Meiosis Flashcards
1
Q
Explain the meiosis cycle
A
- Zygote
- undergoes mitosis
- Forms a person
- undergoes meiosis
-Forms gametes - Leads to fertilisation
2
Q
Why is sexual reproduction an advantage
A
- Related to genetic diversity
- Success shows the value
- Increases adaptations within population as genetic diversity is increased
3
Q
Explain genetic diversity
A
- The higher the genetic diversity within a species the greater the chance of survival if the environment changes for any reason
4
Q
What happens if all the species are genetically identical
A
- And the environment changes, none of the species may be adapted to those changes and all may die
- Genetically identical species are able to live under warm temperatures
- The environment changes and is now significantly colder – none of the individuals can survive – the species goes extinct.
5
Q
What happens if individuals are genetically different
A
- Some individuals may be able to cope with changes in the environment while others may die.
- This means the species may experience some death but some individuals may be able to cope and reproduce under new environmental conditions
6
Q
What leads to low genetic diversity
A
- Small populations
- Which means high inbreeding level
7
Q
What type of reproduction leads to an identical population
A
- Asexual reproduction
- A single change in the environment can wipe out the population
8
Q
What type of reproduction leads to a diverse population
A
- Sexual reproduction
- Boots chance that at least some members of the population will survive a changing environment
9
Q
What is the outcome of meiosis
A
- Gametes
- each gamete contains one gene for each characteristic from the parent and contain half the number of chromosomes
10
Q
Explain the expression of a specific trait
A
- Is determined by the two units of information received from the parents; one unit from each parent.
- We refer to each unit as an allele – alternate forms of a gene
- When two gametes combine (fertilization) the resulting zygote again contains two alleles for each characteristic
11
Q
Explain homologous sets of chromosomes
A
- A sexually reproducing organism consists of diploid cells (2n) which contain two full sets of chromosomes, one set inherited from each parent
- Of the 23 pairs (46) of chromosome pairs in a human cell,
- 22 pairs are autosomes or chromosomes that are the same for both sexes
- A homologous pair of chromosomes is a matching pair of chromosomes that look alike and have the same sequence of genes
- Homologous chromosomes, however, are not identical and the two homologs differ in the combination of alleles or versions of the genes they carry
12
Q
Explain meiosis being essential in sexual reproduction
A
- In the case of sexual reproduction, the chromosome number of each gamete must be half (haploid) that of the parent cell (diploid) in order for the zygote to be diploid again
- If this did not happen then each subsequent generation would have had double the chromosome number of the immediate parents
13
Q
Explain meiosis in a nutshell
A
- In a nutshell we can say that meiosis involves three steps in terms of chromosome number, i.e.
- Doubling – DNA replication – sister chromatids
- 46 duplicated chromosomes (92 chromatids) - Halving – splitting of homologous chromosomes
- 23 duplicated chromosomes (46 chromatids) - Halving again – splitting of sister chromatids
23 chromosomes/chromatids
14
Q
What happens in interphase
A
- Duplication of chromosomes takes place just before prophase I, and each duplicated chromosome (sister chromatids) remains attached at the centromere
15
Q
What happens in prophase 1
A
- As in prophase of mitosis, similar behavior of nuclear membrane, nucleolus, centriole and spindle. Duplicated chromosomes are visible as condensed threads, and each duplicated form draws close to its homologue through process of synapsis.
- Crossing-over occurs between non-sister chromatids and results in exchange of genetic material - genetic variability is increased
