Variation and reproduction - 2.3 Flashcards
Sexual reproduction def
Where two parents reproduce together, passing down one chromosome from each pair, to produce genetically distinct offspring.
Asexual reproduction def
Where one parent reproduces on its own, passing down both pairs of chromosomes, producing genetically identical offspring.
Advantages of sexual reproduction
Greater variation
Greater response to selection pressures
Greater resistance to parasites
Disadvantage of sexual reproduction
Only half a genome is passed on meaning successful genome is disrupted.
Only half the population will be able to produce offspring, meaning that population can grow more slowly.
Advantage of asexual reproduction
Can reproduce faster and repopulate an area much faster
Can be effective in narrow stable niches and environments
Vegetative cloning and parthenogenesis will decrease the number of individuals in a species which fail to reproduce.
Disadvantage of asexual reproduction
Lacks genetic diversity
Can decrease the chance of surviving selection pressures
Organisms which asexually reproduce will have lower resistance to parasites.
Red queen hypothesis link to sexual reproduction
Hosts which sexually reproduce will be more successful since this will increase genetic diversity of offspring, which will allow for the offspring to potentially have alleles which make them resistant to parasites, and increase the chance of survival and passing on genes further.
Vegetative cloning
Where a plant will produce a genetically identical copy of itself from a smaller part of the organism.
Parthenogenesis
Where a female will reproduce without fertilising their own gamete.
Examples of asexual reproduction in eukaryotes
Vegetative cloning and parthenogenesis
Parthenogenesis ideal conditions
Cooler climates with low parasite load and density
Method of increasing genetic diversity in asexual reproduction
Parthenogenesis allows for asexual reproduction which doesn’t produce an identical clone of the parent, this is due to a haploid gamete forming the zygote.
Example of parthenogenesis
Sharks
Example of vegetative cloning
Perennial weeds such as onions
Advantage of horizontal gene transfer
Allows for evolution occur faster since genes can be passed between organisms of the same generation.
Meiosis steps in order
Interphase 1
Prophase 1
Metaphase 1
Anaphase 1
Telophase 1 and cytokinesis
Prophase 2
Metaphase 2
Anaphase w
Telophase
Somatic cells definition
Cells that she not gametes
Gamete definition
Haploid cells which fuse together to form a zygote.
Mitosis steps
Prophase
Metaphase
Anaphase
Telophase
Interphase.
Mitosis definition
Where somatic cells divide to form more somatic cells.
Interphase
The chromosomes duplicate to form sister chromatids attached at the centromere
Centromere definition
The section where two sister chromatids are pulled apart by spindle fibres.
Centrioles
Opposite ends of a cell.
Prophase 1
The nuclear membrane will be removed and chromosomes will be arranged into homologous partners, chiasmata will be formed and there is the potential for crossing over of sections of chromosomes.
Anaphase 1
Chromosomes line up randomly on the metaphasic plate and kinetochores of each chromatid will bind to spindle fibres.
Chiasma def
The site in sister chromatids where recombinant strands can be formed from crossing over.
Metaphasic plate
The centre line elf the cell where chromatids line up
Kinetichores
Sites on sister chromatids where spindle fibres bind
Random assortment
Where sister chromatids randomly line up on the metaphasic plate increasing the variation of the daughter cells.
Crossing over
Where sections of a chromosome will swap with their homologous partner
Anaphase 1
Spindle fibres contract which will pull the homologous chromosomes to opposite poles.
Prophase 2
Nuclear membranes formed break down, and centrioles will be duplicated again, spindle apparatus is formed.
Metaphase 2
Chromosomes line up on metaphasic plate and spindle fibres will bind to kimetochores
Anaphase 2
Sister chromatids are pulled apart to opposite poles forming individual chromosomes
Telophase 2
Nuclei form at the poles and cytokinesis occurs (cytoplasm divides) 4 haploid daughter cells are formed.
Difference in mitosis and meiosis
Meiosis forms 4 daughter cells
Mitosis forms 2 daughter cells.
Meiosis forms distinct haploid daughter cells
Mitosis forms identical diploid daughter cells.
Linked genes
Genes which are inherited together often due to being close together.
Meiosis cells type of cell
Somatic cells
Independent assortment
Random assortment
SRY gene
The gene in the Y chromosome which determines maleness
human chromosome break down
23 chromosome pairs consisting of 22 autosome pairs and 1 sex pair
Autosomes
Chromosomes which aren’t involved in sex
Male sex chromosome combination
XY
Female sex chromosomes combination
XX
Homogametic
Female -XX
Heterogametic
Male - XY
Y chromosome length
60 genes
X chromosome length
1000 genes
Explanation of why males develop genetic conditions more than females
Males contain XY sex chromosomes instead of females XX chromosomes.
This female X chromosome is much larger than the males Y chromosome and contains more genes.
The male Y chromosome is missing genes that would normally be expressed instead of a faulty gene such as in females.
Problem of females XX chromosomes
Homogametic females non homologous section can potentially double dose due to two X chromosomes present.
This means that one X chromosome will randomly inactivate. (Random X inactivation)
Natural examples of random X inactivation
Tortoiseshell cat
Hermaphrodites
Species containing both male and female reproductive organs in one individual.
Where are hermaphrodites found
Where it is unlikely to find a reproductive partner - typically in sessile animals and parasites.
Sex determination by non genetic means
Population Size, competition, parasitic infection and temperature
Temperature effect on sex determination
Some species such as turtles only produce female offspring if incubation occurs above a certain temperature.
