cell division and inheritance revision 1 · •€€the dna in the cell from each embryo is tested...

Cell Division and Inheritance Revision 1

56 minutes

56 marks

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Q1. People have different shaped ear lobes, either ‘hanging’ or ‘attached’.

The diagrams show the two shapes of ear lobe.

A gene controls the shape of a person’s ear lobes.

The diagram shows a family tree.

Parents A and B both have hanging ear lobes.

(a) The key does not show the symbol for a female with attached ear lobes.

Draw the symbol for the key to show a female with attached ear lobes.

Use information in the family tree and the key.

Symbol = ............................................................ (1)

(b) Look at the family tree.

What does the information in the family tree tell you about the allele for hanging ear lobes?

Draw a ring around the correct word to complete the sentence.

(1)

dominant.

The allele for hanging ear lobes is weak.

recessive.

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(c) (i) Parents A and B have three children, C, D and E. All three children are boys.

What are the chances that the next child of parents A and B will be a girl?

Draw a ring around one answer.

(1)

no chance (0 %) a half (50 %) certain (100 %)

(ii) Which statement explains your answer to part (c)(i)?

Tick ( ) one box.

(1) (Total 4 marks)

Some of B’s sperm cells have an X chromosome.

Some of A’s egg cells have a Y chromosome.

All of B’s sperm cells have an X chromosome.

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Q2. Stem cells can be collected from human embryos and from adult bone marrow. Stem cells can develop into different types of cell.

The table gives information about using these two types of stem cell to treat patients.

Scientists are planning a new way of treating a disease, using stem cells.

Use only the information above to answer these questions.

(a) Give three advantages of using stem cells from embryos instead of from adult bone marrow.

1 .....................................................................................................................

2 .....................................................................................................................

3 ..................................................................................................................... (3)

Stem cells from human embryos Stem cells from adult bone marrow

It costs £5000 to collect a few cells. It costs £1000 to collect many cells.

There are ethical issues in using embryo stem cells.

Adults give permission for their own bone marrow to be collected.

The stem cells can develop into most other types of cell.

The stem cells can develop into only a few types of cell.

Each stem cell divides every 30 minutes.

Each stem cell divides every four hours.

There is a low chance of a patient’s immune system rejecting the cells.

There is a high chance of a patient’s immune system rejecting the cells.

More research is needed into the use of these stem cells.

Use of these stem cells is considered to be a safe procedure.

(b) Give three advantages of using stem cells from adult bone marrow instead of from embryos.

1 .....................................................................................................................

2 .....................................................................................................................

3 ..................................................................................................................... (3)

(Total 6 marks)

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Q3. Read the information about stem cells.

Evaluate the use of stem cells from embryos or from adult bone marrow for treating human diseases.

You should give a conclusion to your evaluation.

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(Total 5 marks)

Stem cells are used to treat some human diseases.

Stem cells can be collected from early embryos. These stem cells have not begun to differentiate, so they could be used to produce any kind of cell, tissue or organ. The use of embryonic stem cells to treat human diseases is new and, for some diseases, trials on patients are happening now.

Stem cells can also be collected from adult bone marrow. The operation is simple but may be painful. Stem cells in bone marrow mainly differentiate to form blood cells. These stem cells have been used successfully for many years to treat some kinds of blood disease. Recently there have been trials of other types of stem cell from bone marrow. These stem cells are used to treat diseases such as heart disease.

Q4. Cystic fibrosis is an inherited disorder.

Mr and Mrs Brown do not have cystic fibrosis but they have a child with cystic fibrosis.

(a) Draw a ring around the correct answer to complete each sentence.

(1)

carrier allele.

(i) The allele for cystic fibrosis is a dominant allele.

recessive allele.

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(1)

carriers.

(ii) Mr and Mrs Brown are both immune.

infected.

(b) The diagram shows how the allele for cystic fibrosis can be inherited by Mr and Mrs Brown’s children.

(i) Give the number of one person in the diagram who has cystic fibrosis. (1)

(ii) The chance that Mr and Mrs Brown'� s next child will have cystic fibrosis is

........................................................................................................................ (1)

(c) A genetic counsellor describes to Mr and Mrs Brown one way of screening embryos for cystic fibrosis.

