Week Three Review Notes

Question 1

Define Gene.

Answer 1

A heritable factor that controls a specific characteristic.

Question 2

Define allele.

Answer 2

A specific form of a gene (e.g., blue or brown eye color).

Question 3

What are linked genes?

Answer 3

Linked genes are genes that are located on the same chromosome and are inherited together — unless crossing over happens.

They do not follow Mendel’s law of independent assortment because they’re “linked” — physically close to each other on the chromosome.

Question 4

What are polygenic traits?

Answer 4

🌈 Polygenic traits:

Controlled by more than one gene.
Show continuous variation (like height, skin color).
More genes involved = smoother range of phenotypes.

Question 5

🟪 Q8: Why do males more often show sex-linked traits?

Answer 5

🟩 A: Males only have one X chromosome, so any recessive allele will be expressed.

Question 6

🟪 Q15: How can the environment influence gene expression?

Answer 6

🟩 A: Environmental factors like sunlight, diet, or temperature can affect how genes are expressed.

Question 7

What is gel electrophoresis?

Answer 7

✅ Gel Electrophoresis:

Technique used to separate fragments of DNA based on size.

DNA is negatively charged, so it moves through a gel matrix (usually agarose) towards the positive electrode.

Smaller fragments move faster and farther than larger ones.

Question 8

What is DNA profiling?

Answer 8

✅ DNA Profiling:

1. Collect DNA sample (blood, hair, saliva)
2. Extract and amplify the DNA using PCR
3. Separate DNA using gel electrophoresis
4. Compare DNA patterns to identify individuals

• Compares non-coding regions of DNA (short tandem repeats or STRs) between individuals.
• Used in forensics, paternity tests, and evolutionary studies.

Question 9

What is PCR?

Answer 9

🔁 PCR – Polymerase Chain Reaction
Technique to make millions of copies of a specific DNA segment.
Mimics DNA replication in a test tube!
🧪 Steps:

Denaturation (95°C) – DNA strands separate.
Annealing (50–60°C) – Primers bind to target DNA sequence.
Extension (72°C) – Taq polymerase builds new strands.
✅ Useful for forensic science, diagnostics, ancient DNA analysis, etc.

Question 10

What are pros and cons behind the ethical concerns of genetic engineering?

Answer 10

🧠 Pros:

Cures for genetic diseases.
Improved crop yields and nutrition.
Cloning endangered species or organs for transplants.
⚠️ Cons:

Unknown long-term effects on ecosystems and health.
Loss of genetic diversity in cloned populations.
Animal welfare concerns in cloning.
Ownership of genetic information and GM technology (big companies, patents).

Question 11

What is the evidence for evolution?

Answer 11

• fossil record
• homologous structures
• DNA evidence
• Biogeography

Question 12

What is a homologous structure?

Answer 12

Structures that are similar in different species due to common ancestry, even though they may serve different functions.
Examples: The limbs of humans, whales, and bats all have the same bone structure (humerus, radius, ulna) but function differently (grasping, swimming, flying).

Question 13

What is natural selection?

Answer 13

The process where organisms with favorable traits (those better adapted to the environment) survive and reproduce more successfully than others.

Question 14

What are the key principles of natural selection?
- Darwin’s observations leading to natural selection

Answer 14

1.Variation exists in a population.

2. There is competition for resources.
3. Some individuals have traits that make them better suited to the environment (these are the “favorable” traits).
4. Survival and reproduction of the best-adapted individuals pass on these traits to the next generation.

Question 15

What are 3 sources of genetic variation?

Answer 15

• Mutation: Random changed in DNA create new alleles
• Meiosis: Crossing over and independent assortment shuffle genes
• Sexual Reproduction: Combines alleles from two parents creating unique offspring.

Question 16

What is speciation?

Answer 16

Speciation is the process by which one species splits into two or more new species.

This can happen through mechanisms like:
Geographic isolation: Physical barriers (e.g., mountains, rivers) separate populations, preventing gene flow. Over time, genetic differences accumulate, leading to speciation.

