Chapter 1.5 - Meiosis Flashcards
What is a zygote?
A zygote is the fertilised gametes from both the mother and father
What is meiosis?
Organisms which reproduce sexually produce offspring which are genetically dissimilar from their parents and each other. Meiosis is the replication of gametes.
What is haploid?
A haploid cell has half the number of chromosomes of the original cell. A gamete is a haploid cell as it contains half the number of chromosomes needed.
What is a diploid cell?
A diploid cell contains the full number of chromosomes
What are the different stages of meiosis in order?
1) prophase 1
2) metaphase 1
3) anaphase 1
4) telophase 1
5) prophase 2
6) metaphase 2
7) anaphase 2
8) telophase 2
9) interphase
What happens in prophase 1?
Chromosomes shorten and supercoil (fatten) and come together in homologous pairs to form a bivalent. The chromatids wrap around one another and attach at points called chiasmata where they may break and swap small sections of DNA in a process called crossing over. The nuclear envelope breaks down.
What happens in metaphase1?
Centromeres attach at the spindle fibres and the bivalents arrange themselves randomly on the equator of the cell with each of a pair of homologous chromosomes facing the opposite pole.
What happens in anaphase 1?
One of each pair of homologous chromosomes is pulled by spindle fibres to opposite poles.
What is telophase 1?
Nuclear envelope reform around the chromosomes at each pole and the cell divides by cytokinesis
What happens during prophase 2?
The nuclear envelopes break down again, chromosomes supercoil and spindle fibres form
What happens during metaphase 2?
The chromosomes arrange themselves on the equator of each cell and are attached by their centromeres again to the spindle. Again chromatids are randomly arranged along the equator.
What happens during anaphase 2?
The centromeres divide and the chromatids are pulled to opposite poles by the spindle fibres and te chromatids randomly segregate.
What happens during telophase 2?
Te tetrad of four cells is formed. Each cell has a haploid number of chromosomes and crossing over during prophase 1 has introduced genetic variety giving cells of different composition.
What happens during interphase?
Meiosis is complete, the cell rests until the next meiotic division
Meiosis and germline fertilisation increase genetic variation in a number of ways, what are these was?
1) through the process of crossing over during prophase 1.
2) through genetic reassortment due to random distribution and subsequent segregation of the chromosomes during meiosis 1 and the chromatids during meiosis 2.
3) through random mutation
4) fertilisation itself is random variation: only one sperm contributes to it’s DNA and yet there are 300 million sperm cells all genetically different.