• Some eggs are collected from Mrs Brown.

• The eggs are then fertilised in a dish.

• Several embryos may start to develop.

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The photograph shows how doctors take one cell from each embryo when it is only 3 days old.

©Pascal Goetgheluck/Science Photo Library

• The DNA in the cell from each embryo is tested for cystic fibrosis.

• Doctors select one embryo that is unaffected and place it in Mrs Brown’s uterus.

• The embryo then develops into a baby.

Use the information to suggest one advantage and one disadvantage of screening embryos in this way.

Advantage ......................................................................................................

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Disadvantage .................................................................................................

........................................................................................................................ (2)

(Total 6 marks)

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Q5. The photograph shows some cells in the root of an onion plant.

By UAF Center for Distance Education [CC BY 2.0], via Flickr

(a) Cells X and Y have just been produced by cell division.

(i) Name the type of cell division that produced cells X and Y.

............................................................................................................... (1)

(ii) What happens to the genetic material before the cell divides?

............................................................................................................... (1)

(b) A gardener wanted to produce a new variety of onion.

Explain why sexual reproduction could produce a new variety of onion.

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........................................................................................................................ (3)

(Total 5 marks)

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Q6. People with cystic fibrosis make large amounts of thick, sticky mucus in their lungs. Cystic fibrosis is caused by the inheritance of recessive alleles.

(a) What do each of the following mean?

(i) Alleles

...............................................................................................................

............................................................................................................... (1)

(ii) Recessive

...............................................................................................................

............................................................................................................... (1)

(b) Mr and Mrs Brown have a child with cystic fibrosis. They hope to have another child. They want to know the probability that their next child will have cystic fibrosis. They visit a genetic counsellor who explains, “You are both heterozygous for cystic fibrosis. There is a 1 in 4 (25%) chance that your next child will have cystic fibrosis.”

Use the following symbols in answering the questions.

N = allele for being unaffected by cystic fibrosis n = allele for cystic fibrosis

(i) Mr and Mrs Brown both have the same genotype.

What is their genotype? .................................................................................. (1)

(ii) There is a 1 in 4 chance that Mr and Mrs Brown’s next child will have cystic fibrosis. Use a genetic diagram to explain why.

(3)

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(c) Mr and Mrs Brown do not want to have another child with cystic fibrosis. The genetic counsellor explains two different methods for finding out whether an embryo has cystic fibrosis. The methods are:

• pre-implantation genetic diagnosis (PGD)

• chorionic villus sampling (CVS).

In PGD, eggs are fertilised in dishes and allowed to grow into embryos. A cell is taken from each embryo when the embryo is 3 days old. The photograph shows how the cell is taken.

Photograph: © Pascal Goetgheluck/ Science Photo Library

The DNA in the cell can then be tested. The possibility of a false positive result is about 1 in 6. An unaffected embryo can then be placed in the woman’s uterus. The procedure costs about £6000.

CVS can only be done after 9 weeks of pregnancy. A tiny piece of the placenta is taken out using a tube attached to a syringe. This is grown in tissue culture for about 7 days. The diagram below shows how CVS is done.

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The DNA in the cells can then be tested. About 2 in every 100 women have a miscarriage because of CVS. The possibility of a false positive result is about 1%. The procedure costs about £600. Following a positive result, the parents must then decide whether to terminate the pregnancy.

The genetic counsellor thinks that PGD is a better method than CVS for detecting cystic fibrosis in an embryo.

Evaluate this opinion.

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(Total 10 marks)

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Q7. The diagram shows a strawberry plant.

The parent plant grows side shoots.

New plants grow on the side shoots.

© D.G. Mackean

The new plants will all have the same inherited characteristics as the original parent plant.

Complete the sentences to explain why.

Use words from the box.

(a) The new plant is produced by ..................................................................... reproduction. (1)

asexual differentiation embryos fertilisation

gametes genes mitosis sexual

(b) In this type of reproduction, body cells divide by ............................................................. (1)

(c) The new plant has the same ............................................................. as the parent plant. (1)

(Total 3 marks)

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Q8. When scientists look at dividing cells under a microscope, they can see strands that contain a chemical called DNA.

