Topic 5: Genetics Review Flashcards
The Individual
- is the reservoir of genetic information
( each individual has unique genetic code)
Is the unit of evolution
DNA
An organisms cells contain identical strands
specific to the individual
What is DNA composed of?
is composed of four different nucleotides arranged in an alpha helix
-A,C,T.G
chromosomes
threadlike structures that contain DNA
* dont pass all of DNA to offspring
- come in matched pairs, one from each parent
genes
(code for proteins)
- is organized into discrete subunits
Tay-Sachs Disease
- The individual does not produce an enzyme (protein) called hexosaminidase A without which
fatty tissue develops around nerve cells
locus
particular location of a gene on a chromosome
Alleles
- two or more alternative forms of a gene (code for particular trait)
result from slight differences in the DNA sequence of the gene
cause slight differences in form and function
Heterozygote
– an individual that has different alleles at a particular locus on the pair of
chromosomes (Aa)
Dominant and recessive
When one allele is expressed over another it is dominant, and the allele that is not expressed is
recessive
* blue eyed allele doesn’t produc epigment so if you have 1 gene that produces pigment your eye will be that colour
* everyone’s eye color is naturally blue
Homozygote –
– an individual that has the same alleles at a particular locus on the pair of
chromosomes
-Dominant (AA)
-Recessive (aa)
Explain tay sachs disease using dominant and recessive
A – codes for proper enzyme (protein)
• a – does not code for protein
• If AA, Aa → fine (at least one good copy of the gene)
• If aa → Tay-Sachs disease
* recessive condition is a result of not producing a functional protein
Genotype
all the genetic characteristics of an individual (ie. Aa)
-encoded in the DNA
-FIXED during the life time of an individual
- “set of genetic instructions”
“all the genes, inherited gene from parents and don’t change
Phenotype
= interaction of the genotype of an individual with its environment.
ex- blood types, diff gneotypes producing same phenotype
outward expression of genes in the physiology, appearance or behaviour of an individual
Responses of the individual to the environment may change
• In some cases Not Fixed during the lifetime of an individual
* put an organism in an enviroment with limited fppd= skinny lots of food= fat
Mendelian Inheritance
breeding of two individuals results in multiple combinations of
alleles
• 1 allele present on each chromosome of a parent
• 1 chromosome (allele) is present in each gamete produced by a parent
• Gametes combine in offspring to form a new combination of alleles
genetic recombination
all possible allele combinations from random mating of any combination of individuals in a population
Mendelian Inheritance
- is how genetic variation is maintained
phenotypic plasticity
: the ability of a genotype to alter its phenotypic expression under different
environmental conditions
How can Phenotypic variation be expressed as
- discrete
- continous
Discrete
alternative forms
e.g. Social insects – such as bees and ants
• two types of larvae hatch with essentially the same genetic material
Queens - adults that reproduce
Soldiers/workers – adults that defend the other larvae
* same genotype but diff phenotype
* colony of bees/ aunts all have the same genotype within same colony even though diff morphology
Characteristics controlled by a single gene (one copy inherited from each parent) tend to have phenotypes that fall into separate categories.
Continuous
variations in form (continuously varying phenotypes)
Reaction norm = relationship between response of a continuously varying trait and
environmental conditions
1 genotype can result in many phenotypes
e.g. Daphnia – respond (pigmentation) to varying UV radiation
• level of pigmentation varies continuously in response to UV radiation and
predator abundance
* increased level of pigment protects them from uv radiation
* transparent daphnia- advantage is it helps protect from predators
Most characteristics are controlled by more than one gene and are described as being polygenic.
Polygenic characteristics have phenotypes that can show a wide range of values, with each value following on from the value before.
level of pigmentation varies continuously in response to UV radiation and predation
predator abundance, is this an ex of evolution?
No b/c its an change on an indiv. basis
The Population
: a group of individuals of the same species living together
Where the effects of evolution are observed
Where can evolution occur?
- cant occur within an indivi.
- evolution only occurs within pop.
Hardy-Weinberg Principle
the genetic composition (allele frequencies) within a population does not change (evolution does not occur) unless one of the following
assumptions are broken
List the assumptions of the Hardy-Weinberg Principle
- no mutations
- no migration
- large pop
- random mating
- no selection
STATE ALL 5 ASSUMPTIONS and EXPLAIN how if each of the assumptions was broken evolution could occur according
No mutations
- Mutations result in a change in the DNA sequence of an organism
- For example genes could get deleted or substituted
- This would result in the creation of a new allele
- This mutation would then be passed on to future generations by reproduction
- If this assumption was broken a new allele would be introduced to a population resulting in a frequency of different alleles in a population
- This would result in evolution as the definition states “change in frequency of different alleles”
Random mating
If nonrandom mating were to occur this would mean that individuals would choose their mate based on certain genotypes/ phenotypes
This would not change allele frequencies but would change genotypic frequency which could lead to a change in allele frequencies over generations resulting in evolution
Large population size
- A small population means there is a higher chance that alleles are lost over generations whereas in a large population this is less likely to occur
- For example, in a small population with a small gene pool of just 4 alleles some alleles could get lost to the next generation due to chance events where in a large population this would not occur
- With a smaller population there is more likely a chance event to occur
- If alleles are lost, then evolution would occur as according to the definition there would be a change in allele frequencies over generations due to alleles being lost
No migration
- If migration to a population was to occur this would mean that individuals are leaving their population and new individuals are entering the population
- This would result in new alleles to be brought into populations or alleles to be taken away from that population
- If migration was to occur, in a population evolution could occur due to new alleles being introduced or taken away and resulting in different alleles in the population over generations due to mating
No selection
- If a certain allele is selected against this would mean that it would not be passed onto future generations
- This would alter the allelic frequency in future generation as certain alleles were being selected against and not being passed on resulting in change in allelic frequencies which is know as evolution