Reproductive isolation: Even when populations come into contact again, they may not interbreed because of differences in mating behavior, timing, or morphology.

Question 17

What is allopatric speciation?

Answer 17

Occurs when populations are geographically isolated.

Question 18

What is sympatric speciation?

Answer 18

Occurs when populations diverge in the same geographical area due to factors like dietary preferences, mating preferences, or polyploidy (in plants).

Question 19

What is the acronym for the classification system?

Answer 19

Dear King Phillip Comes Over For Good Soup

Question 20

What is cladistics?

Answer 20

Cladistics is a method used to classify organisms based on shared characteristics that come from a common ancestor.

Question 21

What is the correspondence theory?

Answer 21

Evolution is true because it is based on observed facts.

Question 22

What is the cohernence theory?

Answer 22

Evolution aligns with established scientific knowledge.

Question 23

What is the Hardy Weinberg principle?

Answer 23

A mathematical model that predicts allele and genotype frequencies will remain constant in a population if no evolution is occurring.

🧪 Equation:

p+q=1
Where:

p = frequency of dominant allele (A)
q = frequency of recessive allele (a)
Genotype frequency:

p² = frequency of AA
2pq = frequency of Aa
q² = frequency of aa

Question 24

What is the difference between p and p^2?

Answer 24

p

🔹 p = allele frequency

Specifically, the frequency of the dominant allele (let’s say A) in the gene pool.
It’s not a percentage of individuals — it’s a proportion of alleles in the population.
👉 For example, if 40% of all alleles in the population are A, then:

0.4
p=0.4

🔹 p² = genotype frequency

Specifically, the frequency of individuals who are homozygous dominant (AA).
It tells you what fraction of the population has the AA genotype.
👉 So, if p = 0.4, then:

p2=0.16
That means 16% of the individuals in the population are AA.

Question 25

Conditions needed for Hardy Weinberg Principle.

Answer 25

1. Large population size 2. Random mating 3. No mutations 4. No gene flow (immigration/emigration) 5. No natural selection if any of these happen then evolution occurs

Question 26

What is a gene pool?

Answer 26

✅ Gene Pool: The total collection of alleles in a population at a given time. Evolution = change in allele frequency in a gene pool.

Question 27

What is a genetic drift?

Answer 27

✅ Genetic Drift: Random change in allele frequencies, especially in small populations. Leads to reduced genetic variation. Unlike natural selection, it's not driven by environmental advantages.

Question 28

What is a limiting factor?

Answer 28

An environmental factor that restricts population growth. Density Dependent: Disease, competition, predation Density Independent: Natural disasters, climate events

Question 29

What is carrying capacity?

Answer 29

The maximum population size that the environment can sustainably support. Represented as a plateau on the logistic (S) curve.

Question 30

What is ecological succession?

Answer 30

The natural, gradual change in the types and numbers of species in an ecosystem over time. Primary succession: Bare land (no soil) Lava flow, glacier retreat Secondary succession: Existing soil (after disturbance) Forest fire recovery

Question 31

What are the key stages of succession?

Answer 31

🔄 Key stages: Pioneer species (e.g., mosses, lichens) Grasses and small plants Shrubs and trees Climax community – stable, mature ecosystem ✅ Biodiversity increases with succession!

Question 32

What are the two types of conservation strategies?

Answer 32

In situ; Protect species in their natural habitat ex. National parks, nature reserves Ex situ; Remove species from the wild for protection ex. Zoos, seed banks, captive breedin

Question 33

What is the 10% rule for trophic levels?

Answer 33

10% Rule: Only about 10% of energy is passed on to the next level. The rest is lost as heat through respiration, excretion, or uneaten material.

Question 34

What are the key processes of the carbon cycle?

