GENETICS

1. GENETICS • The nucleus of a cell carries the genetic information which allows it to control all of the activities of the cell and determines the overall characteristics of the organism nucleus

2. The nucleus of a living cell contains threadlike structures called chromosomes. A chromosome is a threadlike structure which carries genetic information. All the nuclei of the body cells of a living organism contain identical copies of the chromosomes. nucleus chromosomes

3. Chromosome complement The number of chromosomes present in the cells of a living organism is called the chromosome complement and depends on the species. Humans have 46 chromosomes in every body cell.

5. Chromosomes and Genes Chromosomes are made from tightly coiled molecules of DNA. DNA is a long chain made up of a backbone with bases attached. DNA = deoxyribonucleic acid!!

6. Label the following diagram DNA of 1 gene uncoiling DNA backbone Centromere bases Positions of individual genes DNA coiled into a chromosome = Adenine (A) = Guanine (G) = Thymine (T) = Cytosine (C)

7. There are 4 different types of base within a strand of DNA. - Adenine (A) - Thymine (T) - Guanine (G) - Cytosine (C) The DNA carries pieces of coded genetic information. An individual section of DNA with a single piece of genetic information is a gene. Chromosomes are thought of as lots of genes in a chain

8. The Function of DNA DNA molecules carry genetic instructions which allow the cell to make specific protein molecules. Proteins are made from amino acid units linked together to form long chains. The order of DNA bases encodes the information for the sequence of amino acids in proteins

9. Sets of 3 BASES on a DNA strand carry the codes for…………. DNA backbone ….a chain of amino acids which join up to make a protein molecule. AMINO ACID R AMINO ACID S AMINO ACID T AMINO ACID S Protein molecule forming An amino acidis a unit of protein structure. A baseis a part of DNA structure

10. DNA base sequence Amino acid coded for P This table shows the information about the base sequences for some amino acids Q R It is your job to decode the next few diagrams of pieces of DNA and to draw the chain of amino acids they encode. S T

11. 1. 2. 3. 4. 5.

12. S R P Q R R T T P Q Q P S P T 1. 2. 3. 4. 5.

13. Protein Structure & Function • The chains of amino acids are folded and twisted to give the molecules 3-D shapes. • The sequence of amino acids is determined by the sequence of the DNA bases. • The sequence of the amino acids dictates the structure and function of the protein produced.

14. e.g. Enzymes Enzymes are made of protein. The folding of the chains of amino acids allows the formation of the active sites which makes the enzymes specific to their substrate.

15. Relationship between proteins present in a cell and the organisms characteristics • Inherited characteristics are the result of many biochemical processes controlled by enzymes (which are made of protein!) • In humans, enzymes control the reactions that lead to the formation of hair or a certain texture, eye irises of a certain colour etc.. • The protein haemoglobin gives red blood cells their red colour. • The body also possesses many hormones which are also made of protein. Hormones are chemical messengers around our body.

16. MEIOSIS • Meiosis is the name given to the process which produce gametes (sex cells).

17. Chromosome revision centromere one chromatid single chromosome Double chromosome In cells that are not about to divide, chromosomes are found as single chromosomes. In cells that are about to divide, the DNA makes an extra copy of itself (shown above as the dark strand) and the chromosomes become double chromosomes. Each strand is called a chromatid and the chromatids are held together by a centromere.

18. sperm cell meiosis fertilisation zygote Sperm mother cell meiosis Egg mother cell Egg cell Zygote ready to divide

19. The Process of Meiosis 1) Gamete mother cell containing 4 double chromosomes 2) Matching chromosome pair and line up across the middle

20. 3) The pairs separate to either end of the cell and the cell divides into 2 4) The chromosomes turn and line up. Each cell then divides again.

21. 5) The centromeres split and the chromatids are pulled apart. After the chromatids are separated from each other they are known as single chromosomes 6) 4 gametes are produced, each with only 1 set of single chromosomes.

22. Meiosis reduces the total number of sets of double chromosomes from 2 matching sets in the gamete mother cell to 1 set of single chromosomes in each gamete. SO: Gamete mother cell = 2 sets chromosomes Gametes = 1 set chromosomes The 2 sets of chromosomes are restored at fertilisation.

23. Chromosome shuffling • The different ways that the matching chromosomes can pair increases the total number of gamete varieties. • Any process which increases the number of different gametes must also increase the variety of offspring. • The random assortment of chromosomes during meiosis leads to variation in offspring.

