Download Genetics Year 3 Notes and worksheets

New Topic
Genes and Inheritance
Fertilisation
The pictures and sentences below describe what happens when fertilisation happens in plants and animals.
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Cut out the pictures and sentences.
Match each sentence with the correct picture. Put the pairs into the correct order and stick them into
your book.
Design a table to show the similarities and differences between fertilisation in plants and in animals.
[ knowledge]
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An egg cell is contained in an
ovule found in the ovary.
The fertilised egg cell grows
into a seed.
The sperm cell joins with the
egg cell and fertilises it.
Pollen grains are produced by
the male part of the plant.
The nucleus from the pollen
grain enters the egg cell and
fertilises it.
A pollen tube grows from a
pollen grain.
An egg cell is made in an
ovary.
Pollen grains are carried by
insects or the wind.
Sperm cells are made in the
The egg cell is released from
testes and contain half the
the ovary and travels down the
genetic information of a
oviduct.
normal body cell.
During sex, sperm cells are
released and travel through the
female’s uterus.
A fertilised egg cell is
produced, with genetic
information from the mother
and father.
Pollen grains land on the
stigma of another flower.
DO NOT MAKE A DOUBLE SIDED
PHOTOCOPY OF THIS WORKSHEET
Inheritance
1
Label the diagrams using words from the box.
male
female sex cell
sperm cell
egg cell
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3
genetic information
nucleus
fertilisation
fertilised egg cell
Look at the drawing of a sperm cell. Write
down two ways in which it is adapted to its
function.
A sperm cell at a magnification of x2000.
i
_____________________________________________________________________
ii
_____________________________________________________________________
Look at the drawing of an egg cell. Write
down two ways in which it is adapted to its
function.
i
_____________________________
_____________________________
ii
_____________________________
_____________________________
An egg cell at a magnification of x 500.
Double trouble!
Identical twins are formed when one sperm cell fertilises a single egg cell. This fertilised egg cell then
divides and separates to form two cells. Each cell grows and divides and two individuals with exactly the
same genetic information are born. The twins will have the same skin colour, the same sex and all their other
inherited characteristics will be the same. The environment may have an effect on their personalities or their
bodies which may cause them to be different but, genetically, the twins are identical.
Twins that are not identical (fraternal twins) are formed when two sperm cells fertilise two egg cells at the
same time. Each gamete contains genes with slightly different genetic information. For example, one sperm
cell may contain the gene for brown eyes while another sperm cell may contain the gene for blue eyes.
Therefore, when the egg cells are fertilised the individuals will be genetically different. Many of their genes,
however, will be the same.
Fraternal twins are very similar, genetically, to normal brothers and sisters with the same parents. They are
all formed from the meeting of any sperm cell with any egg cell, whereas identical twins share the same
sperm cell and egg cell and, therefore, contain the same genes.
Sometimes when a couple cannot have children
they have gametes removed from them. The egg
cells are fertilised with the sperm cells outside
the body. The fertilised egg cells are then
replanted back inside the mother’s uterus. Lots
of fertilised egg cells are placed inside the
mother in case some don’t grow. If many of
them grow then the mother will give birth to
many babies – this is known as a multiple birth.
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How are identical twins formed?
Why are identical twins more similar than ordinary brothers and sisters?
Can identical twins be different sexes?
Why are brothers and sisters similar?
Will multiple births, when many egg cells are fertilised outside the body and then implanted, produce
identical or similar offspring?
a
Draw a diagram to show how identical
twins are formed. Start your diagram
like this:
b
Draw a diagram to show how fraternal
twins are formed.
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The gene that contains the genetic information for brown eyes is said to be dominant. This means
that if a person’s body cells contain one gene for brown eyes and one gene for blue eyes, the blue-eye gene is
not allowed to work. The person will have brown eyes. Explain how two parents might have a child with
blue eyes even if they both have brown eyes.