Answer 34

Key processes: - Photosynthesis: Plants absorb CO₂ to make sugars. - Respiration: Organisms release CO₂. - Decomposition: Dead organisms release carbon. - Combustion: Burning fossil fuels releases CO₂. - Fossilization: Dead organisms → fossil fuels. 🌍 Increased CO₂ from human activity → major contributor to climate change.

Question 35

What are the key processes of the nitrogen cycle?

Answer 35

Key processes: Nitrogen fixation – Bacteria convert N₂ → ammonia. Nitrification – Ammonia → nitrites → nitrates. Assimilation – Plants absorb nitrates. Denitrification – Bacteria convert nitrates → N₂ (back into atmosphere). Decomposition – Returns nitrogen to the soil. 🧠 IB tip: Plants can’t absorb nitrogen gas (N₂) — they rely on bacteria to convert it.

Question 36

What is the greenhouse effect?

Answer 36

Sunlight passes through the atmosphere, hits Earth, and some is radiated back as infrared (heat). Greenhouse gases absorb some of this heat and trap it, keeping Earth warm. Gases: carbon dioxide, methane, nitrogen

Question 37

What is the negative impact of humans on ecosystems?

Answer 37

🚫 Negative impacts: Deforestation → habitat loss, more CO₂ Pollution → air, water, soil degradation Overfishing → collapse of food webs Invasive species → outcompete native species Climate change → shifts ecosystems and species distributions

Question 38

What are postive strageties to help ecosystems?

Answer 38

✅ Positive strategies: Protected areas (national parks, reserves) Captive breeding & reintroduction Habitat restoration Sustainable farming & fishing Legislation & international agreements (e.g., Paris Agreement)

Question 39

What is short wave radiation?

Answer 39

Comes from the Sun 🌞 Includes visible light, ultraviolet (UV), and some infrared. Has a high frequency and high energy. Passes easily through Earth’s atmosphere. ➡️ This is the energy that heats Earth’s surface!

Question 40

What is long wave radiation?

Answer 40

Emitted by Earth’s surface 🌍 (after it absorbs sunlight). Mostly infrared radiation. Has a lower frequency and less energy than short-wave radiation. ➡️ This is the heat that Earth tries to radiate back into space, but ends up trapping it in the atmosphere.

Question 41

What is recombination?

Answer 41

Happens during prophase I of meiosis via crossing over. Creates new allele combinations (recombinants) not found in the parents. Recombination frequency is used to map genes on a chromosome.

Question 42

What is gene knockout therapy?

Answer 42

A method to turn off a gene to study its function. CRISPR 1. Guide RNA directs Cas9 to the target gene. 2. Cas9 enzyme cuts the DNA 3. Cell repairs DNA, either deactivating or modifying the gene

Question 43

What are pathogens?

Answer 43

Pathogens are organisms or viruses that cause disease. Include: bacteria, viruses, fungi, protozoa, and parasites. Diseases are caused when pathogens disrupt the normal physiology of infected organisms.

Question 44

What are the first line of defense barriers?

Answer 44

Skin: Physical barrier; produces sebum, which lowers pH (hostile to microbes). Mucous membranes: Found in trachea, vagina, urethra, etc. Trap pathogens; cilia help sweep them out. Other secretions: Tears (lysozyme), saliva, and stomach acid destroy or inhibit pathogens.

Question 45

What is the second line of defense?

Answer 45

Phagocytic white blood cells (e.g. macrophages) engulf pathogens via phagocytosis. Inflammatory response: Swelling, redness, heat, and pain caused by increased blood flow and immune activity. Production of antimicrobial proteins and fever as systemic responses.

Question 46

What is the third line of defense?

Answer 46

Lymphocytes (white blood cells) involved: B cells: Produce antibodies. Helper T cells: Activate B cells. Cytotoxic T cells: Kill infected cells.

Question 47

What are antibodies?

Answer 47

Produced by plasma cells (activated B cells). Each antibody is specific to an antigen (a marker on the surface of a pathogen). Antibodies work by: Neutralization: Binding to toxins/pathogens. Agglutination: Clumping pathogens together for easy removal. Activation of complement system: A cascade that helps destroy pathogens.

