Unit 2- Asexual, Sexual Reproduction and Parental Investment Flashcards
What are the advantages and disadvantages of asexual reproduction?
- The metabolic costs of asexual reproduction are lower than sexual reproduction as it is based on the normal cell cycle and produces many identical offspring.
- Asexual reproduction is more rapid because the process is relatively simple and every member of the population can reproduce.
- It allows deleterious alleles to be removed quickly and organisms can occupy niches very quickly.
- All alleles are guaranteed to be passed on to the next generation but variation can still be gained through horizontal gene transfer.
- However, this is only a good strategy in very stable environments.
What are the advantages and disadvantages of sexual reproduction?
- Males are unable to produce offspring so only half the population can actually reproduce reducing the reproductive effectiveness of the population as a whole.
- Combining the genetic material of two parents to make new offspring means that only half of each parent’s genome is passed onto offspring, so this disrupts successful parental genomes.
- However there is an increase in variation which provides the raw material required for natural selection so that organisms can continue adapting to changing environments or to the ever-changing parasite-host balance.
Describe Meiosis 1
- At the start of meiosis, the chromosomes coil up and become visible.
- In Interphase 1 the chromosomes duplicate to form sister chromatids attached at centromeres.
- In Prophase 1 the homologous chromosomes condense and are arranged to form bivalents during the removal of the nuclear membrane. As the pairs align chiasmata form. Each chiasma is a potential site for crossing over leading to recombinant strands and increasing the chance of variation.
- The next stage is Metaphase 1 where the chromosomes line up on the metaphasic plate arranged in their pairs. This allows the second chance for variation as random assortment occurs.
- Anaphase 1 then takes place where a chromosome is pulled to each pole using spindle fibres.
- In Telophase 1 and cytokinesis the chromosomes reach the poles, the nuclear membrane reforms and the cell divides. The chromosomes do not decondense.
Describe Meiosis 2
- In Prophase 2 the centrioles are duplicated again and spindle apparatus is formed.
- Then in Metaphase 2 the kinetochores are orientated so chromatids are facing opposite poles.
- In Anaphase 2 the chromatids are separated and drawn to opposing poles.
- Finally, in Telephase 2 nuclei form at the poles and cytokinesis starts. The result is 4 haploid variable daughter cells/gametes.
How is variation further increased in Meiosis
Independent Assortment and Crossing Over
Describe X-inactivation
Female cells produce twice as much of the proteins from the genes on their two X chromosomes. During early embryonic development in females there is random inactivation of an X chromosome in each cell. The inactive chromosome is packaged into heterochromatin (basically associated with proteins which make it inaccessible for transcription- it is called a Barr body). This inactivation is random meaning even if you have a carrier female half of the tissue cells will be producing the correct gene so the female will not be affected. The inactivation of the X is permanent in the cell and it is maintained into daughter cells in that line.
Name 4 environmental factors that can change the sex of an embryo
Temperature, Size, Competition, Parasitic Infection
Define hermaphroditic
They are either capable of forming both female and male sex structures or that they can move between male and female forms.
Why is there an inequality between the energy invested in producing egg and sperm?
Eggs are much larger as they must contain an energy store for new offspring whereas sperm have to be fast moving in order to reach the egg. Human females produce a fewer eggs and males produce large amounts of sperm.
How do sessile organisms reproduce?
They use external fertilisation where they synchronise the release of gametes. Many sessile organisms also use asexual reproduction to produce clones. Plants will use wind or insect pollination to allow their gametes to move from one plant to another.
What are species that are suited in their life history to maintain a stable population with low fluctuations called?
K-selected
What are species that are suited in their life history to rapid population growth called?
R-selected
What is the difference between r and k selected species.
K-selected species live in stable environments with a long maturation period, they usually have a long life span with a low death rate. It takes them a long period to reach reproductive age and they will often have few larger offspring which they will invest a lot of parental care in .
R-seleced species live in unstable environments with a short maturation period, they have a short life span and a high death rate. They don’t take long to reach reproductive age and will have many small offspring with no parental care.
What are 3 features of homologous chromosomes?
Same centromere position, same genes at same loci, same size
How do animals reproduce asexually?
By the process of parthenogenesis where females can produce offspring from unfertilised eggs.
