Genetics

1. Genetics Sub topic (b) Inheritance

2. Inherited variation • In subtopic (a)Variation we learned that certain characteristics are determined by genetic information received from the parents. • Examples of this are tongue rolling, red hair in humans and leaf shapeand flower colour in plants

3. Phenotypes • For each inherited characteristic an organism possesses there may be a number of different phenotypes. • The phenotype describes the appearance of the inherited characteristic • e.g. in humans the characteristic of eye colour has two phenotypes: blue eyes and brown eyes. • In mice the characteristic of coat colour has two phenotypes: black fur and brown fur

4. Identifying phenotypes • Inherited characteristic = fur colour in mice • Two phenotypes • black fur brown fur

5. Identifying phenotypes 2 • Inherited characteristic = wing type in fruit flies • Two phenotypes • Normal (straight) wing Short (vestigial) wing

6. Identifying phenotypes 3 • Inherited characteristic = stem length in pea plants • Two phenotypes • TallDwarf

7. Monohybrid Crosses • Mendel performed early monohybrid crosses using varieties of pea plant which possessed characteristics showing discontinuous variation: • Working with large numbers of plants • Studying one characteristic at a time • Counting the offspring produced Gregor Mendel (1822-84)

8. Mendel Pea Characteristics

9. Pea cross fertilisation

10. P F1 F2 same phenotype same phenotype

11. true breeding black offspring true breeding The ________ of the F1 in a true breeding cross are always ________ – always the same phenotypes uniform

12. No, male is white and female is black yes Black fur White fur F2 Black fur

13. one -black fur black fur – F1 are all black, ¾ of F2 are black (a) ¼ = 20 (a) ¾ = 60

14. (a) P (b) F1 (c) F2 Parental and F2 vestigial winged Normal winged (a) ¾ = 900 (a) ¼ = 300

15. Complete boxes 1-3 • Which mice are true breeding? • If there were 10 mice in the F1, how many were black • If there were 160 F2 mice, how many will be • (i) black • (ii) brown P Parents and F2 brown mice F1 All F1 are black 120 40 F2 The parents in m_________ crosses are usually _____breeding and show d________ phenotypes of the same c___________(CREDIT) onohybrid true ifferent haracteristic

16. Chromosomes and cells • Every animal or plant has • body cells e.g. heart cell brain cells or leaf cells • And sex cells e.g. spermegg or pollen • Each body cell has two matching sets of chromosomes • Humans have 46 chromosomes and are arranged in two matching sets

17. Sex cells (Gametes) • Sex cells of organisms are called gametes and they contain only one set of chromosomes • There are never pairs of chromosomes in sex cells. • The reduction of the number of chromosomes to a single set occurs during gamete formation.

19. Fertilisation • During reproduction in animals and plants the matching sets of chromosomes are re –united. • One matching set is from the male parent, the other comes from the female parent. • At fertilisation a complete double set is achieved when the nucleus of the male gamete fuses (joins) with the nucleus of the female gamete.

20. Fertilisation in fruit flies Two sets of 4 chromosomes ( a total of 8 chromosomes)

21. Fertilisation in humans

22. Chromosomes and Genes All development is controlled by the information stored on your chromosomes. Chromosomes are thread-like structures made of DNA found in the nucleus of cells. Genes areparts of a chromosome which control inherited characteristic. e.g chromosome eg. height gene eg. eye colour gene eg. hair colour gene

23. Genes • A characteristic is controlled by two forms of a gene • Each parentcontributesoneof thetwo forms • Each gamete carries one of the two forms of the gene • All the genesof anorganismare called itsgenotype • Thedifferentformsof ageneare called alleles (CREDIT) Chromosome Pairs True breeding NOT true breeding

24. Genes and sex cells Tongue rolling in humans is controlled by two forms of a gene. T is for tongue rolling and is dominant to t which is for non rolling

25. Tongue rolling fertilisation 1 T t Tt roller

26. Tongue rolling fertilisation2 t t Non roller tt

27. Horns (H) F1

28. True breeding cross

29. parts chromosomes two parent controlled one forms offspring one two gamete Control inherited characteristics alleles All the genes of an organism TT tall Tt tall tt dwarf tall T t

