Lesson 5 - Variation Flashcards
Variation
The differences in characteristics between organisms
Interspecific variation
Between members of different species
Eg. Birds have 2 legs but cats have 4
Differences between organisms within a species?
Intraspecific variation
Causes of variation?
- Genetic material (inherits from parents leads to genetic variation)
- Environment (environmental variation)
How does genetic material lead to variation?
- Alleles (variants)
- Mutations
- Meiosis
- Sexual reproduction
- Chance
Explained example of alleles causing genetic variation?
Different alleles produce different effects.
- Three alleles form human blood types.
Depending on parental combination of these alleles 4 different blood groups can be produced.
Individuals in a species population may inherit different alleles of a gene.
Mutations cause genetic variation?
Lead to changes in DNA sequence. This can change the proteins that are coded for. This can affect physical and metabolic characteristics.
Mutation in somatic (body) cells: affect individual
Mutation in gametes: passed on to organism’s offspring.
Meiosis cause variation?
Before the nucleus divides and chromatids of a chromosome separate, genetic material inherits from the 2 parents is mixed up by independent assortment and crossing over.
Gametes of individual show variation.
Sexual reproduction for variation?
Offspring inherits genes from each of the parents.
Individual produced differs from parents.
Chance in variation?
Many different gametes produced from the parental genome.
Chance of which two gametes combine (random fertilisation).
- Individuals produced therefore different from siblings and contain a unique combination of genetic material.
Asexual or sexual reproduction produces more variation?
Sexual
How is variation achieved in organisms that reproduce asexually?
mutations
Example of environmental variation: roses?
- Rose bushes planted in different positions in a garden
- One that has greater access to sun will generally grow larger than one in a shadier position.
Example of environmental variation?
Scars. These can not be inherited from a parent.
- Occurred as a result of accident or disease.
Genetic and environmental effects on height?
Tall parents = tall offspring
Bad diet = small offspring
Genetic and environmental effects on skin colour?
Skin colour at birth is decided by genetics.
Skin colour decided by pigment melanin. More melanin = darker skin.
- Expose skin to sunlight, more melanin produced to protect skin from harmful UV rays.
Skin turns darker.
Nature VS nurture argument
Scars:
- Cause is environmental
- Genetics affect how easily skin heals.
Identical twins
- Brought up in different environments = variation
- Brought up in same environment = variation
Jim twins ***
Similar characteristics:
- 6 feet tall
- body mass of 82 kg
- bite fingernails
- suffered migraine headaches
Surprising similar characteristics:
- Both had a dog with the same name
- Both married twice (both wives had the same name)
- Both smoked same brand of cigarettes
- Both studied carpentry and mechanical drawing.
Combined affect / interaction?
When an individuals genetics and environment can both influence a particular trait.
Interspecific variation definition:
The differences between any two species.
Intraspecific variation definition:
Differences between members of the same species.
Types of variation within sexual reproduction?
- Random assortment
- Crossing over
- Random fertilisation
Types of genetic variation in gene mutations?
Insertion
Deletion
Substitution
Types of genetic variation in mutations?
- Chromosome Mutations
- Gene Mutations
Non-sense mutation?
- Occurs when a substitution of a base occurs leading to a premature ‘stop codon’ being coded for
- This would lead to the premature end of the synthesis of a polypeptide.
- Successful synthesis of the final protein would be very unlikely and it would almost certainly not be able to function normally
- Stop codons are: UAA, UAG, UGA
Mis-sense mutation?
- Mis-sense mutation occurs when a change in base leads to a different amino acid being coded for
- The polypeptide will have a single amino acid that is different
- Effect determined by the role of the amino acid in the final polypeptide. May be involved in the formation of bonds for the structure of the active site. If this occurs then the enzyme will no longer have a specific and complementary structure and will be unable to catalyse a reaction.
Silent mutation?
- By changing the base in the mRNA / DNA sequence, there is no change in the amino acid that the sequence codes for.
- This is because genetic code is degenerative.
Deletion of bases?
- DNA nucloetide is lost from DNA sequence
- Deleting a base can lead to the codons no longer being read properly
- This is due to the fact that bases are read in triplets, therefore the subsequent bases would all be shifted forward by one base.
- the amino acid sequence of ‘new’ code would be entirely different
A population with greater genetic diversity will show…
greater intraspecific variation.
Polygenes:
different genes at different loci that all contribute to a particular aspect of phenotype
