Heredity and Genetics (BIO 3105)

Correct Answer B. the cell would be unable to separate its chromosomes during cell division

Explanation

The spindle apparatus is essential for the separation of chromosomes during cell division, specifically in mitosis and meiosis. If the cell cannot form a spindle apparatus, the chromosomes cannot align and separate properly, which would lead to cell division errors, often resulting in cell death or genetic abnormalities.

Why other options are wrong

A. the cell would be unable to reform its cell wall following cell division

The ability to reform the cell wall is a function of the cell's machinery for cytokinesis, particularly in plant cells. While the spindle apparatus is crucial for chromosome separation, it does not directly affect the formation of the cell wall.

C. the cell would be unable to produce ATP

ATP production is carried out by the mitochondria, not by the spindle apparatus. The spindle apparatus is involved in cell division, not energy production.

D. the cell would be unable to synthesize proteins

Protein synthesis occurs in the ribosomes, not the spindle apparatus. While cell division may be disrupted, protein synthesis would still occur if the spindle apparatus were absent, as it is a separate cellular function.

Correct Answer C. Affected by the trait and in the second generation

Explanation

In a pedigree, filled symbols typically represent individuals affected by a genetic trait. The Roman numeral II indicates that the person is in the second generation of the family. Therefore, the individual is affected by the trait and belongs to the second generation.

Why other options are wrong

A. Not affected by the trait and in the second generation

This option is incorrect because a filled symbol represents someone affected by the trait, not unaffected.

B. Affected by the trait and is the second-oldest child in the family

The Roman numeral II indicates the generation, not the birth order within that generation. This option focuses on the child’s order, which is not specified by Roman numerals.

D. Affected by the trait and has an identical twin

While this person is affected by the trait, the pedigree symbol and Roman numeral do not provide information about whether the individual has a twin.

Correct Answer C. Organelles composed of ribosomal RNA and protein.

Explanation

Ribosomes are cellular organelles that play a crucial role in protein synthesis. They are composed of ribosomal RNA (rRNA) and proteins, and they function by translating messenger RNA (mRNA) into proteins. Unlike membrane-bound organelles, ribosomes can either be free in the cytoplasm or attached to the endoplasmic reticulum.

Why other options are wrong

A. Membrane-bound organelles responsible for energy production.

This is a description of mitochondria, not ribosomes. Mitochondria are membrane-bound organelles responsible for energy production through cellular respiration.

B. Structures made of DNA and protein that store genetic information.

This is more applicable to the structure of chromosomes or the nucleus, not ribosomes. Ribosomes do not store genetic information; they are involved in protein synthesis.

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 B. Heterozygous

Explanation

An individual who possesses two different alleles for a specific gene is described as heterozygous. In a heterozygous pair, one allele may be dominant, and the other may be recessive, or both could be different dominant alleles, depending on the gene. Heterozygosity contrasts with homozygosity, where the two alleles for a gene are identical.

Why other options are wrong

A. Homozygous

This is incorrect because homozygous refers to having two identical alleles for a specific gene, not two different ones. An individual with a homozygous genotype has either two dominant alleles or two recessive alleles for a particular gene.

C. Hemizygous

This is incorrect because hemizygous refers to having only one allele for a gene, often used when referring to sex chromosomes in males (e.g., males have one X chromosome and one Y chromosome, making them hemizygous for X-linked genes). Hemizygosity is different from having two different alleles.

D. Polygenic

This is incorrect because polygenic refers to traits that are influenced by multiple genes, not a condition where an individual has two different alleles for a specific gene. Polygenic inheritance involves the combined effect of many genes on a single trait.

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. 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 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 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.