4.3 Genetic diversity Flashcards
What does meiosis produce?
Haploid gametes - genetically different
Where does meiosis take place?
Sex organs
Why is it important that gametes are haploid?
So they can fuse together during fertilisation forming a diploid zygote
What is a chiasmata?
The point where the chromosomes join during crossing over
What is the full sequence of meiosis?
Interphase
Meiosis 1
Cytokinesis 1
Meiosis 2
Cytokinesis 2
What happens to the chromosomes during meiosis?
The no. Of chromosomes in each cell produced is decreased by half
What happens during meiosis 1?
Separation of bivalents
Produces 2 haploid daughter cells
What happens during meiosis 2?
Separation of sister chromatids
Produces 4 haploid daughter cells
What happens during prophase 1 in meiosis 1?
The chromosomes condense and become visible arranged as bivalents
The nuclear membrane breaks down
Spindle fibres same as mitosis
What happens during metaphase 1 of meiosis 1?
The bivalents align at the equator of the spindle apparatus
What happens during anaphase 1 of meiosis 1?
Spindle fibres shorten
Bivalents move to opposite poles - chiasmata break
What happens during prophase 2 of meiosis 2?
Chromosomes condense and become visible again
Nuclear membrane breaks down
Spindle fibres develop
What happens during metaphase 2 of meiosis 2?
The chromosomes are aligned on the equator or the spindle apparatus
How do the chromosomes align on the equator differently in meiosis 2 to meiosis 1?
The chromosomes align at right angles during meiosis 2 to the way they were aligned in meiosis 1
What happens in anaphase 2 in meiosis 2?
The centromere of each chromosome divides and the sister chromatids are separated
Spindle fibres shorten
What does it mean that meiosis is reduction division?
The no. Of chromosomes half
How does meiosis increase genetic diversity?
Crossing over
Random fusion of gametes
Independent segregation
How do you calculate the number of genetically different gametes produced by independent segregation?
2 to the power of n
Where n is the no. Of homologous chromosome paira
What is random fusion of gametes?
Lots of genetically different gametes produced
We cannot predict which male gamete will fuse with which female gamete- random fusion
How does random fusion of gametes create genetic diversity?
each parent is genetically different
produces gametes which have a unique combination of alleles
fertilisation = the zygote has an unique combination of alleles
How does crossing over happen?
chromosomes condense and tangle during Prophase 1
they cross over to form Chiasmata - the genetic info is swapped if chromosomes are heterozygous
each chromosome then has a new combination of alleles - recombinant chromosomes
What are recombinant chromosomes?
the new combination of alleles after crossing over are not present in either pair of parent chromosomes
What is independant segregation?
The random separation of homologous chromosomes in meiosis 1 that produces genetic variation
How do the chromosomes become tangled?
when the bivalents condense and they supercoil close to each other
What is genetic diversity?
the total number of different alleles in a population - the greater no. of different alleles, the greater genetic diversity
Why will induvidual’s do better in environment changes with genetic diversity?
theres a wider range of alleles so a wide range of characteristics, so a greater probablitity that an induvidual will have a characteristic to suit the environment
How can a gene mutation have no effect on an individual?
changes the amino acid but not the tertiary structure
the new allele produced is recessive
genetic code is degenerate
How can a gene mutation have a positive effect for an individual?
results in change in polypeptide that positively changes the properties of the protein
may result in increased reproductive success or survival
