Kolbe Biology Fall 2024

The definition of Biology

1. the study of living organisms, divided into many specialized fields that cover their morphology, physiology, anatomy, behavior, origin, and distribution.

   • the plants and animals of a particular area.

     "the biology of Chesapeake Bay"

   • the physiology, behavior, and other qualities of a particular organism or class of organisms.

     "human biology"

What is the basic unit of matter?

The basic unit of matter is an atom. 

What is ecology?

Ecology is the scientific study of how living organisms interact with each other and their physical environment, examining the relationships between plants, animals, and their surroundings, including factors like climate, soil, and other living things within an ecosystem; essentially, it's the study of the "economy of nature."

How does an enzyme speed up a reaction?

An enzyme speeds up a reaction by lowering the activation energy needed for the reaction to occur, essentially creating an easier pathway for the reaction to take place, allowing it to happen faster; this process is called catalysis. 

The three stages of cellular respiration (just the names of the stages)

The three stages of cellular respiration are: glycolysis, the Krebs cycle (also called the citric acid cycle), and the electron transport chain. 

Explanation:

• Glycolysis: The initial stage where glucose is broken down into pyruvate. 

• Krebs cycle (citric acid cycle): The second stage where pyruvate is further broken down, producing energy carriers like NADH and FADH2. 

• Electron transport chain: The final stage where electrons are transferred along a chain, generating the majority of ATP

Photosynthesis formula

The process of photosynthesis is commonly written as: 6CO₂ + 6H₂O → C₆H₁₂O₆ + 6O₂. This means that the reactants, six carbon dioxide molecules and six water molecules, are converted by light energy captured by chlorophyll (implied by the arrow) into a sugar molecule and six oxygen molecules, the products.

The three parts of the cell theory

The three parts of the cell theory are: all living things are composed of one or more cells, cells are the basic unit of life, and all cells come from pre-existing cells. 

Explanation:

• All living things are made of cells:

  This means that every organism, from single-celled bacteria to complex animals, is made up of one or more cells.

• Cells are the basic unit of life:

  This states that cells are the fundamental building blocks of all living organisms and carry out all necessary life functions.

• All cells come from pre-existing cells:

  This principle emphasizes that new cells are always created by the division of existing cells, not spontaneously generated. 

How much energy is produced from one molecule of glucose during cellular respiration (all three
stages)?

During cellular respiration, one molecule of glucose produces approximately 30-32 ATP molecules across all three stages (glycolysis, Krebs cycle, and electron transport chain). 

• Glycolysis: Produces 2 ATP molecules. 

• Krebs cycle: Produces 2 ATP molecules. 

• Electron transport chain: Generates the majority of ATP (around 30-32 molecules) through oxidative phosphorylation

ATP- what is it?

Adenosine triphosphate (ATP) is a molecule that stores and provides energy for cells in all living organisms

Definition of Genetics

the study of heredity and the variation of inherited characteristics.

• the genetic properties or features of an organism, characteristic, etc.

  plural noun: genetics

What are different forms of genes called?

Different forms of a gene are called alleles. 

Explanation: An allele is a variant form of a gene, meaning that different versions of the same gene are considered alleles. When you inherit a gene, you receive one allele from each parent, which can interact to determine your traits.

How to complete a Punnett square

To complete a Punnett square, you can follow these steps:

1. Determine the genotypes of the parents: The genotype is the alleles an organism has for a specific characteristic. You can use any letter you like, but it's best to choose one with a clearly different lowercase. For example, you could use Aa, Bb, or Dd. 

2. Write down the cross: The cross is the mating of the parent organisms. 

3. Draw the Punnett square 

4. Split the alleles for each parent: Write the possible allele combinations for each parent on the edges of the Punnett square. One parent's gametes go on the top edge, and the other parent's gametes go on the left edge. 

5. Fill in the Punnett square: Complete the genotypes in the square by filling it in with the alleles from each parent. 

6. Summarize the results: Summarize the genotypes and phenotypes of the offspring.

RNA and DNA contain what? (A=T/U, C=G)

RNA and DNA both contain the nitrogenous bases Adenine (A), Cytosine (C), and Guanine (G); however, DNA contains Thymine (T) while RNA contains Uracil (U), meaning the base pairing rule for both is "A=T/U, C=G". 

