KA3 Variation and sexual reproduction Flashcards
What are some features of Homologous pairs of chromosomes
- Same centromere position
- Same size
- Same genes at same loci
- inherited from different parents
What is meiosis
Meiosis is the division of the nucleus which results in the production of haploid gametes from a diploid gametocytes
Explain the reason for meiosis
Meiosis increases genetic variation
What occurs before the process of meiosis I
The chromosomes are replicated and each consist of two genetically identical chromatids attached to the centromere
What are the 7 steps in the process of meiosis I
1) The chromosomes condense and the homologous chromosomes pair up
2) Chiasmata form at points of contact between the non-sister chromatids of a homologous pair - and sections of DNA are exchanged
3) This crossing over of DNA is random and produces genetically different recombinant chromosomes
4) Spindle fibres attach the the homologous pairs and line them up at the equator of the spindle
5) The orientation of the pairs of homologous chromosomes at the equator is random
6) The chromosomes of each homologous pairs are separated and move towards opposite poles
7) Cytokinesis occurs and two daughter cells form
What occurs in the process of meiosis II
Each of the two cells produced in meiosis I undergo further division to which the sister chromatids of each chromosome are separated
What does haploid mean
One set of chromosomes
What does diploid mean
Two sets of chromosomes
What could be a difference between homologous chromosomes
A difference could be the alleles of the genes
What does independent assortment result in
Independent assortment results in new combinations of alleles and increases variation
What is a chiasma
A chiasma is a point of contact between two chromatids which belong to homologous chromosomes
How do linked genes arise
Genes on the same chromosome are said to be linked and the further apart the two linked genes are on a chromosome, higher the chance of a chiasma forming between them and greater frequency of recombination
How does the crossing over of homologous pairs bring about increased variation
As the crossing over of DNA is random and produces genetically different recombinant chromosomes resulting in new combinations of alleles = increased genetic variation
What does recombination frequency indicate and what is it used for
It indicates the distance between the linked genes on the same chromosome and is used to measure how close together linked genes are
What is parthenogenesis
When an offspring is produced from a female gamete without fertilisation
Give an example of parthenogenesis in animals
A species which carries out parthenogenesis is the whiptail lizard
Where is parthenogenesis found
Parthenogenesis is found in areas with lower parasitism
who is parthenogenesis disadvantageous to
It is disadvantageous to parasites as it occurs in cooler climates and regions where there is low parasite density or diversity
What is horizontal gene transfer between individuals
Organisms that reproduce principally by asexual reproduction have mechanisms for horizontal gene transfer between indivuals to increase variation eg plasmids of bacteria and yeast
What occurs through horizontal gene transfer of plasmids of bacteria and yeast
These allow for the exchange of genetic material and help to increase the rate of evolution
What are hermaphrodites
Hermaphrodites are species that have functioning male and female reproductive organs in each individual
What are examples of hermaphroditism
An example of hermaphrodites are plants and land snails
What does heterogametic mean
Males are heterogametic as they have two different chromosomes (XY)
Give an example of a heterogametic animal
an example of a heterogametic animal would be ——————— idk
How does a gene on the Y chromosome determine the development of maleness
The SRY gene on the Y chromosome determines the development of male characteristics
Why can heterogamesis in males lead to sex-linked patterns of inheritance
As males have XY chromosomes resulting in the single X chromosome being affected by the recessive gene as the Y chromosome is not able to cover it up
What are environmental factors that can influence sex and an example
- Temperature
- Size - eg clown fish
- Parasitic infection
- competition
What does the random inactivation on X chromosomes in females prevent
The random inactivation on the X chromosome in females prevents a double dose of gene products
Why does the random inactivation on X chromosomes in females prevent a double dose of gene products
As if both genes were to have a double dose of gene products it could be harmful, therefor one of the X chromosomes will inactivate and prevents a double dose of gene products
