Heredity and Genetics (BIO 3105)

Correct Answer C. Human traits are predominantly determined by genetic inheritance

Explanation

Hereditarianism is a theory that emphasizes the primary role of genetic inheritance in shaping human traits and behaviors. It asserts that most aspects of a person’s physical and psychological makeup are influenced more by heredity than by environmental factors. While this perspective may not account for environmental influences, it underscores the dominant role of genes in human development.

Why other options are wrong

A. Human traits are solely influenced by environmental factors

This view contradicts the core idea of hereditarianism. While environmental factors do play a role in shaping human traits, hereditarianism specifically argues for a genetic predominance. Asserting that traits are solely influenced by the environment overlooks the significant contributions of DNA and hereditary mechanisms.

B. Human traits are a result of both genetics and environment

This perspective is more in line with modern epigenetics or interactionist theories, not hereditarianism. While it is a more balanced view, it does not represent the primary assertion of hereditarianism, which leans heavily toward genetic determination rather than a combination.

D. Human traits are entirely random and unpredictable

This statement disregards decades of scientific understanding in both genetics and developmental biology. Hereditarianism is rooted in predictability based on heredity, so this option misrepresents the concept entirely and lacks scientific foundation.

Correct Answer B. The maximum number of times a cell can divide before entering senescence

Explanation

The Hayflick Limit refers to the number of times a normal, somatic (non-reproductive) cell will divide before cell division stops and the cell enters a state called senescence. This limit is influenced by the shortening of telomeres, which protect the chromosomes during cell division. Once the telomeres shorten beyond a critical length, the cell can no longer divide and enters senescence.

Why other options are wrong

A. The maximum length of a chromosome

The Hayflick Limit is not about the length of chromosomes but rather the number of times a cell can divide. The length of a chromosome can vary, but this is not related to the Hayflick Limit.

C. The maximum length of a telomere

The Hayflick Limit is related to telomere shortening, not the length of a telomere. As telomeres shorten with each cell division, it contributes to the limit on how many times a cell can divide.

D. The G1/S cell cycle checkpoint

The G1/S checkpoint is a control mechanism in the cell cycle that checks for cell size, DNA integrity, and nutrient availability. It is unrelated to the Hayflick Limit, which specifically deals with the number of divisions before senescence.

E. The maximum number of times a cell can divide before undergoing apoptosis

The Hayflick Limit refers to senescence, not apoptosis. Apoptosis is a programmed cell death process, whereas the Hayflick Limit concerns cellular aging and division cessation.

F. The G2/M cell cycle checkpoint

The G2/M checkpoint is involved in ensuring the cell is ready to undergo mitosis, checking for DNA damage or errors. It is unrelated to the Hayflick Limit.

Correct Answer A. segregation and independent assortment

Explanation

During meiosis, the principles of segregation and independent assortment govern how genes are distributed into gametes. Segregation ensures that each gamete receives one allele from each gene pair, while independent assortment describes how genes on different chromosomes are distributed independently. These principles make it possible to predict the inheritance patterns of traits across generations using tools like Punnett squares.

Why other options are wrong

B. segregation and crossing over

Although segregation occurs during meiosis, pairing it with crossing over does not fully explain the predictability of inheritance patterns. Crossing over introduces genetic variation but does not follow a predictable Mendelian pattern. It disrupts gene linkage but does not substitute for the role of independent assortment.

C. independent assortment and crossing over

This option overlooks the essential role of segregation, which is a foundational concept in Mendelian inheritance. While independent assortment and crossing over contribute to genetic variation, segregation is necessary for ensuring that alleles separate into different gametes, which allows for predictable outcomes.

D. random assortment and segregation

"Random assortment" is not a defined principle in classical genetics. The term is likely a misrepresentation of "independent assortment." While segregation is correct, pairing it with a vague or inaccurate term makes this option incorrect in the context of established genetic principles.

Correct Answer A. Determined only by genes

Explanation

Hereditarianism is the belief that human traits, including intelligence, behavior, and physical characteristics, are solely determined by genetic inheritance, with minimal or no influence from environmental factors. This perspective views genetics as the primary determinant of an individual's traits.

Why other options are wrong

B. Partly influenced by the environment

This is incorrect because hereditarianism specifically emphasizes the role of genetics over environmental influences. The idea that traits are partly influenced by the environment would be more aligned with modern views that emphasize gene-environment interactions.

C. Influenced equally by genes and the environment

This contradicts hereditarianism, which posits that traits are determined predominantly by genetics, not by an equal balance of genetic and environmental factors.

