modes of reproduction Flashcards
(19 cards)
define Asexual reproduction
Asexual reproduction is the process resulting in the production of genetically identical offspring from one parent without the fusion of gametes. It involves mitosis.
definie 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
what is prophase
chromatin threads comprising DNA condense, coil and shorten to form compact chromosomes.
each chromosome consists of two sister chromatids attached at the centromere.
what is metaphase
chromosomes line up at the equator of the spindle. the centromere attaches to a spindle fibre.
what is anaphase
each centromere splits. the spindle fibres shorten and pull the chromatids apart to opposite poles of the cell.
what is telophase
the chromosomes reach the poles of the cell. Nuclear envelope reforms around the chromosomes at each pole. chromosomes decondense to form back chromatin
what is cytokinesis
is a process that occurs right 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 palte forms by the fusioni of vesicles produced by the golgi apparatus.
the importance of mitosis
is to maintain a genetic stability of an organism so that two daughter cells formed are genetically identical and contain the same number of chromosomes as the parental cell.
it helps to produce genetically identical cells, growth and repair of wornout parts of the body
why is it important taht new cells are genetically identical with exisiting cells
so that they carry out the same function
define sexual reporduction
sexual reproduction is the process involving fusion of halpoid nuclei of male and female gametes to form a zygote. it produces a new organism that is genetically distinct from the parents.
what is haploid and diploid
haploid cells have one set of chromosomes where number of chromosomes are represented by N. these cells are the gametes
diploid cells have two sets of chromosomes in the nucleus. human beings, plants and animals are diploid organisms. all cells in the human body are diploid except for gametes. the number of chromosomes is represented by 2N
what are somatic cells
human somatic cells are body cells. they divide by mitosis. each human somatic cell carries 46 chromosomes in the nucleus. somatic cells are diploid cells where n=23 for humans. these 46 chromosomes are arranged into 23 pairs of homologous chromosomes. each homologous chromosome pair is composed of one chromosome from each father and mother
what are gametes
gametes are sperm cells and eggs produced in the gonads or sex organs by meiosis. each human carries 23 chromosomes in the nucleus. gametes are haploid cells where n=23 for humans. gametes carry half as many chromosomes as somatic cells.
state what is meant by homologous pairs of chromosome
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 same location on the chromosome. hence they determine the same traits however they may be different alles of the same genre
what is meiosis
is part of cell division that produces genetically dissimilar cells containing half the number of chromosomes as the parent cell. the chromosome number is halved due to the separation of homologous chromosomes resulting in the production of gamete
explain the need for meiosis prior to fertilisation in sexual reproduction
when the nucleus of two gametes fuse, the diploid number for that species will once again be restored. if reduction dvision did not occur, the fusion of gametes during fertilisation will result in a doubling of chromosome number for each successive generation. therefore meiosis is required to stabilise and maintain a constant chromosome number in every generation of a species.
importance of meiosis
to produce haploid gametes- during meiosis, each pair of homologous chromosomes in the parent nucleus seperates to form daughter cells. each daughter cell only receives one copy of the homologous chromosomes. when the nucleus of two gametes fuse the diploid number for that species can then be restored and maintained.
to produce gametes that are genetically dissimilar- gamates formed through meiosis only contain one set of chromosomes compared to the parents two giving rise to gametes that are genetically different from one another. random fertilization of gametes will give rise to further genetic variation among offspring produced. the greater the genetic variation, the better the species is adapted to changes in the environment. Genetic variation increases the likelihood that at lesast some individuals desirable traits to adapt to new environment.
