Genetic Variation

DNA

Made out of nucleotides, that bond together to create a double helix structure. Contains Nitrogen base pairs, deoxyribose sugar and phosphate molecule. Is anti parallels.

Chromosomes

Made from tightly coiled DNA. Each cell contains a copy of all the organisms chromosomes. Made out of 2 chromatids joined at the centromere.

Karyotype

Set of all the chromosomes in an individual. Chromosome replicates in order for cells to divide so each cell has a karyotype.

Homologous pairs

The chromosomes that have the same genes pair up together.

Gene

A section of DNA that codes for a particular proteins that is responsible for a particular trait.

Allele

Different forms of the same gene (slightly different base sequence) caused by mutations

Autosomes

non sex chromosomes

sex chromosomes

x (female) and y (male) chromosomes that code for sex

Genetic Variation

Differences in the genetic code amongst a population due to: mutations, sexual reproduction, feralization and enviroment

Mutation

Permanent change to the base sequence in a gene. Mutations can be spontaneous or induced by a mutagen such as: UV light, radiation, chemicals, drugs, alcohol, fatty/sugary food.

Silent mutations

a mutation that has no observable effect on the organism

Harmful mutations

a mutation that negatively affects the survival of an organism

Positive mutations

a mutation that provides a trait that is benefitable to the organisms survival.

Non Inheritable mutations

if a mutation occurs in a somatic cell (hair, skin, etc..) then it can't be passed on to the next generation.

Inheritable mutations

If a mutation occurs in a gametic cell (sperm, ova) then the mutation can be passed on to the next generation assuming the cell was involved in feralisation of a zygote.

Chromosome (block) mutations

changes to large sections of chromosomes. (deletion, duplication, translocation, inversion)

Gene (point) mutation

changes in the base sequence of a gene. (insertion, deletion, substitution)

Sexual reproduction

Reproduction of an offspring involving 2 genetically unique gametes which are formed through the process of miosis. It reproduces by combining the genetic information of 2 individuals

Sexual Reproduction Speed

usually slower, as the gametes takes time to meet (looking for mate) and to grow into an organism.

Sexual reproduction variation

There is lots of variation due to miosis as homologous chromosomes go through the process of crossing over and independent assortment which creates genetically unique gametes. Fertalisation increases variation due to the random chance of gametes meeting.

sexual reproduction pros

provides genetic variation meaning an organism can adapt to new environments better and disease is less likely to wipe out a population.

sexual reproduction cons

It tales more time and energy to reproduce. Uncertainty about what traits are passed on. Not possible for an isolated individual to reproduce.

Asexual reproduction

reproduction of an offspring that does not involve the fusion of 2 games. It reproduces by 1 individual, producing an exact copy of itself.

asexual reproduction speed

usually faster as only 1 parent is needed.

asexual reproduction variation

there is no genetic variation as the offspring is a complete clone of its parents.

asexual reproduction pros

Population can increase rapidly as it is more efficient (uses less time and energy) so is faster. Good for knowing the exact traits an offspring will have.

asexual reproduction cons

there is no genetic variation meaning the species will not be able to adapt easily to change. Diseases may wipe out entire populations.

Mitosis

Type of cell division where a cell replicates and makes 2 identical copies (occurs in somatic cells). Useful for growth, repair of damage, replace worn out cells.

Mitosis process

interphase, prophase, metaphase, anaphase, telophase, cytokinesis

Interphase

DNA condenses into the chromosomes

Prophase

DNA and chromosomes replicate. Proteins break apart nucleus with enzymes.

Metaphase

chromosomes line up along equator in single file "independent assortment". Spindle fibers form from the cells and attach to centrome.

Anaphase

Spindle fibers pull replicated chromosomes apart

Telophase

Nucleus reforms and cell pinches in the middle.

