Heredity and Genetics (BIO 3105)

Correct Answer B. Both alleles are expressed in the phenotype.

Explanation

Codominance occurs when both alleles of a gene are equally expressed in the phenotype of a heterozygous individual. In this case, neither allele is dominant or recessive, and both contribute to the observed trait. An example of codominance is seen in human blood types, where both A and B alleles are expressed in individuals with the AB blood type.

Why other options are wrong

A. One allele is dominant over the other allele.

This option describes complete dominance, where one allele is expressed over the other in the phenotype. However, codominance involves both alleles being expressed equally, so this explanation is not correct.

C. Neither allele is expressed in the phenotype.

This option does not apply to codominance. In codominance, both alleles are expressed in the phenotype, so this is not a valid explanation for how codominant traits are expressed.

Correct Answer E. The lysosomes lack sufficient amounts of enzymes necessary for metabolism of lipids.

Explanation

Lysosomes are responsible for breaking down various biomolecules, including lipids, using specific enzymes. Gaucher disease results from a deficiency in one such lysosomal enzyme, glucocerebrosidase, which is required for breaking down a particular lipid. When this enzyme is absent or malfunctioning, lipids accumulate in various tissues, leading to the symptoms observed in Gaucher disease.

Why other options are wrong

A. Mitochondria are most likely defective and do not produce adequate amounts of ATP needed for cellular energy.

While mitochondria are essential for energy production, their dysfunction would cause general energy-related problems, not the lipid storage issues seen in Gaucher disease. This disease is tied to a specific breakdown process in lysosomes, not ATP deficiency.

B. Rough ER contains too many ribosomes, which results in an overproduction of the enzyme involved in lipid breakdown.

This option incorrectly implies that an overproduction of the enzyme would cause disease. Gaucher disease is due to an enzyme deficiency, not an excess. Also, rough ER abnormalities are not a primary feature of this disorder.

C. The peroxisome malfunctions and begins breaking down harmful substances instead of fatty materials.

Peroxisomes are involved in breaking down very long-chain fatty acids and detoxification, but Gaucher disease specifically involves lysosomal enzymes, not peroxisomal function. The breakdown of harmful substances is still a typical role of peroxisomes, making this choice inaccurate.

D. The Golgi apparatus produces vesicles with faulty membranes that fail to transport to the plasma membrane.

Although the Golgi apparatus is involved in modifying and trafficking proteins and enzymes, the root problem in Gaucher disease lies in enzyme deficiency, not vesicle transport errors. Faulty vesicle membranes are not the central issue in this condition.

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 D. Segregation

Explanation

Mendel used monohybrid crosses to discover the law of segregation, which states that during the formation of gametes, the two alleles for a trait separate so that each gamete carries only one allele for each gene. This discovery was crucial in the development of modern genetics.

Why other options are wrong

A. Pangenesis

Pangenesis was a theory proposed by Charles Darwin that suggested all parts of the body contribute to the inheritance of traits. This is not related to Mendel's work, which focused on heredity through discrete units of inheritance (genes).

B. Independent assortment

While Mendel also discovered the law of independent assortment (which states that genes for different traits are inherited independently of each other), he used dihybrid crosses, not monohybrid crosses, to discover this law. The law of segregation is directly related to monohybrid crosses.

C. Preformationism

Preformationism is an outdated theory that suggests offspring develop from miniature versions of themselves inside the sperm or egg. This theory is not related to Mendel's discoveries on inheritance.

E. Blending inheritance

Blending inheritance was a pre-Mendelian theory that proposed offspring are a blend of their parents' traits. Mendel's work contradicted this theory by demonstrating that inheritance follows specific patterns, such as segregation.

Correct Answer A. Increased awareness of human rights

Explanation

The shift in public perception regarding the eugenics movement in the United States was significantly influenced by the growing awareness of human rights. The eugenics movement, which sought to improve the human gene pool through selective breeding, was criticized for its unethical practices, including forced sterilizations and discriminatory policies. As awareness of the rights and dignity of individuals increased, especially in the post-World War II era, the movement's ideas were increasingly rejected.

Why other options are wrong

B. Advancements in genetic research

While advancements in genetic research did contribute to our understanding of heredity, they did not play as significant a role in the decline of the eugenics movement. The shift was more about social awareness and human rights, not scientific breakthroughs in genetics.

C. Support from prominent scientists

This is incorrect because, although some scientists initially supported eugenics, the movement lost support from prominent scientists as its unethical practices were exposed, particularly after its association with Nazi policies.

D. Government funding for eugenics programs

This is incorrect because government funding for eugenics programs initially helped to support and spread the movement, rather than contributing to the shift in public perception. The rejection of eugenics came later when its practices were recognized as harmful and unethical.

Correct Answer B. The trait disappeared in the F1 generation and reappeared in the F2 generation.

Explanation

In Mendel's monohybrid crosses, the recessive trait disappeared in the F1 generation when crossed with a dominant trait. However, this trait reappeared in the F2 generation, leading Mendel to conclude that traits can be dominant (which are expressed in the F1 generation) and recessive (which are masked in the F1 generation but reappear in the F2 generation).

Why other options are wrong

A. The trait was consistently expressed in the F1 generation

This is true for dominant traits, but it does not explain the inheritance of recessive traits, which were the focus of Mendel's observations.

C. The trait was linked to environmental factors

Mendel's experiments focused on inheritance patterns, not environmental influences. The expression of traits he observed was genetic, not influenced by the environment.

D. The trait was present in both the F1 and F2 generations

While traits do appear in both generations, this statement doesn't specifically explain why Mendel concluded that traits can be dominant or recessive. It was the reappearance of the recessive trait in the F2 generation that provided that insight.

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 B. 2003

Explanation

The Human Genome Project, which aimed to map and understand all the genes in the human genome, was completed in 2003. This project has significantly advanced our understanding of genetics and the role of genes in human biology and disease.

Why other options are wrong

A. 1989

While research in genetics was underway during this time, the Human Genome Project was not completed in 1989. The project started in 1990 and concluded in 2003.

C. 2010

The Human Genome Project was completed in 2003, not 2010. However, further research and sequencing of genomes have continued after the project’s completion.

D. Yet to be completed

This statement is incorrect, as the main goal of the Human Genome Project was achieved by 2003. However, continued research and genome sequencing have expanded upon the project's findings.

Correct Answer A. Its misuse for social and political purposes by the Nazis

Explanation

The eugenics movement in the United States declined in the early 20th century after it was associated with the Nazis and their regime's policies, which included forced sterilizations and genocide. The eugenics movement was initially promoted as a scientific approach to improve the human gene pool, but the atrocities committed by the Nazis using eugenics as justification led to widespread rejection of the movement.

Why other options are wrong

B. Violent protests by the medical community

This is incorrect because while there were ethical concerns raised within the medical community, the decline of the eugenics movement was not largely due to violent protests. The movement's discrediting was more significantly tied to its misuse and association with Nazi policies.

C. Breakthroughs in genetic technology

This is incorrect because while breakthroughs in genetics have influenced how we view human genetics, the decline of eugenics in the U.S. was primarily a result of the eugenics movement's misuse by the Nazis, rather than advances in genetic technology. The association with Nazi practices played a crucial role in discrediting it.

D. The ability to manipulate gene expression

This is incorrect because the ability to manipulate gene expression is a relatively modern development in genetics. The decline of eugenics occurred before these technologies were fully developed or understood. The discrediting of eugenics in the early 20th century was more related to its unethical application during the Nazi era.