Meiosis and Specialisation of cells Flashcards
Sexual reproduction involve 2 sex cells called?
Gametes
The 2 gametes fuse together to produce a fertilised egg -
Zygote
Gametes contain half the number of standard chromosomes and therefore are classed as?
Diploid = N, or the chromosome number of each reproduction would double.
Gametes are formed by?
Meiosis, the nucleus divides twice to produce 4 daughter cells (gametes), which contain half the genetic material in the chromosomes.
Due to the gamete containing half the number of chromosomes compared to its parent cell or a zygote, meiosis is known as?
Reduction division.
Homologous chromosome - (SAME)
The nucleus of most organisms contain 2 sets of genes, a pair of genes for each trait. Therefore the nucleus of organisms contains matching sets of chromosomes (the SAME) (Homologous pair) The same pair of genes at the same loci)
Loci -
Specific area of a gene on a chromosome, homologous chromosomes have the same genes in the same positions, they are the same length and size.
Allele -
Variation of a gene, or different versions of the same gene.
Stage 1 of meiosis (Meiosis I) - Points
- Reduction division
- Pairs of homologous chromosomes are separated into two cells
(Homologous chromosomes contain 2 full sets of genes) - So each of the 2 cells will be haploid because they only contain one full set of genes instead of the original 2.
Meiosis II is similar to?
Mitosis
Stage 2 of meiosis
- Pairs of chromatids in each daughter cell are separated, forming 2 more cells.
- Production results in 4 haploid daughter cells
Meiosis 1 - prophase 1 - Points
- Chromosomes condense
- The nuclear envelope disappears
- The nucleolus disappears
- Spindle formation begins.
Bivalents - M1 - P1
When the homologous pairs of chromosomes pair up forming bivalents
Crossing over -
The chromatids entangling from the movement of large DNA molecules.
Meiosis 1 - Metaphase 1 -
Same as metaphase in mitosis
- The difference is the homologous chromosomes assemble along the metaphase plate, instead of the individual chromosomes.
Independent assortment -
When the position of the homologous chromosomes can face in different directions of the poles and the way they face the poles, leading to genetic variation.
Meiosis 1 - Anaphase 1 - Points
The homologous chromosomes in the metaphase plate are pulled to opposite ends (poles), while the chromatids still stay intact.
Meiosis 1 - Telophase 1 - Points
Essentially the same as in mitosis.
- The chromosomes assemble at each pole and the nuclear envelope reforms round both poles and the chromosomes uncoil.
Cytokinesis of Meiosis 1 -
After T1 the cell divides into 2 cells and the reduction of chromosomes from diploid to haploid is complete.
Meiosis 2 - Prophase 2 - Points
At the point the chromosomes will still consist of 2 chromatids, with them condensing and them becoming visible again with the nuclear envelope breaking down.
Meiosis 2 - Metaphase 2 - Points
The individual chromosomes assemble on the metaphase plate, crossing over occurs, the chromatids are no longer identical so independent assortment occurs (Genetic variation).
Meiosis 2 Anaphase 2 - Points
- Results of chromatids of the individual chromosomes being pulled to opposite poles
- Due to the division of the centromeres
Meiosis 2 - Telophase 2
- Chromatids assemble at the poles.
- The chromosomes uncoil
- With the nuclear envelope and nucleolus becoming visible.
Why does cytokinesis at the end of Meiosis 2 result in reduction division?
Forms 4 daughter cells, and contain half the number of DNA compared to the zygote as it results in gametes which are haploid due to reduction division.
At the end of meiosis the 4 daughter cells will be haploid and genetically different, why?
Due to the processes of crossing over and independent assortment.
Crossing over -
Chromatids entangle from moving through the cytoplasm from the spindle fibres.
Independent assortment -
Orientation of the Homologous chromosomes can vary meaning the the P/MHC can face different poles. (different alleles facing poles). Where the alleles of different genes from the paternal or maternal chromosomes will end up in different gametes.
Level of organisation in multicellular organisms -
Specialised cells - tissues - organs - organ systems - whole organisms
Specialised cells definition -
- The cells within a multicellular organism become specialised.
- Meaning they perform specific functions
Specialised erythrocytes - (Why are they specialised)
- Flattened biconcave shape - Increasing surface area.