A photograph of these strands can be cut up and re-arranged.

The diagram shows an arrangement of the strands from a human cell.

(a) What name is given to the strands containing DNA shown in the diagram?

Draw a ring around one answer.

(1)

alleles chromosomes genes

(b) Look carefully at the diagram.

(i) The cell was taken from a man and not from a woman.

How can you tell?

............................................................................................................... (1)

(ii) What evidence is there that the strands are from a body cell, and not from a gamete?

Tick ( ) one box.

(1)

The strands are arranged in order of size.

The strands are in pairs.

Gametes are made in the testes and ovaries.

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(iii) When a human cell is not dividing the strands containing DNA are not clearly visible.

Draw a ring around the correct answer to complete the sentence.

(1) (Total 4 marks)

cell membrane.

In a human cell, the DNA is normally found in the cytoplasm.

nucleus.

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Q9. Cats normally have four toes on each back paw.

The picture shows the back paw of a cat with an inherited condition called polydactyly.

By Onyxrain (Own work) [Public domain], via Wikimedia Commons

The family tree shows the inheritance of polydactyly in three generations of cats.

(a) What combination of alleles did the original parents, A and B, have?

Explain how you work out your answer.

You may use a genetic diagram in your answer.

Use the symbol H to represent the dominant allele.

Use the symbol h to represent the recessive allele.

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A = ................................................... B = ...................................................... (4)

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(b) (i) Give two possible combinations of alleles for cat D.

1 .................................................... 2 .................................................... (1)

(ii) You cannot be sure which one of these two is the correct combination of alleles for cat D.

Why?

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...............................................................................................................

............................................................................................................... (1)

(Total 6 marks)

Q10. A certain allele increases the chance of women developing one type of breast cancer.

A woman has this allele. She wants to be sure that she will not have daughters who also have the allele.

Doctors:

• collect several eggs from her ovaries

• fertilise the eggs with sperm, in dishes.

(a) The doctors expect half the embryos produced to be female.

Explain why.

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........................................................................................................................ (2)

(b) The embryos grow to around 100 cells.

Doctors:

• remove one cell from each embryo

• check the cell for the allele.

Complete the sentence.

This process is known as embryo ............................................................ . (1)

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(c) One of the female embryos did not have the allele. This female embryo was implanted into the woman’s uterus.

Evaluate the advantages and disadvantages of the whole procedure.

Use information from all parts of this question and your own knowledge.

Remember to give a conclusion to your evaluation.

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(Total 7 marks)

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M1. (a)

the shape must be (roughly) circular and not shaded, for the mark accept the shape drawn in the key if it is not contradictory

1

(b) dominant 1

(c) (i) a half (50%) 1

(ii) Some of B’s sperm cells have an X chromosome 1

[4]

M2. (a) comparisons are not required but should be credited accept a clear indication of the statement even if incomplete

can develop into most other types of cell 1

each cell divides every 30 minutes 1

low chance of rejection by the patient’s immune system 1

(b) any three from:

• cheaper / only costs £1000 this must be comparative ignore costs £1000

• can collect many (stem) cells

• adults give permission for their own bone marrow to be collected comparisons are not required but should be credited

• safe 3

[6]

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M3. Marks should not be awarded for simply copying the information provided A mark may be awarded for a comparison between treatments if the answer only involves copied information

any four from:

For all 4 marks to be awarded, there must be at least 1 pro and 1 con

embryo stem cells – examples of

pros

• can treat a wide variety / lots of diseases / problems

• many available / plentiful

• using them better than wasting them

• painless

cons

• (possible) harm / death to embryo

• (relatively) untested / unreliable / may not work allow long term effects not known or may be more risky

• embryo can’t be ‘asked’ / ‘embryo rights’ idea

adult bone marrow stem cells – examples of

pros

• no ethical issues (in collection) or permission given

• quick recovery

• (relatively) safe allow does not kill (donor) / low risk

• well tried / tested / know they work

cons

• operation hazards eg infection

• few types of cell / tissue produced or few diseases / problems treated

• painful so may deter donors 4

Conclusion to evaluation:

A reasoned conclusion from the evidence 1

[5]

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M4. (a) (i) recessive allele 1