Conjoined twins
Conjoined twins (often called Siamese twins) are like identical twins except that parts of their bodies are
joined together. Normally with identical twins, one fertilised egg cell splits into two. For conjoined twins the
two fertilised egg cells do not split completely. When the two cells grow and divide they form twins which
are joined by some part of the body. Some conjoined twins may be joined in places like the fingers – these
twins will be easy to separate by a simple operation. The twins are free to live their lives as healthy
individuals. Other conjoined twins are never separated but still enjoy happy lives attached to their twin.
Conjoined twins may share major organs, like the heart.
These twins will be very weak and if they are operated on
they may die. Jodie and Mary were conjoined twins from an
island called Gozo, near Malta. They were joined by a major
blood vessel called the aorta. Mary’s heart and lungs did not
work and she relied on Jodie’s heart to pump blood around
both of their bodies. If they had stayed joined together then
both would have died within six months, Jodie’s heart could
not have coped with having to pump blood for both of them
and Mary would have died without Jodie. If the twins were
separated Mary would definitely die as her major organs
were not functioning, but Jodie would be able to live a nearly normal life.
A decision was made to separate them and, as predicted, Mary died.
The decision to separate Jodie and Mary and thereby end Mary’s life was criticised by Roman Catholics and
pro-life groups who feel that everybody has a right to live. They felt that by separating the twins Mary was
deprived of her right to live.
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How are conjoined twins different from identical twins?
What part of the body were Jodie and Mary joined by?
What would have happened if the twins were not separated?
What happened when they were separated?
Why did some organisations and religions think separation was a bad decision?
Draw a simple diagram to show how conjoined twins are formed.
Variation and varieties Investigation
What are the differences in mass between different apple varieties?
There are many different varieties of apple. In this experiment you will compare
two varieties.
Apparatus
•
•
5 apples of one variety (variety 1)
5 apples of another variety (variety 2)
•
Balance
Do not eat the
apples.
Method
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Keep the varieties in two separate piles so they don’t get mixed up.
Measure the mass of each apple from variety 1 and record your results in a table.
Repeat step 2 for variety 2.
Recording your results
1
Record your results in a table, showing the masses of all five apples of each variety.
Considering your results/conclusions
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Do all the apples in variety 1 have the same mass?
Do all the apples in variety 2 have the same mass?
Calculate the mean mass of each variety.
All of the apples in a variety have the same genetic information. What could have caused apples in
each variety to have different masses to each other?
Compare the mean mass of variety 1 with the mean mass of variety 2.
a
Which has the largest mass?
b
Why do you think that is?
a
Do you think variety 1 and 2 have the same genetic information?
b
What has made these apples have different masses?
c
Is a difference in genetic information the only cause of variation?
Evaluation
8
Do you think you have enough results to be able to say that one variety of apples is always heavier than
the other? Explain your reasoning.
Genes and the environment
1
Fill in the missing words in the sentences, using words from the box.
You may need to use some words more than once.
Inside every cell in our bodies there is ________________ ________________.
The information is carried on ________________ that tell the cells in our body how to make
us. Many________________ are controlled by genes. Eye colour, hair colour and height are
just a few examples.
Some characteristics are not controlled by genes but by the ________________ .
For example, a ________________ is not something you are born with but some people may
choose to have one. If a person has chickenpox and scratches their spots they may get
________________. You are not born with these characteristics; they are things that you get
during life.
Plants may have all the correct genes that allow them to grow but if the ________________ is
too cold or there is not enough ________________ then they will become weak or die. The
temperature and the amount of water are environmental factors.
There are some characteristics that can be controlled by genes and the ________________ .
An example of this is ________________ . If children have very tall parents then it is likely
they will grow up to be ________________ too. Their parents will have ________________
that have made them tall. These genes may be passed onto their children so they may be tall as
well. However, if the child grows up in an environment where there is not enough food, so
they do not get enough of the essential ________________ , then the child’s growth will be
stunted. This is where the environment has had an effect.
characteristics
genetic information
tall
tattoo
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environment
genes
height
nutrients
scars
temperature
water
In the passage, circle words or phrases which are characteristics controlled by genes.
In the passage, underline words or phrases which are environmental factors.