Key points:

• DNA bases: Adenine (A), Thymine (T), Cytosine (C), Guanine (G)

• RNA bases: Adenine (A), Uracil (U), Cytosine (C), Guanine (G) 

• Describe the human genome. How many chromosomes are in a typical cell? How many chromosomes are autosomal? How many chromosomes would you find in an egg or sperm cell?

The human genome refers to the complete set of genetic information in a human cell, consisting of 23 pairs of chromosomes, totaling 46 chromosomes in a typical cell; 22 of these pairs are autosomal (non-sex chromosomes), while the last pair constitutes the sex chromosomes (X and Y), and an egg or sperm cell would contain only one set of 23 chromosomes (haploid) as they are reproductive cells

• Give an example of a human trait that follows a pattern of simple dominance.

A common example of a human trait that follows simple dominance is freckles; if you inherit even one copy of the dominant allele for freckles, you will have freckles, regardless of whether you also inherited the recessive allele for no freckles. 

Other examples include:

• Widow's peak: (hairline with a point in the middle)

• Dimples

• Attached earlobes: (attached earlobes are recessive to free earlobes)

• Cleft chin

• What is a sex-linked gene? Give an example.

A sex-linked gene is a gene located on a sex chromosome (typically the X chromosome in humans), meaning that its inheritance pattern differs between males and females; a common example of a sex-linked gene is the one responsible for red-green color blindness, which is more prevalent in males because they only have one X chromosome, making them more likely to express a recessive gene on that chromosome if present. 

Key points about sex-linked genes:

• Location: Found on the sex chromosomes (X and Y). 

• Inheritance pattern: Males are more likely to exhibit recessive sex-linked traits because they only have one X chromosome. 

• Example traits: Red-green color blindness, hemophilia, and Duchenne muscular dystrophy

• Explain how a calico cat’s fur is an example of X chromosome inactivation.

A calico cat's fur is a prime example of X chromosome inactivation because the genes responsible for their orange and black coat colors are located on the X chromosome, and in female cats (who have two X chromosomes), one of these X chromosomes is randomly inactivated in each cell during early development, resulting in patches of fur with different colors depending on which X chromosome is active in that area; essentially creating a mosaic pattern of orange and black fur patches on the cat's body. 

Key points about this phenomenon:

• X-linked gene: The gene responsible for fur color in cats is located on the X chromosome.

• Random inactivation: During early embryonic development, one of the two X chromosomes in a female cat is randomly inactivated in each cell.

• Patchy appearance: Because the inactivation is random, different patches of fur cells will express either the orange or black allele, leading to the distinctive calico pattern.

• Know the symbols used for pedigree charts (see page 397).

• What is nondisjunction? Name the three nondisjunction disorders your book mentions.

Nondisjunction is a genetic error where chromosomes fail to separate properly during cell division, resulting in an abnormal number of chromosomes in the daughter cells; the three nondisjunction disorders commonly mentioned are Down syndrome (trisomy 21), Edwards syndrome (trisomy 18), and Patau syndrome (trisomy 13). 

Explanation:

• Down syndrome: Caused by an extra copy of chromosome 21.

• Edwards syndrome: Caused by an extra copy of chromosome 18.

• Patau syndrome: Caused by an extra copy of chromosome 13

• What type of enzymes do scientists use to cut DNA into manageable pieces?

Scientists use restriction enzymes (also called restriction endonucleases) to cut DNA into manageable pieces by recognizing specific sequences of nucleotides and cleaving the DNA at those points; this allows for precise manipulation of DNA fragments in laboratory settings. 

• What field of study came out of the Human Genome Project?

The field of study that emerged directly from the Human Genome Project is called genomics. Genomics focuses on the structure, function, evolution, mapping, and editing of genomes, which is the complete set of DNA within an organism, including all its genes. 

• What is epigenetics?

the study of changes in organisms caused by modification of gene expression rather than alteration of the genetic code itself.

WORDS TO KNOW

genome, karyotype, sex chromosome, autosome, sex-linked gene, pedigree, nondisjunction, restriction enzyme, gel electrophoresis, bioinformatics, genomics

• Define selective breeding. Explain how humans use selective breeding and name/define the two common methods.

Selective breeding, also known as artificial selection, is a process where humans intentionally choose organisms with desirable traits to breed together, aiming to produce offspring that inherit and amplify those desired characteristics across generations; essentially, humans control the breeding process to cultivate specific traits in plants and animals, like increased crop yield or specific physical features in pets. 

• Explain how scientists use biotechnoligical techniques to increase genetic variation in a population.

