Heredity and Genetics (BIO 3105)

Correct Answer C. Endoplasmic reticulum

Explanation

Ribosomes are primarily located on the rough endoplasmic reticulum (ER), which is studded with ribosomes on its surface. These ribosomes are responsible for protein synthesis. Some ribosomes also float freely in the cytoplasm and synthesize proteins that function within the cell.

Why other options are wrong

A. Nucleus

While the nucleus contains the genetic material and is the site of RNA synthesis, ribosomes are not located within the nucleus. Ribosomes are synthesized in the nucleolus within the nucleus, but they are located outside the nucleus, either on the rough ER or floating in the cytoplasm.

B. Golgi apparatus

The Golgi apparatus is responsible for modifying, sorting, and packaging proteins for secretion or use within the cell. It does not house ribosomes. Ribosomes are mainly found on the rough ER and in the cytoplasm.

D. Mitochondria

Mitochondria have their own ribosomes for synthesizing proteins specific to their function, but the majority of ribosomes in the cell are located on the rough ER and in the cytoplasm, not in mitochondria.

Correct Answer C. Genes

Explanation

Gregor Mendel referred to "factors" as the units of heredity that determine traits, based on his experiments with pea plants. Today, these "factors" are known as genes—segments of DNA that encode for proteins or functional RNA and influence the traits of an organism. Genes are the fundamental units of inheritance in modern genetics.

Why other options are wrong

A. Nucleotides

Nucleotides are the building blocks of DNA and RNA, consisting of a sugar, phosphate group, and nitrogenous base. While genes are made of nucleotides, they are not equivalent to the term Mendel used for hereditary factors.

B. DNA

DNA is the molecule that carries genetic information, including genes. However, DNA encompasses much more than individual genes, and Mendel’s "factors" refer more precisely to specific hereditary units—genes—rather than the entire molecule.

D. Bases

Bases (adenine, thymine, cytosine, guanine) are part of nucleotides and make up the "rungs" of the DNA ladder. They are essential for genetic coding, but they are not synonymous with Mendel’s “factors.” Genes consist of many base pairs arranged in a specific sequence, so bases are components, not the whole.

Correct Answer C. Cells in G0 are assumed to live in a condition completely different from G1 state, they are metabolically inactive and useless

Explanation

Cells in G0 are often quiescent, meaning they are not actively dividing, but they are not metabolically inactive or useless. Many G0 cells maintain normal metabolic functions and can even re-enter the cell cycle under specific conditions. Some highly specialized cells, like neurons, remain in G0 permanently and perform critical functions throughout the organism's life.

Why other options are wrong

A. Cells in G0 are also called senescent, quiescent or resting cells

This is a true statement. The G0 phase includes cells that have exited the cell cycle and are often referred to as resting or quiescent. Depending on the context, these may also be senescent if they’ve exited permanently.

B. G0 is technically nor part of the loop of the cell cycle, as it represents a state of arrest

This statement is true. G0 is considered a separate, non-dividing state that exists outside the main loop of the cell cycle (G1, S, G2, M). It is a form of arrest in which cells do not proceed through the cycle unless reactivated.

D. Some cells enter G0 under environmental stress, others to prevent an attempt to divide, like fully differentiated neurons

This is accurate. Cells may enter G0 in response to stress to prevent damage during replication, or because they are terminally differentiated and no longer need to divide, as in the case of neurons or muscle cells.

Correct Answer C. rrYY and Rryy

Explanation

The F1 generation had round, yellow seeds, which indicates that the round seed (R) and yellow seed (Y) alleles are dominant over their respective recessive traits. The round and yellow phenotype can only result from one parent contributing a dominant allele for both traits. The other parent must contribute the recessive alleles, as shown in the genotypes rrYY (homozygous recessive for seed shape and homozygous dominant for seed color) and Rryy (heterozygous for shape and homozygous recessive for color).

Why other options are wrong

A. rrYy and RRyy

This combination would lead to offspring with both round and wrinkled seeds, but the offspring in the F1 generation had only round seeds. Therefore, these parental genotypes would not produce the observed results.

B. rrYy and Rryy

This combination would lead to some offspring with wrinkled seeds, but the F1 generation had only round seeds. Hence, this genotype pair would not produce all round seeds.

D. rrYY and RRyy

This pair would produce offspring with only yellow seeds (from rrYY) and only round seeds (from RRyy), but the F1 generation had round, yellow seeds, which requires different combinations of dominant and recessive alleles than those listed here.

Correct Answer B. After telophase 1

Explanation

In meiosis, a cell becomes haploid after telophase 1. During meiosis I, homologous chromosomes are separated into different cells, but the sister chromatids remain together. Once telophase 1 is complete and cytokinesis occurs, the resulting daughter cells are haploid, meaning they have only one set of chromosomes.

