BIO 104: Exam 2

Briefly describe the specific function of DNA. Why does this function cause children to resemble their parents?

It encodes the instructions to make proteins, and these proteins determine traits.

 Explain why hydrogen bonds between complementary bases are more desirable than covalent bonds.

1. The hydrogen bonds hold the two strands together while still allowing them to separate easily when needed.

2. If connected through covalent bonds, the strands would be too strongly attached and would not be able to “unzip” during replication or transcription

Explain base complementarity

When bases pair specifically (A with T, and G with C), which provides reliable instructions for making proteins and allows DNA to be accurately copied and used during transcription and translation.

Explain how cells in your skin can be different from the cells in your brain despite having the same DNA.

even though skin cells and brain cells have the same DNA, they are different because different genes are turned on or off in each cell type. This process, called gene expression, allows cells to make the proteins they need to perform their specific jobs.

Identify instances in transcription, translation and DNA replication that involve base complementarity

Base complementarity is involved in DNA replication when new DNA strands are copied using A–T and G–C pairing, in transcription when RNA is made from DNA using complementary base pairing (A–U, G–C), and in translation when tRNA anticodons pair with mRNA codons to add the correct amino acids.

Explain how base complementarity ensures the reliability of information transfer from nucleic acid "language" to protein "language"

Base complementarity ensures reliability because specific base pairing (A–U, G–C) allows RNA codons to be accurately matched with tRNA anticodons during translation, so the correct amino acids are added in the proper order to make the correct protein

List the three types of RNA and their general functions in the process of protein production

The three types of RNA are messenger RNA (mRNA), which carries the genetic message from DNA, transfer RNA (tRNA), which brings amino acids to the ribosome, and ribosomal RNA (rRNA), which forms part of the ribosome and helps assemble proteins.

Use a metaphor to explain the concept of gene regulation that allows cells to be differentiated despite having the same DNA.

Gene regulation can be compared to a piano—every cell has the same DNA (like all 88 keys), but gene regulation determines which “keys” (genes) are played and when, so different cells produce different proteins and functions even though they have the same DNA.

Describe the specific function of DNA that leads to the resemblance of parents and their Offspring 

It encodes the instructions to make proteins, and these proteins determine traits.

What is the basic function of mitosis? Briefly explain the steps of mitosis?

The basic function of mitosis is to produce two identical daughter cells from a single parent cell, helping with growth, repair, and replacement of cells in an organism.

• Prophase – Chromosomes condense and become visible, and the nuclear membrane starts to break down.

• Metaphase – Chromosomes line up in the middle of the cell (the metaphase plate).

• Anaphase – Sister chromatids are pulled apart to opposite ends of the cell.

• Telophase – Nuclear membranes reform around each set of chromosomes, which start to uncoil.

• Cytokinesis – The cell membrane pinches in, splitting the cell into two identical daughter cells.

Consider a bird with 30 chromosomes in each body cell. If one of those body cells divides, how many chromosomes will be in each daughter cell? 

Each daughter cell has 30 chromosomes

How many chromosomes are in each of the bird’s gametes (i.e., sex cells)? How many chromosomes will the body cells of the bird’s son have?

1. Each gamete has 15 chromosomes (30/2)

2. Son’s body cells have 30 chromosomes (15 eggs + 15 sperm) = 30

List and describe the 4 sources of genetic variation. Why is genetic variation so important from a biological perspective?

1.  Mutation - errors in DNA replication

2. Crossing-over = occurs in meiosis when homologous pairs come together, & chormosme pieces can be traded between homologous chromosomes. It creates individual chromosomes that have some maternal gene versions (alleles), and some paternal = more on slide 17

3. Segregation + independent assortment = when homologous pairs separate, each gamete gets one of each chromosome pair, but for each pair, it's random (like a coin flip) which chromosome (maternal/paternal) the gamete gets. With three pairs of chromosomes 2³ = 8 possible gamete combos, for a human, 23 chromosomes, 2²³ = 8,388,608 that can be produced by a single human, that does not include increased variation due to crossing over

4. Sexual reproduction = male/female gametes combine to form a new individual organism, diverse sperm x diverse eggs (lots of potential variation in offspring), asexual reproduction using just mitosis, generates much less genetic variation because it essentially clones the parent

5. Genetic variation makes populations stronger, more adaptable, and able to evolve.

Briefly describe 2 ways in which meiosis and mitosis are similar. Briefly describe 2 ways in which they are different.

1. Similarities: Both start with a single parent cell and involve chromosome replication during interphase. Both go through stages like prophase, metaphase, anaphase, and telophase.