Scientists utilize biotechnological techniques like gene editing, transgenesis (introducing foreign genes), mutation breeding, and molecular marker-assisted selection to increase genetic variation in a population by deliberately introducing new genetic combinations or mutations into an organism's genome, which can then be propagated through breeding to diversify the population further; this is particularly useful in agriculture to develop crops with improved traits like disease resistance or higher yield potential. 

Key methods:

• Mutation breeding:

  Exposing organisms to chemicals or radiation to induce random mutations, potentially creating new genetic variations that can be selected for desired traits. 

• Transgenesis:

  Inserting a gene from one organism into the genome of another, allowing for the introduction of novel traits not naturally present in the population. 

• Genome editing (e.g., CRISPR-Cas9):

  Precisely modifying specific genes within an organism's genome to introduce targeted mutations or alterations, enabling the creation of tailored genetic variations. 

• Molecular marker-assisted selection (MAS):

  Utilizing genetic markers to identify individuals with desirable traits, facilitating more efficient selection during breeding programs to increase the frequency of those traits in the population

• What is polyploidy?

Polyploidy is a genetic condition where an organism has more than two complete sets of chromosomes, meaning it possesses extra copies of its entire genome; essentially, it's a condition where a cell or organism has multiple sets of chromosomes instead of the typical two sets found in most diploid organisms.

• What technique is used to isolate specific DNA sequences? Explain how the technique works.

The technique used to isolate specific DNA sequences is called Polymerase Chain Reaction (PCR), which essentially makes numerous copies of a desired DNA fragment by repeatedly cycling through a series of temperature changes, allowing for selective amplification of a specific target DNA sequence within a larger sample. 

How PCR works:

• Primers:

  Short DNA sequences, called primers, are designed to specifically bind to the start and end points of the target DNA region. 

• DNA template:

  The DNA sample containing the target sequence is added to the reaction mixture. 

• DNA polymerase:

  A heat-stable DNA polymerase enzyme (like Taq polymerase) is used to extend the DNA strands by adding nucleotides. 

The PCR cycle:

1. 1. Denaturation:

   The DNA sample is heated to a high temperature (around 95°C) to separate the double stranded DNA into single strands.

2. 2. Annealing:

   The temperature is lowered to allow the primers to bind to their complementary sequences on the single stranded DNA.

3. 3. Extension:

   The temperature is raised to the optimal temperature for the DNA polymerase, which then extends the DNA strands from the primer binding sites, creating new DNA copies. 

• What process would scientists use to make many copies of a gene?

To make many copies of a gene, scientists use a process called polymerase chain reaction (PCR), which allows them to rapidly amplify a specific DNA sequence in a test tube by repeatedly cycling through heating and cooling steps to replicate the desired region of DNA. 

Key points about PCR:

• Primers:

  Short DNA sequences designed to specifically bind to the start and end of the target gene, guiding the DNA polymerase where to begin replication.

• DNA polymerase:

  An enzyme that builds new DNA strands by adding nucleotides, typically a heat-stable polymerase like Taq polymerase is used.

• Thermal cycling:

  The process involves repeated cycles of high temperature denaturation (to separate DNA strands), annealing (primers bind to the DNA), and extension (new DNA strands are synthesized).

• What is recombinant-DNA technology?

Recombinant DNA technology is a laboratory technique that involves manipulating and combining DNA fragments from different organisms to create new genetic combinations, essentially "splicing" DNA from different species to produce a new DNA molecule that can be inserted into a host cell, allowing for the production of desired proteins or other genetic modifications; it is also known as genetic engineering or gene splicing

• Give an example of why scientists might insert human DNA into a bacterial cell.

Scientists often insert human DNA into a bacterial cell to produce large quantities of a specific human protein, like insulin, by using the bacteria as a "factory" to express the human gene and synthesize the protein, which can then be harvested and used for medical treatments like diabetes management

• What is a transgenic organism?

A transgenic organism is a living creature whose genome has been artificially altered by introducing DNA from another species, essentially creating an organism with genetic material that wouldn't occur naturally; in simpler terms, it's a genetically modified organism (GMO) where a new gene from a different species has been inserted into its DNA, allowing for specific desired traits to be developed. 

• Define cloning. Explain why human cloning is morally problematic.

