Genetics

1. Genetics

2. Assumed Knowledge • The central dogma • Basic genetic terminology • DNA replication, transcription, translation • Chromosome structure • Mitosis and Meiosis • Mendel’s laws of inheritance/ Hardy-Weinberg

3. The central dogma

4. Some Basic Terminology DNA – stands for deoxyribonucleic acid. DNA is a nucleic acid that contains the genetic material of a cell. DNA is composed of two strands of nucleic acids arranged in a double helix.

5. RNA – stands for ribonucleic acid. Involved in the conversion of genetic material in DNA to proteins. A single stranded sequence of nucleic acids.

6. Nucleic Acids – these are linear strands of nucleotides Nucleotides – these have three parts • A phosphate group • A sugar group • A base

7. DNARNA Sugar Deoxyribose Ribose Base Adenine (A) Adenine (A) Thymine (T) Uracil (U) Guanine (G) Guanine (G) Cytosine (C) Cytosine (C)

8. Codon – these are sequences of three adjacent nucleotides Each codon encodes for a specific amino acid e.g. AAA will encode lysine, AGU will encode serine

9. Anticodon – these are sequences of three adjacent nucleotides that are complimentary to a specific codon Each codon encodes for a specific amino acid e.g. UUU will be complimentary to AAA and encode lysine, UCA will be complimentary to AGU and encode serine

10. Genome – the entire genetic content of an organism. Basically, all the DNA.

11. Genes – these are the regions of DNA that code for proteins. Not every bit of DNA gets converted to protein – DNA contains a lot of junk (~1.5% of the genome encodes for proteins) 1 Gene = 1 Protein

12. Chromatin – a complex of DNA and protein.

13. Chromosomes – These are large condensed segments of DNA formed from the condensation of chromatin. Each chromosome contains many genes. Humans have 46 chromosomes – 23 pairs

15. Karyotype – the number and appearance of chromosomes in the nucleus of a cell.

17. Allele – these are alternative forms of the same gene e.g. ABO blood groups There are 3 alleles that are recognised - A, B, O As every individual has two copies of there are six possible genotypes (combinations of the alleles) AA, AO, BB, BO, AB, OO

18. Genotype – this is the genetic make up of an individual e.g. is their ABO blood group AA, AB, BB???

19. Phenotype – this is an organism’s observable traits e.g. is their eye colour blue, green, brown

20. Alleles may be dominant or recessive Dominant alleles require only one allele of the two copies to be present for the phenotype to be observed Recessive alleles require both copies of the allele to be present for the phenotype to be observed

21. DNA Replication DNA is compose of two complimentary strands Sugar group and phosphate group form a backbone with the bases projecting into the center of the helix to form bonds with bases on the opposite strand Backbone reads as sugar, phosphate, sugar, phosphate

22. DNA strands have a 5’ and a 3’ end. This gives the strand directionality (a head end and a tail end!!!): • 5’ > 3’ or • 3’ > 5’ The two complimentary strands of DNA are arranged in opposite directions

23. In RNA uracil is the complimentary base to adenine, not thymine

24. DNA Replication • Unwinding of the two strands of DNA (helicase) • Each parent strand acts as a template for a new strand of DNA • Formed by adding complimentary nucleotides (DNA polymerase)

25. Yields two identical strands of DNA, each with one old strand and one new strand Semi-conservative

26. http://www.youtube.com/watch?v=zdDkiRw1PdU&feature=related

27. Transcription & Translation Transcription DNA > RNA Translation RNA > Protein

28. Transcription • Takes place in the nucleus • Unwinding of the DNA strands • Using one strand of DNA as a template, there is formation of a complimentary strand of messenger RNA (mRNA) • RNA contains uracil instead of thymine • All steps catalyzed by RNA polymerase

30. Splicing – this is the removal of the junk DNA • Remember 1 gene = 1 protein • Genes contain useful regions (exons) and junk regions (introns) • Introns are removed from the mRNA by splicing • Ensures only the exons carry on to translation and protein formation

32. Transcription • Performed by the ribosome in the cytoplasm and also involves tRNA (transfer RNA) • Every three nucleotides on mRNA will encode an amino acid (codons) • tRNA contains a specific anticodon and also has attached an amino acid corresponding to that anticodon

33. tRNA anticodons bind to their complimentary sequences on mRNA • The ribosome removes the amino acid attached to the tRNA and forms a chain of amino acids – a protein

35. http://www.youtube.com/watch?v=erOP76_qLWA

36. Chromosome Structure & Number • DNA wraps around specialised proteins called histones – beads on a string • These condense to form chromatin (DNA + protein) • Further condensation to form a compact chromosome

37. During the non-divided phase of the cell cycle DNA exists as uncondensed chromatin that is accessible for transcription • During the dividing phase of the cell, chromatin condenses to form a four arm chromosome consisting of two identical sister chromatids joined in the center at the centromere • Remember, DNA replication forms an identical copy of DNA – a chromatid is one of these copies

39. Humans have 46 chromosomes – 23 pairs • 22 autosomal pairs • 1 sex pair Females = XX Males = XY

40. Monosomy– one copy of the chromosome is missing Trisomy – an extra copy of the chromosomes is present

41. Mitosis and Meiosis Mitosis – cell division required for production of an identical set of chromosomes, forms two genetically identical diploid daughter nuclei Meiosis – cell division required for sexual reproduction, forms four genetically different haploid daughter nuclei Haploid (n) – only one copy of the chromosome is present Diploid (2n) – two copies of the chromosome are present, they exist in pairs

42. Cell Cycle • Interphase – cell growth, protein production, DNA replication • Nucleus division – via mitosis or meiosis • Cytokinesis – division of the cytoplasm to form two separate cells

43. Pneumonic – Pour Me Another Tea Mitosis • Prophase– chromatin condensation to form chromosomes composed of identical sister chromatids. Formation of spindle fibers • Metaphase– alignment of the chromosomes along the equatorial plane. Attachment of spindle fibers to the centromere of the chromosome • Anaphase – shortening of spindle fibers pulls sister chromatids apart to opposite poles of the cell • Telophase – formation of a new nuclear membrane around each chromosome group

45. Meiosis – composed of meiosis 1 and meiosis 2

46. Meiosis 1 • Prophase 1 - chromatin condensation to form chromosomes composed of identical sister chromatids. Formation of spindle fibers • Recombination – chromosome crossover resulting in non-identical sister chromatids. Provides genetic variation in gametes • Metaphase 1 • Anaphase 1 • Telophase 1

48. Meiosis 2 • Prophase 2 • Metaphase 2 • Anaphase 2 • Telophase 2 • Cytokinesis There is no DNA replication during meiosis 2, this means each daughter cell will be haploid and only contain 23 chromosomes

50. Mendel’s Law of Inheritance Law of dominance – offspring that inherit a dominant gene will have only the dominant phenotype Law of segregation – during formation of the gamete, genes responsible for a trait are separated and only one is passed to the offspring. During fertilization, maternal genes are combined with paternal genes producing the genotype of that individual