Cystic fibrosis
Cystic fibrosis (CF) is a genetic disorder. Sufferers have inherited ‘faulty’ genetic information from their
parents and this makes them produce extra mucus. Mucus is a slimy substance that traps microbes.
Normally, ciliated epithelial cells sweep the mucus out of your lungs and you swallow it. However, CF
sufferers produce so much mucus that this does not happen. The mucus builds up in their lungs and they find
breathing difficult. The mucus also encourages bacteria to grow and CF sufferers often get lung infections.
To get rid of this mucus, CF sufferers have
physiotherapy sessions. A physiotherapist slaps
them on the back to make them cough up the mucus
and help them breathe better.
Most CF sufferers have problems with other organs
too. Cystic fibrosis affects the pancreas. The
pancreas produces enzymes which digest food. The
extra mucus blocks the small tube leading from the
pancreas to the small intestine and so the enzymes cannot get to the small intestine. CF sufferers take tablets
containing digestive enzymes.
Not many people with CF live past 30 years of age, although with modern treatments more and more
sufferers are living longer and longer.
For a person to have cystic fibrosis they must have a CF gene from their mother and a CF gene from their
father. People who have only one CF gene are called carriers. Carriers are perfectly healthy, but two parents
who are both carriers may have children who have cystic fibrosis. Half of the man’s sperm cells will contain
the CF gene and the other half will contain the normal gene. The same is true for the mother’s egg cells. Half
of her egg cells will contain the CF gene. One person in 25 carries this ‘faulty’ gene.
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How do people get cystic fibrosis?
What builds up in their lungs so they can’t breathe?
What grows on the mucus that can be harmful?
What is done to make the cystic fibrosis sufferer feel better?
Give an example of an organ that may not work properly in CF sufferers.
a
What is a ‘carrier’?
b
What percentage of people are carriers?
c
Why do only half of a carrier’s gametes contain the faulty CF gene?
a
Draw a diagram to show how two parents who are both carriers can produce a child who has
cystic fibrosis.
b
Explain why only 25% of their children get cystic fibrosis.
Genetic diseases
Different genes which carry the genetic information for different versions of the same thing are called alleles
(pronounced ‘al-leels’). For example, the gene that causes brown eyes is one allele and the gene that causes
blue eyes is another. Some alleles are dominant, which means that they will stop other alleles (called
recessive alleles) from working. The brown-eye allele is dominant over the blue-eye allele. People with one
of each allele will have brown eyes. The characteristics that alleles cause are called phenotypes. The alleles
that people have are called genotypes.
Genotypes are written down as letters. Dominant alleles have a capital letter and recessive alleles have a
small version of that capital letter. Someone with brown eyes could have these genotypes: BB (both alleles
cause brown eyes) or Bb. Someone with blue eyes must have the genotype bb (both alleles cause blue eyes).
1
Huntington’s disease is a serious genetic disease that causes sudden jerky movements. It is caused by a
dominant allele and usually only develops after the age of 40. This family tree shows how it has
affected a family.
a
2
Using H to represent the dominant allele and h to represent the normal allele, give the genotype
of Richard. Explain your reasoning.
b
Give the genotype of Glenn. Explain your reasoning.
c
What chance is there that Laurie also has Huntington’s disease? Give your answer as a
percentage.
Cystic fibrosis is another genetic disease. It is caused by a recessive allele. Using N to represent the
normal dominant allele and n to represent the cystic fibrosis allele, answer the following questions.
a
Copy and complete this diagram to show what the possible genotypes would be if two parents,
both of genotype Nn, had children.
Male
Gametes
Female
N
n
N
n
b
c
What percentage of the children would have the disease?
A ‘carrier’ is someone who does not have a genetic disease whose cells contain one allele for the
disease. What percentage of the children would be carriers?
Inheritance – true or false?
For each statement, say if it is true or false. For each false statement, write out a correct version.
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The colour of your eyes is a characteristic that is inherited.
You inherit characteristics from your mother only.
Your brothers or sisters inherit exactly the same characteristics as you.
