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Name _________________________
Unit 3
Our Cells at Work
DNA , Chromosomes, & Genes
DNA is a molecule made of base pairs attached
to two strands of sugars and phosphates (the
“backbone”). The base pairs in DNA are:
A pairs with ____
T
____
C pairs with ____
G
____
The order of the base pairs in DNA determine
the order that the amino acids are linked
together when proteins get built.
Proteins are what living things are made up of;
your traits (characteristics) are proteins….
which means, your DNA is the instructions to
make you!
You got these instructions from your biological
parents. When a sperm fertilizes an egg, the
nuclei combine….so ½ your DNA came from your
biological mother, and ½ came from your
biological father.
Because we have so much DNA, it is organized into
chromosomes (as shown in the diagram), which are protected in
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the nucleus of the cell. Humans have a total of ______
chromosomes in the nucleus of every body cell….which means, ½ of
23 chromosomes came from your biological mother’s egg
that, or ____
23 chromosomes came from your biological
(gamete) , and _____
father’s sperm (gamete).
A segment (piece) of DNA is a gene. Each gene carries the
instructions to build just one protein.
Your genome has about 25,000 genes, so there are many genes on
each chromosome.
Each chromosome you got from your mother “matches” up with a
chromosome that you got from your father…..so it is the
“combination of instructions” that you received in those 23 pairs of
chromosomes that makes you unique.
Protein Synthesis (building proteins from the instructions in DNA)
Protein Synthesis is the process that causes traits to be expressed…..the process that created
your eye color pigments, your skin tissue and color, your muscle, your digestive enzymes, etc.
The “instructions” (DNA) are stored and protected in the cell’s nucleus…..but proteins get built outside
of the nucleus (at ribosomes). To get the instructions out of the nucleus, another nucleic acid – RNA –
is needed…..
A gene is transcribed by mRNA
(messenger RNA). It does this by
“paring up with” the genetic code on
DNA – the only difference is there
are no “Ts” in RNA, so, when there is
an “A” in DNA, RNA will pair that
with a “U”. C’s still pair with G’s.
Once transcribing is complete, the
instructions to build that protein are
carried by mRNA out of the nucleus
to a ribosome.
When mRNA arrives at the
ribosome, tRNA (transfer RNA)
arrives carrying an amino acid.
When tRNA locates the “drop off
point” by reading the code on mRNA,
it lets go of the amino acid so it can
be linked to the others.
A chain of amino acids is a protein.
If this were a skin cell, the protein
made might be the pigment melanin
that gives your skin color. If the cell is a muscle cell, the protein made might be “myosin or actin” which
are the proteins that muscle tissue is made of. If the cell was in your mouth, the protein made might be
an enzyme in your saliva that helps break down food.
Review:
6. Protein Synthesis
Every organism that reproduces sexually has an even number of chromosomes in the nucleus
egg
of each of their body cells…..this is because ½ of them came from the mother’s ______
and
sperm
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½ came from the father’s ___________. For example, humans have a total of ______
23 came from the sperm, and ____
23 came from the egg.
chromosomes in every body cell -- ____
Chromosomes neatly package all of the DNA of that organism, and DNA is the instructions to
make all of the proteins that make up that organism and allow that organism to function.
What is the relationship between DNA , genes , and chromosomes?
Both chromosomes and genes contain the molecule DNA.
Chromosomes are structures that contain condensed DNA. Genes are specific sequences of
DNA that code for proteins. Because genes contain DNA, genes are also found in chromosomes.
What is the relationship between proteins, genes, and traits (characteristics)?
Genes code for proteins which are expressed as traits based on the function of those proteins.
For example, a gene coding for freckles will produce proteins that will express that trait.
Proteins Synthesis
Name the process that causes traits to be expressed in offspring: __________________
This is how it works:
1. A gene (segment of DNA) =
GTC ATT GCA
2. …..is transcribed by mRNA = __CAG UAA CGU__ ; this takes place in the
_nucleus__ of the cell.
3. ….mRNA caries the copy out of the nucleus to a _ribosome_
4. ….at the ribosome, tRNA arrives carrying an _amino___ __acid____ that will be
linked together to make a ___protein_______
5. Proteins are your traits/characteristics.
What is a characteristic of DNA that determines what protein is made?
