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BIODIVERSITY Objective 2
NAME___________________
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Objective 2 : To interpret the nature of reproductive processes
and their role in transmitting species characteristics
This objective is further broken down into four outcomes
• Outcome 2A: Distinguish the types of asexual
and sexual reproduction
• Outcome 2B: Describe examples of variation
within a species and identify discrete and
continuous variation
• Outcome 2C: Describe the transmission of
characteristics from parents to offspring
• Outcome 2D: Distinguish heritable and nonheritable characteristics
Everywhere you look there are examples of organisms that look more or less like their
parents. How are these characteristics passed on from generation to generation? You have
already learned that the characteristics of organisms vary greatly within a species. How does
reproduction allow for variation?
Not only do the physical traits of organisms vary, but the ways in which organisms
reproduce show variation as well. When a seed germinates, the new plant will have
characteristics of both its parents. Whether you examine reproduction in bacteria, maple trees, or
elephants, you will notice characteristics that are passed on from parent to offspring. These traits
are said to be inherited or heritable. Such traits are passed on in the genetic material, a subject
you will learn more about. Living organisms display a wide variety of methods or reproductive
strategies for passing on their genetic information to their offspring.
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• Outcome 2A: Distinguish the types of asexual and sexual reproduction
Reproductive strategies
• Asexual reproduction
Asexual reproduction occurs when only one parent supplies the information to the offspring. The genetic
material of the offspring, and thus their inherited characteristics, are identical to those of the parent. This type
of reproduction is common among bacteria and fungi. One advantage of asexual reproduction is that there is no
need for an organism to find a mate. Also, reproduction can occur quite rapidly. As long as the environment
does not change much, offspring produced by asexual reproduction will be able to survive and reproduce as their
parents did. There are various forms of asexual reproduction. They include: Binary Fission, Budding, Spore
Production and Vegetative Reproduction. Each one results in
offspring that are clones (genetically identical copies) of the
parent. Let’s look at each one separately.
o Binary fission: Many one-celled organisms such as the
amoeba (seen to the right) reproduce asexually using a
form of cell division called binary fission. The cell first
duplicates its contents; including the DNA in the nucleus
and other organelles. It also doubles in size during this
process. After the amoeba divides, each new cell has a copy
of the genetic material, and is the same size as the original
“parent” cell. As a result the offspring are identical.
o Budding: Organisms such as hydra and yeast reproduce
asexually by budding. During budding, the parent produces
a small bud, or a smaller version of itself. The bud is
genetically identical to the “parent” cell and will eventually
grow to be identical in size as well. In animals, such as the
hydra (see diagram to the right), the bud eventually
detaches and becomes a new individual identical to its
parent. This is also true of yeast, which is a unicellular
fungus. Yeast is the organism that causes bread to rise in the
oven.
o Spore production: Some non-flowering plants such as
ferns reproduce by producing spores. Some people confuse
spores and seeds. Spores are produced by the division of
cells of the parent, not by the union of two cells like seeds.
One individual will produce many spores, and each spore
can develop into a new individual identical to the parent.
Often, thousands of spores can be seen on a plant and the
wind will blow the spores to new areas where a plant
identical to the parent will grow. Another difference
between a spore and a seed is that a spore doesn’t contain
nutrients to enable the spore to grow and it must therefore
land directly in a suitable environment that will
immediately support the growth of the new organism.
o Vegetative Reproduction: Many plants produce offspring which grow right from their roots or
grow a part called a runner which will take root and grow. This is one type of vegetative
reproduction, in which a genetically identical plant grows from the parent plant (there are other
BIODIVERSITY Objective 2
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types of vegetative reproduction, but runners are all you need to know for now). The plants
produced through vegetative reproduction will be genetically identical to the parent.
• Sexual reproduction
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Sexual reproduction involves two individuals. Most species of animals and flowering plants
reproduce sexually. The offspring of sexual reproduction will have a mix of the characteristics of both
individuals, ensuring that there is always a mix of characteristics in each generation. This allows for
variation within a species. Sexual reproduction in plants or animals relies on the union of two specialized
cells known as gametes. A gamete is a cell that has one role only, which is to join with another gamete
during reproduction. This joining of gametes results in the DNA necessary for the offspring to grow.
