Demonstrate understanding of biological ideas relating to genetic variation

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

2. 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 Outcomes

3. 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 Outcome

4. 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 Specific Learning Outcomes

5. 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

6. 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 DNA Structure

7. 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 Importance of DNA

8. 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 DNA, Alleles, Genes, Chromosomes and Characteristics

9. 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 Alleles

10. The double strands of DNA coil up into a helix Each of the two newly formed DNA double helix molecules will become a chromatid • 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 DNA replication

11. 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 Parent cell Chromosomes line up to so that one copy can go to each cell Chromosomes now split Cell Division - Mitosis 2 daughter cells identical to original

12. Meiosis is the processto 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 Homologous pairs separate into 2 cells Replicated chromosomes separate Cell Division - Meiosis 4 non-identical daughter cells produced

13. 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) Strawberry runner Puppy Yes No No Yes Yes Yes No Yes Yes No No Yes Sexual v Asexual Reproduction

14. 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 XX XY Sex determination

15. 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 X Y b b X B Bb bb XY XX X XX XY bb b Bb A man who is heterozygous for eye colour and a woman who has blue eyes (bb) Sex determination Inheritance and Punnett Squares

16. 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 Pure Breeding

17. 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 g Gg Gg g Gg gg Gg Gg Gg gg g g Heterozygous ½ grey offspring, ½ white Homozygous – no white offspring Test Cross

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

19. Pedigree Example

20. 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 Variation

21. 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 Evolution