F215 Flashcards
1
Q
What happens in Prophase I?
A
- Chromatin condenses
- Supercoil
- Homologous pairs form bivalents
- Non-sister chromatids wrap around each other at chismata
- Crossing over occurs
- Spindle fibre forms
2
Q
What happens in Metaphase I?
A
- Bivalents line up across the equator of the spindle
- Bivalents are arranged randomly (Random assortment)
- Homologous pairs facing at opposite poles
- Allows the chromosomes to independently segregate when they are pulled apart in Anaphase I
3
Q
What happens in Anaphase I?
A
- Homologous chromosomes in each bivalent are pulled by the spindle fibres to opposite poles
- The centromeres do not divide
- Chiasmata separate and lengths of chromatid that have been crossed over remain with chromatid to which they have become newly attached
4
Q
What happens in Telophase I?
A
Animal cells:
- Two nuclear envelops form; one around each pole
- Brief interphase occurs + chromosomes uncoil
5
Q
What happens in Prophase II?
A
- If a nuclear envelop reformed it, break down again
- Nucleolus disappears; chromosomes condense and spindle form
6
Q
What happens in Metaphase II?
A
- Chromosomes arrange themselves on the equator of the spindle; attached to spindle fibres at the centromere
- Chromatids of each chromosomes are randomly assorted
7
Q
What happens in Anaphase II?
A
- Centromeres divide and the chromatids are pulled to opposite poles; randomly segregated
8
Q
What happens in Telophase II?
A
- Nuclear envelops reform around the haploid daughter nuclei
- In animals: Two cells now divide to give four haploid cells
- In plants: A tetras of four haploid cells is formed
9
Q
How does Meiosis increase genetic variation?
A
- Crossing over occurs; shuffling of alleles in Prophase I
- Random assortment in Metaphase I
10
Q
What is Succession?
A
- The directional change in a community of organisms over time
11
Q
What is Primary Succession?
A
- Colonisation of inhospitable environment by organisms known as primary species
12
Q
What is secondary succession?
A
- Succession takes place on a previously colonised but disturbed or damaged habitat
13
Q
What is an ecosystem?
A
Any group of living organisms and non-livings things occurring together and the interrelationships between them, can be thought of as an ecosystem
14
Q
What is a habitat?
A
- The place where an organism lives
15
Q
What is a population?
A
- All of the organisms of one species that live in the same place at the same time and that can breed together
