Heredity and Genetics (BIO 3105)

Correct Answer A. Alleles of different genes segregate independently of one another

Explanation

The principle of independent assortment states that alleles for different traits segregate, or separate, independently of each other during the formation of gametes. This allows for the random combination of alleles for different genes in the offspring.

Why other options are wrong

B. All alleles are inherited together as a single unit

This is incorrect because it contradicts the principle of independent assortment. While alleles on the same chromosome may be inherited together due to genetic linkage, independent assortment applies to alleles on different chromosomes.

C. Genes located on the same chromosome are always inherited together

This is incorrect because genes on the same chromosome may be inherited together, but they are not always inherited together due to the possibility of crossing over during meiosis, which can separate linked genes.

D. Independent assortment only occurs in organisms with multiple chromosomes

This is incorrect because independent assortment occurs whenever genes are located on different chromosomes, regardless of the number of chromosomes an organism has. It is not restricted to organisms with multiple chromosomes.

Correct Answer A. Insertion of normal genes to act in place of mutant genes

Explanation

Gene therapy is a medical treatment that involves inserting or altering genes within a person's cells to treat or prevent disease. The goal is typically to replace defective or missing genes with normal ones to correct genetic disorders.

Why other options are wrong

B. Mapping of all human genetic information

This refers to the Human Genome Project, not gene therapy. The Human Genome Project focused on sequencing and mapping human DNA, while gene therapy focuses on treating genetic diseases by replacing or repairing faulty genes.

C. Cloning of genes to produce and purify therapeutically useful proteins

This describes recombinant DNA technology, not gene therapy. While gene therapy may involve genes, recombinant DNA technology focuses on cloning and producing proteins like insulin, but not necessarily inserting them into human cells to treat diseases.

D. Insertion of human genes into other organisms

This describes genetic engineering, where genes from humans (or other organisms) are inserted into different species, not gene therapy. Gene therapy specifically focuses on treating human diseases by directly altering the genetic material of the patient.

Correct Answer B. The exchange of genetic material between homologous chromosomes during meiosis

Explanation

Genetic recombination occurs during meiosis when homologous chromosomes exchange genetic material through a process called crossing over. This results in the production of new combinations of alleles in the offspring, contributing to genetic diversity. Recombination is a crucial mechanism in heredity that increases variability within populations.

Why other options are wrong

A. The process by which DNA is replicated.

DNA replication is a process in which a cell copies its DNA before division, ensuring that each daughter cell has a complete set of genetic material. While this is important for cell division, it is not considered genetic recombination, as there is no exchange of genetic material between chromosomes.

C. The mutation of genes due to environmental factors.

Gene mutations caused by environmental factors, such as radiation or chemicals, can change the DNA sequence. However, this is not considered genetic recombination, which specifically involves the exchange of genetic material during meiosis.

D. The formation of new alleles through random mutations.

While mutations can lead to the creation of new alleles, this is not the same as genetic recombination. Recombination involves the mixing of existing genetic material between chromosomes, whereas mutations create new genetic variants.

Correct Answer A. The accumulation of fat in white blood cells

Explanation

Gaucher disease is caused by a deficiency in the enzyme glucocerebrosidase, which leads to the accumulation of fatty substances in various organs, including the liver, spleen, and bone marrow. This accumulation is particularly notable in macrophages, which are a type of white blood cell.

Why other options are wrong

B. The spontaneous breakdown of red blood cells

While Gaucher disease can affect blood cells, it is not primarily caused by the breakdown of red blood cells. The condition is linked to the accumulation of fat in certain types of white blood cells, particularly macrophages.

C. The breakdown of the myelin sheath around nerves

The breakdown of the myelin sheath is associated with diseases like multiple sclerosis, not Gaucher disease. Gaucher disease mainly affects organs like the liver and spleen, and the nervous system may be involved in some cases, but the primary issue is the accumulation of lipids, not nerve damage due to myelin loss.

D. The lack of critical liver enzymes

The problem in Gaucher disease is not specifically the lack of liver enzymes, but rather the lack of glucocerebrosidase, an enzyme that is needed to break down certain lipids. This enzyme deficiency leads to the buildup of fatty materials in various organs, including the liver, but it is not the liver enzymes themselves that are deficient.

