mitosis and meiosis and mitosis and meiosis and mitosis and meiosis

Question 1

Mitosis:

Answer 1

production of diploid cells for growth and repair

Question 2

Meiosis:

Answer 2

production of haploid cells (gametes)

Question 3

Mitosis stages

Answer 3

Interphase, Prophase, Metaphase, Anaphase, Telophase, Cytokinesis

Question 4

Mitosis; interphase

Answer 4

replication of all 46 chromosomes to make 92

Question 5

mitosis; prophase

Answer 5

• Original chromosomes and replications condense (coil up) and stick together with their sisters (allowing them to become visible under the microscope)
• Original and copy pair up and attach via a centromere. Each side is called a chromatid – together called a chromosome or sister chromatids.
• Nuclear membrane beings to break down and spindle fibres begin to form.

Question 6

mitosis: metaphase

Answer 6

• They meet vertically in the equator of the cell

Question 7

mitosis: TELOPHASE

Answer 7

nuclear membrane forming around each set of chromosomes

Question 8

mitosis: CYTOIKINESIS

Answer 8

cytosplasm constrict in the centre of the cell, between the two daughter nuclei (genetically identical)

Question 9

Meiosis phases

Answer 9

Interphase, prophase 1, metaphase 1, anaphase 1, telophase 1, cytokinesis 1, prophase II, metaphase II, anaphase II, telophase II, cytokinesis II

Question 10

interphase I

Answer 10

• Membrane is intact.

- DNA replication occurs (not visible), giving double the amount of DNA

Question 11

prophase I

Answer 11

• DNA chromatid condense (coils up) now visible under microscope.
• Original and copy pair up and attach via a centromere. Each side is called a chromatid, together called a chromosome.
• Genetic variation: homologous chromosomes pair up (consist of two similar chromosomes – one maternal and other paternal in origin). Their replicated chromatid is attached.
• Genetic variation: crossing over / synapsis
  The inside chromatids of homologous chromosomes cross over and swap genes. The chromatids of homologous chromosomes now contain different combinations of genes. Crossing over increases variation – no two chromatids are identical. The arms of the pair of homologous chromosomes are called bivalent. The points at which they meet are called chiasmata.

Question 12

metaphase I

Answer 12

• Chromosomes (homologous) line up along the equator
• Genetic variation: independent assortment
  The pairs of homologous chromosomes line up at the equator independent of each other. The maternal chromosomes may be on the right or left for each pair. There are 223 different combinations for how 23 pairs of chromosomes can sort themselves.

Question 13

anaphase I

Answer 13

• Spindle fibres contract, pulling the homologues to separate poles of the cell

Question 14

telophase I

Answer 14

• Spindle fibres disappear

- Nuclear membrane form around each set

Question 15

cytokinesis I

Answer 15

• Cytoplasm constrict in the centre of the cell, between the two daughter nuclei

Question 16

prophase II

Answer 16

• Original and copy pair up and attach via a centromere.

- Nuclear membrane begins to break down and spindles form.

Question 17

metaphase II

Answer 17

• Chromosomes line up along the equator

Question 18

anaphase II

Answer 18

• spindles contract, pulling the chomatids to separate poles

Question 19

telophase II

Answer 19

spindle fibres disappear, nuclear membrane form around each set

Question 20

cytokinesis II

Answer 20

• Cytoplasm constricts in the centre of the cell
• Four sex cells (gametes) are produced
• Each is haploid (half the normal number of chromosomes)
• Each sex cell has a different combination of genes on their 2 chromosomes

Question 21

genetic variation occurs:

Answer 21

Genetic variation occurs due to: independent assortment, crossing over and random fusion of gametes.

Question 22

law of independent assortment

Answer 22

Law of independent assortment: the combination of maternal and paternal homologues passed to each gamete is unique

Question 23

law of random segregation

Answer 23

Law of random segregation: one parental homologous chromosomes, but not both, is passed into each gamete; it’s random whether the maternal or paternal chromosomes will be passed.

