UNIT 2 - KA3 Flashcards
What are the costs of sexual reproduction
- males unable to produce offspring
- only half of each parents genome passed onto offspring distrusting successful parental genomes
What are the benefits of sexual reproduction
Benefits outweigh costs due to an increase in genetic variation in the population
What does genetic variation provide
Genetic variation provides the raw material needed for adaptation,giving sexually reproducing organisms a better chance of survival under changing selection pressures
What may do evolutionary interactions between parasites and hosts select
Co-evolutionary interactions between parasites and hosts may select for sexually reproducing hosts
What hosts have greater fitness
Hosts better able to resist and tolerate parasitism have greater fitness.
Which Parasites have greater fitness
Pasties better able to feed, reproduce and find new hosts have greater fitness
What happens to hosts if they reproduce sexually
If hosts reproduce sexually, the genetic variability in their offspring reduces the chances that all will be susceptible to infection by parasites
Why can asexual reproduction be a successful reproduction strategy
Asexual reproduction can be a successful reproductive strategy as whole genomes are passed on from parent to offspring
In asexual reproduction who can produce daughter cells
In asexual reproduction just one parent can produce daughter cells and establish a colony of virtually unlimited size over time
When is maintaining the genome of the parent an advantage
Maintaining the genome of the parent is an advantage in very narrow, stable niches or when re-colonising disturbed habitats
Examples of asexual reproduction in eukaryotes
Vegetative cloning in plants and
parthenogenesis in lower plants and animals that lack fertilisation are examples of asexual reproduction in eukaryotes
Parthogenesis
Parthogenesis is reproduction from a female gamete without fertilisation
How much offspring can be produced with asexual reproduction
Offspring can be reproduced more often and in larger numbers with asexual reproduction
Where is parthenogenesis more common
Parthenogenesis is more common in cooler climates which are disadvantageous to parasites or regions of low parasite density or diversity.
What are asexually reproducing populations not able to do
Asexually reproducing populations are not able to adapt easily to changes in their environment but mutations can occur that provide some degree of variation and enable some natural selection and evolution to occur
What type of mechanisms do organisms that reproduce principally by asexual reproduction have
Organisms that reproduce principally by asexual reproduction also often have mechanisms for horizontal gene transfer between individuals to increase variation for example the plasmids of bacteria and yeasts
How can prokaryotes exchange genetic material
Prokaryotes can exchange genetic material
horizontally, resulting in faster evolutionary change than in organisms that only use vertical transfer.
What is meiosis
Meiosis is the division of the nucleus that results in the formation of haploid gametes from a diploid gametocyte
How do chromosomes appear in diploid cells
In diploid cells chromosomes typically appear as homologous pairs
What are homologous chromosomes
Homologous chromosomes are
chromosomes of the same size, same
centromere position and with the same
sequence of genes at the same loci.
Stage 1 meiosis 1
The Chromosomes which have replicated prior to meiosis 1 each consist of two genetically identical chromatids attached at the centromere
Stage 2 meiosis 1
- The chromosomes condense and homologous chromosomes pair up
- chiasmata form at points of contact between the non-sister chromatids of a homologous pair and selections of DNA are exchanged
Stage 3 meiosis 1 -
- spindle fibres attach to the homologous pairs and line up at the equator of the spindle
- each pair of homologous chromosomes is positioned independently of the other pairs
Stage 4 meiosis 1
- The Chromosome’s of each homologous pair are separated and move towards opposite poles. Cytokinesis occurs and two daughter cells form
What are linked genes
Linked genes are those on the same chromosome
What can crossing over result in
Crossing over can result in new combinations of the alleles of these genes
What is the orientation of the pairs of homologous chromosomes at the equator
The orientation of the pairs of homologous chromosomes at the equator is random
What is independent assortment
Each pair of homologous chromosomes in positioned independently of the other pairs, irrespective of their maternal and paternal origin
Where do chiasmata form
Chiasmata form at a random position between the homologous pairs. Chiasmata never form between sister chromatids
Where do non sister chromatids cross over
Non sister chromatids cross over at chiasmata
What is crossing over
Chiasmata allow the shuffling of sections of DNA between homologous chromosomes a process called crossing over
What happens to the DNA strands in relation to chiasmata
The DNA strands break and then rejoin at the chiasmata swapping a section of their genetic material resulting in the recombination of alleles
What can crossing over result in
Crossing over can result in new combinations of the alleles of these genes
What does crossing over of DNA produce
This crossing over of DNA is random and produces genetically different recombinant chromosomes
Stage 1 of meiosis 2
The sister chromatids of each chromosome are no longer identical because of recombination
Stage 2 of meiosis 2
Spindle fibres bind to the centromeres of each chromatid
Stage 3 of meiosis 2
The sister chromatids separate to opposite sides of the cell and are now referred to as chromosomes
Stage 4 of meiosis 2
Cytokinesis occurs and a total of four haploid cells are produced. The cells are all genetically different
How is the sex of birds mammals and some insects determines
The sex of birds mammals and some insects is determined by the presence of sex chromosomes
What does the SRY chromosome determine the development of
In most animals the SRY gene on the Y chromosome determines development of male characteristics
What do heterogametic males lack
Heterogametic (XY) males lack most of the corresponding homologous alleles on the shorter (Y) chromosome
What can the lack of corresponding homologous alleles on Y chromosome result in
This can result in sex - linked patterns of inheritance as seen with carrier females (XBXb) and affected males (XbY)
What happens in homogametic females
In homogametic females (XX) one of the two X chromosomes present in each cell is randomly inactivated at an early stage of development
What is X chromosome inactivation
X chromosome inactivation is a process by which most of one X chromosome is inactivated
What does C chromosome inactivation prevent
X chromosome inactivation prevents a double dose of gene products which could be harmful to cells
What are carries less likely to be affected by
Carriers are less likely to be affected by any deleterious mutations on these X chromosomes
What will half of the cells on any tissue have a copy of
As the C chromosome inactivated in each cell is random half of the cells in any tissue will have a working copy of the gene in question
Hermaphrodites
Hermaphrodites are species that have functioning male and female reproductive organs in each individual
What do hermaphrodites produce
They produce both male and female gametes and usually have a parter with which to exchange gametes
What is the benefit to the individual organism
The benefit to the individual organism is that if the chance of encountering a partner is an uncommon event there is no requirement for that partner to be of the opposite sex
What determines sex and sex ration for other species
For other species environmental rather than genetic factors determine sex and sex ratio
How is environmental sex determination on reptiles controlled
Environmental sex determination in reptiles is controlled by environmental temperature of egg incubation
What can change sex within individuals of some species
Sex can change within individuals of some species as a result of size, competition or parasitic infection
How can the sex ratio of offspring be adjusted
In some species the sex ratio of offspring can be adjusted in response to resource availability