Cloning is the process of creating a genetically identical copy of an organism, meaning a clone is essentially a duplicate of the original with the same DNA; human cloning refers to creating a genetically identical human being, which is considered morally problematic due to concerns about the potential for violating individual autonomy, the slippery slope to eugenics, and the complex social and psychological implications of creating a person who is essentially a copy of another individual, potentially affecting their sense of identity and worth

• Identity and individuality:

  A cloned person might struggle with their sense of identity, feeling like a mere copy of another individual, potentially leading to psychological distress and questioning their own unique value. 

• Eugenics concerns:

  Cloning could potentially be used to select for desirable traits, leading to a slippery slope towards a form of eugenics where certain genetic characteristics are deemed superior, raising ethical questions about who decides these traits and the potential for discrimination against those who don't fit the "ideal". 

• Commodification of human life:

  Some argue that cloning could lead to the commodification of human life, where people could be "produced" to order, potentially devaluing the intrinsic worth of a human being

• Give an examples of how genetic modification is used in agriculture, industry, health, and medicine.

In agriculture, genetic modification is used to create crops resistant to pests and herbicides, like Bt corn engineered to resist insect damage, or soybeans modified to tolerate glyphosate herbicides; in industry, genetically modified bacteria can be used to produce enzymes for food processing or biofuels; in health and medicine, genetic modification is used to produce human insulin in bacteria for diabetes treatment, or to develop vaccines by inserting specific genes into viruses to trigger immune responses.

• What is gene therapy? Is the use of gene therapy always ethical? Why or why not?

Gene therapy is a medical technique that aims to treat diseases by introducing functional genes into a patient's cells to replace or repair defective genes, offering the potential to cure genetic disorders; however, its use is not always considered ethical due to concerns like potential for unintended consequences, germline modification, and the possibility of using it for non-therapeutic enhancements, raising questions about who should have access to such treatments and the potential for discrimination based on genetic makeup

• Ethical concerns:

  • Germline modification: Altering genes in sperm or egg cells could impact future generations, raising significant ethical concerns about "designer babies" and unintended long-term effects. 

  • Access and equity: Concerns exist about who would have access to gene therapy, potentially creating disparities based on socioeconomic status. 

  • Enhancement vs. treatment: Distinguishing between treating a disease and enhancing desirable traits like intelligence or athletic ability can be blurry, raising ethical dilemmas. 

  • Informed consent: Patients must fully understand the risks and benefits of gene therapy before undergoing treatment. 

• What technique is used to study hundreds of genes at once?

The technique used to study hundreds of genes at once is called a DNA microarray (also known as a gene chip) which allows researchers to monitor the expression levels of thousands of genes simultaneously by attaching short DNA sequences to a solid surface and then hybridizing labeled DNA or RNA samples to those sequences to detect binding and analyze gene activity levels.

• What is DNA fingerprinting?What is the process for DNA fingerprinting?

DNA fingerprinting, also called DNA profiling, is a technique used to identify individuals based on the unique patterns in their DNA by extracting DNA from a sample, cutting it into fragments using restriction enzymes, separating those fragments by size through gel electrophoresis, and then analyzing the resulting pattern, which acts like a genetic fingerprint unique to each person; this is commonly used in forensic investigations to link suspects to crime scenes or for paternity testing to establish biological relationships

• Sample collection:

  DNA is extracted from a biological sample like blood, saliva, hair, or tissue. 

• DNA isolation:

  The DNA is purified from other cellular components. 

• PCR amplification:

  Specific regions of DNA called Short Tandem Repeats (STRs) are amplified using Polymerase Chain Reaction (PCR) to generate enough copies for analysis. 

• Restriction enzyme digestion:

  The amplified DNA is cut into smaller fragments using restriction enzymes that recognize specific DNA sequences. 

• Gel electrophoresis:

  The DNA fragments are separated based on their size by running them through a gel under an electric current, resulting in a pattern of bands. 

• Visualization and analysis:

  The separated DNA fragments are visualized using a dye or radioactive probe, and the banding pattern is compared to other samples to identify matches

WORDS TO KNOW:

selective breeding, hybridization, inbreeding, biotechnology, polymerase chain reaction, recombinant DNA, plasmid, genetic marker, transgenic, clone, gene therapy, DNA microarray, DNA fingerprinting, forensics

• What is the process of change over time?

The process of change over time is called evolution. In the context of biology, it refers to the gradual changes in the characteristics of a population of organisms across generations, often driven by natural selection and adaptation to their environment. 

• Describe the three patterns of biological diversity Darwin observed on his travels.

