A concise, bullet-pointed summary on Meiosis. Covers strictly what you need to know for all tests and assessments (as dictated by the SAGS guidelines). Includes annotated diagrams and images to illustrate points mentioned, as well as additional research, helpful when understanding the work
- Chromatin network: the part of the cell nucleus in which all DNA is packaged in order for the
cell to function. Large unwound threads of DNA (interphase)
- Chromatid: each of the two thread-like strands into which a chromosome divides during cell
division
- Chromosome: long strands made of DNA and protein carrying genetic information that are
tightly packed during cell division. Each is made of 2 chromatids
- Genes: distinct sequence of nucleotides forming a part of a chromosome that will determine
specific characteristics and polypeptide molecules
- A small piece of DNA makes up a gene
- Genes control hereditary characteristics and are found on chromosomes in the nucleus of a
cell
- When a cell divides, the DNA needs to replicate to make two sets of information that needs to
be passed on to new cells
- A chromosome is made up of DNA wrapped around histone proteins
- During interphase of a cell’s life cycle, DNA replicates
- The result is two strands of exactly the same genetic material
- Each strand is called a chromatid
- After DNA replication, each chromosome is made up of two chromatids joined to each other at
a point called a centromere
- Each organism is said to have two sets of chromosomes, this is known as the diploid condition
(2n)
- The gamete of each only has one set of chromosomes and are thus said to be haploid (n)
- Gametes are produced during meiosis of diploid cells
- During meiosis, the number of chromosomes is halved
- Meiosis only takes place in the ovaries and testes of animals and in the ovaries and anthers of
plants
- In humans there are 22 pairs of chromosomes (autosomes) plus one pair of sex chromosomes
- There are two types of sex chromosomes (gonosomes): X and Y
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, Chloë van Beukering Life Sciences Notes 2020
- Females are XX and males are XY
Karyotyping
- A karyotype represents a set of chromosomes in an organism, usually in a picture /
diagram form
- Shows the number, size and shape of the chromosomes during metaphase of mitosis
- A high-magnification print of a complete set of chromosomes is made as early on in mitosis as
possible
- Late prophase and metaphase will provide the clearest view as the chromosomes are in a
replicated and condensed state. Also the nuclear membrane is not visible so the
chromosomes have been ‘released’ into the cytoplasm and will spread out, not tangled up
together
- Chromosome pairs are numbered, and the karyotype headed
- Once done, the sex and chromosomal abnormalities of the child can be determined
Meiosis vs Mitosis
Recap on phases of mitosis:
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