chapter 15: modes of reproduction

What is asexual reproduction?

• Asexual reproduction is the process that results in the production of genetically identical offspring from one parent

• without the fusion of gametes

• Asexual reproduction involves mitosis.

Mitosis

• Mitosis is a type of cell division giving rise to genetically identical cells in which the chromosome number is maintained

• once mitosis begins in a dividing cell, it proceeds as a continuous process until two daughter nuclei are produced

Importance of mitosis

1. asexual reproduction

2. growth in multi-cellular organisms

3. repair of damaged tissues

examples of asexual reproduction

1. stem tuber

2. rhizome

3. runner

stem tuber

• swollen end of an underground stem

• has many buds

• The buds will use up the food stored in the tuber to grow into new plants

• There will be as many new plants as there are buds.

• example: potato

rhizome

• A rhizome is an underground storage stem

• bears scale leaves and buds

• each bud can grow into a new plant

• example: ginger

runners

• shoot that arises from a bud in the parent plant

• grows horizontally over the surface of the soil

• buds develop along its length, develop roots and leaves becoming plants

• example: oxalis, strawberry

advantages of asexual reproduction

• only one parent is required

• fusion of gametes is not required

• all of the beneficial qualities are passed on to the offspring

• faster than sexual reproduction

disadvantages of asexual reproduction

• there is no genetic variation in the offspring → species are not well-adapted to changes in the environment

• if parent does not have resistance to a particular disease, the offspring would also not have resistance

• the whole population could be wiped out by a particular disease

stages of mitosis

PMAT

1. prophase

2. metaphase

3. anaphase

4. telophase

stage before mitosis

• interphase

• occurs to prepare for cell division

• cell growth and dna replication occurs during interphase

atge after mitosis

• cytokenesis

• splitting of the cytoplasm to form two cells after telophase

1. prophase

• dna condenses into chromosomes to become more visible

• the membrane around the nucleus disappears

2. metaphase

• chromosomes line up randomly at the equator of the cell

• nucleus is gone

3. anaphase

• sister chromatids are pulled to different ends of the cell

• each sister chromatid becomes a new chromosome

• When the two sister chromatids are joined at the centromere, they are counted as one chromosome

4. telophase

• nuclear membranes form around the chromosomes at each end of the cell

structure of a chromosome

• before dna replication, 1 chromosome = 1 chromatid

• after dna replication, 1 chromosome = 2 sister chromatids joined together at the centromere

what is sexual reproduction?

• the process involving the fusion of two gametes to form a zygote

• produces genetically dissimilar offspring

gametes

• haploid cell used for sexual reproduction

• male gamete → sperm

• female gamete → egg

diploid cell (2n)

• cell with 2 sets of chromosomes

• one set from the male parent and another form the female parent

• halving the chromosome number through meiosis allows a sexual life cycle with fusion of haploid (n) gametes to form a zygote

haploid cell

• cell with one set of chromosomes

what happens during meiosis

• parent cell (2n) divides to produce 4 genetically dissimilar daughter cells → 4 haploid gametes (n)

• since each gamete produced contains half the number of chromosomes as the parent cell, meiosis is a reduction division

importance of reduction division

• prior to fertilisation in sexual reproduction

• the offspring that develops from the zygote would have the same chromosome number as its parents

• ensures genetic stability throughout generations of the same species

genetic stability

• refers to maintaining DNA sequences and chromosome numbers accurately across generations

• maintains the identity of the species (correct chromosome number)

• prevents harmful mutations or genetic disorders

human body cells

• 23 pairs of chromosomes (2×23 chromosomes) in each diploid hmuan body cell

• 22 pairs of autosomes

• 1 pair of sex chromosomes

homologous chromosomes

• A pair of chromosomes that has the same shape, size and the same sequence of genes

• one chromosome is inherited from the male parent, one from female parent

Why is meiosis important?

1. Meiosis produces haploid gametes

2. produced genetically dissimilar gametes

importance of meiosis: produces haploid gametes

• Each pair of homologous chromosomes in the parent nucleus separates to form daughter cells.

• Each daughter cell only received one copy of the homologous chromosomes

• during fertilisation, when the nucleus of the male gamete fuses with the nucleus of the female gamete → normal diploid number restored in the zygote

importance of meiosis: genetically dissimilar gametes

• greater genetic variations → species to be better adapted to changes in the environment

• avoid the entire population being wiped out at once

• those that survive will pass on their favourable genes to their offspring

advantages of sexual reproduction

• offspring may inherit beneficial qualities from both parents

• there is genetic variation in the offspring that is better adapted to changes in the environment

disadvantages of sexual reproduction

• two parents requires (except in plants with bisexual flowers)

• fusion of gametes is requires

• slower than asexual reproduction

differenced between sexual and asexual reproduction

• asexual does not involve the fusion of gamete, while sexual does

• asexual requires one parent while sexual requires two

• asexual produces children genetically identical to the parent, while sexual produces genetically dissimilar offspring

• asexual is relatively quicker method of producing offspring.