2. Differences between mitosis and meiosis: 

• Mitosis produces two identical daughter cells (diploid), while meiosis produces four genetically different cells (haploid).

• Meiosis has two divisions (meiosis I and II) and includes crossing over, while mitosis has only one division and no crossing over.

Why does DNA replication always precede mitosis? Why does DNA condense into coiled-up chromosomes prior to mitosis?

1. DNA must replicate before mitosis so that each daughter cell gets a full, identical set of chromosomes

2. DNA condenses into chromosomes to protect it and ensure each daughter cell gets a complete, accurate copy during mitosis.

Mendelian inheritance

describes how single-gene traits are passed from parents to offspring through dominant and recessive alleles

Gene

physical and functional unit of heredity, a sequence of DNA that codes for a protein.

 Allele

Alternative forms of genes that arise by mutation and exist at the same relative locations on homologous chromosomes

Genotype

underlying genetic makeup, consisting of both physically visible and non-expressed alleles, of an organism

Phenotype

observable traits expressed by an organism

Dominant

refers to an allele (version of a gene) that masks the effect of another allele (recessive) when both are present in an organism.

• If a dominant allele is present, its trait will show in the organism’s appearance (phenotype), even if the other allele is different.

Recessive

refers to an allele whose trait is hidden when a dominant allele is also present.

• A recessive trait only shows in the organism’s appearance (phenotype) if both alleles are recessive (homozygous recessive).

 Segregation

paired unit factors (i.e., genes) segregate equally into gametes such that offspring have an equal likelihood of inheriting any combination of factors

independent assortment

genes do not influence each other with regard to sorting of alleles into gametes; every possible combination of alleles is equally likely to occur

sex linkage

any gene on a sex chromosome

Pleiotropy

A situation in which the product of a single gene influences multiple aspects of an organism’s phenotype

polygenic inheritance

A situation in which variation in a single phenotypic trait is determined by the genotype of multiple genes

incomplete dominance

in a heterozygote, expression of two contrasting alleles such that the individual displays an intermediate phenotype

 codominance

in a heterozygote, complete and simultaneous expression of both alleles for the same characteristic

Identify several reasons why an organism's phenotype does not always directly reflect its underlying genotype

1. Environmental influence (sunlight & diet) → nature vs. nurture

2. Some alleles are dominant and mask recessive alleles

3. Pleiotropy

4. Mutations

5. incomplete dominance and codominance 

How does the environment impact trait development and expression

The environment affects how genes are expressed, so traits come from both genes and surroundings.

Heterozygote

having two different versions (alleles) of a specific gene—one inherited from each parent.

 Give examples to illustrate how phenotypes are generally the result of an interaction between genetic predisposition and environmental influences

1. Skin color (tanning): You inherit genes for skin pigmentation, but sunlight exposure increases melanin production, making skin darker.

2. Height: You inherit genes that influence height, but nutrition and health affect how tall you actually grow.

3. Behavior/personality: Genes may influence tendencies, but life experiences and environment shape how those traits are expressed. 

Malignant

invasive and may spread = it is not good, it is not contained, will keep moving - like uncontrolled fire 

Benign

 contained within a capsule  = it is good, not causing problems, it is contained = like fire that is controlled = stove

 Metastasis

 cells travel to start new tumors

Angiogenesis

form new blood vessels to nourish themselves

Apoptosis

programmed cell death

In one sentence, what is a general definition of cancer?

is a large group of diseases characterized by the uncontrolled growth, division, and spread of abnormal cells,

Explain why cancer is considered a “genetic” disease. Discuss the ways in which the environment can also influence cancer.

1. is a disruption of the cell cycle → cellular reproduction occurs indefinitely, caused by mutations in DNA, Mutations disrupt normal cell cycle control, and Cells divide uncontrollably → form tumors

2. Smoking

3. Exposure to UV without protection

4. Diet

5. Pollution/Chemicals

Explain how proto-oncogenes and tumor suppressor genes are related to the cell cycle and cancer. If scientists were able to remove proto-oncogenes and tumor suppressor genes from healthy people, would that be a good strategy for cancer prevention? Why or why not?

Proto-oncogenes promote cell division like a gas pedal, and tumor suppressor genes stop cell division and trigger apoptosis like brakes; mutations in these genes disrupt the cell cycle, leading to cancer. Removing them from healthy people would be harmful, not preventative, because both are essential for normal cell growth, repair, and regulation.

Explain how conditions such as obesity and cardiovascular disease relate to the “nature vs. nurture” debate.