All animals inherit some characteristics from their parents.
Plants are not able to inherit characteristics.
Not all characteristics are inherited.
The environment has no effect on your characteristics.
Genes carry genetic information and are found inside every cell.
There are half as many genes in gametes as there are in normal body cells.
Fertilisation is when a sperm cell fuses with an egg cell.
A fertilised egg cell only contains half the genetic information of a normal body cell.
Identical twins form from a single egg cell and a single sperm cell.
Selective breeding
1
Look at these sheep.
A
The Balwen mountain
sheep is able to live in cold,
harsh conditions.
a
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B
The Bluefaced Leicester
sheep produces good
quality wool.
C
The Polled Dorset sheep
produces good quality
meat.
D
The Friesian Milk sheep
produces a lot of milk.
Each of these sheep has been produced by selective breeding. For each sheep write down one
characteristic that has been selected.
Farmers often want to breed two different breeds of sheep together. This is called cross-breeding. The
offspring produced by this method should have characteristics from both parent sheep.
b
Which of the sheep above might a farmer use to breed sheep with good meat and good wool?
c
Which of the sheep might a farmer use to produce sheep with good wool that can survive in the
Welsh mountains?
A sheep farmer has a flock of Wensleydale sheep.
To win a prize at the local farming show, he wants to have
sheep with very long wool. Some time ago, he took the ewes
(female sheep) and rams with the longest wool and allowed
them to breed. He allowed the new lambs to grow and then kept
the ones with the longest wool and allowed them to breed. The
others were sold at market. It took him eight years to produce
sheep with wool long enough for him to win a prize.
a
What is a male sheep called?
b
Why is this farmer’s method an example of selective breeding?
c
Suggest why it took him so long to win a prize.
a
Think about the weather conditions where you live. Write down a list of characteristics that a
sheep should have if it were to be farmed in your area.
b
What other characteristics would you like your sheep to have and why?
New breeds
Farmers select animals with useful features and breed from them. If they continue selecting the same
characteristics over and over again, they may eventually end up with a new breed.
Breeds of hen have now been created that lay eggs earlier in their lives so that farmers get a greater yield of
eggs during the hen’s life.
Today people are very conscious of the amount of fat they consume. New breeds of chicken, pig and cow
that are leaner with not as much fat have been produced because people prefer this sort of meat.
When a cow gives birth she will be able to produce milk for ten months. The more milk a cow can produce
in this time, the more useful she is to a farmer. A typical dairy cow produces between 5000 and 6000 litres
of milk a year and some breeds produce even higher yields. Cows that produce the most milk will be
selected for breeding.
Farms also have stud bulls. These are bulls that have useful characteristics that farmers would like the
offspring to inherit. The sperm cells the bull produces are collected and used to make cows pregnant. Some
stud bulls are so popular that many farms in the area use them to make their cows pregnant.
1
Name one useful characteristic of cows.
2
Name one characteristic you think stud bulls would have to make them popular.
3
Name two useful characteristics of chickens.
4
Name two useful characteristics of sheep.
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The process of selecting a useful characteristic and breeding only using animals which have this
characteristic is called selective breeding.
a
Explain what a farmer would do to breed cows that produce more milk than cows already on the
farm.
b
Selective breeding is sometimes called artificial selection. Why do you think it is called artificial
selection rather than natural selection?
c
How many litres of milk will a typical cow produce per day?
Pea practical
There are different varieties
of plants, some share
particular characteristics and
others do not. You have a
fresh and a frozen variety of
garden pea. You are going to
design an experiment to
compare these different
varieties of pea.
Planning
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What characteristics do these peas have that you could measure?
Choose one of these characteristics and write down a method for your investigation. You will need to
think about these questions.
•
What will you measure?
•
What sample size will you use?
•
What apparatus will you use?
•
How will you make this a fair test?
•
How will you make sure that you stay safe?
Show your method to your teacher before you begin.
Recording your results
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Record your results in a table.
Draw a bar chart to show your results.
