Chapter 3: HEREDITY AND VARIATIONS

for teaching aids

1. CHAPTER 3 HEREDITY AND VARIATION

2. 3.1 CELL DIVISION

3. Genes Genes are the basic units of inheritance that determine the characteristics of the individual . Genes carry genetic information from one generation to another. Genes are located in long molecules known as deoxyribonucleic acid (DNA)

4. CHROMOSOMES Are located in the nucleus Carrying information that determines our characteristic Each chromosome is made up from DNA

5. Relationship between gene, chromosome, and DNA .

6. Type of Cell Division . the processes of reproduction and growth of any organism involve cell division there are two types, which is : mitosis meiosis

7. Mitosis

8. Is a type of cell division which occurs in somatic cell . Each cell divides into two part identical daughter cells Only occurs in somatic cell but not in reproductive cells

9. Genetic content of the new cells is the same as that the parent cell . The new cells have the same number of chromosomes as the parent cell

10. the importance of mitosis : Increases the number of cells during growth Replace dead or damaged cells Repairs injured cells

11. Meiosis

12. the process of cell division to produce gametes Contain half of the number of chromosomes of the parent cell. occurs only in the reproductive organs .

13. occurs in the testis of a male and the ovary of female who have attained sexual maturity. meiosis also occurs in the anther and ovary of plants.

14. the importance of meiosis : The daughter cell have the same number of chromosomes as parent cell after fertilization has taken place Genetic variation between the offspring increases because of crossing-over between the chromatids The offspring produces will have different characteristic because of variation

15. Comparison between meiosis and mitosis

16. 3.2: The principles and mechanism inheritance

17. Dominant genes are represented by the letter ‘T’

18. Recessive genes are represented by the letter ‘t’.

19. The dominant and recessive characteristic in human Dominant traits Recessive traits Black hair Brown hair Curly hair Straight hair Free ear lobes Attached ear lobes Able to roll the tongue Unable to roll the tongue Tall Short Black/ brown eyes Blue eyes Cheeks with dimples No dimples on the cheeks

20. The mechanism of trait inheritance Gregor Mendel (1822-1884) was an A ustrian scientist known as the father of genetics because he discovered the principle of inheritance.

21. Genotype refers to the genetic information found in the genes of an organism Phenotype refers to the physical properties which can be seen in organism. The genotype of an organism determines the phenotype of the organism

22. PLEASE SEE VIDEO

23. combination of gametes at the first filial generation, F 1 , can be shown in the Punnett Square . Gen T t T TT Tt t Tt tt

24. 3.3 Sex Determination and the occurrences of twins in human being

25. Sex Determination . the sex of child is determined by the father according to the type of sperm that fertilises the ovum. if a sperm that carries the x chromosomes fertilises an ovum, a baby girl is born . the y chromosomes fertilises an ovum, a baby boy is born . the probability of having a male child or female child is the same> 50 : 50

26. Occurrence of twins in humans, normally one ovum fertilised by one sperm to form one zygote which will develop to form an embryo. sometimes more than one embryo is produced in a pregnancy. twins - two babies born to a mother in a pregnancy and generally at the same time. there are two types of twins  identical twins  non-identical twins

27. Comparison between identical and non-identical twins Similarities two babies born in a pregnancy

28. Differences Identical Twins Non-identical twins     Formation Formed when an ovum fertilised by a sperm divides into two to form two similar embryos. Formed when two ova are released by the ovary at the same time and fertilised separately by two sperms to form two different embryos.   Placenta The two embryos formed will grow in one shared placenta in the mother’s uterus. The two embryos formed when grow in separate placentas in the mother’s uterus

29.     Genetic make-up Same genetic make-up. Therefore, identical twins have the same appearance and the same sex. Different genetic make-up since they originate from two different ova and sperms. Therefore, non-identical twins have different appearances.   Sex The sex of identical twins are the same. The sex of non-identical twins may be the same or different.

30. sometimes the division of the embryo is not complete, therefore Siamese twins are formed. Siamese twins may share certain organs like brain, stomach, or heart and maybe joined to one another at the head, abdomen, breast, or buttocks. they can be separated by surgery if they do not share important organs like brain, heart, kidneys, or lungs.

31. 3.4 Mutation is the spontaneous change to the structure of genes or chromosomes of an organism. causes change of characteristics in a child. occurs in somatic cells or in gametes . the effect of mutation will be inherited by one generation to another . there are two types of mutation gene mutations chromosome mutations

32. Gene Mutations involve changes in the structure of gene. gene mutations change or produce the new genes to replace normal genes. genes that have undergone mutation are called mutants .

33. Heredity disease caused by gene mutation Brief explanation Albinism albinisms is caused by the change in the gene that controls skin colour. the newly produced genes are unable to produce skin pigment. the skin and hair of albinos are white and their eyes are pink.

34. Albinism

35. Sickle cell anaemia sickle cell anaemia is a type of disease caused by the change in the genes that produce haemoglobin. haemoglobin that has undergone mutation is not efficient in transporting oxygen.

36. Sickle cell anaemia

37. Colour-blindness is a sex-linked disease determined by a recessive gene on the X chromosome. a colour-blind person cannot see or differentiate the colours red and green.

38. Colour-blindness

39. Haemophilia caused by the deficiency if a type of protein in the blood required for blood clotting. haemophilia is caused by the deficiency of a type of protein in the blood required for blood clotting. haemophilia is a sex-linked disease determined by a recessive gene on the X chromosome. a patient who has wound will experience continuous bleeding or will take a long time for the blood to clot thus this condition way lead to death.

40. Haemophilia

41. Chromosome Mutations involve changes in the number of chromosomes or arrangement of genes in chromosomes. sometimes, a portion of a chromosome may break away and go missing, or become attached itself to other chromosomes. this causes the arrangement of a chromosome to change and differ from normal. the number of chromosomes can be increased or decreased chromosome mutations can cause hereditary diseases like Down’s syndrome, Klinefelter’s syndrome, and Turner’s syndrome

42. Down’s syndrome this heredity disease is caused by the presence of one extra chromosome at chromosomes 21 in the somatic cells. incomplete separation of chromosomes during meiosis causes the zygote to have an extra chromosome : 47 in total.

43. characteristics of a down’s syndrome patient : slanting eyes metal retardation short fingers wide distance between eyes small mouth but big tongue protruding tongue causing the mouth to remain partially open

44. Klinefelter’s syndrome a person who suffers from this hereditary diseases has one extra X chromosome : XXY

45. Turner’s syndrome a person who suffers from this hereditary lacks one X chromosome. people with Turner;s syndrome have only one sex chromosome which is XO.

46. Factors that cause mutation . mutation can occur naturally, caused by substances found in food or environment. agents causes mutations are called mutagens. chemical substances like pesticides, nicotine in cigarettes, drugs, nitrous acid and some preservatives, colouring and artificial sweetener can cause mutation.

47. radiation radioactive radiation can cause mutation gamma ray can affect growth and cell division ultraviolet rays and X-ray rays can cause skin cells to mutate and this may cause cancer temperatures which are too high or too low can also cause mutation.

48. Advantages and disadvantages of mutation. not all occurrences of mutation bring adverse effects to organisms. advantages of mutation mutation causes variations in organisms which allow them to adapt to the environment. species that are more resistant to disease, weather, and polluted environment can be produced.

49. disadvantages of mutation some mutations cause diseases like colour-blindness and haemophilia cannot be cured. sometimes, disease like haemophilia and sickle cell anaemia can cause death. Klinefelter’s syndrome causes infertility. mutation causes physical, mental, or foestus retardation.