SB3b - Meiosis
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34 Terms
what is a zygote?
a single fertilised egg cell
how is a zygote formed?
two gametes (sex cells) fuse during fertilisation
what does the zygote forms and how?
a ball of cells using mitosis (cell division)
what does the nucleus of a zygote store?
instructions that are identical for almost all human cells, control each individual cell, and shape, coordinate and control the body
what is the length of the diameter of the nucleus of the zygote? (µm to copy)
about 6µm (micrometre) or 0.006mm
what is the length of the diameter of a human zygote?
0.1mm
how and where are the instruction for an organism found?
as code in a molecule called DNA
what is the DNA of an orginism?
its genome
what do most cells contain?
a complete copy of an organism’s genome
where is the human genome found?
on 46 very long molecules of DNA
where is each DNA molecule found?
inside a chromosome
what are genes?
DNA sections along the length of a DNA molecule that each contain a code for making protein
what are proteins?
polymers
how are proteins made?
by linking different amino acids together in a chain
what controls the order of amino acids?
a gene
how many genes do humans have?
about 20 000
how many different chromosomes are in humans?
23
what do most nuclei contain?
two of each type of chromosome
what does a human body cell overall contain?
two sets of 23 chromosomes, making 46 in all
what does a cell with two sets of 23 chromosomes called?
diploid (2n)
what does n represent?
a full set of chromosomes (23 in humans)
what is the shorthand for a diploid cell?
2n
why do gametes need to have only one set of chromosomes?
because if two diploid cells joined in fertilisation the zygote will have four sets of chromosomes
what are gametes?
haploid
what is the shorthand for a haploid cell?
1n
what does mitosis produce?
diploid cells
what process is used to produce gametes?
meiosis
state step 1 of meiosis.
each chromosome replicates (makes a copy of itself)
describe the look of step 1 of meiosis.
the two chromosome copies remain attached, making each chromosome look like an X
what is step 2 of meiosis?
the two sets of chromosomes ‘pair up’ forming 23 pairs, and the pairs get separated into two new cells
what is step 3 of meiosis?
the two copies of a chromosome in each X-shape split into two new cells.
what does meiosis produce?
four haploid daughter cells, which is how gametes are produced
what does each chromosome in a pair contains?
different versions of the same genes that are genetically different
why are gametes all different?
they contain genetically different chromosomes