A Level CIE Biology: 17 Selection and Evolution

phenotype

observable characteristics of an organisms

phenotypic variation

difference in phenotypes between organisms of the same species

what can phenotypic variation be explained by

• genetic factors - 4 diff blood groups observed in human pop due to diff individuals within pop having 2/3 possible alleles for single abo genes

• environmental factors - clones of plants w same dna/genetic info will grow to diff heights when grown in diff environmental conditiosn

• combination of genetic and envi - recessive allelle causing sickle cell has high frequency in pops where malaria is prevalent due to heterozygous individuals being resistant to malaria

phenotype =

genotype + environment. how its determined 

do organisms of same species have similar _____ but 2 individuals (even twins) different ______

genotypes, between DNA base sequences

are there big differences between individulas of the same species

considering size of genomes, diffs are small, called genetic variation

genetic variation is transferred from

one gen to the next and it generates phenotypic variation within a species population

3 processes causing genetic variation as they result in new combination of alleles in gamete or individual

• independent assortment of homologous chromosomes during metaphase I

• crossing over fo non sister chromatids during prophase I

• random fusion of gametes during fertilisation

mutation results in what?

• generation of new alleles

• new allele may be good or bad or have no effect on phenotype because genetic code is degenerate (single aa may be coded for by more than 1 triplet code)

• new alleles not always seen in individual they first occur in and can remain hidden within pop for several generations before contributing to phenotypic variation

how do genes have varying effects on organisms phenotype

• phenotype may be affected by single gene or by several

• impact that gene has on phenotype may be large, small and or additive

independent assortment of homologus chromosomes during metaphase I mechanism

random alignment of chromosomes result in different combinations of chromosomes and different allele combinations in each gamete

independent assortment of homologus chromosomes during metaphase I consequences

genetic variation between gametes

crossing over of non sister chromatids during prophase I mechanism

exchange of genetic material between non sister chromatids leads to new combinations of alleles on chromosomes. it can also break the linkage between genes

crossing over of non sister chromatids during prophase I consequence

genetic variation between gametes

random fusion of gametes during fertilisation mechanism

any male gamete can fuse with any female gamete (random mating in species pop)

random fusion of gametes during fertilisation consequence

genetic variation between zygotes and reuslting indiviudals

mutation mechanism

ranodm change in dna base sequence results in the generation of a new allele. mutation must exist within gametes for it to be passed on to future generations

mutation consequence

genetic variation between individuals within species population

different environmetns affect what conditions (5)

changes in factors above can affect how orgs grow and develop (e.g. plants w tall genotype growing in environment that is depleted in minerals, sunlight and water will not be able to grow their full potential determined by genetics).

• length of sunlight hours (may be seasonal)

• supply of nutrients (food)

• availability of water

• temp range

• oxygen levels

can environmentally caused phenotypic variations be inherited by offspring

no, only alterations to genetic component of gametes