o Sexual reproduction in animals: Almost all animal species, from salmon to dragonflies to
bears, reproduce sexually. Although the details may vary, the important events in animal reproduction
are the same. Sexual reproduction involves specialized cells known as gametes (sex cells). The male
gametes are called sperm cells, and the female gametes are known as egg cells. The union of the sperm
cell with the egg cell occurs during mating and is called fertilization. The cell created by the joining of
the two gametes is known as a zygote. The zygote is the first cell of a new individual that has the
complete set of DNA. The zygote then divides billions of times until a multi-cellular life form
resembling a human is formed. When a life
form that resembles the basic structure of the
parents is first seen, the life form is referred to
as an embryo. Depending on the species, the
development of the embryo may occur inside
the female parent, which happens in most
mammals, or outside, in an egg, which happens
in most other types of animals. The new
individual will show some of the
characteristics of its female parent and some of its male parent. Although the new individual may
resemble one parent more than the other, it will not be identical to either parent.
o Sexual reproduction in plants: As in animals, sexual
reproduction in plants requires the joining of a male gamete
with a female gamete. Most plants produce both male and
female gametes. Pollen contains the male gametes of a plant
and is produced by the anther of the plant. It is pollen that
you often see floating around the air in the summer. When this
pollen reaches the stigma, cross pollination has occurred.
The pollen is then transferred to the egg where cross
fertilization occurs and a zygote is formed (plants can
pollinate and fertilize themselves which is just called
pollination or fertilization). Just like animal reproduction, this
zygote turns into an embryo that will grow to have a blend of
characteristics from the male and female. The embryo will
eventually develop into a new individual. In most plants, the
embryo is produced inside a seed. The seed protects the
embryo and stores food for the embryo to use when it begins to grow into a new individual.
• Some species can reproduce asexually and sexually
You learned above that yeast reproduced asexually through budding. Yeast
can also reproduce sexually. You will later learn about what types of
environmental conditions will lead to some species producing asexually at
times and sexually at other times. Many types of plants can also reproduce
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either way. You learned above that many plants can reproduce asexually through vegetative
reproduction, but many of those plants can also reproduce sexually through seeds, which results in genetic
variation in the offspring.
1. How many “parent(s)” are needed for asexual
5. The sex cells (either male or female) of an animal are
reproduction to occur?
known as – gametes -. The male gamete is
One
sperm - while the female gamete is
called the – egg -. When the gametes join this is
called – fertilization - . This results in the
called the –
2. Explain binary fission and give an example of an
organism that reproduces this way
-The splitting of a parent cell into
two identical cells -The amoeba
3. Explain why the following sentence is false !
When an organism reproduces by budding, the new
organism(s) created are genetically identical but
smaller than the “parent” throughout their life
first cell of a new individual. This cell is called the
– zygote - and after many cell divisions results
in a multicellular –
embryo
-.
6. The anther of a plant produces the male gamete
called – pollen -. When this male gamete reaches the
-They grow to be the same size
4. When a species reproduces sexually, are there any
individuals that are genetically identical to the
generation before it?
stamen of another plant – cross - – pollination has occurred. When the male gamete reaches the
female gamete (also known as the – egg -), of
No
another plant –
occurred.
Use the following information to answer the next question
cross
-
-
fertilization
- has
------
7. At what step above (W, X, Y or Z) does fertilization occur?
X
------
8. Put a checkmark in the box if the statement refers to that type of reproduction
Binary
fission
Budding
Spores
Vegetative
Reproduction
Sexual
Reproduction
Produces offspring identical to its parents
Fertilization must occur by 2 gametes joining
Most plants that use this type of reproduction
can also reproduce sexually
Parent splits into two identical cells
A smaller version of the parent splits off from
the parent and then grows
9. Put a checkmark in the box if the statement refers to that type of sexual reproduction
Plant sexual
reproduction
Fertilization must occur by 2 gametes joining
A sperm joins an egg for fertilization
Pollen joins an egg for cross fertilization
Animal sexual
reproduction
BIODIVERSITY Objective 2
A zygote forms when gametes join
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An embryo develops from the zygote
The offspring will have genetic similarities, to the parents but will
never be genetically identical to them
--------
• Outcome 2B: Describe examples of variation within a species and identify
discrete and continuous variation
Variation
Why do some people have blue eyes, while others have brown eyes? What makes some people redheads and
others brunettes? Are some people born great musicians, or do their talents simply develop with practice? We
know that certain characteristics (also known as traits) are passed on from one generation to another, but
sometimes strange things seem to happen. You may know someone who is the “jock” of her family, while her brother
can't throw a ball straight no matter how hard he tries.
For thousands of years, people have tried to explain how
parents' traits are passed on to their children. Why are
some traits passed on and others are not? Does one
parent have more influence than the other? Why
are some traits more common than others? Are all
traits passed on in the same way?
