Demonstrate understanding of biological ideas relating to genetic variation Science 1.9 (AS90948)

Specific Learning Outcomes Role of DNA in carrying instructions ◦Explain DNA structure and label a diagram  Include: ◦ Nucleotide, Triplet, Sugar, Phosphate, Base, Base pair, ◦Explain why DNA is important in making each organism unique  Include ◦ Gene, Allele, Cell, Organism, Characteristic, Genetic code ◦Explain DNA replication ◦Explain mitosis

Specific Learning Outcome Role of DNA in determining phenotype ◦Explain how sex is determined ◦Explain meiosis ◦Explain how chromosomes and genes are inherited ◦Explain how the genetic code determines our characteristics ◦Use a punnett square/pedigree tree to predict genotype and phenotype ◦Use a punnett square/pedigree tree to help explain how you test for a pure bred organism

Specific Learning Outcomes Link between phenotype, variation and species survival Explain the ways inheritable and non- inheritable variation occurs Discuss how phenotypes related to survival value Discuss advantages and disadvantages of sexual and asexual reproduction

DNA DNA (deoxyribonucleic acid) has 2 functions ◦To control cell activities ◦To pass genetic information from generation to generation DNA is made up of small units called nucleotides

DNA Structure All living things have the same basic DNA structure ◦2 chains made up of nucleotides that looks like a ladder ◦Each chain is joined at the bases (A,T,G,C) ◦The bases, paired A-T and C-G, are called base pairs ◦This ladder exists in a helix shape to save room

Importance of DNA DNA provides the information for all cells The sequence of bases on each strand forms the genetic code Each organism has its own unique code because its order of bases is unique Sections of the code are called genes and code for certain characteristics (traits) The particular trait we display is called our phenotype

DNA, Alleles, Genes, Chromosomes and Characteristics Our DNA is wound up into chromosomes We have 2 copies of each chromosome (1 from our Mum and 1 from our Dad) Each of the chromosomes could have a different version of the same trait (alleles) The particular combination of alleles is called our genotype Gene 4 Tour

Alleles A genotype can be either: ◦Homozygous (2 alleles that are the same) ◦Heterozygous (2 alleles that are different) As well as ◦Dominant (always shows up) ◦Recessive (only shows up if homozygous) BB = black coat because dominant B allele is present Bb = black coat because dominant B allele is present bb = white coat because dominant B allele is not present

DNA replication DNA replication When an organism grows, repairs itself, reproduces or replaces old cells, new cells need to be made Every new cell needs its own copy of the DNA so it is replicated The double strands of DNA coil up into a helix Each of the two newly formed DNA double helix molecules will become a chromatid

Cell Division - Mitosis Mitosis Mitosis is the process of cell division for growth and repair It makes an exact copy of the original cell to produce 2 identical daughter cells 2 daughter cells identical to original Chromosomes line up to so that one copy can go to each cell Chromosomes now split Parent cell

Cell Division - Meiosis Meiosis Meiosis is the process to produce sex cells It produces 4 daughter cells each with half the number of chromosomes Due to crossing over and independent assortment, these cells produce inheritable variation Replicated chromosomes separate Homologous pairs separate into 2 cells 4 non-identical daughter cells produced

Sexual v Asexual Reproduction Sexual reproduction involves 2 parents and produces offspring that are genetically different to the parent Asexual reproduction involves 1 parent and produces offspring that are identical to that parent (clones) Asexual ReproductionSexual Reproduction Name of an example Are gametes involved Is fertilisation involved Is mitosis involved Is meiosis involved Are the offspring genetically identical Can it be done by only one parent Strawberry runnerPuppy No Yes No Yes No

Sex determination Our sex is determined by either an X or a Y chromosome Females are homozygous males are heterozygous During sexual reproduction an egg and a sperm come together. Every egg has an X but the sperm has a 50/50 chance of being an X or a Y due to its formation in meiosis XY XX

All genes are inherited through sexual reproduction We can use a punnett square to determine what the chance of offspring having certain traits is going to be Inheritance and Punnett Squares X X X Y Sex determination b B bb A man who is heterozygous for eye colour and a woman who has blue eyes (bb) Bb bb XX XY XX

Pure Breeding A pure bred organism is one that is homozygous for the trait concerned (AA or aa) A pure bred organism always breeds pure and has no hidden genetic characteriestic

Test Cross A test cross is used to determine whether an individual with the dominant phenotype pure bred or not You cross your individual with one that is homozygous recessive When you complete the cross, if any offspring have the recessive trait the individual must have been heterozygous Eg In mice, grey coat is dominant (G) over white. A breeder wants to know if his grey male is homozygous for colour G G g g Homozygous – no white offspring Gg gg Gg g g gG Heterozygous ½ grey offspring, ½ white

Pedigrees Pedigree trees show inheritance patterns They show the phenotypes over various generations and can be used to determine most genotypes

Pedigree Example

Variation Variation is the differences in a population that can come from inherited genes and the influence of the environment Variation in inherited genes can come during sexual reproduction (crossing over and independent assortment) or from mutations Variation is important for the survival of a species because if the environment changes, some of the population should be able to survive and continue to reproduce if the traits that they have are favourable

Evolution Evolution is a result of this variation Natural selection is the fact that the traits that are favourable are “selected for” in an environment Eventually these traits will become the norm, this is how evolution occurs