Sections of the DNA molecule which “code” for specific proteins are called genes. Genes have a
specific starting point and ending point so the gene produces the exact same RNA every time in
an individual. Differences in base pair sequences between individuals for any specific gene are
called alleles. Different alleles “code” for different proteins which causes different
characteristics in a population.
So, describe how a rabbit ends up with pink eyes.
The gene that determines eye color produces the RNA which is then translated into the protein
that creates the red eye pigment.
____ COE: “It’s in the
Genes #1”
Mutations
DNA
Mutations are changes in _____
Mutations are fairly common in
DNA, and, luckily most are
harmless.
Mutations can occur in several
ways:
Random errors during DNA
replication – these are fairly
common and occur when a
nucleotide is substituted,
inserted, or deleted from a
gene. Since mRNA will copy the
error, an incorrect amino acid
will be inserted when the protein is being built.
Exposure to certain chemicals and radiation can also cause DNA mutations.
If a mutation occurs in a body cell of an organism…..like a skin cell, liver cell, muscle cell,
bone cell, etc., it can cause “bad proteins” to be built and cause a defect in those cells and
tissues. A body cell mutation will only impact the individual with the mutation….they _____
will
______
be passed on to the offspring!!!
not
If a mutation occurs in a gamete, or sex cell (sperm or egg) then it will not affect the “parent
organism”, but the mutation ___________
cause a defect in an offspring – again, because
could
“bad proteins” could be made from the error in the “instructions” (DNA).
Sometimes mutations can benefit an individual. So, if the gamete mutation resulted in a new
trait that made that individual more likely to survive and reproduce, then that mutated gene
would most likely be passed on to the next generation. …….and the next generation…….and the
next…..
If that gene gets passed on to enough individuals (through several generations), over time,
most of the population will express this beneficial gene mutation --- so the population would
have “changed”…..or evolved.
Review:
7. Mutations
DNA
Mutations are changes in ___________
Original DNA strand:
Mutated DNA:
Mutated DNA:
Mutated DNA:
ATC GGC AAC
G
ATC GTC AAC
*compare all mutations to the original DNA
ATC GGA CAA C
G
ATG GCA AC
(A inserted between G and C)
Type of mutation: Insertion
___________________
Original DNA Strand: CGT AAT CTG
(T substitutes for G)
Type of mutation: Substitution
___________________
(G deleted between G and C)
Type of mutation: Deletion
___________________
All of the mutations above are called point mutations.
CGT TAT CTG
Show what a substitution might look like: __________________________
CGT ATC TG
Show what a deletion might look like: _____________________________
CGT AAA TCT G
Show what a insertion might look like: ____________________________
An original DNA strand and the same strand after a mutation are shown below. Describe the type of
mutation that has occurred in the strand.
DNA:
Mutated DNA:
TAC GGT CCA
TAC GTC CA
In your description, be sure to:
 Identify the type of mutation
 Describe one way this mutation can occur
Type of Mutation:
The mutation is a type of point mutation called a deletion. In the example,
a G was deleted from between the G and T.
One way this mutation can occur:
The following mutagens may cause mutations like the one above:
1) Chemical (smoking, alcohol, diet)
2) Physical (UV light, X-rays, gamma rays)
3) Infectious agents (HPV)
A local pond has been receiving fertilizer run-off from a new farm nearby; the pond is now surrounded
year around with green, lush vegetation. A mutation occurred in a duck egg resulting in offspring with a
darker, greener coloration. Describe how this trait could allow the offspring to survive and reproduce in
its pond ecosystem.
A darker, green coloration may enable the offspring to avoid predators (camouflage) and or to
better catch prey. This adaptation would both help the offspring stay alive longer and be better fed
(healthier) than ducks of other coloration within the population. This may result in the dark-green
ducks having a higher rate of reproduction relative to other colorations (unless of course dark green
is not a desirable trait regarding sexual selection).
Imagine that there is a new mutation in a skin cell (body cell) of a frog. What effect could this
mutation have on this organism (the frog)? If the same frog has a mutated sperm (gamete) what
effect could this mutation have on this organism (the frog)?