The passing on of DNA (and therefore traits) from
parents to their offspring is called heredity. The branch
of science that deals with the study of heredity is
called genetics. Pea plants (shown to the right) are
one of the first species that scientists studied
when they became interested in heredity, genetics
and variation. Some of the variations that you will
find in pea plants are shown to the right. Of course, every species will show variations of its own.
There are two main types of variation; Continuous and Discrete. These are explained below.
• Continuous variation
Continuous variation refers to differences in traits that have a
range of forms. They are not one form or another. For example, the
height of adult humans can range from 1.2 m to 2.1 m, with an endless
number of different heights in between. In squirrels, mass can range
anywhere between 133 g and 249 g. Human skin color is another type
of continuous variation. There is countless skin colors in-between
very light and very dark skin. It is difficult to study traits that show
continuous variation because the “instructions” for these traits comes
from many different areas of our DNA. For example, scientists estimate that there are at least 100
different spots on your DNA that controlled the color of your skin. Scientists
however, are far from actually identifying where these spots are or how they
interact with each other to determine skin color.
• Discrete variation
Other traits are examples of discrete variation. Discrete variation refers to
traits that have a limited number of possibilities. For example, the ability to curl
your tongue is genetic. There are only two possibilities: you can do it or you
cannot. The ABC blood group is another example of a discrete genetic trait. In this
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case there are four possibilities: blood group A, B, AB, or O. Gender (male or female) is another
example of discrete variation. Discrete variation is like a report card that uses letter grades such as A,
B, C, D or F. Our knowledge of genetics is focused on "discrete" traits because they are easier to
understand and test. The reason for this is that the “instructions” for these traits comes from one single
area of our DNA. Because of this, scientists have been able to more easily identify areas that provide
instructions for various traits that show discrete variation.
10. Height, intelligence, length of pinky finger, and eye color are all examples of characteristics that
people have. What is another word for characteristics?
Traits
11. What does heredity mean?
The passing on of DNA and traits from one generation to the
next
12. Describe the difference between traits that show continuous vs discrete variation
Traits that show continuous variation have a range of forms
Traits that discrete variation have a limited number of forms
13. Why is it easier to find the DNA responsible for traits that show discrete variation rather than
continuous variation?
The instructions for discrete traits are found in only one area
of the DNA
14. Put a C beside any of the following traits that are continuous variation. Put a D beside any that
are discrete variation
Blood type
Height
Gender
Hand size
Skin color
Ability of immune system to fight cancer
Ability to bend thumb back (hitchhikers thumb) or not
D
C
D
C
C
C
D
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• Outcome 2C: Describe the transmission of characteristics from parents to offspring
Variation
Long before research scientists discovered chromosomes and genes, plant and animal breeders were
conducting experiments in controlled breeding. To prevent unwanted outcomes, only animals with the
most desirable characteristics, or traits, were allowed to reproduce. A trait can be physical (such as eye
color or blood type) or behavioral (such as being lazy or hyperactive). Early experiments in controlled
breeding were not always successful. For example, mating fast running male horses with fast running
female horses did not always produce fast running offspring. But by keeping written records of failures as
well as successes, the breeders began to detect certain basic patterns of inheritance. Scientists now explain
the patterns they discovered in terms of genes. A gene is a segment of DNA that provides instructions on
a specific trait. Each of your parents gave you a gene for each trait you have. Therefore, every trait has 2
separate genes and they may not be the same. So you have two genes for each trait, but to determine
which one was actually used to make up that specific trait may have depended on which gene was the
“stronger” one. • Dominant versus Recessive gene
Each of your parents gave you a gene for each of your traits. The two genes together make up
your genotype for any given trait. Sometimes they both gave you the same gene (the same set of
instructions), in which case you will have the same trait as both of your parents. For example, they both
may have given you the gene for being able to roll your tongue. But sometimes, one parent will give you
one gene (set of instructions) for a certain trait, and the other parent will have given you a different set
of instructions for the same trait. Which one you will have depends of which one was dominant and
which one was recessive. If you have a dominant gene and a recessive gene
for any given trait, the dominant gene will be the one represented (it will
win). This is best explained using Punnett squares.
• Punnett squares
A Punnett square is a chart which shows all possible gene
combinations for a set of parents for a particular trait. Punnett squares are
named for an English geneticist, Reginald Punnett. Lets look at a Punnett
square for the fur color of cats.
