B17 - Variation and Selection Flashcards
Variation
differences between individuals of the same species
mutation
genetic change
how are new alleles formed?
mutations (change the sequence of DNA bases which results in different proteins being coded for)
what does discontinuous variation result in?
limited number of phenotypes with no intermediates
what does continuous variation result in?
range of phenotypes between 2 extremes
3 examples of genetic variation
-eye colour
-biological sex
-blood group
3 examples of environmental variation
-piercings
-tattoos
-accent
3 examples of both environmental and genetic variation
-sporting ability
-height
-weight
3 examples of continuous variation
-weight
-height
-leaf surface area
3 examples of discontinuous variation
-blood groups
-eye colour
-skin colour
2 main causes of variation are?
-genetics (alleles and genotype)
-environment
whats the type of variation passed on to our chidren?
genetic variation
how does fertilisation lead to more variation?
the fertilised egg contains genes from both parents, which is a new mixture. Mix of alleles from both parents gives more variation
how does formation of gametes lead to variation?
during meiosis, sex chromosomes cross over (meiosis) and create new combinations of genes. This leads to all eggs and sperms being genetically different
what are 3 factors that cause mutations?
-radiation
-chemical
-natural causes
what are the 5 steps of selective breeding?
1) decide which characteristic is most important (desired characteristics / features) and select parents that show high levels of this characteristic
2) breed these individuals
3) select the best offspring
4) breed again
5) repeat the process over many generations and eventually all sheep will have the important characteristic chosen
3 desired characteristics in animals
-muscle mass (meat)
-produce more milk
-produce more wool
2 desired characteristics in plants
-increased yield (to feed our increasing population)
-disease resistant
selective breeding
when humans artificially select the organisms that breed so that the frequency of alleles for desired characteristics increases in a population
selective breeding has changed the characteristics of wheat, making it: [2]
-easier to harvest
-giving higher yields
2 problems of selective breeding
-increased risk of genetic disease (pugs have short stubby noses and may have breathing problems)
-reduction in variation (if that type of allele is not resistant to a disease, and almost all the organisms have that allele, they may become extinct / the other variations that have not been bred can go extinct)
why is it useful to a farmer for a crop to ripen at the same time and grow to the same height?
-farmers use machines that can’t differenciate ripe and not ripe crops so in order to get all the ripe crops and not cut off un-ripe crops
-those machines also cant move according to the height of the crop, it just cuts the crop all in the same place so some crops may have longer, unnecessary stems and others may not get cut all the way
-If done by hand, difficult and troublesome to choose the ripe and not ripe crops
formula for percentage increase in yield
(new-old / old) x 100
6 steps of natural selection
1) There is genetic VARIATION is every population
2) All organisms OVERPRODUCE (to not go extinct) when conditions are favourable
3) this leads to COMPETITION for resources (water, food, light, mates)
4) competition, predators, and disease means some organisms are better adapted to SURVIVE
5) those organisms that survived REPRODUCE
6) then the ALLELES for the advantageous characteristics (characteristics of organisms that survived) will be passed onto their offspring and become more common in the population over many generations