Cytokinesis

cell divides creating 2 identical daughter cells

Meiosis

Type of cell division (reduction) where a cell produces 4 unique gametes. Occurs in ovaries' (females) and testes or stamen antha (males) to produce eggs (female) and sperm (male) Gametes only have half the chromosomes (haploid), so when 2 join together in feralisation the combined DNA forms the total amount of chromosomes (diploid.)

Meiosis process

Interphase, Prophase 1, Metaphase 1, Anaphase 1, Telophase 1 / cytokinesis 1 / prophase 11, Metaphase 11, Anaphase 11, Telophase 11, Cytokinesis 11

Interphase

DNA condenses into the chromosomes

Prophase 1

DNA/chromosomes replicate. Proteins break apart nucleus membrane using enzymes.

Metaphase 1

Homologous chromosomes exchange sections of DNA "crossing over" Chromosomes line up in pairs along cells equator and spindle fibers attach (independent assortment)

Anaphase 1

Homologous chromosomes get pulled apart

Telophase 1 / cytokinesis 1 / prophase 11

Cell pinches and divides creating 2 unique cells. New spindle forms.

Metaphase 11

Chromosomes randomly line up at equator and spindle fibers attach (independent assortment)

Anaphase 11

Spindle fibers pull unique chromatids apart

Telophase 11

nucleus reforms around chromosomes and cell pinches in the middle

Cytokinesis 11

Cell divides creating 4 unique daughter cells (gametes) called segregation.

Independent assortment

homologous chromosomes line up randomly at the cells equator (not all maternal or paternal on the same side). Its random what orientation the chromosomes line up in.

Crossing over

Non sister chromatids touch at a random location/s. The location is called a chiasma. The sections of the chromosomes swap over causing the alleles in these chromosomes to shuffle. Crossing over only occurs in one chromatid not both.

Segregation

Where the cell divides each cell receives a different combination of alleles. This is due to independent assortment and crossing over.

Feralisation

Meiosis leads to the production of gametes that are genetically different from each other. When a sperm fertilises an egg, it forms a single diploid cell zygote.

Fertilisation Variation

it is completely random which egg has been released and which sperm will fertilise it

Environmental Variation

can impact variation without changing genetic make up: diet - size and health, sun - skin tone, tattoos, piercings etc.

Phenotype determination

determined my both your genotype and the environment.

Dominant allele

An allele that only requires one copy to be present in order to show up in a phenotype.

Recessive allele

the allele that requires two copies present in order to show up in the phenotype

Homozygous

a genotype that has 2 alleles that are the same (bb, BB).

Heterozygous

A genotype that has 2 different alleles (Bb)

Genotype

The combination of alleles present in a trait for an individual (BB, Bb, bb)

Phenotype

The physical / observable expression of a genotype

Monohybrid Inheritance

inheritance for only one gene

monohybrid cross

crossing of 1 gene where there is only 2 possible alleles/gametes per parent

Punnet squares

A prediction of how offspring will inherit alleles. They show only the probability of what might occur and not what actually happens.

Conditionality

Each feralisation is not conditional to the last. What the last offspring inherits has no effect on the next offspring and are independent to each other.

Pure breading

there is no variation in the trait being studies. Homozygous are bure bread as they receive the same 2 alleles (BB, bb). Heterozygous are not pure bread as they receive 2 different alleles.

Test cross

helps determine the genotype of a dominant phenotype by beading the unknow individual with a homozygous recessive individual.

Test cross results

If any offspring are recessive, you know for certain that the individual is heterozygous as it must have contributed a recessive allele. If you see a dominant phenotype you will need to continue breeding more times. You can't be 100% sure it is pure bread as it may just by chance only be passing on the dominant allele.

Pedigree chart

a diagram that shows the occurrence and appearance of a certain gene across multiple generations.

circle

female

square

male

coloured

dominant trait

colourless

recessive trait

Roman Numerals

represents generations

horizontal line

mating pairs

vertical line

represents offspring. Siblings are connected with short vertical lines from a horizontal line.