Each cat has two genes for fur color. Which one is represented
depends on which one is dominant and which one is recessive. The
dominant trait is always expressed when mixed with a recessive trait. Black
fur is the dominant trait when it comes to cats and white fur is recessive.
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For the following Punnett square “B” represents the gene for black fur, and “b” represents
the gene for white fur. The mother and the father both have one of each of the genes. If we fill in the
Punnett square we have the 4 potential offspring genotypes. Each time a kitten is born, it will have a
25% chance of inheriting each one of the genotypes.
If a kitten is born with the genotype “BB” it inherited two genes for black fur so of course it will be
black. There are two genotypes above that are “Bb”. Since “B” is dominant over “b”, any cat with the
“Bb” genotype will also be black, but will have the gene for being white hidden in its DNA. Any
kitten born with the “bb” genotype will be white. In the example above, there is a 3 in 4 chance of any
kitten being black and a 1 in 4 chance of it being white.
o Differences/Similarities between parents and offspring
When it comes to comparing an offspring’s traits to his/her parents, there are 4 possibilities
for the offspring. (Let’s use the cat example we were using above).
1) The kitten can be the same as both of his/her parents (ex: both parents are black and the
kitten is as well).
One of the sets of genotypes for the mother and father is “BB” and “Bb” respectively.
With these genotypes both parents would be black. The combinations of different
offspring can be determined
Notice how no offspring will be white because they all have at least one dominant “B”
gene in their genotypes. There are other genotype possibilities that the parents could
have had. For instance “BB” and “BB” would produce all black kittens. Genotypes
“Bb”, “Bb” would result in a 75% chance of each kitten being born black (try making a
Punnett square to test it out)
2) The kitten can be different from both parents (ex: both parents are black and the kitten is
white).
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There is only one possible genotype for this situation to occur because each parent has to
be carrying at least 1 recessive “b” gene.
Notice that in this particular situation there was only a 1 in 4 chance of the kitten being
born white (the “bb” genotype)
3) The cat can be the same as one parent (ex: one parent is black, one is white, and the kitten is
black).
The mother must have a “bb” genotype since she is white. The father could either have a
“BB” or a “Bb”. In the example below, the father has a “BB” genotype, which would result
in 100% of his offspring being born black since there is a “B” in every one of the boxes.
4) For the 4th situation, Punnett squares are not needed: In this situation, the offspring is a cross
between the 2 parents.
The above dominant-recessive pattern of inheritance does not always prevail because some
traits do not have genes that are dominant or recessive. Instead, each gene has equal
strength. For example, when a purebred snapdragon
bearing red flowers is crossed with a purebred
snapdragon bearing white flowers, the offspring are
neither red nor white. Instead, the flowers are pink, a
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color intermediate between red and white. This pattern of inheritance is known as
incomplete dominance. Both the white-flower gene and the red-flower gene have played a
part in determining the flower.
15. Each of your parents gave you a set of
instructions that determine whether you can
roll your tongue or not. What is each of these
sets of instructions called?
A gene
17. Peas can either be green or yellow. The gene for
being green is dominant and the gene for being
yellow is recessive. If a pea has a genotype with
one of each gene, will the pea be green or
yellow?
Green (it is dominant)
16. For the trait of being able to bend your thumb
back (hitchhikers thumb) or not being able to
bend your thumb back, each of your parents
gave you a gene. When both of these genes
are together in your DNA, this is called your
-genotype
-
……
…..
Use the following information to answer the next 6 questions
Peas can either be Round (R) or wrinkled (r).
Round is dominant while wrinkled is recessive
24. Think for yourself! Give an
example of a human characteristic
that shows incomplete dominance
Skin color
25. Pick the correct bolded terms below
18. An individual pea is round. What are its 2 possible genotypes?
RR
Rr
19. An individual pea is wrinkled. What is it’s only possible
genotype?
rr
20. If one parent has the genotype of Rr and the other has a genotype
26. Pick the correct bolded terms below
of rr, what percentage of offspring should be born round? Use
and fill in any blanks.
the Punnett square to help you
21. If one parent pea is smooth with the genotype RR and the other
is wrinkled (rr), what is the chance of these two peas having a
wrinkled offspring?
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22. If both parents are wrinkled, what is the chance that they will
have a wrinkled offspring? Draw and complete a punnett square
to find out the answer
23. A pea is born wrinkled but both of the parents are smooth. What
is the only possible genotype of both the mother and the father?
