Question 1

Sex-linked disorders associated with the X chromosome are:

Accepted Answer

Sex-linked disorders are caused by mutant genes on the X chromosome. Females have two X chromosomes while males have one X and one Y chromosome. Therefore, if a male inherits a mutant gene on his only X chromosome, he will show the symptoms of the disorder. Females, on the other hand, would need to inherit two copies of the mutant gene (one on each X chromosome) to show symptoms, which is less likely.

Question 2

_____ genes are expressed when an individual is heterozygous for a trait that follows a Mendelian inheritance pattern.

Accepted Answer

When an individual is heterozygous for a trait following Mendelian inheritance, the dominant gene will be expressed while the recessive gene is masked.

Question 3

A male zygote has the _____ pattern of sex chromosomes.

Accepted Answer

A male zygote inherits one sex chromosome from each parent, resulting in a pattern of XY.

Question 4

Which factor is the basis of evolution?

Accepted Answer

Mutations are the basis of evolution. They create new genetic variations that can be passed on to the next generation, leading to changes in the gene pool over time. Random assortment of chromosomes and the process of crossing over also contribute to genetic variation, but they are not the primary driving force behind evolution.

Question 5

Kody, a boy, and Shakira, a girl, are brother and sister. They both inherit the same recessive allele for Trait T on their X chromosome from their mother. What is the relative likelihood of Kody and Shakira expressing Trait T?

Accepted Answer

Kody, being male, has only one X chromosome, so if he inherits the recessive allele, he will express Trait T. Shakira, being female, has two X chromosomes, so she would need to inherit the recessive allele from both parents to express Trait T.

Question 6

In regard to the chromosomes that parents pass on to their offspring, parents pass on:

Accepted Answer

During meiosis, homologous chromosomes can exchange genetic materials through a process called crossing-over, which results in chromosomes that are constituted differently than the parents' chromosomes. Additionally, during gamete formation, the random shuffling of maternal and paternal chromosomes and the independent assortment of homologous pairs further increase the genetic diversity in offspring. Therefore, offspring do not receive exact copies of their parents' chromosomes.

Question 7

A change in a section of DNA that is the result of either a random, spontaneous error or environmental factors is referred to as:

Accepted Answer

A change in DNA that is not inherited but occurs spontaneously or due to environmental factors is known as a mutation. The other options (polygenic inheritance, dominant-recessive pattern, random assortment) do not refer to changes in DNA but rather modes of inheritance or genetic processes.

Question 8

The gene that codes for Characteristic X has two alleles. Allele D is dominant, and Allele r is recessive. If the father is homozygous for Trait X with Allele r and the mother is heterozygous for Trait X, the chance that one of their offspring will exhibit form r for Trait X is _____.

Accepted Answer

The father is homozygous recessive (rr) and the mother is heterozygous (Dr). The possible offspring genotypes are Dr and rr, giving a 50% chance of exhibiting the recessive trait (rr).

Question 9

Developmental changes such as puberty, graying hair, and the reduced organ capacity that comes with age are caused in part by:

Accepted Answer

Developmental changes such as puberty, graying hair, and reduced organ capacity that come with age are regulated by regulator genes. These genes contain instructions that control gene expression, directing the development and functioning of different organs and tissues at different stages of life.

Question 10

Regulator genes are responsible for:

Accepted Answer

Regulator genes are responsible for controlling the expression of other genes, which means they can activate or deactivate them during development. They don't play a direct role in ensuring fertilization or determining an embryo's sex, though they can indirectly affect these processes through gene expression.

Question 11

Geneticist Geri notices that a woman exhibits Trait L. With certainty, she asks the woman, "Which of your parents also exhibits this trait?" The woman is surprised that Geri knew that one of her parents had to also display Trait L. Knowing which fact would have cleared up the woman's confusion?

Accepted Answer

If Trait L is governed by a dominant allele, then the woman only needs to inherit one copy of the allele from either parent in order to exhibit the trait. This would explain why Geri knew that one of her parents must also display Trait L. If Trait L is governed by a recessive allele, then both of the woman's parents would need to carry at least one copy of the allele in order for her to exhibit the trait. If Trait L involves polygenic inheritance, then it could be that multiple genes contribute to expressing the trait and it may not necessarily require one parent to display the trait in order for the woman to exhibit it.

Question 12

Which statement about genes is true?

Accepted Answer

Genes are not isolated units of function, and they are part of extensive networks of genes. The expression of genes is also affected by interactions with the environment, so B is incorrect. A is also incorrect, as genes that are turned off can sometimes be turned back on.

Question 13

Crossing over refers to:

Accepted Answer

Crossing over is a process that occurs during meiosis where two members of a homologous chromosomal pair exchange sections of DNA. This leads to genetic recombination and increases genetic diversity in offspring. The other choices are not correct definitions of crossing over.

Question 14

If an individual is heterozygous for a trait, he has inherited two:

Accepted Answer

Heterozygous means having two different alleles for a specific trait, one inherited from each parent. In contrast, homozygous individuals have two copies of the same allele for the trait. Therefore, option B is the correct choice.

Question 15

Which list is the correct order of events in the development of a male?

Accepted Answer

The Y chromosome encodes the SRY gene which triggers the prenatal formation of the testes. The testes then produce testosterone, which initiates the development of male reproductive structures and secondary sex characteristics. Therefore, the correct order is Y chromosome encodes protein, then prenatal formation of testes, and finally production of testosterone. Option B lists these events in the correct order.

Question 16

A recessive gene governs Trait M. If a child exhibits Trait M, then:

Accepted Answer

In order for a child to exhibit a recessive trait, they must inherit two copies of the recessive gene, one from each parent. Therefore, both parents must have at least one copy of the recessive gene for Trait M in order for their child to exhibit the trait.

Question 17

Different forms of a gene are referred to as:

Accepted Answer

Different forms of a gene are referred to as alleles.

Question 18

Which statement about gene expression is true?

Accepted Answer

Some genes are expressed only during specific stages or conditions in a cell's life, such as during development or in response to environmental changes.

Question 19

Which statement about mutations is true?

Accepted Answer

Mutations can provide an organism with a beneficial trait that increases its chance of survival and reproduction, such as resistance to a disease, and therefore more likely to pass on that trait to its offspring.

Answer: B
 Mutations can occur in both somatic cells and germ cells, but only mutations that occur in germ cells can be passed on to offspring.

Answer: C
 While some genetic diseases are caused by mutations, there are other causes of genetic diseases, such as chromosomal abnormalities or inherited traits.

Answer: D
 Mutations can occur due to a variety of causes, such as errors during DNA replication or exposure to radiation, and are not limited to chromosome swapping.

Question 20

Which statement about sex determination is true?

Accepted Answer

The presence of a Y chromosome is responsible for the development of a male individual. This is because the Y chromosome carries the SRY gene that triggers the development of testes and subsequent male characteristics. Therefore, only option D is true.

Quiz 3: Section 2: Biology and Behavior