Genes, Inheritance and Selection 13/11/2018 13/11/2018 Genes, Inheritance and Selection OCR Gateway 2016 Biology topic 5 W Richards The Weald School

B5.1 Inheritance 13/11/2018

Section of a chromosome: Genome and Phenotype 13/11/2018 Genetic information is stored by genes which are arranged on chromosomes: Section of a chromosome: Genes for eye colour Genes for blood group: Genes for hair colour Definitions of key terms: The “genome” is the entire genetic material of an organism. The “phenotype” of an organism is the set of observable characteristics of an individual resulting from the interaction of its genotype with the environment.

Examples of Continuous and Discontinuous Variation 13/11/2018 Examples of Continuous and Discontinuous Variation No. of people with this eye colour Brown Blue Green No. of people in this height range Below 140cm 140-145cm 145-150cm 150-155cm 155-160cm 160-165cm Above 165cm Which table shows continuous data and which one shows discontinuous data?

Variation 13/11/2018 Variation is a name given to differences in a species, e.g. dogs: Variation in any species is due to each animal having different genetic information in their cells. These variations arise from mutations and these mutations can: Have no effect on phenotype Influence phenotype Determine phenotype

Genetic mutations (Bio HT only) 13/11/2018 Here’s a sequence of bases in DNA: A T C G Q. What happens if this sequence is changed? For example, what if a mutation caused this to happen? A T C G A Genetic variation may influence phenotype by: In coding DNA, in can alter the activity of a protein by changing the shape of the active site In non-coding DNA in can alter how genes are expressed by stopping transcription of mRNA

Sexual vs. Asexual reproduction 13/11/2018 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)

Sexual vs asexual reproduction (Bio only) 13/11/2018 Advantages of sexual reproduction Advantages of asexual reproduction No need to find a mate Increased variation, which may cause an evolutionary advantage Which form of reproduction is better? More time and energy-efficient Faster than sexual reproduction Selective breeding can be used to increase food production Produces a clone of a good animal

Cell growth revision - Mitosis 13/11/2018 Each daughter cell has the same number of chromosomes and genetic information as the parent – a “diploid cell”.

Cell growth 2 - Meiosis 13/11/2018 Each daughter cell has half the number of chromosomes of the parent – a genetically different haploid gamete.

Mitosis vs. Meiosis Mitosis: Meiosis: 13/11/2018 Mitosis: Used for growth and repair of cells Used in asexual reproduction Cells with identical number of chromosomes and genetic information are produced (“clones”) Meiosis: Used to produce haploid gametes for sexual reproduction Each daughter cell has half the number of chromosomes of the parent During meiosis copies of the genetic information are made and then the cell divides twice to form four daughter cells.

Fusing gametes during Fertilisation 13/11/2018 Egg Sperm 46 chromosomes in a fertilised egg 23 chromosomes in here Fertilisation 23 chromosomes in here

Basic genetics - Boy or Girl? 13/11/2018 Note that the Y chromosome is “dominant” and the X is “recessive”. The Y chromosome dictates the development of testes. X X Y “Allele” “Phenotype” XX XY Girl Boy Heterozygous Homozygous

Boy or Girl? Mother Son Daughter Father 13/11/2018 Mother During sexual reproduction, children inherit two alleles of each gene (one from each parent). Son Daughter Father

Genetic Diagrams 13/11/2018 Here’s what happens (genetically) when an egg is fertilised: Mother Father xx xy Equal (50%) chance of being a boy or a girl x x y xx xy xx xy

x y Genetic Diagrams Here’s another way of drawing it: Father Mother 13/11/2018 Here’s another way of drawing it: x y Father Mother

Key words Genotype Phenotype Allele Dominant Recessive Homozygous 13/11/2018 13/11/2018 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

Eye colour 13/11/2018 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) 13/11/2018 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 13/11/2018 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 Note – in reality, characteristics like this are usually depend on the instructions of multiple genes and other parts of the genome.

