DNA, Heredity &
Adaptations
Ch’s 4 (end), 5 & 6(a little)
DNA
n
An organic
molecule that contains information that an organism needs to grow and function
n
Made up of a code
alphabet that consists of 4 “letters”
n
With these 4
letters, all life is “spelled out”
Watson & Crick
n
1952, Rosalind
Franklin discovered that DNA is in two chains
n
From Franklin’s research and the research of others, James Watson
and Francis Crick (1953) made a model of DNA
n
They ended up
being correct and won the Nobel Prize
DNA Structure
n
The structure of
DNA is similar to a twisted ladder
n
The sides of the
ladder are made up of sugar-phosphate molecules
n
The rungs of the
ladder are made up of nitrogen bases
n
There 4 bases:
Adenine (A), Guanine (G), Cytosine (C) and Thymine (T) (our 4-letter code
alphabet)
n
A always bonds
with T, C always bonds with G
Genes
n
Genes are
sections of DNA on a chromosome
n
Genes contain the
instructions for making specific proteins
n
Humans have about
20,000 to 25,000 genes
Protein Production
n
RNA (ribonucleic
acid)
n
RNA is
single-stranded and instead of Thymine, there is Uracil
as a nitrogen base
n
Messenger RNA
(mRNA) carries the code that directs the order in which the amino acids bond
from the nucleus to the ribosome
n
“Reads” a
specific gene for that protein and makes a copy
n
Ribosomal RNA (rRNA) makes up ribosomes, where
proteins are built
n
Transfer RNA (tRNA) brings amino acids to the ribosomes
to build the protien
Acquired Traits
n
Acquired traits are traits that result from
things that happen to you in your life
n Ex:
learning, physical accidents, etc.
n Once
thought to be heritable
Heredity
n
Heredity is the
passing of traits from parent to offspring
n
Genes on
chromosomes control the traits that show up in an organism
n
Ex: gene for ear
lobes
n
The different
forms of a trait that a gene may have are called alleles.
n
Ex: 2 alleles for
ear lobes: attached and unattached
Heredity
n
During meiosis, a
pair of chromosomes separates and the alleles move into separate cells
n
Each chromosome
now contains one gene for each trait
n
Either the trait
from the organism’s mother or the trait from the father
n
So each gamete
(reproductive cell) ends up with one allele for every gene
n
How many alleles
for each gene do the rest of your cells have?
n
Why does this
need to happen?
Gregor Mendel
n
Gregor Mendel is referred to as the father of modern
genetics
n
Genetics is the
study of how traits are inherited
n
Mendel was an
Austrian monk who studied math and science
n
Was also a
gardener
n
Mendel was the
first to use the mathematics of probability to explain heredity and to trace
one trait for several generations
n
He mainly looked
at pea plants
Mendel’s Experiments
n
When he would
cross two plants with different characteristics, the offspring would look like
one of the parents
n
He called these
new plants hybrids
n
A hybrid is an
organism that receives different genetic information for a trait from each
parent
n
In one
experiment, he found that if he bred purebred tall plants with purebred short
plants, all of the offspring would be tall
n
He called the
tall trait dominant – because it dominated, or covered up the short form
n
He called the
short trait recessive – because it seemed to disappear
Another Cross
n
Mendel crossed
these new hybrid plants (he called them the F1 generation)
n
What do you think
the results were?
n
He found that, on
average, 3 of the next generation were tall, and one was short
n
So the recessive
trait (we call it an allele) did not disappear, it was just covered up
n
He looked at many
traits and found similar results
Probability
n
Probability is a
branch of mathematics that helps you predict the chance that something will
happen
n
Probability =
outcome/possible outcomes
n
Ex: if you flip a coin, what is the probability
that you will get heads?
n
Probability = 1
(it can only land on one side & get one outcome) / 2 (there are two
possibilities on a coin)
n
So, the
probability of heads is ˝ or 50%
n
Also, the more
trials you perform, the closer you will get to the expected probability
n
Let’s toss some
coins.
Punnett Squares
n
A Punnett square can help you predict what an offspring will
look like
n
Dominant alleles
are represented by upper-case letters
n
Recessive alleles
are represented by lower-case letters
n
Ex: “A” is tall,
“a” is short
n
What is the
probability of tall offspring?
n
What is the
probability of short offspring?
n
Let’s practice a
couple on the board
Genotype and Phenotype
n
Genotype is the
genetic makeup of an organism
n
Ex: Aa, aa,
AA
n
An organism with
a homozygous genotype has two alleles for one trait that are the same
n
Ex: aa,
AA
n
An organism with
a heterozygous genotype has two alleles for one trait that are different
n
Ex: Aa
n
Phenotype is the
way an organism looks and behaves as a result of its genotype
n
Ex: tall or short
Genetics Since Mendel
n
Mendel got almost
everything right
n
He got stuff
right he didn’t even know the specifics of
n
He just didn’t
have any knowledge of DNA, genes, meiosis, etc
Incomplete Dominance
n
Neither allele
for a trait is dominant
n
The phenotype of
a heterozygous individual is intermediate between the two homozygous parents
n
Ex: Snap Dragon
n
Red flowered (RR)
x White Flowered (R’R’)
n
What will the F1
generation be?