Question 24

prokaryotic and eukaryotic cells

Answer 24

Prokaryotic: no nucleus, 1-5um, DNA is free moving in the cytoplasm (nucleic region), no membrane bound organelles, unicellular, examples: archaebacteria / eubacteria

Eukaryotic: true nucleus, 10-100um, DNA contained within a membrane bound nucleus, membrane bound organelles include mitochondria, multicellular,

Question 25

DNA: prokaryotic cells

Answer 25

• contains a single chromosome, a circular strand of DNA with no membrane that is free in the cytoplasm (in the nucleoid region)
• circular dna can supercoil and form a loop around a central dense protein (called the scaffold) to form a nucleiod
• genomes are compact (contain little repetitive DNA and no introns)
• contains plasmids (non-chromosomal DNA) - which codes for non-essential features but for selective advantages such as antibiotic resistance

Question 26

DNA: eukaryotic

Answer 26

• DNA in a membrane bound nucleus
• individual DNA molecules are arranged into separated chromosomes
• introns are a large proportion of non-coding DNA
• linear, double helix shape
• DNA wrapped around histones which coil up to make chromosomes
• Non-nuclear DNA is not contained within the nucleus
• genomes contain large amounts of non-coding and repetitive DNA (introns)
• linear shape
• Non-chromosomal: codes for proteins and respiration
• -> mitochondrial DNA (mt DNA) found in the respiratory cells, can be used to trace maternal inheritance – very small, 70nm with only 37 genes (13 for respiratory functions, 24 for RNA molecules)
• each cells has 100-1000 mitochondria and each contains 5-10 circular DNA molecules

Question 27

Genetic stability definition

Answer 27

pass on of consistently accurate genetic information

Question 28

genetic variation

Answer 28

occasional intorudction of variation of some genetic information (mutation) allows for species adaptation and increased survival in changing environment

Question 29

effective reproduction

Answer 29

the individual reaching maturity and either sexually or asexually producing offspring (dependent on cell replication)

Question 30

purpose of genetic continuity

Answer 30

Purpose of genetic continuity: ensure continuation of a species, because it ensures new cells of organisms have all the genes they need, in working order, to survive. A lack of genetic continuity results in death or disease.

Question 31

How is genetic continuity ensured?

Answer 31

• Mitosis: two daughter cells must have the same number and types of genes as the original cell
   in the case it doesn’t occur correctly – this could be detrimental to the survival of the organism
  o Key processes:
   DNA replication including the ‘proofing’ and repairing of mistakes
   Chromosome duplication to form two chromatids, joined by centromere
   Chromatids faithfully separating into different daughter cells (cytokinesis ensuring both daughter cells are viable)
• Meiosis: the resulting offspring must have the same number of genes as the parent organism
  o Key processes:
   Crossing over of paired chromatids, resulting in exchange of genes and DNA along a chromosome
   Random and independent segregation of chromosomes
   Halving of the number of chromosomes in the first reduction division to allow fertilisation of gametes

Question 32

genetic level

Answer 32

stability arises when chromosomes are replicated accurately to give rise to identical daughter chromosomes

Question 33

species level

Answer 33

successful, desirable traits must be passed on, along with some random errors (mutations). This allows a species to evolve if an environmental change occurs – driving natural selection

Question 34

for successful genetic continuity

Answer 34

• Consistent replication prior to cell division
• Orderly distribution of chromosomes during formation of gametes
• Fertilisation methods that ensure successful breeding
• Methods to ensure embryo survival (protection or large production of gametes)
• Natural selection so that fittest survive and pass on their genes

Question 35

mechanisms resulting in genetic variation include:

Answer 35

• Mutation: may be spontaneous or mutagen induced
• Mixing of parental genes during sexual reproduction (crossing over, independent assortment, random fertilisation of gametes )