modes of repro

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asexual reproduction

asexual reproduction is the process resulting in the production of genetically identical offspring from one parent. without fusion of gametes.

asexual repro involves mitosis. The offspring produced asexually are genetically identical to the parent.

advantages and disadvantages of asexual repro

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advantages and disadvantages of asexual repro

advantages	disadvantages

Cell Theory

The cell theory states that all new cells derive from pre-existing cells through the process of cell division. Cell division consists of nuclear division and division of cytoplasm (cytokinesis). There are two types of nuclear division, namely MITOSIS and MEIOSIS.

Mitosis

Mitosis is a part of cell division which produces two daughter cells that are GENETICALLY IDENTICAL to each other. The chromosome number is maintained.

consists of prophase, metaphase, anaphase, and telophase. (Prop drops on Meta AI and Ana uses the telephone)

cell division

cell division = mitosis + cytokinesis

Cytokinesis definition

Cytokinesis is a process that occurs straight after mitosis. This is the division of the cytoplasm to produce two completely separated daughter cells.

Cytokinesis in animal cells

• A cleavage or furrow appears between the two nuclei in the cytoplasm.

• It deepens until the parent cell pinches into two daughter cells, each with a complete nucleus and share of organelles.

Cytokinesis in plant cells

A cell plate forms by the fusion of vesicles produced by the golgi apparatus.

importance of mitosis in growth, repair and asexual reproduuction

The importance of mitosis is to maintain the genetic stability of an organism. This means that the two daughter cells formed are genetically identical and contain the same number of chromosomes as the parental cell.

The maintenance of A identical chromosomal numbers, B exact genetic information and C diploid set of chromosomes, is crucial as new resulting cells must be identical to the cells they are replacing in growth repair and asexual reproduction.

what mitosis does in growth, repair, and asexual reproduction

Growth	Repair	Asexual reproduction
Increase the number of cells within the organism e.g. development of a fertilised egg into an adult human being.	Regeneration and replacement of cells and tissues lost in normal processes of wear and tear, ageing, damage and disease. E. g. Replacement of worn-out body parts, such as skin cells.	Reproduction of an organism without production of gametes. e.g. vegetative propagation in ferns, potatoes, onions and ginger.

Explain the need for the production of genetically identical cells.

It is important that new cells are genetically identical with existing cells so that they can carry out the same function. New cells that replace damaged cells must be exact copies of the original cells for the tissue to function properly.

Haploid

Haploid cells have only one set of chromosomes, where the number of chromosomes is represented by n. These cells are the gametes or sex cells (sperm and ovum). 

Diploid

Diploid cells are those with two sets of chromosomes in the nucleus. Human beings, most animals and many plants are diploid organisms. All cells in the human body are diploid except for the gametes. Number of chromosomes in the diploid cell is represented by 2n.

Somatic cells (body cells)

Human somatic cells are all body cells except the gametes. they divide by mitosis.

Each human somatic cell carries 46 chromosomes in the nucleus. Somatic cells are diploid cells (2n), where n = 23 for humans.

These 46 chromosomes are arranged into 23 pairs of homologous chromosomes. Each homologous pair is composed of one chromosome from the mother and one from the father. 

Gametes

Gametes are sperm cells and ova/eggs produced in the gonads or sex organs by meiosis.

Each gamete (human) carries 23 chromosomes in the nucleus. Gametes are haploid cells (n), where n = 23 for humans. Gametes carry half as many chromosomes as somatic cells.

For humans, the number of chromosomes in a haploid cell is 23, consisting of one set (n=23); the number of chromosomes in the diploid zygote and all somatic cells arising from it is 46, consisting of two sets (2n=46). 

Sexual Reproduction

Sexual reproduction is the process involving the fusion of the haploid nuclei of the male (sperm) and female (ovum) gametes to form a zygote. 

The male and female gamete both contribute one copy of each chromosome, to create a new cell with two copies of each chromosome that will develop into a new organism. 

it produces a new organism that is genetically distinct from the parents.

Homologous chromosomes

Homologous chromosomes are a pair of chromosomes having identical structural features. One of the chromosomes is inherited from the mother, the other from the father. They have:

• same length, size and shape

• same centromere position

• genes for the same biological features at the corresponding location on the chromosomes, thus they determine the same traits, e.g., blood group, hair colour etc. However, they may be different alleles of the same gene.

Alleles

An allele is an alternative form of a gene which occupies the same location on a pair of homologous chromosomes. For example, while the gene for eye color on one of the homologous chromosomes may code for blue eyes, the other may code for brown eyes.

Meiosis

Meiosis is a part of cell division that produces genetically dissimilar cells containing half the number of chromosomes (reduction division) as the parent cell. The chromosome number is half due to the separation of homologous chromosomes. This occurs to maintain the consistency of the number of chromosomes from generation to generation, as when the nucleus of two gametes fuse, the diploid number for that species will be restored.

need for reduction division

Meiosis results in the production of gamete cells with half the number of chromosomes compared to the parent cell, due to reduction division. 

If this does not occur, the fusion of gametes during subsequent fertilisation will result in a doubling of chromosome number for each successive generation.

Meiosis, therefore, stabilizes and maintains a constant chromosome number in every generation of a species.

importance of meiosis

1. Meiosis produces haploid gametes.

   During meiosis, each pair of homologous chromosomes in the parent nucleus separates to form daughter cells. Each daughter cell only receives one copy of the homologous chromosomes i.e. haploid number of chromosomes. When the nucleus of two gametes fuse, the diploid number for that species can then be restored and maintained. 

2. Meiosis produces gametes that are genetically dissimilar.

   The greater the genetic variation, 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 out the whole population. Genetic variation increases the likelihood that at least some individuals would possess desirable traits to adapt to the new environment.