6. Modes of Reproduction Flashcards
Asexual Reproduction
Definition
Asexual reproduction is the process resulting in the production of genetically identical offspring from one parent, without the fusion of gametes.
Asexual reproduction involes mitosis.
Advantages & Disadvantages of Asexual Reproduction
Advantages:
- Only one parent is required.
- Fusion of gametes is not required.
- All the beneficial qualities are passed on to the offspring.
- This method of producing offspring is faster than sexual reproduction.
Disadvantages:
- There is no genetic variation in offspring. Hence, species are not well-adapted to changes in the environment. For example, if the parent does not have resistance to a particular disease, the offspring too would not have resistance to the disease. This means that the whole population of plants could be wiped out by a particular disease.
Cell Division
What it is
Cell division consists of nuclear division and division of cytoplasm (cytokinesis). There are two types of nuclear division, namely mitosis and meiosis.
Importance of DNA Replication
DNA replication causies a doubling in the number of DNA, so that the daughter cells receives exactly the same number of DNA that the parent cell has after mitosis.
Mitosis
Definition
Mitosis is a part of cell division which produces two daughter cells that are genetically identical to each other. The chromosome number is maintained.
Cell division = mitosis (division of nucleus) + cytokinesis (division of cytoplasm)
Stages of Mitosis
Mitosis has 4 stages:
- Prophase: Longest stage; chromatin condense, coil, and shorten to form chromosomes.
- Metaphase: Chromosomes line up at the equator. ‘M’ for middle.
- Anaphase: Chromatids are apart. ‘A’ for apart.
- Telophase: Nuclear envelop re-forms at the poles. Chromosomes decondense to form chromatin. ‘T’ for two nuclei.
Chromosome
Structure
After DNA replication, a chromosome consists of two sister chromatids attached at the centromere.
Sister chromatids are genetically identical as they are 2 identical copies of DNA produced by DNA replication.
During prophase, chromatin condense, coil, and shorten to form chromosomes.
During anaphase, chromosomes decondense to form chromatin.
Cytokinesis
Describe
Cytokinesis is a process that occurs straight after mitosis.
It is the division of the cytoplasm to produce two completely separated daughter cells.
In animal cells, a cleavage or furrow appears.
In plant cells, a cell plate forms by the fusion of vesicles produced by the Golgi apparatus.
Importance of Mitosis
- Mitosis is important to maintain the genetic stability of an organism.
- The maintenance of identical chromosomal numbers, exact genetic information, and 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.
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 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 & Diploid
Definition
Haploid cells have only one set of chromosomes.
- The number of chromosomes is represented by n
- These cells are the gametes (sperm cells and ova) produced in the gonads/sex organs by meiosis.
- Each human gamete carries 23 chromosomes in the nucleus.
Diploid cells have two sets of chromosomes.
- The number of chromosomes is represented by 2n
- All body cells in the human body are diploid except for the gametes.
- Each somatic cell carries 46 chromosomes in the nucleus.
- These 46 chromosomes can be arranged into 23 pairs of homologous chromosomes.
- Each homologous pair is composed of one chromosome from the mother and one from the father.
Sexual Reproduction
Definition
Sexual reproduction is the process involving the fusion of the haploid nuclei of the male and female gametes to form a zygote.
It produces a new organism that is gentically distinct from the parents.
Sexual reproduction involes meiosis.
Advantages & Disadvantages of Sexual Reproduction
Advantages:
- Offspring may inherit beneficial qualities
- Genetic variation
Disadvantages:
- Two parents are usually needed
- Fusion of gametes needed
- Slower
Asexual vs Sexual Reproduction
Similarities:
- Both processes pass on genetic materials to the offsprings.
- Both processes produce new offsprings.
Differences:
- Fusion of gametes: Asexual reproduction involves no fusion of gametes while sexual reproduction involves fusion of gametes.
- Number of parents: Asexual reproduction requires only one parent while sexual reproduction requires two parents
- Offspring genetics: Asexual reproduction produces genetically indentical offspring while sexual reproduction produces genetically dissimilar offspring.
- Speed: Asexual reproduction is faster while sexual reproduction is slower.
- Type of nuclear division: Asexual reproduction involves mitosis while sexual reproduction involes meiosis
State what is meant by homologous pairs of 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, & shape
- same centromere position
- genes for the same biological features at the corresponding location on the chromosome, thus they determine the same traits. However, they may be different alleles of the same gene.
