VARIATION 2

VARIATION 2

1. mutation & recombination generate novel genetic variation in the individuals within a population

   • some of these novel genotypes may be maintained, while many others will be lost from a population
     • to understand evolution must understand how & why this occurs

2. evolutionary biology is most dedicated to analysing & understanding variation - profoundly important feature of all biological systems

3. phenotype - refers to characteristic in an individual organism, or in a group of individuals that are alike in this respect

   • all features of an organism except DNA may be called phenotypes, ranging from level of transcription of a gene to aspects of organisms morphology, behaviour & life history

4. genotype - genetic constitution of an individual organism, or group of organisms that are alike in this respect, at one or more loci singled out for discussion

5. locus (loci) - site on a chromosome, or more usually the gene that occupies that site

6. allele - particular form of gene, usually distinguished from other alleles by its effects on the phenotype

   • number of alleles or loci that contribute to genetic variation in a phenotypic trait differs from case to case
     • in simplest of cases, 2 alleles at single locus account for most of the variation, eg colour forms of snow goose
     • in Homo sapiens, alleles at several or many different loci contribute to variation in 'quantitative characters' such as skin pigmentation, hair colour & texture, & facial features
   • variation in phenotypic character (incl gene expression) can have several sources other than those encoded in DNA sequences

7. haplotype - one of the sequences of a gene or DNA segment that can be distinguished from homologous sequences by molecular methods such as DNA sequencing

8. gene copy - term used when counting number of representatives of a gene

9. environment - directly affects development or expression of many features, eg temperature, nutrition, host availability

   • these may be permanent effects on an individuals phenotype
     • some environmental factors act on an embryo before birth or hatching, eg determination of sex of many turtles by temperature at critical stage of development, consumption of drugs & tobacco by pregnant women

10. epigenetic inheritance - reversible & heritable changes in phenotype without alteration in DNA sequence

    • may be induced spontaneously or in response to environmental factors
    • no evidence yet that epigenetic variation contributes to evolutionary change