diversity, classification and variation

two nuclear divisions which creates four genetically different haploid daughter cells from one single diploid parent cell

independent segregation of homologous chromosomes crossing over between homologous chromosomes both occur in meiosis one

in meiosis 1, homologous pairs of chromosomes line up opposite eachother at the equator of the cell it is random which side of the equator the maternal and paternal chromosomes from each homologous pair lie these are separated so one of each homologous pair ends up in the daughter cell

we can use the formula 2n where n= the number of homologous pairs e.g for humans it would be 2^23 = 8388608 possible combinations so there is lots of variation

when homologous pairs line up opposite eachother at the equator in meiosis 1, parts of the chromatids can become twisted around eachother this puts tension on the chromatids, causing parts of the chromatid to break the broken parts of the chromatid recombine with the other chromatid this results in a new combination of alleles on that chromatid

meiosis: -two nuclear divisions -haploid cell (one set of chromosomes) -introduces genetic variation mitosis: -one nuclear division -diploid cells (two sets of chromosomes) -creates genetically identical cells

meiosis involves a diploid (2n) parent cell dividing to become a haploid (n) cell

it is random which egg and sperm will fuse in fertilisation which increases variation this is before crossing over is considered

(2^n)^2

when the chromosomes or chromatids do not split equally during anaphase

changes in whole sets of chromosomes- when organisms have three or more set rather than the usual 2 mainly occurs in plants

changes in the number of individual chromosomes- sometimes individual chromosomes fail to separate during meiosis this non disjunction results in a gamete having one more or one less chromosome e.g downs syndrome is due to 3 copies of chromosome 21

the number of different alleles of genes in a population natural selection can only occur if there is genetic diversity within a population

the change in allele frequency over many generations in a population

evolution species becoming better adapted to their environment- these adaptations can be physiological, anatomical or behavioral

new alleles for a gene are caused by random mutations if the new alleles increase the chances of the individual to survive in that environment, then they are more likely to survive and reproduce reproduction passes the advantageous allele to the next generation over many generation the new allele increases in frequency in the new population

one of the extremes has the selective advantage occurs when there is a change in environment the modal trait changes

the modal trait has the selective advantage occurs when there is no change in environment the modal trait stays the same standard deviation decreases as individuals with the extreme trait decrease e.g human birth weight

for successful mating and species recognition synchronises mating behaviour- indicates the individuals are sexually mature and in season to ensure survival of the offspring by forming a pair bond and choosing a strong and healthy mate

a group of genetically similar organisms that can breed to produce fertile offspring

a sequence of behaviours which is unique to each species- this is how individuals identify members of their own species to reproduce with most courtship rituals are performed by males- why theyre usually more brightly coloured usually include a sequence of dances, sounds releasing of pheromones, display of colourful feathers or fighting females observe and decide whether they want to mate with the male

to pass on advantageous alleles to ensure survival of their species

the more similar a courtship sequence is between different species, the more closely related the species are

universal way to name organisms first name is genus (first letter is always capital) second name is species always written in italics if the same genus- the more closely related they are