Effect of body cell mutation on the organism:
Most mutations are neutral, meaning they produce no effect. However, a possible effect of a gene
mutation in a body cell of the frog would be to disrupt the cell’s growth cycle, perhaps causing the
cell to become cancerous. This may result in the death of the frog.
Effect of sperm mutation on the organism:
A mutation in a sperm cell may cause that gamete to become sterile. However, since many more
healthy sperm are being produced by the frog, the mutation will most likely not have any effect on
the reproductive success of the organism.
On the other hand, a mutation could cause the sperm to become more productive, like making the
sperm swim faster than others. If this sperm fertilizes an egg, the resulting offspring would inherit
this mutation.
Imagine that there is a new mutation in a skin cell (body cell) of a frog. What effect could this have on
the organism’s offspring (the baby frogs)? Imagine that there is a mutation in a sperm
(gamete/sex cell) of the frog. What effect could this have on the organism’s offspring (the baby
frogs)?
Effect of body cell mutation on the offspring:
Because a body cell was affected, there would be no heritable effect on the offspring. The only
way offspring could be affected is if the skin cell became cancerous and killed the parent while the
offspring were still dependent on the parent for survival.
Effect of gamete mutation on the offspring:
Most DNA does not code for proteins or have any regulatory function. Therefore, most
mutations will have no effect on the offspring. However, a mutation in a gamete’s gene that
regulates some aspect of development may produce a visible variation in the offspring’s
phenotype. For example, an inherited mutation could change the number or position of spots on
the skin of a frog.
Now let’s imagine that this frog’s sperm mutation gives the offspring the ability to produce a
new skin protein that tastes really nasty. How can this mutation help the baby frogs survive
and reproduce in their environment?
Any predator that happens to eat a bad-tasting baby frog will likely remember the experience, and
avoid eating any frogs that look like they might taste bad. Frogs under reduced predation
pressures will have more opportunities to move about and feed themselves. These baby frogs will
have a better chance of growing to a breeding age compared to tasty-looking frogs.
How can that one mutation eventually benefit the entire population of frogs in this particular
pond ecosystem?
The process of natural selection could increase the population of nasty-tasting frogs and any frogs
that mimic them.
Because the mutation produces a nasty taste, predators that experienced it (the taste) would avoid
eating any frog that closely resembles the bad tasting ones. With less predation, more frogs that
look like they taste bad will survive and reproduce, increasing the frog population in the pond.
____ COE: “It’s in the Genes #2”
How New Cells are Formed
Before a cell can divide, it must make another copy of its DNA – so that the new cell has all of
the DNA, too! This process is called DNA Replication…
After replication, chromosomes look like this; the copy
stays “attached” until it is time to for the cell to
divide…then one copy goes to each cell.
Mitosis
Mitosis is the way you get more body cells for growth,
development, repair of damaged tissues, replacing dead
cells, etc.
DNA replication occurs before a cell divides because
there needs to be two copies of each chromosome --enough for each new cell to get a “full set”
So, during mitosis, a cell that starts with 4
chromosomes will divide one time to create two cells,
each with 4 chromosomes. ….so an identical cell is
created.
From the time an egg is fertilized, the organism grows
and develops by creating new cells – and the process that
makes new cells is mitosis.
Mitosis is an organized way to divide the chromosomes into two separate nuclei….when this is
done, the cell can divide.
Different organisms have different numbers of chromosomes in their body cells:
If that is true, then how
come gorillas have the same
number of chromosomes as
potatoes (48); pigs have the
same number as cats (38);
and chickens have the same
number as dogs (78)?
Meiosis
Meiosis only takes place
in specialized cells located
in reproductive structures
of organisms.
After DNA replication,
the cell divides twice to
create four cells, each
with ½ the original
chromosome number.
So, meiosis is the organized
way to reduce chromosome
number so that each
gamete only has one copy
of each chromosome. This
produces the gametes
(sperm & egg). So, our
organism with 4
chromosomes in every body
cell, will produce gametes
containing 2 chromosomes.
Then, when the sperm
fertilizes the egg, a new
organism with 4
chromosomes will be
produced.