Considering your results/conclusions
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If you can, calculate the means and show them on your chart.
Compare your results with other groups’ results.
What have you learned from this experiment? What conclusions can you draw? Try to explain why
you got the results you did.
Evaluation
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10
If you could do this experiment again, what would you do differently? Why?
Was your experiment a fair test? Explain why or why not.
Breeding plants
1
Look at this list of characteristics of tomato plants.
big tomatoes
plants will not die in temperatures below 4 °C
plants produce lots of tomatoes
tomatoes are bright red
tomatoes stay fresh for six days
plants are resistant to disease
tomatoes are juicy
tomatoes are very tasty
tomatoes grow in clumps of four
small leaves
a
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3
Draw a table to show whether each of these characteristics can or cannot be seen when you look
at the plants.
b
Name the three characteristics in the list that you think are the most important to shoppers in a
supermarket. Explain your choices.
c
Name the three characteristics that you think are the most important to farmers. Explain your
choices.
d
Imagine you are a plant breeder. Write down three characteristics from the list that you would
like your new variety of tomatoes to have. Explain your choices.
a
To breed plants a plant breeder takes pollen grains from one flower and puts them onto the
stigma of another. Is this process called pollination or fertilisation?
b
Are the pollen grains the male or the female sex cells?
c
Once on the stigma, a pollen grain grows a tube down towards an egg cell which is contained in
an ovule. The nucleus from the pollen grain goes into the egg cell. Is this process called
pollination or fertilisation?
The drawings show two flowers. Flower A is a normal flower and flower B has had pollen added to its
stigma by a plant breeder.
Flower A.
a
b
Flower B.
Apart from adding pollen, what else has the plant breeder done to flower B?
Suggest why the plant breeder has done this.
Characteristics review
1 The drawing shows a family.
a
Copy and complete the following sentences.
Characteristics that you get from your parents are said to be i________________.
The information for these characteristics is called g________________ information.
b
c
d
e
f
This information is found on g________________.
Where are the things that you named in the last sentence of part a found? Explain in as much
detail as you can.
Name two characteristics that the girl has got from her mother.
Name two characteristics that the boy has got from his father.
Why do the children have characteristics from both their parents? Use a diagram to help you
explain, if you wish.
The boy has a scar on his face. Is this caused by any of the things that you named in part a?
Explain your answer.
2
a
b
c
What is a species?
What is a variety?
What is a breed?
3
A plant breeder takes pollen grains from one flower and puts them onto the stigma of another flower.
Each pollen grain grows a tube from the stigma down the style to the egg cells inside the ovules. Here,
the nucleus from the pollen grain enters the egg cell.
a
What is the name of the process in the first sentence?
b
What is the name of the process in the second sentence?
c
Which is the male gamete and which is the female gamete?
d
Plant breeders need to make sure that only the pollen grains that they select get onto the stigma.
Describe one way in which this is done and explain why it works.
e
Name two characteristics that a plant breeder might want in orange trees.
f
For one of these characteristics, explain how the plant breeder could produce a new variety of
orange tree with this characteristic.
g
If a plant breeder breeds two different varieties of plant together, what is this process called?
4
A hill farmer wants to farm sheep that he can sell for meat. Suggest characteristics that the farmer
might look for when deciding which sheep to farm. Explain your suggestions.
Breeding plants 2
When farmers are planning to plant a field of vegetables they want a crop that will grow well and produce a
high yield so that they get more vegetables for their money. The farmers also want a crop that can withstand
very cold temperatures over the winter or very high temperatures and drought over the summer. They will
want plants that are resistant to disease and pests. Most of all they will want a crop that looks and tastes good
so people will want to buy it.
For over 10000 years farmers have saved the seeds from successful crops to produce the next year’s crop.
They didn’t realise it then but they were selecting useful genes.
Today, plant breeders choose plants that they know have good characteristics. They have developed simple,
yet effective techniques for cross-pollination (the transfer of pollen from the anther of one plant to the stigma
of another plant).
First of all the breeder must decide which plant is to produce the pollen and which will receive the pollen on
its stigma. These must be clearly marked, perhaps with different coloured thread or a tag.