Why other options are wrong

A. After anaphase 1

Anaphase 1 is when homologous chromosomes are separated into different cells, but the chromosomes are still in pairs, and the daughter cells are still diploid (containing two sets of chromosomes). They do not become haploid until after telophase 1 and cytokinesis.

C. After anaphase 2

Anaphase 2 involves the separation of sister chromatids in meiosis II, but the cells are already haploid at this point. Therefore, meiosis does not result in haploid cells immediately after anaphase 2, but rather after telophase 1.

D. After telophase 2

While telophase 2 is part of meiosis II and produces haploid cells, the cell becomes haploid earlier, during telophase 1 after meiosis I has divided the chromosome pairs.

Correct Answer A. Period of growth (RNA, protein, and organelle synthesis)

Explanation

The G1 phase of the cell cycle is the first phase of interphase, during which the cell grows and carries out normal cellular activities, including the synthesis of RNA, proteins, and organelles. This phase is crucial for the preparation of DNA replication in the next phase (S phase) of the cell cycle.

Why other options are wrong

B. The stage of DNA synthesis.

DNA synthesis occurs during the S phase (Synthesis phase), not during G1. In the S phase, the cell replicates its DNA in preparation for cell division. G1 precedes this phase and focuses on growth and preparation for DNA replication.

C. The stage of actual cell division.

The actual cell division occurs during the M phase (Mitosis), not during G1. In G1, the cell is preparing for cell division, but division itself does not occur in this phase.

D. The stage just prior to meiosis.

Meiosis is a type of cell division that occurs in specialized cells, like gametes. The G1 phase is part of the interphase in the mitotic cycle, not directly related to the stages of meiosis. Meiosis involves different phases and occurs in cells that will give rise to gametes.

Correct Answer C. A fixed position on a chromosome where a gene is located.

Explanation

In genetics, a locus refers to the specific physical location of a gene or a genetic marker on a chromosome. Each gene occupies a particular locus, which is essential for determining the gene’s relationship to other genes and genetic traits.

Why other options are wrong

A. The observable properties of an organism

This refers to the phenotype, not the locus. The phenotype is the outward expression of an organism's traits, not the location of a gene on a chromosome.

B. The corresponding alleles on two chromosomes

This describes the concept of alleles, which are different forms of a gene. The locus refers to the position of the gene, not the alleles themselves.

D. The total genetic constitution of an individual

This describes the genotype, which refers to the entire genetic makeup of an individual, not the location of specific genes on chromosomes.

E. A group of alleles of different genes on a single chromosome

This describes a genetic linkage group or a haplotype, not a locus. A locus refers to the specific location of one gene, not a collection of alleles on a chromosome.

Correct Answer A. Cellular growth and preparation for DNA replication

Explanation

During the G1 phase of the cell cycle, the cell grows and prepares for DNA replication in the S phase. This phase involves the synthesis of proteins and RNA necessary for DNA replication. Additionally, the cell assesses its internal and external environment to ensure it is ready to enter the next phase of the cycle. It is characterized by intense metabolic activity and growth.

Why other options are wrong

B. DNA replication

DNA replication occurs during the S phase, not the G1 phase. In G1, the cell is focused on growth and preparation, while DNA replication is reserved for the subsequent phase of the cell cycle.

C. Chromosome segregation

Chromosome segregation occurs during mitosis, specifically during anaphase. This process ensures that the chromosomes are divided equally between the two daughter cells. It does not occur during G1.

D. Cell division

Cell division occurs in the M phase of the cell cycle, after the S and G2 phases. The G1 phase precedes DNA replication, which is why it is a preparation phase, not a division phase.

Correct Answer A. The phenotype refers to traits in an organism that can be observed

Explanation

The phenotype is the observable physical or behavioral traits of an organism, which are determined by its genetic makeup (genotype) and environmental factors. These traits can include characteristics like eye color, height, and hair texture. The phenotype represents what is visible or measurable in an organism, distinguishing it from the genotype, which refers to the underlying genetic code.

Why other options are wrong

B. The phenotype is the set of genes in an organism.

This is incorrect because the phenotype refers to the observable traits, not the set of genes. The set of genes in an organism is called the genotype. The genotype influences the phenotype but is not the same as it.

C. A gene consisting of a single allele is said to be polymorphic.

Polymorphism refers to the occurrence of two or more different alleles at a particular locus within a population, not a gene consisting of a single allele. A gene with only one allele would not be considered polymorphic.

D. Genotype is a synonym of locus.

This is incorrect. The genotype refers to the genetic makeup of an organism, while the locus refers to the specific location of a gene on a chromosome. They are not synonymous; the locus is a location, while the genotype refers to the actual genetic information present at that location.