1. 2.5.6 Genetic Inheritance

2. Lesson Objectives At the end of this lesson you should be able to 1.Give a definition for a gamete 2.Understand gamete formation 3.Define fertilisation and sex determination

3. From a cell to DNA

4. How many chromosomes? How many chromosomes are there in human sex cells? There 46 chromosomes (23 matching pairs) in each new human body cell produced by mitosis 23 unpaired chromosomes

5. How many chromosomes? Human sex cells have a set of 23 unpaired chromosomes – that’s half the usual number. Sex cells have to be produced by a special type of cell division called meiosis. Sex cells in animals and plants follow the same rules. They have half the usual number of chromosomes. They have a complete set of single chromosomes. Why is this important for fertilization and reproduction?

6. Gametes are.. haploid cells that are capable of fusion.

7. Fertilization and cell division – animation

8. Identical twins – animation

9. Non-identical twins – animation

10. Fertilization animation FLASH 6 – Fertilisation FLASH 2 – Mitosis drag & drop

11. Chromosomes and fertilization

12. Outline of Fertilisation Gametes join together by fertilisation Form a diploid zygote This develops into an embryo Eventually into a new individual which resembles each parent but whom is identical to neither. Definition: Fertilisation is when two gametes fuse together to make a zygote

13. Learning Check 1.What are reproductive cells called? 2.Where are they found? 3.Are they haploid or diploid cells? 4.How are they formed? 5.What is a zygote?

14. 1.Define allele 2.Differentiate between the terms homozygous and heterozygous 6.Differentiate between genotype and phenotype 7.Differentiate between dominant and recessive Lesson Objectives

16. Genotype Def A genotype is the set of genes that an organism has.

18. Inheritance of a trait Say that the gene that controls eye colour is always found on chromosome no. 7. But we get a no 7 chromosome from each of our parents - so we have two genes controlling eye colour! There are many different forms of gene controlling eye colour : gene for blue eyes, gene for brown eyes etc! Def - Alleles are different forms of the same gene

19. Def If both of your alleles are of the same form then it is called homozygous. Def If both of your alleles are of different form than it is called heterozygous

20. Example: This person’s genotype for eye colour is BB. She is homozygous for eye colour. Example: Say that B is the symbol for the brown eye allele and b is the symbol for the blue eye allele.

21. Phenotype A person’s genotype (genetic make up) determines what their physical make up will be – their appearance etc. Phenotype is the physical make up of an organism

22. Phenotype Here the girl’s phenotype for eye colour is brown!

23. Example: What is this man’s genotype for eye colour? bb Is he homozygous or heterozygous for eye colour? Homozygous What is his phenotype for eye colour? Blue

24. Example: What is this man’s genotype for eye colour? BbBb Is he homozygous or heterozygous for eye colour? Heterozygous What is his phenotype for eye colour? Brown

25. Heterozygous genotypes and their phenotypes When there are two different alleles than one can override the effect of the other Example: Here the brown allele overrides the effect of the blue allele! The brown allele is called dominant The blue allele is called recessive

26. Dominant allele Def: A dominant allele is the allele that masks the recessive allele The dominant allele is given the capital letter! Example: in the case of eye colour the Brown eye allele is dominant so B is used to describe it.

27. The recessive allele is the allele that is masked by the dominant allele. Recessive allele The recessive allele is given the small letter! Example: in the case of eye colour the blue eye allele is recessive so b is used to describe it.

28. Check your learning.. What is an allele? How many alleles for a gene does a person have in a normal cell? What is it called when two alleles are the same? What does heterozygous mean? Which is the dominant gene? Which is the recessive gene?

29. Lesson Objectives 6.Be able to complete monohybrid crosses and state the genotypes and phenotypes of parents and offspring 7.Understand the 3:1 ratio for heterozygous cross

30. Genetic crosses Used to show how traits are passed on from parents to offspring. Progeny = the offspring F1 progeny = the first generation of offspring (also called first filial generation)

31. Example question There is a cross between two cats with the genotypes BB and bb. In cats the black colour coat is dominant and the white coat colour is recessive. Find the possible genotypes and phenotypes of their offspring.

33. Example question In fruit flies a long wing type is dominant and the short wing type is recessive. For a cross between two fruit flies: One is homozygous for long wing type and the other is homozygous for short wing type. Find the possible genotypes and phenotypes of their offspring.

35. Example 3 In the pea plant the green pod colour is dominant to yellow pod colour. Two pea plants are crossed, which are both heterozygous for the pod colour gene. Show by means of a diagram all of the possible genotypes and phenotypes for the F1 generation of this cross.

37. Example 4 In the fruit fly the grey body is dominant to black body. Two fruit flies are crossed, which are both heterozygous for body colour gene. Show by means of a diagram all of the possible genotypes and phenotypes for the F1 generation of this cross.

39. Example 5 In cattle the allele for straight coat is dominant to the allele for curly coat. Show all of the possible genotypes and phenotypes of a cross between a curly coat bull and a straight coat cow( who is heterozygous for this trait). What is % chance of having a curly coat calf?

40. Objectives for today’s lesson Today you should learn about What incomplete dominance is and how it effects inheritance

41. Incomplete dominance For some traits neither allele will be fully dominant over the other. This is called incomplete dominance. Def: Incomplete dominance occurs when both alleles are expressed in the heterozygous condition

42. In snapdragons flower colour shows incomplete dominance. GenotypePhenotype RRRed colour flower rrWhite colour flower RrPink colour flower

43. A red flowered snapdragon is crossed with a white flowered snapdragon. What will the genotypes and phenotypes for all the resulting progeny be?

45. A pink flowered snapdragon is crossed with a pink flowered snapdragon. What will the genotypes and phenotypes for all the resulting progeny be?

47. Objectives To study sex determination in animals An introduction to Mendel’s work and his 2 laws

48. Human Chromosomes Altogether humans have 46 chromosomes, or 23 pairs. 44 of them ( the first 22 pairs) are called autosomes, - the non sex chromosomes! The other 2 chromosomes (the 23 rd pair) are the sex chromosomes:

49. Male chromosomes

50. Female Karyotype

51. The genes that control whether a person will be male or female are located on the sex chromosomes, which there are two possible types: X and Y Sex Determination Females has two X chromosomes Males have an X and a Y chromosome

52. Parent Phenotype Parent genotype Gametes combinations Possible offspring phenotypes Possible offspring genotypes XX XY Female Male

53. Exceptions to this rule… In birds, moths and butterflies it is the other way around! Females have XY genotype Males have an XX genotype