There are three events that take place during meiosis that lead to unique combinations of genes
in the gametes:
1. Independent Assortment – the way that the chromosomes line up to start meiosis is
completely random…..and then when they separate into the gametes, it is random as to
which chromosome goes to which gamete. So it’s kind of like “shuffling a deck of cards and
dealing out half the deck”……each gamete gets a different combination of genes.
2. Crossing Over – This occurs when the
chromosome pairs first line up next to each other
at the start of meiosis……some of the chromosomes
“swap parts”, creating new combinations of genes
3. Mutations – it is possible for random mutations
to occur during DNA replication that precedes
meiosis; these “mistakes” can then end up in the
egg or sperm and passed on to the offspring.
8. Mitosis
Describe mitosis in a goldfish cell; or how a goldfish makes new body cells:
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1. Each gold fish cell starts with ______
chromosomes in each body cell
replication
2 copies of
2. DNA _______________________
has to occur first so there are ____
each chromosome before the cell divides.
3. The cell makes sure that the chromosomes get separated correctly then divides
one
_______
time
4. After mitosis, there are _____
cells, and each one has _____
chromosomes in the
2
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nucleus.
9. Meiosis
egg
sperm
Meiosis is the type of cell division that produces gametes, or ___________
and ________.
This only takes place in very specialized cells in the organism’s body, and it reduces the total
chromosome number by ½.
How many chromosomes would be in the sperm or eggs of each of the following organisms?
39 dog
____
3
____
mosquito
19 cat
____
23 human
____
9 cabbage
____
Describe meiosis in a goldfish; or how a goldfish makes gametes:
94
1. Each gold fish cell starts with ______
chromosomes in each body cell, and in the
specialized cells that produce sperm and egg.
replication
2 copies of
2. DNA _______________________
has to occur first so there are ____
each chromosome before the cell divides.
3. The cell divides __________
twice
4. After meiosis, there are _____
4 cells, and, in a goldfish, each one has _____
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chromosomes in the nucleus – which is ____
the
original
chromosome
number.
1/2
Describe one event that takes place during meiosis that results in “unique” sperm or eggs.
1) Chromosome tetrads are able to independently assort during metaphase I of meiosis. For
example, independent assortment in humans can produce 223 new chromosome
combinations, or 8,388,608 unique cells.
2) Crossing over of non-sister chromatids in prophase I produce an almost limitless number
of unique DNA recombinants. Coupled with independent assortment, the number of
unique cells that can be produced is inexhaustible.
Genes are pieces of DNA that code for specific proteins. You have your eye color because you
inherited certain genes from your parents. We often describe genes with letters, and alleles
are different forms of the same gene. You may have inherited a dominant brown eye allele (B)
from one parent, and a recessive blue eye allele (b) from the other parent, so the combination
of genes you inherited (your genotype) is Bb.
Mom and Dad both have brown eyes (BB or Bb); two of their kids have brown eyes (BB or Bb),
and two of their kids have blue eyes (bb). What is one event that occurs during the
formation of egg or sperm (meiosis) that makes it possible for these two brown-eyed
parents to have kids with brown eyes and kids with blue eyes?
Mom and Dad must both be Bb. One event that makes it possible for blue eyes to appear in their
children is the segregation of chromosomes during metaphase I and metaphase II that places
either a B (brown allele) or a b (blue allele) in each sperm or egg cell. The second event is the
complete randomness by which sperm and egg unite during fertilization. Both the B and b alleles
from each parent have an equal chance of coming together in the formation of a zygote.
Fertilization – Creating unique new organisms through sexual reproduction
Fertilization
sperm
_____________________
occurs when the male gamete (___________)
combines its genetic
material (chromosomes) with the female gamete (_______)
to
egg
create a fertilized egg, called a zygote.
Each gamete only has ____
1/2 set of chromosomes, so when they unite,
they restore the original chromosome number, in the case of
46 (or ____
23 pairs)
humans, that number is _____
In the case of a dog……
39
39
78
Review:
10. Fertilization
Punnett Squares are used to show the probability of outcomes if fertilization were to occur.