Multiple Alleles
n
A gene that has
more than two possible alleles is said to have multiple alleles
n
Traits that are
controlled by multiple alleles produce more than three phenotypes
n
Ex: Blood Type
n
There are three
alleles for blood type
n
IA, IB, and i
n
IAIA
or IAi – blood type A
n
IBIB
or IBi – blood type B
n
IAIB
– blood type AB (also an example of something called codominance)
n
ii – blood type O
Polygenic Inheritance
n
A group of gene
pairs acts together to produce a trait, which creates more variety in
phenotypes
n
Many human traits
are controlled by polygenic inheritance
n
Ex: Skin Color
n
It is estimated
that eight gene pairs control your skin color
n
This provides for
a greater variety of skin tones
n
Even more control
your hair and eye color
Impact of the Environment
n
You only get
“potential” from genes
n
Your environment
plays a role in how some of your genes are expressed or whether they are expressed
at all
n
Ex: the reason
male birds are more colorful than female birds is due to the different
chemicals present in the different genders (also why males go bald in humans
more often than females)
n
Ex: you may inherit a greater chance of getting
diabetes, but if you take better care of yourself, you are less likely to get
diabetes
Mutations
n
A mutation is any
permanent change in the DNA sequence of a cell’s gene or chromosome
n
Mutations are
caused by outside factors like X-rays, sunlight, and some chemicals
n
A change in a
gene or chromosome can change the traits of an organism
Mutations
n
A mutation can be
harmful, beneficial, or have no effect
n
Chromosome
disorders are caused by more or fewer chromosomes than normal
n
Ex: Down Syndrome is caused by an extra copy of chromosome 21
Recessive Genetic Disorders
n
Both parents need
to have had a recessive allele for the disorder to be passed on to a child
n
The parents
usually do not have the disorder
n
The parents are
heterozygous
n
Ex: Cystic
Fibrosis
n
Most common
genetic disorder leading to death among Caucasian Americans
n
A thin fluid is
produced that lubricates the lungs and digestive tract
n
In Cystic
Fibrosis, a mucus builds up and makes breathing and digesting difficult
Sex Determination
n
Organisms that
have two sexes will have a chromosome that determines gender
n
In humans, it’s
the 23rd chromosome
n
Females are XX
n
Males are XY
n
All eggs from
females give one X to offspring
n
Sperm can contain
either an X or a Y
n
Males determine
gender
n
Sometimes, a
gamete will get more than one allele (extra X or Y)
n
A number of
chromosomal disorders can occurs
n
So what is the
probability that a child will be a male?
A female?
Sex-Linked Traits
n
An allele
inherited on either the X or the Y chromosome is said to be sex-linked
n
X-linked
recessive traits much more common in males
n Why?
n
Color Blindness
n Caused
by a recessive allele on the X chromosome
n Much
more common in males
Sex-Influenced Traits
n
Some traits are
expressed differently in males and females
n
Why do you think
that is?
n
Males and females
produce different hormones that influence gene expression
n
Baldness is an
example
n
Much more common
in males because of the male hormones (or lack of female hormones)
Pedigrees
n
A pedigree is a
virtual tool for tracing a single trait through generations of a family
n
I.e. – sickle cell
anemia, blue eyes, etc.
n
Males are squares
�
n
Females are circles O
n
A filled in
circle or square means the person has the trait being traced ln
n
A circle that is
not filled in means the person doesn’t have that trait O
n
A circle or
square that is half filled in means the person is a carrier for the trait
n
This means they
are heterozygous for the recessive trait and it is not expressed in them, but
can still be passed on
n
A circle and
square connected horizontally means the two individuals had children o �
n
From that couple,
a vertical is drawn downward
and the offspring are written in
n
Example on next
slide
Pedigree Example
Uses of Pedigrees
n
For a geneticist, it is useful to understand who
has had a trait to discover it’s pattern of inheritance
n Recessive? Dominant? Sex-linked?....
n
This is why many geneticists come to Utah
n We
have done lots of good geneology
Genetic Engineering
n
Changing the
arrangement of DNA that makes up a gene
n
Recombinant DNA
n
Bacteria are
wonderful at reproducing
n
A useful segment
of human DNA is inserted into a bacteria (the U of U uses E. coli )
n
The bacteria
produces many copies of that gene
n
I.e. – an insulin
gene for diabetic patients
Gene Therapy
n
A normal allele
is placed into a virus, which delivers the normal allele when it infects its
target cell
n
Hopefully, the
normal allele replaces the infected one (doesn’t always work)
n
Has been used to
control cystic fibrosis
Genetically Engineered Plants
n
For a long time,
people have been selectively breeding plants to get the best crops
n
Now, geneticists
can insert genes into plants that produce desired traits
n
A gene for
tomatoes that allows growers to pick them when they are green and transport
them so they are in the store ripe and red
Species
n
A species is a
group of organisms that share similar characteristics and can reproduce among
themselves to produce fertile offspring
n
Characteristics
of a species are inherited from parent to offspring
n
Any change in
these characteristics over time is called evolution
Acquired Traits
n
Jean Baptiste de Lamarck (1809)
proposed that characteristics, or traits, developed during a parent organism’s
life are passed on to its offspring
n
ex: If you work
hard and become smart (even though you were born stupid), your kids will
inherit “smartness”
n
The reason
giraffe got a long neck was because it “wanted to” and then passed it on to
children
Natural Selection
n
Charles Darwin (1831 through 1859) proposed that
organisms with traits best suited to their environment are more likely to
survive and reproduce
n known as natural selection
n the next generation will be more like the “fittest” parents
Variation
n
A variation is an
inherited trait that makes an individual different from other members of its
species
n
result from permanent changes, or mutations, in organisms
genes
n
Examples:
n
shape of human hairlines, coat color of squirrels, seed
types in fruit, etc.
Adaptation
n
Some variations are more helpful than others (ex: bad eyesight)
n
An adaptation is any variation that makes an
organism better suited to its environment
n
ex: camouflage, speed, higher order thinking (only
occurs in some humans)