and is known
as the "father of modern genetics" .
He used artificial selection to cross pollinate pea
plants and was the first person to trace the
characteristics of successive generations of a living
thing.
He established the concept of dominant and recessive
traits.
Mendel Video
Patterns of Inheritance Video
Mendel Rap
Between 1856 and 1863, Mendel bred over 28 000
pea plants and analyzed how traits, or
characteristics, were passed from parent to
offspring.
His work was largely ignored until supporting evidence
began to emerge in 1900, about 16 years after his
death.
Purebred vs. Hybrid
To produce purebred organisms, breeders
choose purebred parents (parents whose
ancestors have produced only the desired
characteristic).
Eg. Tall X Tall
This is called true-breeding.
If a breeder chooses two different 'truebreeds' then a hybrid is produced.
eg. Tall X Short
Dominant Traits
Crossbreeding two different true-breeds
results in all of the offspring having the same
characteristic (the dominant trait).
Only the DNA instructions for the dominant
trait are expressed.
Dominant traits are represented by an upper
case letter, and recessive by the lowercase of
the same letter.
Crossing round (R ) and wrinkled (r)
plants produce all round plants
because the round trait is
dominant over wrinkled.
Dominant Traits
Mother
(Pure Bred White)
Father
(Pure Bred Black)
Offspring
(Hybrid Black)
Q: Which trait is dominant?
Recessive Traits
When crossbreeding hybrids, the average results will
produce 75% of the offspring with the dominant trait
and 25% of the offspring with the recessive trait.
A recessive trait only appears in the offspring if two
recessive alleles are inherited.
Recessive Traits
Mother
(Hybrid Black)
With one black and one white allele
Offspring
75% Black
25% White
Father
(Hybrid Black)
With one black and one white allele
The gametes of parents only have one allele
for a trait, so offspring receive 2 alleles
for any trait in four possible combinations.
Pea plants:
dominant trait
recessive trait
The Punnet Square:
a diagram that is used to predict the outcome of a particular
cross or breeding experiment.
Note: Capital letters
represent dominant
traits
What fur color will the four offspring have?
Punnet Square
Calculator:
Click Here!
Other Patterns of Inheritance
Incomplete dominance
When the alleles are neither dominant, nor
recessive
both alleles are expressed as an intermediate
form of the trait (a combination of the two
traits). Eg. red X white = pink 4 o’clock flower
Co-dominance
Both alleles are equally dominant so both
traits are expressed.
Eg. red X white = roan coat color (white and
red hairs)
Red shorthorn bull
White shorthorn cow
Roan shorthorn heifer
Offspring unlike Either Parent.
More than one gene location or set of alleles
may be responsible for some traits.
eg. Hair color, eye color, skin color
The complex mixing of the possible
combinations for that particular trait may
account for the variation of traits an
offspring has.
The
effect of polygenic traits is sometimes
additive and sometimes subtractive. Skin color
is a good example of a trait that is affected by
two genes with an additive effect:
Black
Skin
AABB
Dark Skin
AABb or AaBB
Intermediate
AaBb or AAbb or aaBB
Light Skin
Aabb or aaBb
White Skin
aabb
The more dominant genes present, the
darker the phenotype.
Environmental Factors can also have a bearing on how
DNA is interpreted and developed.
Fetal alcohol syndrome is a result of alcohol
consumption during the developing stages of the
offspring.
The alcohol affects the DNA and the fetus may not
develop normally.
Taking drugs can also affect the DNA and defects in
the organism can occur. Eg.Thalidomide use resulted
in children being born without limbs
Do Check and Reflect P.54 #1-4, and 6
Do Section Review P.55 # 2,4,5,6,8, and 10
Here’s a cool genetics link:
Science Museum Link
http://www.sciencemuseum.org.uk/online/genes/index.asp
To review for Unit A Exam:
P.84
S1 2,6,7,9
S2 11, 13-17
S3 20-25
S4 27-29, 32,39
Use exambank or quest a+, KEY
booklet, and do the practice test in your
booklet!