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

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

Genes, Chromosomes and DNA 22/04/2017

How genes work Some facts: 22/04/2017 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

Variation 22/04/2017 “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:

Environmental differences 22/04/2017 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

22/04/2017 B1.2 “It’s in your genes”

Sexual Reproduction 22/04/2017 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.

Sexual vs. Asexual reproduction 22/04/2017 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)

Boy or Girl? 22/04/2017 X X Y “Allele” XX XY Girl Boy

Boy or Girl? 22/04/2017 Mother Son Daughter Father

Key words Genotype Phenotype Allele Dominant Recessive Homozygous 22/04/2017 22/04/2017 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

Androgen 22/04/2017 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.

What would the offspring have? Eye colour 22/04/2017 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?

X X Eye colour BB bb Bb Bb (FOIL) 22/04/2017 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

Eye colour 22/04/2017 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

Another method – the “Punnett square” 22/04/2017 Example 3: A heterozygous brown-eyed father and a blue-eyed mother: B b B b Bb bb Father Mother

22/04/2017 B1.3 Inherited diseases

Example questions 22/04/2017 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).

X X X Inherited diseases Ff Cc cc Ss 22/04/2017 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

Family Pedigree Charts 22/04/2017 22/04/2017 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?

Genetic testing 22/04/2017 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 14-16 weeks 0.5% chance of miscarriage Small chance of infection

Genetic testing 2) Chorionic villi testing: Done at 8-10 weeks 22/04/2017 2) Chorionic villi testing: Done at 8-10 weeks 2% chance of miscarriage Virtually no chance of infection

Genetic testing Possible outcomes: Outcome Test result Reality 22/04/2017 Possible outcomes: Outcome Test result Reality True positive Fetus has the disorder True negative Fetus does not have the disorder False positive False negative

The Ethics of Genetic Testing 22/04/2017 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

Genetically engineered people in TV: Embryo selection 22/04/2017 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

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

Words – clones, damp, independent, roots, identical Cloning Plants 22/04/2017 22/04/2017 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

Cloning Plants by tissue culture 22/04/2017 22/04/2017 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

Cloning Animals 1 22/04/2017 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:

Cloning Animals 2 22/04/2017 Animals can be cloned by taking the nucleus from an adult body cell and transferring it to an empty, unfertilised egg: Host mother Clone

Should these embryos be treated as humans? Stem cell research 22/04/2017 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?