Biology: Genetics & Variation

DNA

deoxyribonucleic acid: the hereditary material in organisms that contains the instructions needed for it to develop, thrive and reproduce.

genes

specific sequence of information on the DNA that codes for a particular trait by controlling the production of a particular protein

allele

alternate forms of a gene

chromosomes

thin, thread-like structures which carry genetic information. long DNA strands wrapped around a histone. comprised of two chromatids

dominant allele

an allele that expresses itself phenotypically, usually masking the recessive allele

recessive allele

an allele that only expresses itself phenotypically in the absence of the dominant allele

phenotype

the set of observable physical traits due to the genetic composition of an organism

genotype

the genetic makeup of the organism, the type of alleles inhereted

homozygous

a pair of identical alleles for a particular trait

two types of homozygous

homozygous dominant

homozygous recessive

heterozygous

a pair of two different alleles for a particular trait

progeny

descendants of a generation

the father of genetics

Gregor Mendel

dominance

one allele is expressed completely (represented by a capital letter), the other is recessive (represented by a common letter)

co-dominance

both alleles are expressed equally

incomplete dominance

neither allele is dominant over the other, there will instead be a blend.

• e.g. a red and white flower produce a pink one

variation

the phenotypic difference between individuals in a species, either due to genes inherited by parents or environmental factors

types of variation

continuous

discontinuous

continuous variation

individuals in a species have characteristics that fall within two extremes that cannot be grouped into two definite groups, instead are susceptible to change. dependent on genetics and environmental factors

• e.g. height, weight, skin colour

discontinuous variation

individuals in a species have a distinct feature that allows them to be grouped into two definite groups: presence or absence of the feature.

• these features never change

• ONLY manipulated by genetics

ways an organism can become variated

1. Random fertilization

2. Crossing over during meiosis/recombination

3. Independent Assortment

4. MUTATION

5. Environmental adaptation

mutation

changes in genes or chromosomes resulting in the formation of new characteristics in a population. they provide the environment for natural selection and formation of new species

Two types of genetic diagrams

test cross

Punnet square

Genetic test cross structure

1. Phenotype of parent

2. Genotype

3. Gametes

4. Actual test cross

5. Genotype

6. Phenotype of F1 Generation

7. Optional (percentages)

Punnet square

Contains 9 boxes

Cross goes in the top left box

Gametes go on the left and at the top

Cross

List percentages and ratios after

sex-linked traits

these are traits that are carried on the x chromosome ONLY, including STDs.

in genetic diagrams, we use the same system but we use Xs and Ys and then the capital/common letter as an exponent

true/false: men can be carriers

false

blood groups A and B are

codominant

blood group O is

recessive

speciation

the formation of a different species from existing ones

reasons for the death of a species

1. Competition

2. Invasive species

3. Natural disaster

4. Disease

reason a species stays constant in number

due to limited resources, even if large amounts of a species were created through reproduction, limited resources would cause them to die out and the population to remain constant

the 4 concepts that all species abide by

1. Morphological: they must have similar structures that differentiate them from others

2. Ecological: they must prefer the same habitats

3. Evolutionary: they must evolve from the same ancestory

4. Biological: they must have suitable gonads and gametes to reproduce to produce FERTILE offspring

all of these concepts must be met by ALL species

why aren’t hybrids considered species

because they are sterile, usually due to the number of chromosomes they have being uneven. this means they can’t create homologous pairs and thus don’t undergo meiosis

natural selection

the process by which organisms with traits that are better adapted to their environment survive and reproduce more successfully than others, leading to evolutionary changes in a population over time

selective pressure

the condition that causes organisms of a species to either adapt or die, can be natural or artificial

the person who came up with the concept of natural selection

Charles Darwin

selected for

the organisms with the favorable trait that survive and reproduce

selected against

the organisms with the unfavorable trait that causes them to die out

examples of natural selection

• sickle cell anaemia in a country with a high malaria population

• dark coloured moths surviving more than clear moths after industrialization

• antibiotic resistant bacteria becoming commonplace

artificial selection

the process by which humans create organisms with desirable characteristics (by prevention and enabling of reproduction) in horticulture, agriculture and leisure industries

advantages of artificial selection

1. Faster than natural selection

2. Produces organisms with desirable traits

3. Produces organisms resistant to disease

4. Higher quality organisms

5. Higher yield of organisms

6. Reduced production costs

Disadvantages of artificial selection

1. Poor quality of life for resulting organisms

2. May result in mutations in future generations

3. Organisms may not be able to survive in the wild

Natural vs Artificial Selection

Speed: Artificial selection is faster

Selective pressure: artificial selection’s selective pressure is humans, and natural selection is environmental conditions