Correct Answer A. An observable trait

Explanation

A phenotype refers to the observable characteristics or traits of an organism, such as its appearance, behavior, or physiological properties. These traits result from the interaction of an organism's genetic makeup (genotype) and its environment.

Why other options are wrong

B. A derived trait

This is incorrect because a derived trait is one that is different from the ancestral trait and evolved in a specific lineage. It is a specific type of trait, not a general definition of phenotype.

C. An organism's genes

This is incorrect because genes refer to the genetic code that an organism carries in its DNA, which makes up the genotype. The phenotype is the expression of these genes, influenced by both genetics and environmental factors.

D. An evolutionary trait

This is incorrect because an evolutionary trait refers to a characteristic that has evolved in a population over generations. While phenotypic traits can be evolutionary, the term phenotype itself simply refers to the observable traits of an individual organism.

Correct Answer A. Cytokinesis

Explanation

Spindle fibers are essential for chromosome movement and alignment during cell division, but they are not involved in cytokinesis. Cytokinesis is the process that physically separates the cytoplasm into two daughter cells after nuclear division has occurred. It follows the formation and function of spindle fibers in mitosis or meiosis, making it the phase where spindle fibers are not present or active.

Why other options are wrong

B. Mitosis

Spindle fibers are a critical component of mitosis. They form during prophase and are responsible for aligning and separating chromosomes during metaphase and anaphase. Without spindle fibers, mitosis would not proceed correctly, making this option incorrect.

C. Meiosis 2

In Meiosis 2, spindle fibers form again to separate sister chromatids. This is similar to mitosis and is essential for the correct distribution of chromosomes to the daughter cells. Since spindle fibers are formed and used in this process, this answer is incorrect.

D. Meiosis 1

Spindle fibers also form in Meiosis 1, where they help in separating homologous chromosomes. Their role is crucial for reducing the chromosome number by half in gamete formation. Therefore, it is incorrect to say that spindle fibers do not form in Meiosis 1.

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 B. Chromatid separation

Explanation

During prophase I of meiosis, chromatid separation does not occur. Chromatid separation happens later during anaphase II, after the centromere has been divided and the sister chromatids are pulled apart. Prophase I is primarily concerned with the condensation of chromosomes, crossing over (genetic recombination), and spindle fiber attachment.

Why other options are wrong

A. Crossing over

Crossing over occurs during prophase I, where homologous chromosomes exchange genetic material at the chiasmata, which is a critical event in genetic variation.

C. Chromosome alignment

Chromosomes align at the metaphase plate during metaphase I, not during prophase I. However, the preparation for alignment occurs during prophase I, as chromosomes condense and become visible.

D. Spindle fiber attachment

Spindle fibers attach to the centromere during prophase I, helping to move the chromosomes during subsequent stages of meiosis. This attachment is a crucial part of chromosome separation in later stages of meiosis.

Correct Answer D. It will be unable to complete either mitosis or meiosis.

Explanation

Spindle fibers are crucial for the proper segregation of chromosomes during both mitosis and meiosis. If a cell cannot produce spindle fibers, it will be unable to properly align and separate its chromosomes, preventing successful cell division. This failure often leads to cell cycle arrest or errors in chromosome distribution.

Why other options are wrong

A. It can successfully complete mitosis.

This is incorrect because spindle fibers are necessary for mitosis. Without them, the cell cannot proceed through the stages of mitosis successfully, as chromosome alignment and separation are disrupted.

B. It can successfully complete meiosis.

This is incorrect because meiosis also requires spindle fibers to ensure the proper division of chromosomes. Without spindle fibers, meiosis cannot be completed correctly, resulting in errors during gamete formation.

C. It will undergo apoptosis.

While apoptosis could be triggered due to errors in cell division, it is not a guaranteed consequence. The inability to produce spindle fibers may first result in a halted cell cycle, with apoptosis potentially occurring later as a response to the damage. However, it doesn't always lead directly to apoptosis.