Complete dominance

when the dominant allele completely masks the effect of a recessive allele

incomplete dominance

when the dominant allele does not completely mask the effect of the recessive allele. The result is a heterozygous individual with a combination of the dominant and the recessive allele (an intermediate phenotype)

Co-dominance

When a single gene has more than one dominant allele that are both equally expressed in a heterozygous individual.

Multiple alleles

Genes can have more than 2 different alleles. Some of these alleles can show complete dominance, incomplete dominance or co-dominance.

Lethal Alleles

An allele that produces a phenotype that causes death of an organism. Usually caused by a mutation in an important gene, meaning the protein it codes for can't be produced. These can be completely dominant, incompletely dominant and co dominant.

Lethal Allele phenotype

if a lethal allele kills and individual before birth, then we do not include it in the phenotype. Expected 3affected:1unaffected. Actual 2affected:1unaffected

dihybrid cross

a cross of 2 genes

dihybrid genotype ratio

1:2:1:2:4:2:1:2:1
1 BBCC : 2 BBCc : 1 BBcc : 2 BbCC : 4 BbCc : 2 Bbcc : 1 bbCC : 2 bbCc : 1 bbcc

Dihybrid phenotype ratio

9:3:3:1
9 dominant-dominant : 3 dominant-recessive : 3 recessive-dominant : 1 recessive-recessive

Dihybrid test cross

determines the genotype of an unkown phenotype by breeding the unknown individual with a homozygous recessive for both traits.

Unlinked genes

genes that are located on different chromosomes.
genes that are located on the same chromosome but are far away from each other.
often not inherited together as separated during miosis.

Linked genes

genes that are located on the same chromosome and are very close together.
often inherited together as not separated during miosis

Dihybrid cross with unlinked genes

9 BE : 3 Be : 3 be : 1 be
recombinants are more likely to form as chiasma is likely to form between them.
genetic variation is higher as alleles shuffle more

Dihybrid cross with linked genes

9 BE : 1 Be : 1 bE : 5 be
Recombinants forming is very unlikely due to the chiasma occurring right between the genes is unlikely.
This leads to a higher chance of producing gametes with be & BE alleles and a lower chance of producing gametes with Be & bE alleles.
The genetic variation is lower as the offspring has a higher chance of looking like parent BE or be

dihybrid cross with linked genes - variation

Independent assortment will not shuffle the 2 alleles as the are located on the chromosome so won't matter which way they line up.
Crossing over is very unlikely to separate the alleles if they are locates close together on the chromosome. To separate them crossing over must occur right between these 2 linked genes which is unlinked.

Evolution

the change in characteristics of living things over a long period of time

Natural selection

The mechanism behind the theory of evolution. Natural selection is the process where individuals that have features that support survival are more likely to live on to a reproductive age, pass on their alleles and increase in number. Where the individuals with unfavorable traits are more likely to die out.

genetic diversity

the range of all the different alleles in a populations gene pool. The overall variation in a populations gene pool.

Selectional pressure

An abiotic or biotic environmental factor that affects the survival of an individual and therefore influences its reproductive success.

survival of the fittest

the individuals that have beneficial features allow them to be more fit in there environment. This allows them to survive and individuals with beneficial features (fitter) increase in numbers while individuals with non beneficial features (unfit) will eventually die out. This is how species change over time.

Genetic variation importance

if a population is genetically diverse, there is a more likely ability to be alleles in the population that are beneficial to survival and therefore likely to survive an environment change.

Types of selection

Favorable phenotypes will always be higher in number. Unfavorable phenotypes will always be lower in number. When this is graphed a normal distribution occurs.

Directional Secetion

when selective pressure selects against one extreme of the populations trait, the distribution shifts towards the other extreme

Stabilising selection

When selective pressure selects against the two extremes of the trait, the medium phenotypes are retained and become more common.

Disruptive selection

when sectional pressure acts against individuals in the middle of the traits distribution, it results in the 2 extremes of the curve create their own smaller curves

Artificial Selection

When humans select particular individuals from a population with certain characteristics and breed them to produce offspring with a desired trait.