Mother and father both have genotype of Rr
Lllllllllll
• Outcome 2D: Distinguish heritable and non-heritable characteristics
Heritable vs Non-heritable traits
You learned earlier that traits (characteristics) are inherited (they are heritable) from the generation
before. That is why offspring look so much like their parents. You will learn in this section that while most
traits are inherited, some are non-heritable. You will also learn that the environment has a role in shaping
some traits of individuals. Genetics is the field of science that deals with the study of heredity.
• Traits that are 100% inherited (heritable)
A lot of your traits are inherited. This includes things like your
blood type, number of bones you are born with, and if you can curl
your tongue or not. Any trait that is determined by your genes (DNA)
is considered to be heritable.
• Traits that are 100% non-heritable
Some traits have absolutely nothing to do with your parents and
won’t be passed down to future generations. These are traits like
scars, hearing loss due to listening to loud music, or liver damage due
to excess alcohol consumption. Traits that are non-heritable occur
after an organism is born and are therefore not caused by your DNA.
As a result, they are not passed down to the offspring. • Traits due to inheritance AND the environment
A lot of traits fall into this category. While traits like height have an obvious heritable component,
height can also be shaped by environmental factors. For instance, if a child is not fed right while they are
growing, they would end up shorter than if they were fed right. Scientists debate about the role of
genetics vs the role of environment for many traits:
o Genetics vs Environment
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Not all characteristics are inherited. Some characteristics depend entirely on the
environment. For example, scars and injuries are not caused by genetics. In addition, clothing,
hairstyle, makeup, and even cosmetic surgery can alter person’s characteristics. However, a person's
weight (mass) is due to a combination of factors such as genetics, diet, and activity level. The
interactions between a person's genetics and the environment are complex and not well understood.
The balance between the two is continually being debated. Some believe that "all people are created
equal." They argue that a person's characteristics are due to his or her opportunities and choices and
the environment they are exposed to. Others believe that DNA is responsible for all of someone's
traits, including a person's likes and dislikes. The debate on the role of heredity and the environment
in determining human characteristics continues today. Modern science has tried to separate traits that
are completely inherited from those that are inherited but also can be influenced by the environment.
One method that has been used is to study the similarities and differences between identical twins
that have been separated at birth and raised in different environments. Since
identical twins have the same genetic information, they share inherited traits.
Some of the results of these studies are highly controversial and hard to
explain. In one example, a pair of identical male twins was separated when
they were five days old. When they were reunited, many years later, it
turned out that they were both volunteer firefighters, had the same type of
moustache, and wore the same style of sunglasses. Other identical twins
separated at birth seem to be quite different in many ways. Some people
argue that examples such as these show that many complex behaviors are
inherited.
We now know the environment and our genetics interact to produce many of our characteristics.
At this stage, however, we still have a lot to learn.
1. Think of a 3 traits not mentioned in the above reading that are non-heritable (that are due to
environment only).
- broken bone,
lost tooth,
shaved head
2. Explain the difference between genetics and environment in determining characteristics of an
individual.
Genetics is what is given to you through heredity (your DNA)
and the environment is referring to what you are exposed to
3. Is blood type due to genetics, environment, or both?
genetics
4.
Do you think skin color is due to genetics, environment, or both? Explain
Both: you can tan to change color
5.
Is the ability to be really good at hockey due to genetics, environment, or both?
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Both
6. Is vision loss due to excess staring at the sun due to genetics, environment, or both?
environment
7.
Which of the following is true about traits that are non-heritable
A. They are 100% due to DNA
B. They are 100% due to the environment
C. They are due to a combination of genetics and environment
B
8. Will genetically identical organisms always have the same traits? EXPLAIN WHY OR WHY
NOT
No, because they likely did not grow up in the exact same
environment.
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BIODIVERSITY Objective 2
2A
Strawberries,
like many
other plants,
can reproduce
asexually
through
vegetative
reproduction
as well a
sexually
through seed
production.
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9. Explain asexual reproduction in your own words
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Asexual reproduction occurs when only one parent supplies the
genetic information to the offspring
10. What are 4 main types of asexual reproduction?
-Binary fission -Budding -Spores -Vegetative reproduction
A red female Mystus fish breeds with a white male Mystus fish. They produce 5 red offspring and 1
white offspring. Being red in the Mystus fish must be dominant/recessive. The next offspring will
MOST LIKELY be red/pink/white.
A black male Groeger fish breeds with a while female Groeger fish and they produce 3 grey offspring.
The next offspring will MOST LIKELY be black/grey/white because this trait is showing the pattern of
___________ _____________