C12: Variation Flashcards
3 causes of continuous variation
(environmental factors)
- temperature
- pH value
- light
4 causes of discontinuous variation
(genetic factor)
- crossing over
- independent assortment of chromosomes
- random fertilisation
- mutation
why environmental factors have small effect to variation only
- only involves phenotypic differences
- change allele frequency and genotype frequency
- not change the genotype
- cannot be inherited
example of effect of temperature to variation
- Siamese cat
- produces dark pigment enzyme for fur colour
- function at temperature less than body temperature
- thus, lower temperature body parts are dark in colour
example of effect of pH to variation
- hydrangea sp. plant
- produces blue flower in acidic soil
- pink in alkaline soil
example of effect of light to variation
- alter skin colour
- ultraviolet ray destroy melanin pigment of exposed skin
- more melanin pigment produced
- cause skin to be darker
how crossing over affect the variation
- occurs between non-sister chromatids of homologous chromosomes during prophase 1 of meiosis
- produce new combination of genes
- form gametes with different genetic materials
how independent assortment of chromosomes affect the variation
- happen in metaphase 1 of meiosis
- homologous chromosomes pair is arranged randomly on the equatorial plane
- show two probabilities
- different combinations of paternal and maternal chromosomes
- different genetic content in gametes
how mutation affect the variation
- permanent change occur spontaneously on genes or chromosome
- create new genotypes
- can be inherited if happen in gametes
- cannot be inherited if happen in somatic cell
define variation
the difference in characteristics between a same population or species
what is natural selection
an evolutionary force that selects beneficial genes and removes the non-beneficial one.
3 necessity of variation
- enables natural environment to continue selecting beneficial characteristics and remove the non-beneficial one
- allows cross breeding among species to form new species
- to ensure the survival of species when environment changes
explain continuous variation
- difference in characteristics not distinct
- graph: normal distribution//bell-shaped curve
- quantitative, can be measured and graded
- influenced by environmental factors
- control by many genes
- height, weight, skin colour
explain discontinuous variation
- distinct differences in characteristics
- graph: discrete distribution
- no intermediate characteristics
- qualitative, cannot be measured and graded
- due to genetic factors
- can be inherited
- control by one genes, can be seen easily
- fingerprint pattern, eye colour
why does someone has blue eyes
- low level of melanin content in outer layer of iris
what is mutagen
the substance that causes mutation or increase the mutation rate to a dangerous level
what is mutant
the new genetic material produced by mutation
3 types of mutagen
- physical agents
- chemical agents
- biological agents
2 physical agents cause mutation
- ultraviolet from sun
- ionising rays (X-ray, alpha ray)
4 chemical agents cause mutation
- carcinogen
- food preservations
- formaldehyde
- benzene
2 biological agents cause mutation
- virus
- bacteria
how gene mutation occurs
- known as point mutation
- change in nucleotide base sequence of a gene
- alter the genetic code to synthesise amino acid
- change the protein structure
- new protein form cannot function
3 types of gene mutations
- base substitution
- base deletion
- base insertion
5 genetic diseases caused by gene mutation
- thalassemia
- cystic fibrosis
- sickle cell anaemia
- albinisme
- haemophilia