Question 48

What is neutralization?

Answer 48

Binding to toxins/pathogens

Question 49

What is agglutination?

Answer 49

Clumping pathogens together for easy removal

Question 50

What does a vaccine do?

Answer 50

Introduces a weakened or inactivated form of the pathogen/antigen. Stimulates primary immune response without causing illness. Leads to memory cell formation for a rapid secondary response if exposed in the future.

Question 51

What are antibiotics?

Answer 51

Work only against bacteria, not viruses. Interfere with bacterial processes like cell wall synthesis, protein synthesis, or DNA replication.

Question 52

What happens in the body after an infection or vaccination?

Answer 52

Memory B cells remain in the blood and recognize antigens quickly. Memory T cells provide long-term immunity by rapidly activating the immune system if the pathogen is detected again.

Question 53

What is an autoimmune disease?

Answer 53

The immune system attacks the body’s own self-antigens. Examples: Type 1 diabetes – attacks insulin-producing cells. Rheumatoid arthritis – attacks joints.

Question 54

What are allergies?

Answer 54

Hypersensitive response to non-harmful antigens (allergens). Involves mast cells releasing histamine. Symptoms: inflammation, sneezing, itching, asthma, etc. 🧪 Antihistamines block histamine receptors → reduce allergy symptoms.

Question 55

What is the function of histones?

Answer 55

Condesation of DNA, regulate gene expression, help with DNA repair and regulation

Question 56

What is trisomy 21 and how is it caused?

Answer 56

Trisomy 21 is caused by a chromosomal abnormality where a person has three copies of chromosome 21, instead of the usual two. - 🧬 Trisomy 21 (Down Syndrome) is caused by non-disjunction during meiosis, resulting in an extra copy of chromosome 21 in the zygote.

Question 57

What is adaptive radiation?

Answer 57

Adaptive radiation is the rapid evolution of many different species from a common ancestor, each adapted to a different niche.

Question 58

What is facultative anaerobe?

Answer 58

These organisms can survive with or without oxygen. Prefer to use aerobic respiration when oxygen is present (more ATP!). But if there’s no oxygen, they can switch to anaerobic respiration or fermentation. ✅ Super flexible! 🧫 Example: E. coli (common gut bacteria)

Question 59

What is an obligate anaerobe?

Answer 59

These organisms cannot survive in the presence of oxygen. Oxygen is actually toxic to them. They rely only on anaerobic processes like fermentation. ⚠️ Oxygen = danger! 🧫 Example: Clostridium botulinum (causes botulism)

Question 60

What is an obligate aerobe?

Answer 60

These organisms require oxygen to survive. They use aerobic respiration to generate ATP — no oxygen = no energy = no life. 🧫 Example: Most animals (including humans!) and Mycobacterium tuberculosis

Question 61

What is a saprotroph?

Answer 61

🍄 Saprotroph A saprotroph is an organism (usually fungi or bacteria) that: Externally digests dead organic matter. Secretes enzymes onto the material to break it down. Then absorbs the nutrients. 🧪 Example: Mushrooms growing on rotting logs. ✅ Key trait: digestion happens outside the body before absorption.

Question 62

What is a detrivore?

Answer 62

A detritivore is an organism that: Ingests dead organic matter (detritus) into its body. Then digests it internally using enzymes in its gut. 🧪 Example: Earthworms, woodlice, some crabs. ✅ Key trait: digestion happens inside the body after eating.

Question 63

Explain the role of enzymes in DNA replication?

Answer 63

(1) Helicase unwinds the DNA double helix by breaking hydrogen bonds between base pairs. (1) DNA polymerase adds new nucleotides to the template strand, forming complementary strands. (1) Primase adds short RNA primers to provide a starting point for DNA polymerase. (1) DNA ligase joins Okazaki fragments on the lagging strand. (1) Replication is semi-conservative — each new DNA molecule has one old strand and one new strand.