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Science 1.9

Science 1.9. Demonstrate understanding of genetic variation. SLO’s. The roles of, and the relationship between, chromosomes, genes, alleles and DNA. How DNA carries instructions and how they are passed on through generations.

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Science 1.9

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  1. Science 1.9 Demonstrate understanding of genetic variation.

  2. SLO’s. • The roles of, and the relationship between, chromosomes, genes, alleles and DNA. • How DNA carries instructions and how they are passed on through generations. • The importance of variations within populations for survival and how this variation occurs. • The purpose of mitosis and meiosis, where they occur and the effect on chromosome number (note: the names of stages are not required). • The difference between phenotypes and genotypes. • Simple monohybrid inheritance patterns showing complete dominance, sex determination, possible genotypes, and phenotype ratios.

  3. Chromosome. The chromosome, is the DNA strand, which has coiled up.

  4. DNA (Deoxyribonucleic acid) The DNA strand, consists of ribose sugars, phosphate atoms and base pairs (nucleotides).

  5. Gene The gene, is a section of the DNA strand, which codes for a trait.

  6. Allele A T T C CGG A T T A A G G C C A AA A T T C CC G A T T A A G G C C A AA The mutant allele has one base that is different, this causes the allele to code for a different trait.

  7. A chromosome is a tangle of DNA, when the DNA is unwound, bands can be seen, these are genes. Each gene codes for a protein, which codes for a trait. The variations of a gene, are called the alleles. Putting it all together.

  8. DNA  proteins. • DNA is a code, when it is read by molecules within the cell, it is translated into a protein. • DNA is made up of base pairs of nucleotides. • A- Adenine • T- Thymine • C- Cytosine • G- Guanine • A bonds with T, while C bonds with G.

  9. A = T

  10. C ≡ G

  11. DNA replication. • Before a cell can divide, the DNA must make an exact copy of itself. • This is so each cell can have a full set of DNA. • This occurs in mitosis and the first stage of meiosis. • How does it happen?

  12. Helicase enzyme

  13. Parent strand New strand After the DNA strand is cut in half, new nucleotides come in from the cytoplasm and match up, making 2 strands.

  14. ‘old’ ‘new’ Semi-conservative replication

  15. Triplets. • Each base pair is read as a set of 3. • Each set of 3 codes for an amino acid. • When many amino acids join together, they make a protein. • When the DNA is coding for a protein it is changed to RNA and T becomes U.

  16. Video link http://www1.teachertube.com//googleSearch.php?cx=012339422634307447803%3Ah-vlw-wg9yy&cof=FORID%3A11&ie=UTF-8&q=DNA+translation&sa=Search

  17. Example. CTA-GAA-ACA-ACT Becomes the RNA GAU-CUU-UGU-UGA Becomes the protein asp-leu-cys-stop CAA-TTG-GCA-ACT Becomes the RNA GUU-AAC-CGU-UGA Becomes the protein gly-asn-arg-stop

  18. So what does this mean for us? • We each have a unique DNA code, which we have inherited form our parents, we must then make different variations of these proteins...what does this mean for us? • We all look different! • Complete the transcription worksheet.

  19. Human chromosomes.

  20. Karyotype.

  21. Human chromosomes. • Each of your body cells has 23 pairs of chromosomes, you inherited from your parents. • 22 ‘normal’ chromosomes, which code for your height, hair colour, skin tone etc. • 1 set of ‘sex’ chromosomes, which code for your gender. • XX  female, XY  male.

  22. Male or female? • In every pregnancy there is 50% chance the zygote will be male ♂ or female ♀. • Half of the man’s sperm carry an X chromosome and the other half a Y chromosome. • Complete Pgs 74&5. Female; egg Male; sperm

  23. Why do we look different to each other? • Variation is the difference between you and the person sitting next to you. • We are all humans, so the variation tends to be traits such as height, eye colour skin tone. • There are 2 types of variation; continuous and discontinuous.

  24. Continuous variation. • The trait fits on a range. • E.g. height, hand span. • With a large sample, most traits will form a bell curve. • Complete the exercise on Pg70.

  25. Discontinuous variation. • Also know as either/or variation. • You either have the trait, or you don’t. • E.g. Widows peak • Complete the exercise on Pg 69.

  26. So what causes variation? • Why do we all look different? • Discuss in pairs why we each look different, yet have the same number of eyes, ears and noses. • Why is variation important to species?

  27. Cell division 1; mitosis. • Cell division for growth and repair, is called mitosis (my-toes grow). • Identical copies of the daughter cell are created through a series of steps, each cell has 2 copies of each chromosome. • You can remember ‘IPMATC’ to help you learn the stages. • Pg 72.

  28. Mitosis. • DNA unwinds. • DNA copies. • Copies move to equator. • Copies divide. • Cell pulls apart. • Cell divides. • Two new cells.

  29. Cell division 2; meiosis. • Cell division for sexual reproduction, is called meiosis. • One ‘germ’ cell becomes 4 daughter cells, each with half the chromosome number of a full body cell. • E.g. egg and sperm have only 1 copy of each chromosome. • Pg 73 & meiosis square dance.

  30. DNA unwinds. DNA crosses over & copies. Copies move to equator. Copies divide. Cell pulls apart. Cell divides. Two new cells. DNA moves randomly to each side of the cell. Cells divide again. Four new cells. Meiosis

  31. Early Prophase.

  32. Late prophase.

  33. Metaphase.

  34. Anaphase.

  35. Telophase.

  36. Cytokinesis.

  37. Why only 1 set?

  38. Egg + Sperm = zygote. Egg cell 23 chromosomes • One set from the egg + one set from the sperm = full set for the zygote. Zygote 46 chromosomes (2n) Full set

  39. 2 important processes. • Crossing over; pieces of DNA are swapped between chromatids.

  40. 2 important processes. • Random assortment; which chromatid goes to which cell is random.

  41. Summary notes. • Meiosis halves the number of chromosomes, so when the egg and sperm join at fertilization, the zygote has a full set. • Each gamete has a unique combination of DNA. • The zygote then grows by mitosis, into an embryo. • If the sperm or egg has a mutation or wrong number of chromosomes, the whole embryo is affected.

  42. So why use meiosis and sexual reproduction? • Why go to all the hassle of meiosis? • Why go and find a mate to reproduce with? • More on that later.

  43. Gene-ious words! Genotype Phenotype The appearance of the gene’s inherited. The phenotype is how the organism looks or how it functions. E.g. Hair colour Brown, blonde, ginga. • The gene’s the organism have inherited from its parents. • Organisms have two copies of each gene. • E.g. Hair colour BB, Bb, bb.

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