(ii) carriers 1

(b) (i) 6 allow nn

1

(ii) 1 in 4 / 0.25 / / 25 % / 1:3

do not accept ‘3:1’ / 1:4 / 1 in 3 / 25 1

(c) advantage:

detect CF qualified – eg at early stage / before becoming pregnant or (only) healthy children produced

allow ‘after only 3 days’ allow reduces health care costs

1

disadvantage:

some embryos are destroyed / may damage embryo allow increased risk of miscarriage ignore not natural ignore cost

1 [6]

M5. (a) (i) mitosis

correct spelling only 1

(ii) replicates / doubles / is copied / duplicates accept cloned ignore multiplied / reproduced

1

(b) fertilisation occurs / fusion (of gametes) accept converse for asexual, eg none in asexual / just division in asexual

1

so leading to mixing of genetic information / genes / DNA / chromosomes genes / DNA / chromosomes / genetic information comes from 1 parent in asexual ignore characteristics

1

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one copy (of each allele / gene / chromosome) from each parent or gametes produced by meiosis or meiosis causes variation

meiosis must be spelt correctly 1

[5]

M6. (a) (i) (alternative) forms / types of a / the same gene 1

(ii) only expressed if 2 copies inherited or not expressed if other allele present

allow over ruled / over powered by the other allele 1

(b) (i) Nn

ignore heterozygous 1

(ii) genetic diagram including: accept alternative symbols, if defined

gametes: N and n from both parents

accept alternative symbols if correct for answer to (b)(i) 1

correct derivation of offspring genotypes: NN Nn Nn nn

allow if correct for candidate’s parental genotypes / gametes 1

identification of nn as having cystic fibrosis 1

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(c) Argued evaluation

any four from:

• PGD higher financial cost accept CVS only costs £600

• PGD occurs before pregnancy / implantation accept detected at earlier stage so less unethical / less trauma

• PGD does not involve abortion so less trauma / less pain / ethical • PGD higher incidence of false positive / use of numbers so higher risk of destroying healthy embryo

accept PGD has (surplus) embryos so some destroyed / unethical

• PGD no chance of miscarriage whereas CVS does or PGD less chance of miscarriage

4

[10]

M7. (a) asexual 1

(b) mitosis 1

(c) genes 1

[3]

M8. (a) chromosomes 1

(b) (i) has XY / Y allow female would be XX / has no Y

1

(ii) The strands are in pairs 1

(iii) nucleus 1

[4]

M9. (a) A = Hh B = Hh

may not be in answer space accept heterozygous or description

1

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(allele for) polydactyly is dominant or polydactyly is H,

for marking points 1, 2 and 3 accept evidence in clearly labelled / annotated genetic diagram

1

cats with polydactyly have H accept if polydactyly was recessive all offspring would have polydactyly

1

E or (some) offspring of A and B, does not have polydactyly, so A and B must both have h

1

(b) (i) HH and Hh or homozygous dominant and heterozygous

both required, in either order allow description

1

(ii) any one from:

accept annotated genetic diagram to explain answer

• polydactyly is dominant

• parents are both Hh

• if D is Hh all offspring could inherit H 1

[6]

M10. (a) half / 50% sperm have X (chromosome) or half / 50% sperm have Y (chromosome)

penalise incorrect use of gene / allele once only 1

all eggs have X (chromosome) annotated genetic diagram could gain 2 marks

1

(b) screening ignore selection

1

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(c) any three from:

max 2 if only advantages or only disadvantages discussed

advantages:(max 2)

• (girl / children / women) don’t / less likely to get / inherit (breast) cancer / this / the disease

do not accept reference to allele alone for this point

• future generations get less cancer or less likely to have the allele

• less expensive (for NHS) than treating cancer

disadvantages:(max 2)

• (wrong / immoral to) reject / kill embryos ignore wrong / immoral / religious argument unqualified

• possible harm to embryo (that is implanted) / miscarriage ignore reference to termination

• possible harm to mother (due to operational procedure) allow reference to needing hormone treatment

3

argued conclusion must refer to both advantages and disadvantages and must be at end of answer

1 [7]

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cell division and inheritance revision 1 · •€€the dna in the cell from each embryo is tested...

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