Brown eyes (B) are dominant over blue eyes (b). Mom and Dad both have brown eyes; 2 of
their kids have brown eyes, and two of their kids have blue eyes. What is one event that occurs
during fertilization that makes it possible for these two brown-eyed parents to have kids
with brown eyes and kids with blue eyes? Explain your answer.
Sperm
Both parents must be Bb.
B
b
B
BB
Bb
b
Bb
bb
Egg
If a B sperm fertilizes any egg
(B or b), the offspring will
have brown eyes (75%
chance).
If a b sperm fertilizes a b egg,
the child will have blue eyes
(25% chance)
____ COE: “Bear Crossing #3” (Review 8, 9, & 10 before starting)
Genetics
The genes you inherit from your parents can come in different forms, or ___________.
You only
alleles
inherit one allele from each parent, so the combination you inherit will determine which proteins are
made…..these are your traits.
Some alleles are completely dominant, which means, that if it is present, it will be expressed; we use a
_______________
letter to represent the dominant allele. Some alleles are recessive, which means
capital
that the trait will not be expressed if a dominant allele was also inherited. The only way that a recessive
trait would be expressed is if a recessive allele was inherited from both biological parents. We use a
lower-case letter to represent recessive alleles.
The combination of alleles that an organism inherits is its genotype. So a dominant genotype for a
given trait could be _____
AA or _____;
Aa a recessive genotype would be ______.
aa
If the two alleles in the genotype are the same, it is called homozygous; so _____
AA is a
homozygous dominant genotype. An example of a homozygous recessive genotype would be
aa
______.
If the two alleles are different, the genotype is heterozygous…..he may have inherited a brown eyed
allele (B) and a blue eyed allele (b), but his eyes will be brown because brown is dominant (Bb).
Phenotype is what trait is expressed…or “what it looks like” because of the genes it inherited. So “blue
eyes”, “long fur”, “spotted wings”, “yellow petals”, etc. are all phenotypes.
Practice: Let’s say that in a certain butterfly, blue wings (B) are dominant over red wings (b). Use a
Punnett Square to show the possible outcomes (genotypes and phenotypes) of cross between a
homozygous blue winged bug and a red winged bug.
Egg
Sperm
B
B
Homozygous dominant blue wings = BB
Homozygous recessive red wings = bb
b
Bb
Bb
Genotypes: 100% Bb, or heterozygous (hybrid)
b
Bb
Bb
Phenotypes: 100% Blue wings
hybrids
The offspring produced in this example are called ____________,
or “offspring of different parents”.
Now, cross two of the hybrids and describe the possible genotypes and phenotypes of the offspring.
Egg
Sperm
B
b
Heterozygous parents with blue wings = Bb
B
BB
Bb
Genotypes: 25% BB; 50% Bb
b
Bb
bb
Phenotypes: 75% Blue wings; 25% red wings
In a certain breed of llama, black spots (S) are completely dominant over fur with no spots (s), and long
floppy ears (E) are completely dominant over short, pointy ears (e). Cross a spotted, long floppy eared
male llama (homozygous for both traits) with a female llama that has no spots and short, pointy ears.
Describe the possible genotypes and phenotypes of the offspring.
Sperm
SE
ssee
Genotype of female: ________
Egg
SSEE
Genotype of male: ________
SsEe
se
100% SsEe
Genotypes of offspring: _______
100% Black spots with floppy ears
Phenotypes of offspring: __________________
Note: Since there was only
one type of sperm and one
type of egg possible, it was
not necessary to use more
than one box of the Punnett
square.
The offspring have grown into adult llamas. One llama, Lolla, is ready to reproduce. What are the
possible allele combinations that could be found in Lolla’s eggs after the process of meiosis?
SsEe
Lolla’s genotype: _______
Lolla’s eggs:
SE
Se
sE
se
Review:
11. Genetic Crosses
A dihybrid cross means we are looking two traits, and the probability of outcomes if
fertilization were to occur.
In guinea pigs, brown fur (B) is dominant over white fur (b) and Pink eyes (P) are dominant
over blue eyes (p).
A male guinea pig is homozygous dominant for both traits --- he has brown fur and pink
eyes. He is being bred with a female that is homozygous recessive for both traits – she has
white fur and blue eyes.
