Biology Exam 3 Review: Chapters 8, 9, and 10

A comprehensive set of practice questions and answers covering cellular reproduction, Mendelian genetics, and molecular biology based on the exam review sheet.

What characterizes asexual reproduction in terms of offspring and parental involvement?

Asexual reproduction involves the creation of a genetically-identical offspring from a single parent without the involvement of eggs, sperm, or fertilization.

What is the primary trade-off or sacrifice associated with asexual reproduction?

Genetic diversity is sacrificed because all offspring are exact replicates of the parent.

What are gametes and what is their role in reproduction?

Gametes are sex cells, such as eggs/sperm or pollen/ovule, which combine to form new, unique, and genetically-distinctive offspring.

By what process do prokaryotes reproduce?

Prokaryotes reproduce via binary fission, where chromosomes are replicated and the cell splits in half into $2$.

How many chromosomes do prokaryotes have compared to human cells?

Prokaryotes have $1$ chromosome, while human cells contain multiple chromosomes.

What is the composition of the $46$ chromosomes found in human cells?

They consist of $22$ pairs of autosomes and $1$ pair of sex chromosomes.

What must occur to a cell's DNA before it can divide?

The DNA (chromosomes) must first be replicated.

What are the two identical parts of a replicated chromosome called?

Sister chromatids.

What are the two main phases of the cell cycle?

Interphase and the mitotic phase.

In which phase does a cell spend most of its life, and what occurs during this time?

Most of the cell's life is spent in interphase, which is a period of growth and preparation for cell division, including DNA replication.

What are the three stages of interphase, and in which specific stage does DNA replication occur?

Interphase consists of $G1$, $S$, and $G2$. DNA replication occurs in the $S$ phase.

What are the two components of the mitotic stage?

Mitosis (nuclear division and distribution) and cytokinesis (the physical act of splitting $1$ cell into $2$).

What happens during the Prophase stage of mitosis?

The mitotic spindle forms, chromatin condenses into chromosomes, the nuclear envelope dissolves, and chromosomes attach to the spindle.

What happens during Metaphase?

Chromosomes align perpendicularly at the center of the cell.

What occurs during Anaphase?

Each sister chromatid of the replicated chromosome separates.

What happens during Telophase?

The nuclear envelope reforms, chromatin uncoils, and the mitotic spindle disappears.

How is cancer defined in the context of the cell cycle?

Cancer is a disease of the cell cycle where control over cell division becomes unchecked and unregulated.

What is the result of meiosis regarding chromosome count?

Meiosis results in cells containing half the number of chromosomes as the parent cell.

Where does meiosis occur and what does it produce?

Meiosis occurs only in reproductive organs and produces gametes like eggs, sperm, and pollen.

What is the difference between diploid and haploid cells?

Diploid cells contain $2$ sets of chromosomes, while haploid cells contain only $1$ set.

Which human cells are haploid and which are diploid?

Sex cells (gametes) are haploid, while all other cells are diploid.

In meiosis, what can a homologous pair of chromosomes bear?

They can bear $2$ different kinds of genetic information for the same characteristics, which are different versions of a gene.

What process occurs only in meiosis that results in genetically-new chromatids?

Crossing over.

What is the definition of genetics?

Genetics is the science of heredity.

What are genes at the molecular level?

Genes are discrete units of hereditary information consisting of a specific nucleotide sequence of DNA.

Who was Gregor Mendel and what organism did he study?

Gregor Mendel was the scientist who established the principles of heredity by working with garden pea plants.

In Mendelian genetics, what is a true-breeding line?

A true-breeding line is a group that produces offspring identical to the parent for a specific trait over many generations.

Distinguish between the $F1$ and $F2$ generations in Mendel's experiments.

The $F1$ generation is the offspring of $2$ true-breeding lines for different traits; the $F2$ generation is the offspring of $2$ $F1$ individuals.

What is an allele?

An allele is a version or variant of a gene.

What is the difference between homozygous and heterozygous genotypes?

Homozygous means having two identical alleles for a gene, while heterozygous means having two different alleles for a gene.

Define dominant and recessive alleles.

A dominant allele determines the phenotype even if only one is present; a recessive allele has no noticeable effect on the appearance unless the organism is homozygous for that allele.

What is the difference between genotype and phenotype?

Genotype is the genetic makeup (the alleles), whereas phenotype is the physical expression or appearance.

Why are most genetic disorders recessive?

Because a single dominant allele in a heterozygous individual usually masks the disorder, allowing the carrier to survive and reproduce.

What is a carrier?

A carrier is an individual who is heterozygous for a recessive allele ($ex.\text{ Cc}$), meaning they possess the allele but do not exhibit the trait phenotypically.

What is incomplete dominance?

A pattern of inheritance where the homozygous dominant is one color, the homozygous recessive is another, and the heterozygous is a third, intermediate color.

Which human trait is an example of codominance?

Human blood type.

What are the two nucleic acids and what are they made of?

DNA and RNA; they consist of polynucleotides, which are long chains of nucleotides.

Describe the structure of DNA.

DNA exists as a double helix with $2$ sugar-phosphate backbones and nitrogenous bases positioned between them.

What are the specific nitrogenous base pairings in DNA?

$A-T$ and $C-G$.

How is DNA replication described as a process using templates?

Replication occurs on both strands, where the old parental strand serves as a template for a new daughter strand, resulting in two molecules each containing one parental and one daughter strand.

Which enzyme links DNA nucleotides to a growing daughter strand?

DNA polymerases.

What is the central dogma of molecular biology?

DNA is transcribed into RNA, which is then translated into proteins.

Where do transcription and translation occur in a human cell?

Transcription occurs in the nucleus; translation occurs in the cytoplasm at a ribosome.

What is transcription?

The act of rewriting the code of DNA into messenger RNA (mRNA).

Which DNA strand is used during transcription?

The template strand.

What is the difference between a triplet and a codon?

A triplet is a series of $3$-nucleotide 'words' in the DNA template strand; a codon is a series of $3$-nucleotide 'words' in the messenger RNA.

Which enzyme performs the transcription of a gene into mRNA?

RNA polymerase.

How does base pairing differ when DNA is transcribed into mRNA?

In mRNA, adenine ($A$) in the template strand complements uracil ($U$) instead of thymine ($T$).

What does the genetic code indicate?

It is a set of instructions indicating which codons ($3$-base sequences) are translated into which amino acids.

How many codons code for each of the $20$ amino acids?

There are $1$ to $4$ codons that code exclusively for each amino acid.

Which codon acts as the 'start' signal and what amino acid does it code for?

$AUG$; it codes for methionine.

What are the three 'stop' signal codons?

$UAA$, $UAG$, and $UGA$.

What does it mean that the genetic code is 'nearly universal'?

The same codons code for the same amino acids in nearly all organisms, including bacteria.

What is translation?

The process where ribosomes take the information from an mRNA molecule and build a polypeptide by laying down amino acids one by one.

What is a mutation and which types are generally the most harmful?

A mutation is a change in the nucleotide sequence; insertions and deletions are the most harmful.

What is a mutagen?

An agent that causes mutations.