1. You and your genes (OCR 21st Century) M Barker Shirebrook Academy
22/04/2017
You and your genes
(OCR 21st Century)
M Barker
Shirebrook Academy

2. 22/04/2017
B1.1 What are genes?

3. Genes, Chromosomes and DNA
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4. How genes work Some facts:
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Some facts:
- Genes are sections of very long DNA molecules that make up chromosomes in the nuclei of cells
- The DNA contains instructions on how the cell should work
- Genes control the development of characteristics (“it’s in the genes”) by issuing instructions to the cell to produce certain proteins
- These proteins are either structural (used for cell growth and repair, e.g. collagen) or enzymes (used for speeding up reactions, e.g. amylase)
- Some characteristics (e.g. eye colour) are controlled by several genes working together

5. Variation
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“Variation” is the name given to differences between individuals of the SAME species.
Variation is due to GENETIC or ENVIRONMENTAL causes. For example, consider dogs:
Ways in which they are the same:
Ways in which they are different:

6. Environmental differences
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Some of this variation is due to our parents, but some of it is due to our upbringing and the environment in which we live – this is called “Environmental variation”.
Variation due to inheritance only
Variation due to environment only
Variation due to a bit of both

7. 22/04/2017
B1.2 “It’s in your genes”

8. Sexual Reproduction
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We have similar characteristics to our parents due to genetic information being passed down in genes through gametes:
The human egg and sperm cell (“GAMETES”) contain 23 chromosomes each.
When fertilisation happens the gametes fuse together to make a single cell called a ZYGOTE. The zygote has 46 chromosomes (23 pairs) and contains information from each parent.

9. Sexual vs. Asexual reproduction
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Sexual reproduction:
2 parents are needed
Offspring will have “pairs” of chromosomes
This will cause genetic variation
Asexual reproduction:
Only 1 parent needed
Offspring are GENETICALLY IDENTICAL to parent (“clones”)
“Snuppy” – the first cloned dog (Aug 05)

10. Boy or Girl?
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“Allele” XX XY
Girl
Boy

11. Boy or Girl?
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Mother
Son
Daughter
Father

12. Key words Genotype Phenotype Allele Dominant Recessive Homozygous
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Genotype
Phenotype
Allele
Dominant
Recessive
Homozygous
Heterozygous
This allele determines the development of a characteristic
The characteristic caused by the genotype
This allele will determine a characteristic only if there are no dominant ones
This word refers to a pair of chromosomes being made of two different alleles of a gene
The genetic make up in a nucleus
This word refers to a pair of chromosomes being made of two of the same alleles of a gene
An alternative form of a gene

13. Androgen
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Androgen is a hormone that controls the development of male reproductive organs:
Step 1: An egg is fertilised by an X chromosome and a Y chromosome
Step 2: Testes start to develop due to the presence of a Y chromosome
Step 3: The testes start producing androgen
Step 4: Androgen causes male reproductive organs to grow
Sometimes the Y chromosome is present but androgen is not detected. This causes the development of female reproductive organs but the individual is genetically a male and unable to reproduce.

14. What would the offspring have?
Eye colour
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In eye colour the brown eye allele is dominant, so we call it B, and the blue eye is recessive, so we call it b: BB Bb bb
Homozygous brown-eyed parent
Heterozygous brown-eyed parent
Blue-eyed parent
What would the offspring have?

15. X X Eye colour BB bb Bb Bb (FOIL)
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Example 1: A homozygous brown-eyed parent and a blue-eyed parent:
Example 2: 2 heterozygous brown-eyed parents BB bb Bb Bb X X
Parents: B b B b B b
Gametes:
(FOIL) Bb Bb Bb Bb BB Bb bB bb
Offspring:
All offspring have brown eyes
25% chance of blue eyes

16. Eye colour
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Example 3: A heterozygous brown-eyed father and a blue-eyed mother: Bb bb
Equal (50%) chance of being either brown eyed or blue eyed. B b b Bb Bb bb bb

17. Another method – the “Punnett square”
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Example 3: A heterozygous brown-eyed father and a blue-eyed mother: B b B b Bb bb
Father
Mother

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B1.3 Inherited diseases

19. Example questions
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1) In mice, white fur is dominant. What type of offspring would you expect from a cross between a heterozygous individual and one with grey fur? Explain your answer with a genetic diagram.
2) A homozygous long-tailed cat is crossed with a homozygous short-tailed cat and produces a litter of 9 long-tailed kittens. Show the probable offspring which would be produced if two of these kittens were mated and describe the characteristics of the offspring (hint: work out the kitten’s genotype first).

