Variation Review Flashcards
(35 cards)
Variation def + types (4)
Slight differences between individuals within a population (or between populations).
Sexual Reproduction
Meiosis
Mutations
Gene Flow
Sexual Reproduction
the production of new living organisms by combining genetic information from two individuals of different sexes.
- Mix of alleles from two parents
- Fertilisation is random (which sperm fertilises which egg)
- 1 random male gamete fertilises the random female gamete to produce a zygote
Meiosis def + ways of forming new allele combinations (3)
a type of cell division that results in four daughter cells each with half the number of chromosomes of the parent cell.
New allele combinations formed via:
- crossing over
- independent assortment
- segregation
Crossing over
Homologous pairs of chromosomes exchange sections can cause linked genes to become unlinked -resulting in new allele combinations
Independent Assortment
(metaphase) chromosomes lining up randomly, therefore, each gamete ends up with a different combination of alleles.
Segregation
Separates the homologous chromosomes from each other.
Homologous Chromosomes
A pair of chromosomes with matching genes -can have different alleles eg. heterozygous
Mutations
Permanent changes to the base sequence of DNA
- create new alleles
- somatic (body cells) vs gametic (occurs in sex cells, CAN be inherited but not always, depends on what gene randomly ends up in the fertilised egg).
Gene flow
Migration of individuals from 1 population to another.
-change in allele frequencies could bring a new allele
or
-increase the popularity of a certain allele
Monohybrid Inheritance (1 gene) Def + types (6)
A monohybrid cross is a mating between two individuals with different alleles at one gene of interest.
Complete dominance
Incomplete dominance
Co-dominance
Lethal alleles
Multiple alleles
Sex-linked traits
Complete dominance def + example
If the dominant allele is present in the genotype it will always be shown in the phenotype as it MASKS the recessive allele
eg. dimples
Homozygous dominant DD - dimples
homozygous recessive dd - no dimples
Heterozygous Dd - dimples
Incomplete dominance def + example
In the genotype, neither allele dominates therefore when both alleles are present the phenotype will result in a BLEND OF THE TRAITS
eg. Snap dragon (flower)
RR -red
rr -white
Rr -pink
Codominance
Def + example
Both alleles are equally dominant and therefore BOTH WILL BE EXPRESSED in the phenotype.
Eg. Red Roan Cows (flower)
RR -red
rr -white
Rr -red + white
Lethal alleles def + example
A mutation creates a non-functional version of an essential protein, therefore, will die before/shortly after birth.
NOTE: Don’t count the lethal allele in the punnet square ratio ie. instead of 2:1:1 it would just be 2:1
eg. Manx cats
1:2:1
AA : AN : NN
AA = lethal
so ratio is 2:1
Multiple alleles def + example
Genes that have more than two different alleles for a trait
eg. blood type A B o A + A =A A + B =AB A + o = A B + B = B B + o = B o + o = O
Sex Linked Traits
Def + example
Traits found only on the X chromosome, a small number also on Y.
Because females have two X chromosomes if a mutation occurs it will likely only occur on one chromosome and they will be a carrier of the mutation but not present its phenotype. Males however are more likely to exhibit the phenotype as they have less chance of having a dominant allele on the Y chromosome for the same trait.
Eg. Colour Blindness
C = normal
c = colour blind of red + green light
C + C = Female normal
c + c = female colourblind
C + c = female colour blind carrier
C = male normal c = male colourblind
Dihybrid Inheritance (2 genes) Def + types (2)
Dihybrid cross is a cross between two different lines (varieties, strains) that differ in two observed traits.
When calculating the different forms of allele combinations, use FOIL.
general ratio for 2 heterozygous: 9:3:3:1
Linked Genes
Unlinked Genes
Linked Genes
Linked genes are found on the SAME chromosome.
If linked then not all possibilities of variations can occur.
If crossing over occurs they become unlinked and all possibilities can occur.
If the gap between the genes on the chromosome is LARGER than it is MORE likely for crossing over to occur.
If the outcome of a heterozygous cross is NOT 9:3:3:1 then you can assume it is linked. Linked will NoT produce this result.
Unlinked Genes
Unlinked genes are found on different chromosomes.
Should see usual 9:3:3:1
Mechanisms of Evolution
Def + types (2)
Change of Evolution
Natural Selection
Genetic Drift
Natural Selection def + types (6)
Involves the environment selecting for/against certain phenotypes.
Selection Pressures
Stabilising Selection Directional Selection Disruptive Selection Sexual Selection Artificial selection
Selection Pressures def + types (5)
Something that forces a population to evolve.
The extent to which organisms possessing a particular characteristic are either eliminated or favoured by environmental demands. It indicates the degree of intensity of natural selection.
Competition Predators Resource availability Drought High Energy Cost
Competition
Def + example
Is an interaction between two or more species for a resource
Eg. Darwin’s Finch (bird)
same Finch on different islands
birds on different islands eat different foods
beaks evolved to be different sizes to better accommodate their food source
ie. some eat seeds so evolved to have bigger beaks to better crunch down on the larger seeds.
Predators
Def + example
Organisms that prey upon other organisms.
Tend to evolve with their prey over time, ie. prey gets faster to evade them, predator evolves faster to catch prey, prey then evolves faster to evade…
eg. Penguins and Leopard Seals
Penguins evolve to be faster so as to evade the leopard seals.
As a result, leopard seals have to evolve to be faster to catch the speedier penguins.
As a result, penguins continue to evolve faster so as to evade the leopard seals.
This continues, with both species pushing the other one to continue to evolve.