The next step is to ensure that the plant is not fertilised by its own pollen (self-pollination). Some plant
breeders remove the anthers (the male parts, which produce pollen) with tweezers. They may need a
magnifying glass to do this. To prevent cross-pollination (pollination by pollen from another flower)
breeders tie up the petals of the flower with a piece of string or put a polythene bag over the flower to protect
the stigma.
To cross-pollinate, the anther is removed from one plant and placed in a container using tweezers. The
protector, e.g. polythene bag, is removed from the flower of the other plant. The anther is then taken out of
the container using tweezers and is rubbed gently over the stigma of the other plant so pollen is left on it.
The protector is then replaced so the plant is not pollinated by unwanted pollen. Alternatively, a paintbrush
can be used to brush pollen onto the stigma.
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5
Make a list of all the characteristics a plant breeder may look for in:
a
red rose bushes
b
potato plants
c
tomato plants.
Write a list of instructions for pollinating plants for someone who has not done this before.
How do breeders make sure that plants don’t pollinate themselves?
How do breeders make sure unwanted pollen doesn’t pollinate the plants?
Find out how some plants make sure that they don’t pollinate themselves.
Mendelian genetics
Gregor Mendel (1822–1884) was a monk who was very interested in finding out how different plants were created.
Mendel did most of his experiments with pea plants and he did his experiments in three steps.
He allowed individual pea plants to pollinate themselves (pollen from the plant’s own anthers was used to pollinate
the plant). This is self-pollination. From the offspring plants he took only those plants that had the characteristic he
was interested in. He then allowed these plants to self-pollinate. He did the same thing with the next set of offspring
plants and continued doing this until all the plants always produced offspring which all had the characteristic he was
interested in. He called these plants ‘pure-breeding’ or P plants.
Mendel then took one P plant with a certain characteristic (e.g. wrinkled peas) and used this plant’s pollen to
pollinate another P plant that had a variation of this characteristic (e.g. smooth peas). This is cross-pollination. The
offspring were called the F1 generation. In the example of wrinkled and smooth peas, all the offspring produced
smooth peas. He said that the smooth peas were a dominant characteristic. When two F1 plants were cross-pollinated
75% of the offspring (F2 plants) had smooth peas and 25% had wrinkled peas. Mendel said that the wrinkled peas
were a recessive characteristic.
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What is self-pollination?
What is cross-pollination?
How did Mendel produce pure-breeding P plants?
What was the dominant characteristic in the F1 plants?
What was the recessive characteristic in the F2 plants?
We now know about genes. There are two sets of chromosomes in each nucleus of a pea plant, there are two genes for
each characteristic. Each gene may produce a variation in that characteristic. Different genes for the same
characteristic are called alleles. A dominant allele stops the recessive allele from working. A dominant allele is given
a capital letter (e.g. S for smooth peas) and the recessive allele gets a small version of this letter (e.g. s for wrinkled
peas). The set of alleles that a pea plant has is called its genotype. What the plant looks like is called its phenotype.
We can predict the percentages of the genotypes and phenotypes of the offspring using a grid like this:
Parent plants’
alleles in
gametes
S
S
s
Ss
Ss
s
Ss
Ss
The shaded area shows the four different
genotypes possible in the offspring.
This grid shows an SS genotype plant being cross-bred with an ss genotype plant. Remember that each gamete will
only get one allele or the other. All the offspring had a genotype of Ss and so all have a phenotype of smooth peas
because S is the dominant allele.
6
Which step of Mendel’s experiment does this grid show?
7
What is the phenotype of plants that have the genotype ss?
8
What two possible genotypes could plants have if they produced smooth peas?
9a Draw another grid to show what would happen when two Ss plants were bred together. Start your grid like this:
S
s
S
s
10
b
What percentages of smooth and wrinkled peas do you get?
Tall pea plants (T) are dominant to small pea plants (t). Draw another grid to show what would happen
if you crossed Tt plants with pure breeding small pea plants.