Charles Darwin observed three key patterns of biological diversity during his travels: species vary globally, species vary locally, and species vary over time; meaning that different, yet related, species inhabit different regions of the world, different species can be found in close proximity within a local area, and fossil evidence indicated that species change over long periods of time. 

Explanation of each pattern:

• Species vary globally:

  This refers to the observation that different, yet similar, animals can be found in different parts of the world with similar environments, like the rhea in South America, the ostrich in Africa, and the emu in Australia. 

• Species vary locally:

  Darwin noticed that even within a relatively small geographic area, different islands or habitats could harbor distinct variations of the same species, most famously seen in the different types of finches on the Galapagos Islands. 

• Species vary over time:

  Studying fossils, Darwin observed that extinct species often resembled living organisms, suggesting that species change over long periods through a process of evolution.

• Science is a community of ideas. Name the 4 scientists who influenced Darwin and briefly summarize their research.

The four scientists who significantly influenced Charles Darwin were Jean Baptiste Lamarck, Charles Lyell, Thomas Malthus, and Alfred Russel Wallace. 

• Jean Baptiste Lamarck:

  Proposed the theory of "inheritance of acquired characteristics," suggesting that organisms could pass on traits developed during their lifetime to their offspring, like a giraffe stretching its neck to reach higher leaves. (This theory was later disproven). 

• Charles Lyell:

  A geologist who advocated for "uniformitarianism," the idea that geological features were formed by slow, gradual processes over long periods of time, which influenced Darwin's concept of gradual evolution. 

• Thomas Malthus:

  An economist who wrote about population growth exceeding resource availability, leading to competition for survival, which Darwin adapted to explain the concept of "survival of the fittest" in natural selection. 

• Alfred Russel Wallace:

  Independently developed a theory of evolution through natural selection, similar to Darwin's, which prompted Darwin to publish his findings more quickly.

• Define artificial selection.

Artificial selection is a biological process where humans choose which organisms to breed in order to develop specific traits in future generations. It's also known as selective breeding

What is the mechanism of evolution

The primary mechanism of evolution is natural selection; this means that organisms with traits better suited to their environment are more likely to survive and reproduce, passing on those advantageous traits to their offspring, leading to gradual changes in a population over time. 

Other key mechanisms of evolution include:

• Mutation:

  Random changes in DNA sequence that introduce new genetic variation into a population. 

• Genetic drift:

  Random fluctuations in allele frequencies within a population, often due to small population size or chance events. 

• Gene flow:

  Movement of genes between populations through migration, introducing new genetic variations.

• What does the phrase “survival of the fittest” mean?

Survival of the fittest means that organisms that are better adapted to their environment are best suited to survive and successfully reproduce

• Natural selection is a process where organisms with advantageous traits, due to genetic variation within a population, are more likely to survive and reproduce, passing on those beneficial traits to their offspring, leading to a gradual change in the characteristics of a species over time; this process occurs when there is variation within a population, inheritance of those variations, overproduction of offspring, and differential survival and reproduction based on those variations.

• What is the principle of common ancestry? What is meant by “descent with modification”?

The "principle of common ancestry" states that all living organisms on Earth share a common ancestor, meaning they all descended from a single, ancient life form that gradually diversified over time, while "descent with modification" refers to

• Common ancestry:

  This idea suggests that all life forms can trace their lineage back to a shared ancestral organism, which is often visualized as a "tree of life" where different branches represent distinct species that evolved from a common root. 

• Descent with modification:

  This phrase emphasizes that as organisms reproduce, they pass on their traits with slight variations to their offspring, and over many generations, these modifications can accumulate, leading to noticeable differences between populations and the emergence of new species.

• Briefly summarize how each of the following areas of study provide support for evolution: biogeography, geology, anatomy, embryology, and genetics.

• Biogeography:

  By studying the geographical distribution of species, biogeography reveals patterns that align with the movement of continents over time, indicating how related species evolved in different regions and dispersed from a common ancestor; for example, similar species found on different continents separated by oceans suggest a shared ancestry before continental drift. 

• Geology:

  Through the fossil record preserved in rock layers, geology provides evidence of the chronological sequence of life forms on Earth, showing how species evolved and changed over vast geological time scales. 

• Anatomy:

  Comparative anatomy identifies homologous structures, similar anatomical features present in different species due to a shared common ancestor, demonstrating evolutionary relationships between organisms. 