20. X X X Inherited diseases Ff Cc cc Ss
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1) Cystic fibrosis – a disease that causes thick and sticky mucus to coat the lungs, gut and pancreas, making breathing and digestion difficult. It’s caused by faulty recessive alleles: Ff X
2) Huntingdon's disease – a disease of the nervous system that causes shaking, memory loss, mood changes and eventually dementia. It’s caused by a faulty dominant allele: Cc cc X
3) Sickle cell anaemia – a disease that alters the shape of red blood cells, thereby reducing their oxygen capacity, causing weakness and anaemia. It’s caused by recessive alleles: Ss X

21. Family Pedigree Charts
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Consider the following chart of the offspring and grandchildren between two sickle-cell anaemia carriers:
Key:
= male
= female
= S allele
= s allele
Q. Describe the genotype and the phenotype of each of the grandchildren. Also, which member of this family has got sickle-cell anaemia?

22. Genetic testing
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It is now possible to test individuals before they are born for any faulty alleles. There are two main methods:
1) Amniocentesis testing:
Done at weeks
0.5% chance of miscarriage
Small chance of infection

23. Genetic testing 2) Chorionic villi testing: Done at 8-10 weeks
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2) Chorionic villi testing:
Done at 8-10 weeks
2% chance of miscarriage
Virtually no chance of infection

24. Genetic testing Possible outcomes: Outcome Test result Reality
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Possible outcomes:
Outcome
Test result
Reality
True positive
Fetus has the disorder
True negative
Fetus does not have the disorder
False positive
False negative

25. The Ethics of Genetic Testing
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Eliminating genetic diseases
Aborting deformed children
Predicting future diseases
Genetic testing
Genetic information/ profiles stored on computer
Deciding whether or not to have children based on the results

26. Genetically engineered people in TV:
Embryo selection
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Another way of preventing babies born with genetic disorders is embryo selection.
Basically, embryos are harvested from the mother and fertilised in a lab by the father’s sperm (IVF). Healthy embryos are then impmanted back into the mother. This procedure is called pre-implantation genetic diagnosis (PGD).
Genetically engineered people in TV:
Mutant X, a team of genetically engineered mutants.
Khan, from Star Trek 2: The Wrath of Khan

27. 22/04/2017
B1.4 How is a clone made?

28. Words – clones, damp, independent, roots, identical
Cloning Plants
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Plants can reproduce ASEXUALLY. The offspring are genetically ________ to the parent plant and are called _________. The only variation between then will be due to environmental factors. Two examples:
1) This spider plant has grown a rooting side branch (“stolon”) which will eventually become __________.
2) A gardener has taken cuttings of this plant (which probably has good characteristics) and is growing them in a ____ atmosphere until the ____ develop.
Words – clones, damp, independent, roots, identical

29. Cloning Plants by tissue culture
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1) Scrape off a few cells from the desired plant
2) Place the scrapings in hormones and nutrients
3) 2 weeks later you should have lots of genetically identical plants

30. Cloning Animals 1
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Here’s a zygote in its early stages before it turns into an embryo:
Normally, this embryo would grow into one adult. However, the zygote could split into two embryos before maturing, and this causes identical twins with the same genetic information:

31. Cloning Animals 2
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Animals can be cloned by taking the nucleus from an adult body cell and transferring it to an empty, unfertilised egg:
Host mother
Clone

32. Should these embryos be treated as humans?
Stem cell research
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Stem cells are cells that have not yet specialised:
These stem cells have the potential to develop into any kind of cell. The rest of the embryo is destroyed. Most of these embryos come from unused IVF treatments.
Embryo
Egg and sperm
Cloned embryos
The ethical issue:
Should these embryos be treated as humans?