EXAM Q REPRODUCTION HB 2B Q 42 (a) and (b)

Question 42 (20 marks)   (a) After fertilisation, the blastocyst will eventually undergo implantation and an embryo develop. Two types of cell division are necessary to develop gametes for fertilisation and then for the embryo to develop. Discuss these two types of cell division. (10 marks)

Answer 42 a Part 1 Meiosis is the type of cell division that produces four different daughter cells consisting Occurs in the gonads and produces two types of gametes (sperm and ovum) Spermatogenesis (sperm) and oogenesis (ova) Two cell divisions/stages Cells contain the haploid number of chromosomes (half the number) of chromosomes of somatic body cells. This allows fertilization to occur producing a diploid zygote Homologous chromosomes line up together at beginning forming a tetrad Stages of meiosis Meiosis creates variation in the gametes by Crossing over during prophase I and Independent assortment in Metaphase I (Any five points)

Answer 42 a Part 2 Mitosis is the type of cell division that produces two identical daughter cells. This allows growth to occur and the replacement of damaged or worn out cells. Mitosis results in an increase in the number of body cells. Occurs in any body cell during growth/skin, muscle, and bone repair in adults. Homologous chromosomes do not line up at equator in metaphase One cell division only. Mitosis occurs in four continuous stages: Prophase, Metaphase, Anaphase and Telophase. (Any five points)

42 (b) Question 42 (b) (10 marks) DNA replication allows the development of daughter cells; however, exact copies are not always produced. Explain the consequence of incorrect DNA replication if it occurs in either the formation of gametes or the formation of embryonic tissues from the primary germ layers.

Answer 42 b Part 1 Question 42 (b) (10 marks) DNA replication allows the development of daughter cells; however, exact copies are not always produced. Explain the consequence of incorrect DNA replication if it occurs in either the formation of gametes or the formation of embryonic tissues from the primary germ layers. Some gametes will undergo mutations. If mutated gamete undergoes fertilization. Embryo will inherit the genetic defect. All cells in the embryo will contain the genetic defect. The mutation could be lethal and can lead to miscarriage

Answer 42b Part 2 If the baby survives, he/she may pass genetic defect on to his/her offspring in the future Germ layers form specific organs Pluripotent cells so not all cells in body will be affected. If mutation occurs early in development, greater damage will occur to body tissues/organs Apoptosis may occur (cells removed during development) Not affecting germ line cells and therefore lasting effects as will not be passed onto offspring.