D. Traceable to our earliest ancestors

While human traits may be influenced by ancestry, hereditarianism focuses specifically on the belief that genetics, rather than ancestral or environmental factors, are the primary determinants of traits.

Correct Answer A. 1:2:1

Explanation

In incomplete dominance, the heterozygous individuals show an intermediate phenotype between the two homozygous phenotypes. In a typical P1 cross where two homozygous parents (one for each trait) are crossed, the F1 generation will have a 1:2:1 phenotypic ratio. This is because one-quarter will express one homozygous trait, two-quarters will express the intermediate heterozygous trait, and one-quarter will express the other homozygous trait.

Why other options are wrong

B. 3:1

The 3:1 ratio is characteristic of Mendelian inheritance, where one allele is dominant over the other. In incomplete dominance, both alleles contribute to the phenotype, resulting in an intermediate phenotype rather than a dominant/recessive pattern. Therefore, the ratio in incomplete dominance is 1:2:1, not 3:1.

C. 9:3:3:1

The 9:3:3:1 ratio is observed in a dihybrid cross involving two genes with complete dominance, not in incomplete dominance. In incomplete dominance, the resulting phenotype does not follow this pattern because there is no dominance of one allele over the other.

D. 1:1

The 1:1 ratio typically applies to monohybrid crosses between heterozygous and homozygous parents in Mendelian inheritance. It does not apply to incomplete dominance, where the offspring show a range of phenotypes, resulting in a 1:2:1 ratio rather than 1:1.

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 D. More than one of the above

Explanation

Genetic testing can serve multiple purposes, including diagnosing diseases, guiding prenatal care, and determining effective drug treatments. It provides insights into genetic predispositions that can help in making informed medical decisions. Therefore, more than one option listed is valid, making D the most comprehensive and correct answer.

Why other options are wrong

A.  Assesment of therapeutic drug treatment

While this is a valid use of genetic testing, it is only one aspect of its broader application. Genetic testing also includes diagnostic and prenatal uses, which this option does not account for. Limiting the answer to just drug treatment omits other critical applications.

B. Prenatal care

This is another legitimate use of genetic testing, particularly for identifying genetic disorders in a fetus. However, like option A, it does not cover the full range of uses, which include drug response and disease diagnosis. Thus, it is not as complete as option D.

C. Diagnosing disease

Genetic testing is widely used to diagnose inherited conditions and to assess genetic predisposition to certain diseases. However, this answer alone overlooks its use in prenatal care and treatment planning. Selecting only this answer does not fully capture the range of applications.

Correct Answer A. Alleles

Explanation

Alleles are different forms of a gene that can exist at a specific locus on a chromosome. Each individual has two alleles for each gene, one inherited from each parent. The variations in these alleles can result in different traits being expressed.

Why other options are wrong

B. Chromosomes

Chromosomes are structures made of DNA and protein that carry genes. A chromosome can contain many genes, but it is not used to describe the different forms of a gene at a specific locus.

C. Genotypes

Genotypes refer to the genetic makeup of an organism in terms of the alleles it possesses. While alleles contribute to a genotype, the term genotype itself does not describe the variations of a gene at a locus.

D. Phenotypes

Phenotypes refer to the observable traits or characteristics of an organism, which result from the interaction of the genotype and the environment. It is not used to describe variations of a gene

Correct Answer A. It suggests that traits acquired during an individual's lifetime can be inherited by their offspring.

Explanation

The concept of 'soft' inheritance, also known as Lamarckian inheritance, proposes that traits acquired or modified during an individual's lifetime due to environmental influences or personal experiences can be passed down to offspring. This idea contrasts with the more widely accepted concept of 'hard' inheritance, where genetic traits are inherited strictly according to DNA passed from parent to offspring.

Why other options are wrong

B. It emphasizes the role of genetic information passed from one generation to the next.

This is incorrect because this describes the concept of Mendelian inheritance, not soft inheritance. 'Soft' inheritance suggests the inheritance of acquired traits, not the genetic transmission of traits.

C. It asserts that all traits are determined solely by genetics.

This is incorrect because 'soft' inheritance does not focus solely on genetics. It includes the inheritance of traits that have been altered by environmental factors during an individual's life, such as changes in behavior or physical characteristics due to environmental influences.

D. It is a modern and widely accepted theory in the field of biology.

This is incorrect because 'soft' inheritance is not widely accepted in modern biology. The prevailing theory is that inheritance is largely based on genetic information passed through DNA, and the idea of inheriting acquired characteristics has largely been discredited in favor of genetic inheritance mechanisms.