- No nuclei - increasing space for haemoglobin (carries oxygen)
- Flexible (squeeze through capillaries)
Specialised neutrophils (Why are they specialised)
- Immune system
- Multi-lobed nucleus, which makes it easier to squeeze them through small gaps
- The granular cytoplasm contains many lysosomes used to attack pathogens.
Specialised sperm cells - (Why are they specialised) -
- Male gametes
- Contain a flagellum so they are capable of movement
- Contain many mitochondria so they have the energy to move
- The acrosome contain many digestive enzymes, which digest the layers of the ovum allowing the sperm to penetrate.
Specialised palisade cells - (Why are they specialised)
- Present in the mesophyll
- Contain large amount of chloroplasts
- They have very thin cell walls (rate of diffusion)
- Large vacuole (maintain turgor pressure)
Specialised root hair cells - (Why are they specialised) -
- Long extensions of root hair cells, increasing surface area.
- Maximises water and mineral uptake from the soil
Specialised guard cells - (Why are they specialised cells) -
- Form on the surfaces of leaves
- The stomata open to allow carbon dioxide to enter
- When the guard cells lose water they become less swollen and the osmotic forces cause the stomata to close to prevent further water loss.
Tissues definition -
Tissue is made up of a collection of differentiated cells which result in their specialised function/functions, where each is adapted for their own particular function of an organism.
Nervous tissue -
Transmission of electrical impulses
Epithelial tissues -
Adapted to cover body services, internal and external
Muscle tissues -
Adapted for contraction
Connective tissues -
Used to hold tissues together or for such use of transport mediums.
Squamous epithelium -
- “Squa” (squash)
- Flat appearance
- One cell thick
- Present for the need of rapid diffusion across a surface
- Like the lining of the lungs.
Ciliated epithelium -
- Hair like structures called cilia on one surface and move in rhythmic manner.
- Lines the trachea - causing mucus to be swept away
- Goblet cells are also present which release mucous to trap unwanted particles and stop them reaching the alveoli.
Cartilage -
- Connective tissue
- Fibres of elastin and collagen
- Prevent the end of bones from rubbing
- Firm and flexible
Muscle - (tissue)
- Shorten in length In order to move bones
- Which in turn move with different parts of the body.
Epidermis tissue -
Adapted for such use of plant cover and surfaces.
Vascular tissue -
Adapted for transport of water and nutrients
Epidermis (plant tissue) -
Covers the plant of cells, usually covered by waxy, waterproof cuticle to reduce water loss.
Stomata are also present in the epidermis (oxygen out, carbon dioxide in, with water vapour in and out)
Xylem tissue -
Vascular tissue - Responsible for the movement of water and nutrients up and down plants.
- Composed of elongated dead cells
- The cell walls are composed of waterproof material called lignin (structural support)
Phloem tissue -
Another vascular tissue in plants,
- Regulates the movement of organic material particularly sucrose
- The sucrose is made from the leaves and the stems from being made by photosynthesis
- Composed of columns of sieve tube cells
Organ definition -
Collection of tissues that are adapted to perform a particular function in an organism.
- Like the mammalian heart where it is composed of muscle and connective tissue.
Organ system -
Composed of multiple organs working together to carry out a major function in the body.
Stem cells -
Undifferentiated cells, where they are not adapted for a particular function. They have the potential to specialise as different cells in an organisms. (Renewing source of undifferentiated cells)
Stem cells in cell division -
Stem cells are able to undergo cell division again and again, source of new cells for growth and tissue repair leading to development. Once specialised they lose the ability to undergo division and enter G0.
Potency definition -
Stem cells ability to differentiate into different cell types, the greater the distinct number cells stem cells can differentiate into the greater the potency.
Totipotent -
Stem cells can differentiate into any cell they want, fertilised egg or zygote. Potential form a whole organism. Extra-embryonic tissues too.
Pluripotent -
Can form all tissue types but not whole organisms, present in early embryos and the origin of the different tissues of an organism.
Multipotent -
Can only form a number/range of cells within a certain type of tissue. Like haematopoetic stem cells in bone marrow which give rise to the various types of blood cells.
Differentiation -
Such cells differentiate depending on size and what tissue they are from, like blood cells are derived from stem cells in the bone marrow.
Replacement of red blood cells is necessary due to the lack of organelles for maximising oxygen carrying so are replaced by stem cells. Same with white blood cells -
Life span is around 120 days for rbc and 6 hours in wbc, stem cell colonies in the bone marrow produce erythrocytes and neutrophils.