BBPP
Male’s genotype: ____________
bbpp
Female’s genotype: __________
When sperm and egg are formed, each will only have one copy of each “allele” (gene), but each
has to have a “fur color gene” and an “eye color gene”…..
BP
Genes in every sperm: _________
bp
Genes in every egg: __________
BbPp
What will the genotype of the offspring be when the sperm fertilizes the egg? __________
100% Brown fur and pink eyes
What will the phenotype of the offspring be? _________________________________
Now let’s imagine that the offspring are old enough to mate. We will take one female from this
litter, and mate it with a male that has white fur and blue eyes. What are the parent genotypes?
bbbp
Male’s genotype: _______________
BbPp
Female’s genotype: ___________
bp
Genes in every sperm: ___________
Possible gene combinations in eggs:
BP ____
Bp ____
bP ____
bp
____
Determine the possible genotypes and describe the odds of each phenotype for their offspring:
Sperm:
bp
Eggs:
25%
Brown w/ pink eyes: _______
25%
Brown w/ blue eyes: _______
25%
White w/ pink eyes: _______
White w/ blue eyes: _______
25%
BP
BbPp
Bp
Bbpp
bP
bbPp
bp
bbpp
Note: Since there was only
one type of sperm, it was not
necessary to use more than
one column of boxes in the
Punnett square.
In the next pair to breed, the male is homozygous dominant for fur color and
heterozygous for eye color. The female is white with blue eyes.
BBPp
Male’s genotype: _______________
bbpp
Female’s genotype: ___________
Possible gene combinations in sperm:
bp
Genes in every egg: ___________
Bp ____ ____
BP ____
____
Determine the possible genotypes and describe the odds of each phenotype for their offspring:
Sperm:
Eggs:
50%
Brown w/ pink eyes: _______
50%
Brown w/ blue eyes: _______
0%
White w/ pink eyes: _______
0%
White w/ blue eyes: _______
bp
BP
Bp
BbPp
Bbpp
Children inherit traits from their biological parents, because traits are encoded in the DNA that they
receive from the sperm and egg. Describe the process that will cause these traits to be
expressed in the newborn baby.
The process which codes for traits in a newborn baby is called protein synthesis. During
protein synthesis, activated genes transcribe mRNA within a cell’s nucleus. mRNA then
makes its way into the cytoplasm where it is translated into proteins by ribosomes.
Ribosomes “read” the sequence of codons in mRNA and assemble amino acids that
correspond to that sequence. It is the sequence of the amino acids in a protein that
determine the protein’s function.
Humans, like other animals, eat food to acquire energy, attain the required molecules to build and
repair tissues, etc. Describe how you transform the energy from the salad you ate for lunch into a form
of energy that your cells can use for life functions such as growth and development.


Identify the process that transforms the energy in plants into energy that you can use for life
functions
Identify the molecule that contains energy in plants and the molecule that contains the energy
that you can use
The process that plants utilize to transform energy that can be used for life functions is
photosynthesis. Through photosynthesis, plants store energy from sunlight in the
chemical bonds of glucose. When we eat plants or eat animals that eat plants, we obtain
plant-made glucose. We then “burn” glucose during cellular respiration to release its
energy. Some of the energy in glucose is released as heat. The rest is stored in the
chemical bonds of ATP. ATP is what our cells use to carry out metabolic functions.
Many plant products can be used to make biofuels, like ethanol, that are added to gasoline (a fossil
fuel). Describe two similarities and differences between cellular respiration in humans and the burning
of fossil fuels, like gasoline.
Similarities:
 Both processes release energy stored the chemical bonds of fuels.
 Both processes require oxygen to burn the fuel.
 Both processes release heat, water, and carbon dioxide.
Differences:
 Cellular respiration occurs in cells; burning fossil fuels occurs in machines, like cars.
 Cellular respiration uses glucose; burning fossil fuels uses fuels like oil, coal, and natural gas.
 Cellular respiration produces ATP; burning fossil fuels produces ash and soot.
 Cellular respiration releases small amounts of heat; burning fossil fuels releases large
quantities of heat.
____ COE: “Planning a School Garden #4”
____ COE: “Columbia White Tailed Deer #3”