evolution

mutation

permanent change in an organisms dna. this can cause a gene to code for a different protein/ trait. they occur without known cause - mutagens can increase rate at which they occur

somatic and germline mutation

somatic occur in single body cell and cannot be inherited as only tissue derived from mutated cell effected. cancer/ tumour

germline mutations occur in gametes and can be passed onto offspring where every cell in the entire organism is affected. pku

point mutation - subsitution

mutation that may create either a silent, missense or nonsense mutation depending on how change impacts polypeptide sequence

silent mutation occur when the dna change does not alter the amino acid sequence of polypeptide

missense mutation occur when dna change alters a single amino acid - sickle cell anemia

nonsense mutation occur when dna change creates a premature stop codon which truncuate polypeptide - cystic fibrosis

frameshift mutation - insertion or mutation

addition or removal of a single base of dna changing reading frame. this change affects every codon beyond point of mutation and thus may dramatically change amino acid sequence. hence, frameshift mutation typically have significant impact on cellular activity as there is a high likelihood the polypeptide will cease to function

chromosomal mutation - large scale insertion, duplication, deletion, inversion, translocation

changes to segment of chromosome resulting in large scale changes in dna of organism

non disjunction

chromosomes fail to separate correctly, resulting in gametes with one extra or missing chromosome (aneuploidy)

failure of chromosome separation occur via failure of homologues to separate in anaphase 1 or failure of sister chromatids to separate in anaphase 2

mutagen examples

mustard gas, formaldelhyde, ionising radiation like uv, xray, cosmic ray. radiaction from radioactive waste.

if a pregnant woman treated with a large dose of x ray in the first 3 months the baby may be born with intellecutal disability, skeletak malformation, microcephaly

evolution

change in allele frequency in populations over time.

the phenotypes of individuals are a result of genotype of each trait

causes of evolution

genetic mutation, gene flow, sexual selection, decreasing population

natural selection - random

gene flow

movement of alleles from one population to another through processes like migration or interbreeding. between adjoining groups the amount of genetic exchange can increase so populations become more genetically similar as alleles mix or decrease or stop which means populations diverge genetically and may eventually lead to speciation

sexual selection

species choose mate based on arbitary factors

example of bottleneck

island of pingelap suffered population bottleneck in 1775 following typhoon reducing the population to 20 people. as a result complete achromatopsia has current rate of occurrence at roughly 10% with additional 30% being carriers of recessive condition

founder exmaple

amish community in pennsylvania have high rates of certain inherited disorders like ellis van creveld syndrome

natural selection

non random selection of random variations which occur via mutations

charles darwins 3 assumptions

1. variation: all members of a species vary. these variations were passed on from one generation to the next.

2. birth rate: all living organisms reproduce at a rate far greater than that at which their food supply and other resources increase leading to overcrowding and competition

   1. natures balance: although birth rate of organisms was very high, each species numbers tended to remain at a relatively constant level

selection pressures

environmental factors that influence survival and reproductive success of organisms. favour certain phenotypes over others leading to changes in allele frequency within a population over time

reduce variation making population more susceptible to extinction or limiting adaptive potential.

in small population genetic drift can override natural selection

predator, availability of resurces, nutrient supply, disease/ pathogen spread, abiotic factors - temp, c02 levels

principal of evolution

variation: there is variation of characteristics within a species

overpopulation: more offspring of a species are produces than can possible survive to maturity

competition: there is a struggle for existence some will not survive to reproduce

survival of the best fit: individuals with characteristics best suited to that environment have more chance of surviving and reproducing due to selection pressures

inheritance: favourable characteristics are passed onto next generation

change in allele frequency: in the gene pool the proportion of alleles that produce favourable characteristics gradually increase

explain how a feature would have become more common in the population over time (7)

1. variation in presence of —- would have existed in the population

2. there would be a struggle for existence in —- due to more offspring being produced than can survive to maturity

3. those with —- would have been able to —-

4. and would have survived selection pressures and reproduce due to survival of the fittest

5. passing on allele for —- to offspring

6. those without —- wouldve died or failed to reproduce

7. so over time the population would become more alike with —-

population

group of organisms of the same species living together in a particular place at a particular time

gene pool

sum of all alleles in a given population

mutant

organism with a characteristic resulting from mutation

genetic drift

random change in allele frequencies within a populations gene pool overtime due to chance events. non selective mechanism of evolution and doesnt depend on alleles advantage or disadvantage. fixation means allele reaches 100%

more significant in small populations beause each individual allele make up a larger population of gene pool and can lead to loss or fixation of alleles over time. in large pop allele frequencies change more slowly as random fluctuations have less impact

founder effect

type of genetic drift that occurs when a small group of individuals become isolated from a larger population and form a new population. may have reduced genetic variation and a gene pool not representative of original population

bottleneck effect

form of genetic drift that happens when a large population suddenly reduces in size due to a catastrophic event. surviving population has reduced genetic variation and may not represent original gene pool

allele frequency

proportion of specific allele among all alleles for a gene in a population

speciation

evolutionary process in which there is a formation of new species due to genetic divergence. often thru isolation or selection pressures

species

breeds that produce fertile offspring

heterozygous advantage sample answer

1. heterozygous individuals for —- have survival advantage

2. in populations where —- is present

3. homozygous individuals for —- will likely die of —-

4. homozygous normal individuals will likely die of —-

5. heterozygous individuals are more likely to survive to reproduce ensuring allele remains in the gene pool

sickle cell anaemia

single gene mutation that gives red blood cells an abnormal shape which gives resistance to malaria as it is caused by an endoparasite which reproduces inside rbc

in areas with common malaria there is higher incidence of people who are heterozygous. these invididuals produce enough normal blood cells to avoid the more severe affects associated with sca but also produce enough sc to confer an increased resistance to the malarial parasite.