Another method – the “Punnett square” 13/11/2018 Example 3: A heterozygous brown-eyed father and a blue-eyed mother: B b B b Bb bb Father Mother

Example questions 13/11/2018 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 Modern Genetics Mendel’s experiment: 13/11/2018 Guten tag! My name is Gregor Mendel. I am the father of modern genetics because of the work I did on pea plants in 1865… Mendel’s experiment: X Take two plants; one which is pure-bred for tallness and one pure-bred for shortness, and cross them:

Now cross two of these plants… Modern Genetics 13/11/2018 All the plants produced were tall. Now cross two of these plants… 3 out of every 4 plants were tall, leading Mendel to hypothesise that “for every characteristic there must be two determiners”

Modern Genetics 13/11/2018 Achtung! Unfortunately, nobody knew about chromosomes or genes when I published my findings so no one believed me until after my death, when more powerful microscopes were available. Mendel’s work illustrates how scientists develop ideas that account for the data they have collected. We now know that features of organisms (“phenotypic features”) are the result of multiple genes rather than a single gene.

B5.2 Natural Selection and Evolution 13/11/2018

Genetic Variation 13/11/2018 13/11/2018 The world is populated by millions of different species of animals and plants with HUGE genetic variation…

Classification 13/11/2018 13/11/2018 How would you construct a key to classify these organisms?

Classifying organisms 13/11/2018 13/11/2018 All organisms are classified into groups. For example: Organism What is the main difference between these? “Kingdoms” Plants Animals Vertebrates Invertebrates Amphibians Birds Reptiles Fish Mammals Notice that the number of similarities increases as you go down this tree “Species” Dogs Cats

Why use classification? 13/11/2018 13/11/2018 Wasp – “vespula germanica” Human – “homo sapien” Dog – “Canis lupus familiaris” Carolus Linnaeus, 1707-1778 I invented the modern system of naming species. I did this so that species would have the same name in every language and so that we would have a greater ability to understand different species and how they have evolved.

Molecular Phylogenetics 13/11/2018 Modern DNA research shows that all forms of life share a lot of their DNA. This is used by scientists to help them classify species – “molecular phylogenetics”. 98.8% shared DNA 85% shared DNA

Evolution 13/11/2018 13/11/2018 Evolution is the slow change in organisms that happens over a long period of time. All life on Earth has evolved from simple life forms that existed around 3 billion years ago. It happens through a process called “natural selection”, which basically says this: Charles Darwin, 1809-1882 1) Different species show variation due to mutations 2) The “better adapted” ones survive 3) They then have kids who also have the “better” phenotypes

Evidence for Evolution 13/11/2018 Fossil records, showing the development of an organism over a long period of time Antibiotic-resistant bacteria, giving evidence for natural selection Now that the mechanism of natural selection has been understood and with evidence like fossils and antibiotic-resistant bacteria, the theory of evolution is widely accepted.

Evolution 13/11/2018 13/11/2018 Charles Darwin, 1809-1882 As I said, evolution is the slow change in organisms that happens over a long period of time. Who did I work with? Alfred Wallace 1823-1913 I also worked on a theory of evolution and came up with ideas about natural selection. I also realised that warning colours are produced by some species (e.g. Butterflies) – an example of a beneficial adaptation that had evolved through natural selection.

The “Evolution Tree” 13/11/2018 Ideas about evolution have impacted modern biology. For example, consider the evolution tree: Family Hominidae (Great Apes) Family Hylobatidae (Lesser Apes) Subfamily Hominidae Subfamily Ponginae Tribe Homini Tribe Panini Tribe Gorillini Humans Chimpanzees Gorillas Orangutans Gibbons The theory is that we have descended from the same ancestors. Why is that important?

Using ideas about Evolution 13/11/2018 Here are some ways in which theories of modern evolution have impacted modern biology: Classification is now based on evolutionary relationships We know that bacteria can develop resistance to antibiotics and can therefore understand the need to develop new antibiotics and “finish the course” We understand the need to preserve species, e.g. the Millennium Seed bank