• Embryology:

  By studying the development of embryos across different species, embryology reveals similarities in early developmental stages, suggesting a common ancestry, as seen in the presence of gill slits in human embryos. 

• Genetics:

  Analysis of DNA sequences allows scientists to compare genetic similarities between species, providing strong evidence for evolutionary relationships and tracing the lineage of common ancestors at the molecular level. 

• Differentiate between analogous, homologous, and vestigial structures.

Analogous structures are features in different species that perform similar functions but have different structures, indicating they evolved separately to adapt to similar environments; homologous structures are features in different species that share a similar structure due to a common ancestor, even if their functions differ; and vestigial structures are remnants of functional structures in an organism's ancestors that have lost most or all of their function in the current species, serving as evidence of evolutionary change

• Analogous structures: 

  • Similar function, different structure 

  • Evolved independently in unrelated species 

  • Example: wings of a butterfly and a bird 

• Homologous structures: 

  • Similar structure, potentially different functions 

  • Shared ancestry between species 

  • Example: human arm and bat wing 

• Vestigial structures: 

  • Reduced or non-functional structure in current organism 

  • Remnant of a functional structure in an ancestor 

  • Example: human appendix 

• Describe the research of Peter and Rosemary Grant.

Peter and Rosemary Grant are renowned evolutionary biologists who conducted a long-term study of Darwin's finches on the Galapagos Islands, meticulously documenting how environmental changes, particularly variations in food availability, directly influence beak size and shape in the finch populations, providing strong evidence for natural selection in action and demonstrating that evolution can occur rapidly over just a few generations; their research is considered a landmark study in evolutionary biology, showcasing how environmental factors drive rapid evolutionary change in real-time.

WORDS TO KNOW:

evolution, fossil, artificial selection, adaptation, fitness, natural selection, biogeography, homologous structure, analogous structure, vestigial structure

• Define genotype and phenotype.

A genotype refers to an organism's complete set of genes, essentially its genetic makeup, while a phenotype describes the observable characteristics of an organism, which are influenced by both its genotype and environmental factors; in simpler terms, genotype is the genetic code, and phenotype is the physical expression of that code as seen in an organism's traits

• Genotype is internal:

  You cannot see an organism's genotype directly; it is only accessible through genetic analysis. 

• Phenotype is external:

  The phenotype is the observable traits like eye color, height, or behavior that you can see in an organism.

• What is a gene pool? Is the allele frequency of an allele determined by whether the allele is dominant or recessive?

A "gene pool" refers to the collective set of all alleles (different versions of a gene) present within a population, essentially representing the total genetic variation available within that group; the allele frequency of an allele is not solely determined by whether it is dominant or recessive - its frequency depends on how common it is within the population, regardless of its dominance status

• Definition: A gene pool is the sum of all alleles for every gene in a population. 

• Allele frequency: This represents how often a specific allele appears within a population, calculated by counting the number of times that allele is present and dividing by the total number of alleles for that gene. 

• Dominance and allele frequency: While a dominant allele may be more readily expressed in an individual, its frequency within the population is not solely dependent on its dominance status

• What are the sources of genetic variation in a population?

The primary sources of genetic variation in a population are mutation (changes in DNA sequence), gene flow (movement of genes between populations), and sexual reproduction (which creates new gene combinations through processes like crossing over); essentially, new alleles are introduced through mutation, existing alleles can be shuffled around through sexual reproduction, and gene flow brings in new alleles from other populations

Mutation:

This is the ultimate source of new genetic variation, as it directly alters the DNA sequence, potentially creating new alleles that weren't present before.

Gene flow:

When individuals migrate from one population to another, they introduce new alleles into the recipient population, increasing genetic diversity

Sexual reproduction:

Through processes like crossing over during meiosis, genetic material is exchanged between homologous chromosomes, creating new combinations of alleles in offspring

• If you graph the distribution of phenotypes for a polygenic trait, what will it look like?

When you graph the distribution of phenotypes for a polygenic trait, it will typically appear as a bell-shaped curve, with most individuals displaying the intermediate phenotype and fewer individuals at the extreme ends of the trait range.

• How does natural selection work for single versus polygenic traits?

When considering natural selection, single-gene traits experience changes in allele frequencies directly, leading to distinct phenotypic shifts, while polygenic traits exhibit a wider range of phenotypes due to multiple genes involved, allowing for more complex selection patterns like directional, stabilizing, or disruptive selection depending on which traits are favored by the environment.

