modes of reproduction

asexual reproduction is the production of genetically similar offspring from one parent without the fusion of gametes it involves mitosis

mitosis is the type of cell division which produces genetically identical cells in which the number of chromosomes is maintained

2

remains the same (eg. 4 all throughout)

mitosis is important in: • Asexual reproduction : mitosis is involved in asexual reproduction • growth in multicellular organisms : for multicellular organisms to grow, new cells must be produced through mitosis • repair of damaged tissues: new cells produced by mitosis will replace the dead and damaged cells in tissues

if there are no flowers and only one parent is involved

+ves: 1. only one parent is requires 2. fusion of gametes not required 3. this method of reproduction is faster than sexual reproduction 4. all the beneficial traits are passed down from parent to offspring -ves: there is no genetic variation, hence species are not well-adapted for changes in their environment —> for eg. if the parents are not disease resistant, then the offspring will not be disease resistant too. this means that the entire population of plants could be wiped out by a particular disease

sexual reproduction is the process involving the fusion of two gametes to form a zygote, this method produces genetically dissimilar offspring

homologous chromosomes are chromosomes that have the same length, shape and have the same sequence of genes one inherited from mother, one inherited form father

meiosis —> the gamete contains half the number of chromosomes as the parent cell

meiosis is a type of cell division that gives rise to genetically dissimilar cels in which the chromosome number is halved due to the separation of homologous chromosomes

• a haploid cell (eg. a gamete) is a cell with one set of chromosomes • a diploid cell (eg. a zygote) is a cell with two sets of chromosomes, one set from the male parent and the other from the female parent

• meiosis produces haploid gametes: during meiosis, the homologous chromosomes in the parent cells split. the daughter cells will only receive one copy of the homologous chromosomes. during fertilisation, when the nucleus of the male gamete fuses with the nucleus of the female gamete, the diploid number of chromosomes is restored in the zygote • meiosis produces genetically dissimilar offspring : the greater the genetic variations, the better the species is adapted to changes in the environment. for example, if organisms of a species are genetically similar, any change in the environment may wipe our the whole population. if on organism dies because of the change in the environment, all other organisms within the same species will also die. if organisms of the same species are varied, it is unlikely that a change in the environment will destroy the whole species. those that survive will pass on their favourable genes to the offspring

+ves: - offspring may inherit beneficial traits from both parents - there is genetic variation in the offspring that is better adapted to changes in the environment -ve: - two parents are requires (except in plants with bisexual flowers) - fusion of gametes is required - this method of producing offspring is slower than asexual reproduction

asexual reproduction does not involve fusion of gametes whereas sexual reproduction involves the fusion of one male gamete and one female gamete to form a zygote asexual reproduction requires only one parent while sexual reproduction requires step parents (except for bisexual flowers) asexual reproduction results in offspring that are genetically identical to the parent while offspring are genetically dissimilar to the parent asexual reproduction is the relatively quicker method of reproduction while sexual reproduction is a slower method of producing offspring