24. So instead of this arrangement You get this instead

25. Which results in 4 gametes like this

26. Because…..

27. Confused??!!!??!!

28. Sex Determination In humans, each male gamete has an X or a Y chromosome. So males are XY. Each female gamete has an X chromosome. So females are XX. The sex chromosomes of an individual determine their sex.

29. Genetic Symbols = male symbol = female symbol He’s a man, man! Stick in the ‘Sex chromosomes’ cut out

30. All egg cells will contain an X chromosome. • Half of sperm cells will be X and half will be Y. • It is the sperm cells that determine the sex of the baby – the egg will always be X but the sperm will either be X or Y.

31. female male XX XY X Y X X Baby girl XX XY Baby boy

32. Collect a sex determination grid and complete the blank squares to show the 4 possible combinations in the offspring. • Use a crayon lightly to shade the boxes to show the male and female offspring. • Complete the ratio information below the grid

33. The ratio of males to females is 1:1 • But the process of fertilisation is random so it is a matter of chance which sperm will fertilise the egg – X or Y. • It is for this reason that there will be roughly a 1:1 ratio of males to females.

34. Genetics for Beginners! • Genes are parts of chromosomes • Alleles are the different forms of a gene. • Each gamete will carry one allele of the gene.

35. E.g. Gene for height in pea plants. Pea Plants can be tall or dwarf. Each plant will carry 2 copies of a gene, one from each parent. The alleles are represented by letters and will be T for tall and t for dwarf. A tall plant will either be TT or Tt A dwarf plant will be tt.

36. If a tall plant and a small plant cross, the offspring are all tall. • This means that ‘Tall’ is dominant. • ‘Dwarf’ is recessive. • The dominant form of the gene always gets a capital letter e.g. T = tall. • The recessive form of the gene always gets the same letter but lower case e.g. t = dwarf

37. X dwarf tall All tall

38. Complete the Symbols for Alleles Table

39. An individual with 2 of the same allele is said to be HOMOZYGOUS. (e.g. tt or TT) • An individual with 2 different alleles of a gene it is said to be HETEROZYGOUS. (e.g. Tt) • The genetic symbols an individual has is its GENOTYPE, e.g. Tt • The physical appearance an individual has is its PHENOTYPE e.g. Tall

40. E.g. flower colour in pea plants • A pea plant with lilac flowers was crossed with a white flowered plant. • All offspring were lilac. x All lilac

41. Lilac • Which is the dominant characteristic? • What letter would we give the dominant allele? • What letter would we give the recessive allele? • What is the recessive characteristic? L l white

42. homozygous White • If a pea plant had the alleles ll – would the individual be homozygous or heterozygous? • What colour would it be? • If a plant had the alleles Ll – would the individual be homozygous or heterozygous? • What colour would it be? • If a plant had the alleles LL – would the individual be homozygous or heterozygous? • What colour would it be? heterozygous Lilac homozygous Lilac

43. Genotype and Phenotype An organism can have the same phenotype but have a different genotype. Example: Organism: Pea plants Gene height flower colour TT = tall LL = lilac Tt = tall Ll = lilac

44. True Breeding True breedinglilac strain True breedingwhite strain X Parents (P) X 1st generation (F1) X X Members of F1 cross All lilac All white 2nd generation (F2)

45. When 2 lilac parent plants cross, the offspring are all lilac. When the lilac offspring cross, all their offspring are lilac. • When 2 white parent plants cross, the offspring are all _______. When the ______ offspring cross, all their offspring are _______. • So, when the flower colour of the offspring is identical to the parent flower colour, the members of the strain are true breeding. (they are always homozygous, e.g. LL or ll)

46. Terms for Monohybrid Crosses P = parents F1 = 1st filial generation. F2 = 2nd filial generation

47. Monohybrid Crosses A monohybrid cross is a cross that involves only one difference between the original parents, e.g. flower colour or height. Parents in monohybrid crosses are usually true breeding and show different phenotypes

48. How to do Monohybrid Crosses Question: A true breeding black mouse was crossed with a true breeding white mouse. All of the offspring were black. Show this as a monohybrid cross using appropriate symbols right through to the F2 generation X

49. P Black mouse White mouse Black white X phenotype BB bb genotype F1 phenotype All Black Bb genotype X F2 Black Black phenotype Bb genotype Bb B b B b gametes

50. Punnet Square 1BB:2Bb:1bb F2 genotypic ratio 3 black: 1 white F2 phenotypic ratio