Conditions like obesity and cardiovascular disease illustrate nature vs. nurture because genetic makeup (nature) affects susceptibility, while lifestyle factors like diet, physical activity, and exposure to saturated fats (nurture) influence whether these diseases actually develop.

 What is the general function of the endocrine system?

The endocrine system is a network of glands and tissues that secrete hormones into the bloodstream, which act as chemical messengers to regulate body processes and maintain homeostasis.

Briefly explain 4 ways in which endocrine disruptors can interfere with an organism’s endocrine system.

1. Agonists – Endocrine disruptors can mimic natural hormones and bind to receptors, sending false messages and causing too much of a response.

2. Antagonists – They can block hormones from binding to receptors, preventing the normal hormone response.

3. They can increase the production of hormones, leading to hormone imbalances.

4. They can prevent the breakdown or elimination of hormones or increase the number of hormone receptors,

Explain why polar bears (or any top predator) tend to be more susceptible to endocrine disruptors/endocrine disruptors than small fish.

1. When polar bears eat their prey, such as fish, and those fish are carrying the endocrine disruptors, then they are more susceptible to having higher amounts being found within their blood stream. This happens because of bioaccumulation in individual organisms and biomagnification up the food chain.

Bioaccumulation

material gets concentrated within an individual organism during its life

Biomagnification:

Material gets concentrated as it moves up each level of the food chain

Briefly (1-2 sentences each) describe Transgenic organisms:

Transgenic organisms are animals or plants that have new genes added from another species. Scientists use them to study diseases, make medicines, or produce useful proteins

Briefly (1-2 sentences each) describe gene/genome sequencing:

gene/genome sequencing is reading an organism’s DNA to understand how proteins work, how diseases happen, and how species are related. It can also help create personalized treatments, like finding the best chemotherapy for a patient’s tumor.

Briefly (1-2 sentences each) describe Stem cells:

 undifferentiated cells that can become different types of cells. They can repair damaged tissues, especially in cells that don’t regenerate well, but using them from embryos raises ethical concerns.

Briefly (1-2 sentences each) describe CRISPR

is a powerful gene-editing tool that lets scientists precisely add, remove, or modify DNA. It works by using the Cas9 enzyme to cut specific DNA sequences, originally based on a natural bacterial defense system.

.Describe two ways in which transcription and DNA replication are similar. Describe two ways in which they are different.

1. Similar: Both use DNA as a template to make a new strand. AND Both involve complementary base pairing (A pairs with T, C pairs with G).

2. Different: DNA replication makes a whole new DNA molecule, while transcription makes RNA from part of DNA. AND DNA replication uses DNA polymerase, while transcription uses RNA polymerase.

 What is mutation? In what way is mutation a problem for living things? In what way is mutation beneficial for living things?

1. Errors of DNA replication

2. PROBLEM:  It can cause diseases or harmful changes in proteins.

3. BENEFICIAL: It can create new traits that help organisms adapt and evolve.

 List and discuss two reasons why an organism’s phenotype (visible traits) may not give an observer precise information about the organism’s genotype (alleles at various genes).

1. Dominant genes can hide recessive genes. A dominant trait will show even if there’s only one copy of the gene.Example: Smooth seeds (S) are dominant over wrinkled (s). A plant with SS or Ss both look smooth, so you can’t tell the exact genes just by looking.

2. Environment can change how traits look. Things like sunlight, water, or food can affect traits.Example: Two plants with the same genes can grow different heights if one gets more sunlight.

Gregor Mendel did not know about DNA or meiosis. Nevertheless, he concluded that alleles of different genes assort independently when gametes form. Using what you know about meiosis (the formation of gametes, or reproductive cells), explain what independent assortment is, and why it occurs.

Independent assortment means that different genes are passed to gametes randomly and separately, because chromosomes line up and separate independently during meiosis

Gregor Mendel concluded that each trait is determined by a single factor (In other words, each gene specifies a single trait in our phenotype). Explain why this conclusion is incorrect.

because many traits are not controlled by just one gene. Some traits are controlled by multiple genes, which is called polygenic inheritance, and some genes affect more than one trait, which is called pleiotropy. Also, the environment can influence how traits appear.

Why do we look and act the way that we do? And why do offspring tend to look and act like their parents? Provide a clear and organized summary, describing the various factors involved

We look and act the way we do because of our genes (DNA we inherit from our parents) and our environment (our experiences and surroundings). Offspring look and act like their parents because they inherit half of their DNA from each parent through inheritance.