Chapter 2 - Meiosis Flashcards
What is sexual reproduction?
Combines genetic material from 2 parents to form a gentically unique individual
What is one advantage of sexual reproduction
Increases genetic diversity
Increases survival chances
What are the two disadvantages of sexual reproduction?
Takes time and energy to find a mate
Lower rate of offspring production
What are body cells/somatic cells called?
Diploid cells (2n)
What are haploid cells?
Haploid cells are our gametes/sex cells and only contain one copy of a chromosome (n)
What is the total number of chromosome is one somatic cell?
46
(22 pairs of autosomes - non sex chromosome)
(1 pair of sex chromosomes)
What is a homolog/homologous pair?
A pair of chromosomes which contain the genetic code for the same features
What is Meiosis?
Producing four haploid gametes from a single parent cell
Where does Meiosis occur?
Gonads
What differentiates Meiosis from Mitosis?
Meiosis has two deparate division events rather than one because they are producing four haploid gametes.
What happens before meiosis begins?
DNA replication occurs during the S phase to produce identical sister chromatids
What does Meiosis 1 involve?
Separation of homologous chromosome from 2n to n
How many stages are there in total for Meiosis?
8 (Meiosis stage 1 = 4 phases. Meiosis stage 2 = 4 phases)
What is a parent cell called?
Germline cell - diploid (2n)
Describe the events at prophase 1
- replicated DNA condenses
- centrioles start to produce spindle fibres
- Nuclear envelope breaks down
- Spindle fibres attach at centromeres and move to opposite ends
What occurs at prophase 1?
Synapsis
What is synapsis?
The homologous chromosome will pair up
What is crossing over?
The sister chromatids closest to each other cross over
Two chromatids can swap equivalent genetic material
What is a Chiasma?
The point at which crossing over occurs
Describe the events at Metaphase 1
Chromosomes line up in homologous pair at centre
Describe the events at Anaphase 1
Spindle fibres are pulled back
Homologous pair are separated
Sister chromatid remains together
Describe the events at Telophase 1 and cytokineses
Often occur at the same time
Cleavage furrow or cell plate forms and separates the cytoplasm into two separate cells
What does Meiosis 2 involve?
Separates sister chromatids
Which stage of Meiosis is similar to Mitosis?
Meiosis stage 2
Describe the events at prophase 2
Spindle reforms and attaches to centromeres of condensed chromosomes
Describe the events at metaphase 2
Chromosomes line up down the equator of the cell
Describe the events at anaphase 2
Spindle fibres pull back towards centrioles
Sister chromatids are separated
Describe the events at telophase 2 and cytokineses
- Groups of chromosomes reach the poles of the cell
- Nuclear envelope starts to form around the group of chromosomes
- Spindle fibres break down and chromosomes start to unwind
- Cleavage furrow forms
How does meiosis produce genetically different offspring? (3 ways)
- The chromosomes are arranged randomly
- Process of crossing over
- Random fertilisation of haploid gametes
What is the product of Meiosis 2?
Four non-identical haploid gametes