Meiosis Flashcards
How many sets of chromosomes do eukaryotes have?
Most eukaryotes have two sets of homologous chromosomes (“diploid”)
How many chromosomes do humans have?
Humans have 46 chromosomes, but in fact 23 pairs (n = 23, 2n = 46)
What are haploid organisms?
Organisms that have only 1 set of chromosomes (1n) are called “haploid”
What is the maternal set of chromosomes
The set of chromosomes you get from your mother
What is the paternal set of chromosomes?
The set of chromosomes you get from your father
What is the Centromere?
The region of a chromosome to which the microtubules of the spindle attach, via the kinetochore, during cell division.
What are the different types of chromatids in a 2n set of chromosomes.
- The sister chromatids of one duplicated chromosome
- The non-sister chromatids in a homologous pair
- The pair of homologous chromosomes (one is maternal the other is paternal)
Draw and label a diagram of the different chromatids in a 2n set of chromosomes.
https://docs.google.com/document/d/1Nzo4FTzXCbwOZjpoc_J_4IF3gsOXPcoyC2BowELmx0U/edit?usp=sharing
What is sexual reproduction?
The fusion of two cells from different individuals
What would happen if you fused two diploid cells?
If you fused two diploid cells the offspring would have double the amount of chromosomes and therefore double the amount of genes to copy every time a new cell is made and thus it is inefficient. For example:
2n + 2n = 4n then the next generation of 4n would produce double their amount of chromosomes, for example:
4n + 4n = 8n and so on until it simply becomes to slow for the baby to grow because it has to copy so many chromosomes before it can make a new cell.
For sexual reproduction to be possible what needs to be produced?
Organisms need to produce cells with half the number of chromosomes as the parental cell = “gametes”
What is the difference between Mitosis and Meiosis?
Mitosis: Produces two genetically identical diploid cells (ie, each has 2n chromosomes)
Meiosis: Produces four haploid cells with half the number of chromosomes as parent cell (ie, each has 1n chromosome)
What is the first step of Meiosis?
The chromosomes duplicate so that there are two paternal chromosomes and two maternal chromosomes.
What is the second step of Meiosis?
- “Meiosis 1”
- The homologous chromosomes separate into separate cells
- These are called haploid cells with the duplicated chromosomes inside them
What is the third step of Meiosis?
- “Meiosis 2”
- The sister chromatids separate into their own cells creating a gamete.
Draw and label a diagram of the Meiosis cycle
https://docs.google.com/document/d/1Nzo4FTzXCbwOZjpoc_J_4IF3gsOXPcoyC2BowELmx0U/edit?usp=sharing
What are the basic steps of the human life cycle in relation to Meiosis and Mitosis?
- The first step is meiosis, where the ovaries and the testis create the gametes.
- Second is fertilisation, or, the fusion of the gametes
- Third is Mitosis which is the development of the organism
What are the three types of sexual life cycles?
- Animals
- Plants and most algea
- Most fungi and some protists
What are the basic steps of the plant sexual life cycle?
- Many plants have two parts, the sporophyte and the gametophyte.
- The cycle starts with the sporophyte where Meiosis happens, the sporophyte will shoot out spores which are the gametes of the plant
- Next, under optimum conditions, Mitosis will begin to happen. This means that the spores grow and develop into gametophytes
- The gametophytes continue to undergo mitosis until another hapliod cell (aka gamete) comes along and fertilises it
- After it is fertilised the sporophyte part of the plant begins to grow (mitosis) thus starting the cycle over
What are the basic steps of the fungi sexual life cycle?
- The first step is Meiosis
- Once the games have been produced they undergo mitosis and develop into either unicellular or multicellular organisms
- Once they are organisms they are able to find other haploid cells (gametes) and begin fertilisation
- After fertilisation the organism undergoes more mitosis until it is able to reproduce, itself.
What happens in Meiosis 1?
Separation of homologous chromosomes and reduction of the number by half (ie, 2n → n) - There is no DNA replication in this part:
Which phases are part of Meiosis 1?
– Prophase I and Prometaphase I
– Metaphase I
– Anaphase I
– Telophase I and cytokinesis
What is the main goal of Meiosis 2?
Separate sister chromatids (~ mitosis)
Which phases are in Meiosis 2?
– Prophase II and Prometaphase II
– Metaphase II
– Anaphase II
– Telophase II and cytokinesis
What happens in Prophase I (and Prometaphase I)
– Can take several days
– Synapsis form
– There is crossing over
What are synapsis (in regards to Meiosis)?
Homologous pairs of chromosomes that bind together (forming “tetrads”)
What is a tetrad?
A tetrad is a pair of homologous chromosomes that bind together by the chiasmata (the middle section of a chromosome)
What is crossing over (in regards to Meiosis)?
Exchange of large sections of chromosomes between pairs (cross-over region is called “chiasmata”)
What happens during Metaphase 1?
Tetrads align along the metaphase plate
What happens during Ananphase 1?
Attachment between homologous chromosomes break down, and homologous chromosomes move towards opposite poles
What happens during Telophase 1 and Cytokinesis?
Cells split, forming 2 haploid daughter cells with n chromosome (each with 2 chromatids)
What happens during Meiosis 2?
- No DNA replication occurs b/w meiosis I & II
- Meiosis II very similar to mitosis because it produces 4 haploid cells with n chromosome (each with 1 chromatid)
What type of reproduction is Mitosis?
Asexual reproduction (by mitosis)
– Produces 2 identical daughter cells (clones)
– Allows reproduction from a single cell
What type of reproduction is Meiosis?
Sexual reproduction (by meiosis)
– Produces 4 haploid daughter cells (“gametes”), genetically different from parent and from each other
– Requires 2 organisms, each providing 1 haploid (male provides sperm, female provides egg)
What are the advantages of Meiosis?
Meiosis produces much greater genetic diversity than mitosis:
– Independent assortment → new combinations
– Crossing over → mixing chromosomes
Why is genetic diversity advantageous?
Genetic diversity provides greater flexibility to adapt
to changes in the environment
How do mitochondria reproduce and how are they inherited by offspring?
- Mitochondria (and chloroplasts) have their own DNA, and divide by binary fission
- In sexual reproduction, mitochondria are inherited exclusively from the mother (mitochondria in sperm are destroyed by egg after fertilisation)