• Polygenic traits:

  • Controlled by multiple genes, leading to a continuous distribution of phenotypes within a population

Single-gene traits:

• Controlled by a single gene with distinct alleles, resulting in easily identifiable phenotypic variations

• What are the three types of selection for polygenic traits?

Stabilizing selection:

Favors the average phenotype, meaning individuals with traits closer to the middle of the range are more likely to survive and reproduce, narrowing the bell curve

Directional selection:

Favors one extreme phenotype, causing the population to shift towards that extreme on the bell curve.

Disruptive selection:

Favors both extreme phenotypes, leading to a "split" in the population where individuals with intermediate traits are less likely to survive.

Explain genetic drift and describe two types

Genetic drift is a random change in the frequency of alleles within a population, occurring due to chance events and not related to natural selection, which can significantly alter the genetic makeup of a population, especially in small populations; the two main types of genetic drift are the "bottleneck effect" where a population drastically shrinks due to a random event, and the "founder effect" where a small group of individuals establishes a new population with different allele frequencies than the original population

• Bottleneck Effect:

  • Mechanism: A sudden, drastic reduction in population size caused by a natural disaster, disease outbreak, or other random event, leaving only a small sample of the original population to reproduce, which can lead to a significant change in allele frequencies due to the chance selection of survivors.

  • Example: A large population of deer is decimated by a wildfire, leaving only a few individuals to repopulate, potentially leading to a reduced genetic diversity in the new population.

• Founder Effect:

  • Explanation

    The founding individuals only carry a fraction of the genetic diversity of the original population, resulting in a loss of genetic variation in the new population

  • Results

    The new population will have genotypes and physical traits that resemble the founding group, and may be very different from the original population.

Impact on genetic diversity:

Genetic drift tends to reduce genetic diversity within a population as certain alleles may become more or less common due to chance events.

Small population vulnerability:

Smaller populations are more susceptible to the effects of genetic drift because random fluctuations have a greater impact on allele frequencies. 

Evolutionary mechanism:

While not directly related to adaptation, genetic drift can still be a significant factor in evolution, especially when combined with other mechanisms like natural selection

• What five conditions can disturb genetic equilibrium?

Five conditions that can disturb genetic equilibrium are: mutation, gene flow, genetic drift, non-random mating, and natural selection; these are all factors that can disrupt the Hardy-Weinberg equilibrium, a theoretical model of population genetics where allele frequencies remain constant across generations if certain conditions are met.

Mutation:

Changes in DNA sequence can introduce new alleles into a population, altering the genetic makeup.

Gene flow:

Movement of genes between populations through migration, which can introduce new alleles to a population.

Genetic drift:

Random fluctuations in allele frequencies, particularly impactful in small populations

Non-random mating:

When individuals choose mates based on specific traits, rather than randomly, which can skew allele frequencies.

Natural selection:

Differential survival and reproduction based on advantageous traits, leading to changes in allele frequencies. 

Key point: Maintaining genetic equilibrium requires a large population size, no mutations, no gene flow, random mating, and no natural selection.

• What is a species?

A biological species is a group of organisms that can reproduce with one another in nature and produce fertile offspring.

• Name and describe the three types of reproductive isolation.

The three main types of reproductive isolation are: behavioral isolation (different mating rituals or behaviors), temporal isolation (different breeding times), and geographic isolation (physical barriers separating populations) which prevents gene flow between them, leading to genetic divergence over time

Behavioral isolation:

Species use specific behaviors to attract mates, and if these behaviors differ between populations, they cannot mate with each other. For example, different bird species have unique courtship displays.

Temporal isolation:

Species breed at different times of the year or day, preventing them from mating even if they live in the same area.

Geographic isolation:

A physical barrier like a mountain range, river, or ocean separates populations, hindering gene flow and allowing them to evolve independently. 

• How might have the Galapagos finches have evolved?

The Galápagos finches evolved through a process called adaptive radiation, where a single species rapidly evolves to fill different ecological niches: 

• Common ancestor

  The finches' closest known relative is the dull-colored grassquit, which lives on mainland South America.

• Colonization

  The original grassquits colonized the Galápagos Islands a few million years ago. 

• Diversification

  The finches adapted to the different environments on the islands, evolving different beak shapes and feeding habits:

• Long, pointed beaks: Good for catching insects

• Broad, blunt beaks: Good for cracking seeds and nuts