Sexual Reproduction & Meiosis

Question 1

Diploid cell

Answer 1

Multicellular orgarnisms made from rounds of mitosis from a single cell

Question 2

Stomatic

Answer 2

• Do not contribute to inheritance in the next generation
• Diploid cells, two copies/sets of each chromosome (2n), one set inherited from each parent
• Originated and maintained by mitosis

Question 3

Autosomal

Answer 3

• Homologus pain of non sex hormones
• Same size and shape with gene at a specific position (locus)
• Diffrent alleles varient version of gene

Question 4

Sex chromasome

Answer 4

• Pairs of chromasome that determine sex gender at birth
• Diffrent size to autosomal x and y chromasome
• X chromasome larger than Y
• X determines the mitochondrial DNA women

Question 5

Gamates

Answer 5

• Reproductive cells of the organisms involved in sex reproduction
• haploid cells: they contain only one set of chromosomes (n)
• Originated by diploid germ line cells by meiosis. Chromosome number is divided in half in meiosis
• Contribute to inheritance to the next generation

Question 6

Sexual Reproduction

Answer 6

1) Maternal and paternal chromosome sets are partitioned into the single chromosome sets of the gametes
2) Fertilisation (fusion) of gametes regenerates the diploid structure of the somatic cells (zygote with homologous chromosomes from both)
3) The zygote develops into a new individual, through many rounds of mitosis

Question 7

Meiosis

Answer 7

• Process that creates gametes, carries only a single set of chromosomes (n)
• It occurs in specialised germ-line cells that reside in the ovaries or testes
• A cell division that produces 4 non identical daughter cells having half the number of chromosomes of the parent cell (2n to n)
• Meiosis involves one round of DNA replication followed by two rounds of nuclear division (Meiosis I and Meiosis II)
• 2 nuclear division

Question 8

Process of meiosis

Answer 8

• Interphase - constituting in 3 phases: G1, S , G2 and S phase, DNA is replicated (sister chromatids)
• Meiosis I - Separation of the pairs of homologous chromosomes, after the process of pairing of the duplicated homologous similar not identical chromosomes along their entire length
• Meiosis II - with four stages + cytokinesis II separation of the sister chromatids (copies of the same chromosome)

Question 9

Meiosis I

Answer 9

• Chromasomes condense and nuclear envelope breaks down crossing over occours
• Pairs of homologus chromosomes move to the equator of the cell
• Homologus chromosome moves to the poles
• Chromasome gathers at the poles of the cells and the cytoplasm divides

Question 10

Meiosis II

Answer 10

• New spindle fibres form around the chromasome
• Chromasomes line up at the equator
• Centromere divides and Chromatids move to opposite poles of the cell
• Nuclear envelope forms around chromasome and cytoplasm divides

Question 11

Prophase I

Answer 11

• Spindle fibre form and nuclear envelope disapear
• Duplicated chromosomes (with sister chromatids) homologs (and the sex chromosomes) condense and are brought together (lined up) during a process called PAIRING (or synapse)
• Each pairing forms a structure called bivalent, which give rise to a unit of four sister chromatids stuck together (tetrad)

Question 12

Crossing over

Answer 12

• Homologus recombination
• Genetic exchange between DNA segments of the non-sister chromatids within tetrads of homologous chromosomes
• The chromatids break in the same place and sections of chromosomes (alleles) are swapped
• More cross-over events can occur per tetrad at sites called chiasmata
• Major source of genetic variation

Question 13

Metaphase I

Answer 13

• Spindle microtubules from both poles capture each tetrad (through kinetochores), and move them towards the centre of the meiotic plate
• Random orientation of homologus chromasome at metaphase plate (random assortment)
• Checkpoint of attachment of spindle fibres with kinetochores of chromosomes

Question 14

Anaphase I

Answer 14

• Synapsis breaks up
• The homologus chromasomes seperate to poles (1 tetrad to 2 dyad)
• Homologus move to opposite poles

Question 15

Telophase I & Cytokenesis I & interkenesis

Answer 15

• Two nuclear envelopes are formed around one set of duplicated chromosomes
• Daughter cells have one set of chromosome haploids, but duplicated
  and daughter cells are genetically different
• A short interphase occurs between Meiosis I and II
  There is NO replication of DNA