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Flashcards in Variation Review Deck (35):

def + types (4)

Slight differences between individuals within a population (or between populations).

Sexual Reproduction
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


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


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.



Separates the homologous chromosomes from each other.


Homologous Chromosomes

A pair of chromosomes with matching genes -can have different alleles eg. heterozygous



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
-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

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


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
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.

Resource availability
High Energy Cost


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.


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.


Resource Availability
def + example

Lack or excess of resources can result in species evolving to be better adapted to the environment.

eg. not enough of one source of food could lead to a species adapting to being able to eat a second food source as well.


def + example

Droughts can cause permanent damage to plant and animal life by drastically impacting the lower levels in the food chain such as plants and as a result limiting the food sources for all other creatures.
Also, creates a lack of water.

Creatures can evolve to be able to better contain their water.
eg. cactus evolve to hold stores of water inside of them. so as to survive over long drought periods.


High Energy Costs
def + example

If something is not used much/ is no longer necessary, maintaining it requires energy and since it is useless it has a high energy cost with no payback. As a result, creatures evolve to no longer have these factors.

eg. Kiwi (birds)
Used to be able to fly, the main predator became a hawk so it was safer for the kiwi to stay in the underbrush shrubbery.
Stopped using wings, and over time the wings evolved to be smaller so that they required less energy to grow and maintain resulting in more energy going to the Kiwi's growth, reproduction and survival.


Stabilising Selection
Def + example

a type of natural selection in which the population mean stabilises on a particular non-extreme trait value to select against extreme values of the character, leading to a decrease in genetic diversity.

eg. Human babies
most are born 3-4kg
too light or too heavy and they can't survive.


Directional Selection
def + example

a mode of natural selection in which a single phenotype is favoured, causing the allele frequency to continuously shift in one direction.

eg. Darwin's Finch (bird)
over time evolved different shaped/sized beaks to accommodate different diets.


Disruptive Selection
def + example

changes in population genetics in which extreme values for a trait are favoured over intermediate values.

eg. Giraffe's necks
If giraffe were all average height then there would not be enough food to go around. Thus over time they evolved to be either very short or very tall.


Sexual Selection
def + example

a special type of natural selection in which the sexes acquire distinct forms either because the members of one sex choose mates with particular features or because in the competition for mates among the members of one sex only those with certain traits succeed.

eg. Male Peacocks
Female peacocks choose the prettiest male peacock, the one with the biggest and most colourful tail. As a result, the male peacocks evolved to have large colourful tails


Artificial selection
Def + example

The selective breeding of plants and animals to produce desirable traits.

eg. Humans selective breeding of dogs for traits they find cute eg. short ears, squashed face.


Genetic Drift
def + types (2)

RANDOM changes in allele frequencies within a population due to CHANGE

Bigger population = less effect genetic drift has
Smaller population = more effect

Bottle neck effect
Founder effect


Bottle neck effect
def + example

Catastrophic event leaves only a few survivors due to chance
-allele frequency may not be representative of initial/original population.

eg. Lots of orange cats in a population, fire occurs and only 10% of the remaining population is orange furred.


Founder Effect
def + example

Small group inhabit a new area, allele frequency is not representative of the original population.

eg. Lots of orange cats in a population, a few cats branch off and start a new colony which only contains 10% orange cats.