Variation and Classification - Variation Flashcards
define interspecific variation
variation between species
define intraspecific variation
variation within species
what are the two causes of variation
- genetic variation
- environmental variation
how do genes affect variation
the mixture of alleles of genes inherited affect the phenotype of an organism
what causes genetic variation
- random mutations
- recombination of alleles
- random fertilisation of genetically different haploid gametes
what are random mutations that can occur
- chromosome mutations
- DNA mutations
what recombination of alleles can occur
- crossing over during prophase 1 meiosis
- independent assortment of chromosomes during metaphase 1 meiosis
- independent assortment of chromatids during metaphase 2 meiosis
how does the environment cause variation
phenotypic variation can be caused by differences in the environment
what can cause environmental variation
diet, lifestyle, climate
give examples of environmental variation
- etiolation
- chlorosis
what is etiolation
changes in the growth of a plant due to being grown in the dark (tall, spindly, yellow leaves)
what is chlorosis
plants may develop chlorosis due to a lack of chlorophyll
why may a plant lack chlorophyll
- lack of magnesium or iron ions in soil
- lack of light
- viral infection
how can diet cause environmental variation
may interact with genes to affect many characteristics e.g height, body mass
what are the types of variation
- discontinuous
- continuous
what is discontinuous variation
phenotypes fall into distinct and discrete categories with no (or very few) intermediate values
how can discontinuous variation be displayed
bar chart
how is discontinuous variation controlled
- by one gene (monogenic)
- may be controlled by two genes which are epistatic
what does discontinuous variation include
codominance and multiple alleles
with discontinuous variation, is the environment likely to have an effect on the phenotype
likely to have little or no effect of the phenotype
what is continuous variation
a continuous range of values between two extremes, usually forming a normal distribution curve
how is continuous variation usually controlled
by several genes (polygenic). they tend to provide an additive effect on the phenotype
what do the smaller effects of each allele cause
quantitative variation in phenotype
are polygenic characteristics influenced by the environment or genes, or both
both, but influenced by environment more than monogenic characteristics
give examples of discontinuous variation
- blood type
- tongue rolling
give examples of continuous variation
- skin colour
- birth weight