Types of Organisms Produced: artificial selection produces organisms different from the natural environment, natural selection produces organisms that are biodiverse but natural

Populations: artificial selection occurs in domestic populations, natural selection occurs in natural populations

How to form a new species

By the use of pre-zygotic and post-zygotic isolation mechanisms

pre zygotic isolation mechanisms

prevent fertilization

list of prezygotic isolation mechanisms

1. Geological isolation mechanisms: physical barrier that separates organisms in a species, the organisms on each side adapt differently to survive thus producing new species

2. Behavioural: change in mating calls, courtship rituals, they won’t be interested in reproducing with one another creating two different species

3. Ecological: there is a change in habitat of the species as different organisms in the species prefer a specific habitat (e.g. land and mountain goats)

4. Temporal: they have a different breeding season

5. Mechanical: they have incompatible gonads or gametes

Post zygotic isolation

involves formation of a hybrid, fertilization occured

post zygotic isolation list

1. sterility: organism matures and it can’t breed

2. inviable: organism dies from embryonic stage

speciation can be divided into

• allopatric: physical barrier, undergoing specific adaptations on either side

• sympatric: no physical barrier, instead other things such as behaviour and mutation prevent organisms from breeding

• hybridization: hybrids formed and unable to produce gametes

genetic engineering

The process by which an organism’s genes are modified through the insertion, removal, or alteration of (foreign) genetic material.

Uses of genetic engineering

1. Medicine (produces hormones - insulin, human growth hormone, vaccines)

2. Increase agricultural yield

3. Produce GMOs (genetically modified organisms) - such as golden rice with added nutrients

4. Gene therapy - insertion of normal genes to mitigate against genetic diseases such as cystic fibrosis

donor

the organism that contains the desired gene

recipient

the organism that will receive the desired gene

restriction enzyme

an enzyme that isolates a particular gene from a strand of DNA by cutting it at specific sequences

importance of restriction enzymes and using the same for the donor and recipient

they cut at specific places to produce complementary sticky ends in the donor and recipient, allow for smooth joining of the genes from each

steps of genetic engineering

1. Restrictive enzymes cut the desired gene from the donor

2. Vector is taken out of the recipient organism, restrictive enzymes cut that too

3. The desired gene and vector are glued together using DNA ligase

4. The vector is placed back inside the recipient

5. The benefits of the genetic modification are reaped (insulin, hormones, vaccines, etc)

6. The recipient is said to be transgenic

transgenic organism

an organism containing foreign genetic material from another

advantages of genetic engineering

1. increase crop yield - stopping food shortages and boosting economies

2. increases nutritional yield - preventing deficiency

3. Creates more efficient vaccines - increases survival and resistance, longer lasting vaccines than ones that use attenuated pathogens

4. Overcomes ethical concerns of taking things from animals (insulin from pigs for example)

5. Larger quantity of drugs like insulin and human growth hormone produces - can help more people, lowers costs

Disadvantages of genetic engineering

1. Can result in poor quality of life for some organisms, as they are not able to adapt readily to the environment once released

2. Can unintentionally affect other organisms - for example humans eating genetically modified food and getting cancer

3. Plants genetically modified to be species resistant may cause other types of species that feed on them to die out, affecting the food web

4. Can be used for evil - eugenics

5. Can result in new invasive species - species may mutate to overcome resistant plants, creating new species through natural selection

6. Increased allergens in food due to genes that cause allergic reactions through transgenic genes

Ethical concerns of genetic engineering

1. Quality of life of organisms produced

2. Using it for malicious purposes - eugenics

3. Risk of GMOs to human health

4. Effect of GMOs on habitats and communities

steps of cloning

1. The nucleus of a somatic cell of an organism is placed inside an egg cell with its nucleus removed

2. The egg cell is stimulated to develop into an embryo

3. This embryo is implanted into a surrogate mother who carries the offspring

Ethical concerns of cloning

1. Quality of life of organism produced

2. Identity of clone; just seen as a clone of someone else

3. Reduces the uniqueness of populations

4. Expensive process that isn’t equally accessible to all, meaning all of that power is in the hands of very few people