leading to pain, anaemia, and organ damage.

barriers

geographical - river, mountain, lake canyon

reproductive - mating patterns

temporal barriers (time) nocturanl, seasons

anatomical barrier - sex organs are incompatable

physiological - sperm and egg incomptabilbe

fixation

100% of individuals in the population have the same allele meaning there is no variation left at that gene locus

Describe how isolation, in conjunction with natural selection, can lead to new species forming through the process of speciation

Speciation occurs when a population is split by a barrier (geographical or reproductive). Isolated groups experience different mutations and selection pressures, causing divergence in allele frequencies. Over time, accumulated differences result in reproductive isolation, meaning they can no longer interbreed to produce fertile offspring. This defines them as separate species.

symptoms and causes of a thalassemia

Caused by deletions or mutations in α-globin genes, resulting in reduced α-globin production. Symptoms include anaemia and fatigue

symptoms and causes of b thalassemia

Mutation in the β-globin gene reduces β-globin production, causing severe anaemia and bone deformities.

symptoms and causes of tay sachs

Caused by a mutation in the HEXA gene, leading to accumulation of fatty substances in the brain. Symptoms include neurodegeneration and early death.

Explain why, in some gene pools, the frequency of the alleles for sickle-cell anaemia, α thalassemia, β thalassemia and Tay-Sachs is affected by the different mortality rates of homozygous and heterozygous individuals

In some cases, heterozygous advantage maintains harmful alleles in the gene pool. For example, individuals with one sickle-cell allele (heterozygotes) are resistant to malaria, giving them a survival advantage in regions with high malaria rates. Homozygous individuals often die young, but because heterozygotes survive and reproduce, the allele remains common in the population.

Discuss the risks, ethical issues and benefits associated with storing genetic information (informed consent, confidentiality/privacy, ownership/access)

• Benefits: Allows early detection of genetic conditions, personalized medicine, and informed reproductive choices.

• Risks: Potential misuse of data by insurance companies or employers.

• Ethical issues:

  • Informed consent: Individuals must fully understand how their data will be used.

  • Confidentiality/privacy: Genetic data must be securely stored and protected.

  • Ownership/access: Debate over whether individuals, governments, or companies own genetic data.

dna replication

copies whole genome once

1. unzipping: enzyme helicase opens up double strand of dna helix

2. annealing: millions of different rna primers produced by primase bind throughout genome and prime the copying process by annealing a small primer to the exposed base

3. elongation: copy dna using enzyme dna polymerase to catalyse the polymerisation of individual nucleotide bases

polymerase chain reaction

artificial method of replicating dna under lab conditions. technique used to amplify large quantities of a specific sequence of dna from an initial minute sample

each reaction cycle doubles the amount of dna. standard pcr sequence of 30 cycle create over 1 billion copies

pcr components

dna sample, primers, nucleotides, taq polymerase, pcr tube

pcr process

1. denaturation: open up double strand of dna helix by melting strands apart. heat test tube to 94-96

2. annealing: primers bind to the exposed bases of single dna strand. test tube 50-60

3. elongation: enzyme taq polymerase from hot spring extremophile to catalyse the polymerisation of individua nucleotide bases with complimentary nucleotides to the sections originating with a primer

4. repeat process 30-40 times to make 2^30-40 copies of one gene

gel electrophoresis

technique to separate dna strands based on their lengths. results in pattern of bands which are individuals dna profile/ dna fingerprint

gel electrophoresis process

1. dna sample amplified via pcr and cut with restriction enzymes into different lengths (re cut at specific recognition sites so unique length between individuals due to eveyrone having unique genome)

2. dna pieces placed in well in semi solid gel immersed in a solution of electrolytes as a buffer solution

3. electrodes at either end of gel with negative close to dna and positive on the opposite side to dna

4. electric current passes through gel, negatively charged dna moves towards positive electrodes

5. smaller dna pieces move faster than larger ones and are located further from negative electrodes when current is stopped

paternity test

child receive 50% of dna from mum and 50% from dad. every band in child profile needs to appear in either parent. if a band appears in childs dna and doesnt correspond to suspected mother/father it rules out the male as the father

phylogenic trees

diagram that represents the evolutionary relationships among a group of organisms. it visually depicts how different species are related to each other through a shared ancestry showing how they diverged over time

a node represents speciation and a root represents a common ancestor

mrca: most recent common ancestor

bioinformatics

comparing the amino acids sequencing of an ubiquitous protein (found in all living organisms) can assist in building a phylogenetic tree and determining the relationship between organisms (most recent common ancestors

comparative genomics

the complete set of dna in each cell of an organism called the genome

comparative genomics compares genome sequences of different species revealing a high level of similarity between closely related organisms such as humans and chimpanzees

endogenous retroviruses

erv are remnants of ancient retroviral infections that have integrated into the germline dna of their hosts and are passed down through generations, evolving over time to become part of the host genome

the patterns of erv insertions, shared by related species at specific chromosomal locations, provide strong evidence for common ancestry