30. TT

31. RR roller rr non roller Rr roller

33. 1 bb BB 84 : 21 divide each by 21 84/21 = 4 : 21/21 = 1 Bb BB/Bb bb What are the two phenotypes? Which is dominant? What is the ratio of black to gold in the F2? Show the genotypes of the fish using B = black, b = gold Black and gold Black 4: 1

34. A and E B and J Vestigial winged normal winged Normal winged C + D, C+ E, C+F J ¾ of 1280 = 960

35. Tasters and non tasters 4

36. T t t t

37. Genotypes and monohybrid crossesCREDIT • Genotype is the genetic make up of an individual – all the genes it contains • An allele is one of the two forms of a gene controlling a characteristic The letter chosen to represent the gene is usually the first letter of the dominant allele. eg. Pea plants – Tall is dominant , so the dominant allele is represented by T. The recessive would be represented by the lower case of the same letter – t.

38. Monohybrid crosses CREDIT

39. Tongue rolling Monohybrid Cross RR x rr P1 CREDIT Gametes All R All r F1 genotype All Rr All round phenotype P2 Rr x Rr Gametes R and r R and r F2 genotypes male gametes F2phenotypic ratio 3:1 ¾ round : ¼ wrinkled F2 genotypic ratio 1:2:1 r R R RR Rr female gametes r Rr rr

40. Punnett square practiceCREDIT • Use the following genes and symbols • T = tall plants, t = dwarf; G = grey body flies, g = black; R = tongue roller, r = non roller; N = normal wings, n = vestigial wing • Draw out a punnett square and work out ratios of genotypes and phenotypes for the following crosses • Tt x Tt • Rr X rr • Gg x Gg • Nn x nn • Gg x gg • Rr x Rr

41. a) Tt x Tt b) Rr x rr r r T t R Rr Rr T TT Tt r t rr rr Tt tt 1 roller (50%) : 1 (50%) non roller 1 Rr : 1 rr 3 tall (75%) : 1 dwarf (25%) 1 TT : 2 Tt : 1 tt c) Gg x Gg d) Nn x nn n n G g N Nn Nn G GG Gg n nn nn g Gg gg 1 normal : 1 vestigial 1 Nn (50%) : 1 nn (50%) 3 grey : 1 black 1 GG : 2 Gg : 1 gg

42. e) Gg x gg CREDIT g g G Gg Gg g gg gg 1 grey : 1 black 1 Gg : 1 gg f) Rr x Rr R r R RR Rr r Rr rr 3 rollers : 1 non roller 1 RR : 2 Rr : 1 rr

43. CREDIT • On the family tree complete the genotypes of the grandmother and grandchildren • What are the phenotypes of the grandchildren? • Name two individuals with the same phenotype but different genotypes In humans brown eye colour (B) is dominant to blue eye colour (b). Bb Brown eyed Mother + grandmother/grandfather/children (d) If the grandson marries a blue eyed woman what are the chances of their children being brown eyed Bb Bb 50%, 1 in 2

44. CREDIT E e e E ¼ EE ½ Ee ¼ ee E e grey grey ebony E EE Ee ¾ grey : ¼ ebony e Ee ee 36 12

45. CREDIT Bb bb B and b b Bb bb

46. 1 = red eyes, 2 = green stem, 3 = black coat, 4 = Round seed 1 = 2.88 : 1, 2 = 3.27:1, 3 = 3:1, 4 = 3:1 3 :1 OR ¾ : ¼ ¾ black = 75% , ¼ albino = 25%

47. Ratios of phenotypes CREDIT • The differences between observed and predicted figures in monohybrid crosses are due to • Fertilisation being a random process • And • Death of seedlings / embryos • Failure of seeds to germinate (in plants)

48. Sex determination

49. Sex determination The sex of a child is determined by specific chromosomes called X and Y chromosomes ( sex chromosomes) Females have 2 X chromosomes (XX). Males have an X and a Y chromosome (XY). In humans, each male gamete may have an X or a Y chromosome Each female gametehas an X chromosome

50. X X X Y Father Mother So, X XY XX Gametes X and Y X and X XX XX children female female XY XY male male And so, half of the offspring will be female and the other half male.