Question 1

Which of the following statements best describes the sickle-cell trait?

Accepted Answer

The sickle-cell trait is caused by a single mutation in the HBB gene, which codes for the beta-globin protein. This mutation creates a variant form of hemoglobin called HbS, which can cause red blood cells to become sickle-shaped and prone to getting stuck in blood vessels. Individuals with the trait have one copy of the mutated HBB gene and one copy of the normal HBB gene. Therefore, they possess both a dominant and recessive allele for the disorder. Individuals with sickle-cell trait typically do not display symptoms of the disease, but may be at risk for complications under certain conditions (e.g. extreme physical exertion, exposure to high altitude, dehydration).

Question 2

In people with sickle-cell anemia, certain red blood cells in their bodies are different from normal. What is different about these red blood cells?

Accepted Answer

The red blood cells in people with sickle-cell anemia are different from normal because they have an abnormal crescent or sickle-like shape, which can cause them to get stuck in small blood vessels and impede blood flow.

Question 3

Linda has one allele for curly hair and another for straight hair. What kind of alleles are these?

Accepted Answer

Linda has two different alleles for the same trait (hair type), which makes them heterozygous. Polyzygotic and dizygotic are not terms used in genetics, and homozygous alleles would mean that Linda has two identical alleles for the same trait.

Question 4

Which of the following analogies could be used to complete the phrase, "Genotype is to phenotype as"?

Accepted Answer

Genotype refers to the genetic makeup of an organism, while phenotype refers to the observable characteristics or traits of that organism, which can be influenced by the genotype and the environment. The analogy with "chromosome pattern is to facial features" is appropriate because the chromosome pattern (genetic information) influences the development of facial features (an observable trait), similar to how genotype influences phenotype.

Question 5

Which of the following comparisons can be used to complete the phrase, "Homozygous is to heterozygous as"?

Accepted Answer

Homozygous and heterozygous describe different types of genetic traits. Homozygous means two copies of the same allele, while heterozygous means two different alleles. Therefore, the best comparison to complete the phrase is "same is to different."

Question 6

Joseph is homozygous for normal blood cells. What does this mean?

Accepted Answer

Homozygous means that an individual has two matching alleles for a particular trait. In this case, Joseph has two normal alleles for blood cells, meaning he does not carry the recessive allele for sickle-cell anemia.

Question 7

What do we call the threadlike structures in the nucleus of a cell that contain genetic material?

Accepted Answer

Chromosomes are the threadlike structures in the nucleus of a cell that contain genetic material. They carry the genetic information necessary for the development and function of all living organisms. Germ discs, ectoderms, and phenotypes are not related to chromosomes or genetic material in the nucleus.

Question 8

Which of the following examples best illustrates the concept of genetic incomplete dominance?

Accepted Answer

Genetic incomplete dominance occurs when the heterozygous genotype produces an intermediate phenotype that is different from the dominant and recessive phenotypes. In example C, the individual inherits one allele for obesity and one for thinness, resulting in an average weight phenotype that is distinct from the extremes of obese or thin. The other examples (A, B, D) do not show incomplete dominance as they result in a dominant or recessive phenotype based on the alleles inherited.

Question 9

Kali is 180 centimetres (5 feet, 11 inches) tall, plays tennis, and is an all around nice person. What is this is a description of?

Accepted Answer

Kali's height, activity, and personality are observable traits or characteristics, which are part of her phenotype. Alleles (A) and genotype (B) refer to genetic makeup, while homozygosity (C) describes a state where an individual has two identical copies of a gene.

Question 10

Torey and Bill consult a geneticist regarding the risk that their baby will inherit sickle-cell disease. They are told that Torey carries the affected allele and Bill does not. What does this mean?

Accepted Answer

Torey is a carrier for the sickle-cell allele, meaning she has one copy of the normal allele and one copy of the sickle-cell allele. Bill does not carry the sickle-cell allele. Therefore, each of their children will inherit one copy of the normal allele from Bill, and one copy of either the normal or sickle-cell allele from Torey. There is a 50% chance the baby will inherit the sickle-cell allele from Torey and be a carrier like her, but there is no chance the baby will inherit two copies of the sickle-cell allele and develop the disease. Therefore, the baby has a 50% chance of inheriting sickle-cell trait and a 50% chance of inheriting only normal alleles.

Question 11

Which chromosomes are known as autosomes?

Accepted Answer

Autosomes are the chromosomes that are not associated with determining sex, so they exclude the sex chromosomes (X and Y). Humans have 23 pairs of chromosomes, and the last pair is the sex chromosomes. Therefore, the autosomes are the first 22 pairs.

Question 12

Ian is approached by a mad scientist who says he will pay Ian either $100 for each pair of his autosomes or $500 for each pair of his sex chromosomes. Assuming Ian wants to make as much money as possible, which offer should he take?

Accepted Answer

Humans have 22 pairs of autosomes and 1 pair of sex chromosomes. Taking $100 for each pair of autosomes would yield $2200 (22 pairs x $100), while taking $500 for the pair of sex chromosomes would yield only $500. Therefore, Ian would make more money by choosing the offer for his autosomes.

Question 13

Approximately how many genes does the average child have?

Accepted Answer

The average human has around 25,000 genes, though this number can vary slightly between individuals. Option A is far too low as even some viruses have more than 25 genes, and option C and D are both far too high.

Question 14

Which term describes the functional units of heredity?

Accepted Answer

Genes are the functional units of heredity that determine specific traits and are composed of DNA. Alleles are variations of a gene, DNA is the genetic material that carries the instructions for the development and function of all living organisms, and chromosomes are structures made up of DNA that hold genes. However, genes are the most specific and accurate answer to describing the functional units of heredity.

Question 15

Kirk is heterozygous for cheek dimples but is born with big dimples in both cheeks. What does this say about the allele for cheek dimples?

Accepted Answer

If Kirk is heterozygous and still exhibits the trait, then the allele for cheek dimples must be dominant.

Question 16

What makes up DNA?

Accepted Answer

DNA is made up of nucleotides, which consist of a nitrogenous base (adenine, thymine, guanine, or cytosine) bonded to a sugar molecule (deoxyribose) and a phosphate group. These nucleotides are then joined together in a repeating pattern to form long strands that make up the double helix structure of DNA.

Question 17

Which letter is used to designate one of the human sex chromosomes?

Accepted Answer

The human sex chromosomes are X and Y, and the letter Y is used to designate the male sex chromosome.

Question 18

Which process can best be explained by alleles?

Accepted Answer

Alleles are different forms of a gene that arise by mutation and are found at the same place on a chromosome. They can explain the genetic variation in traits such as the shape of red blood cells, which is relevant to conditions like sickle cell anemia. The other options are not directly explained by the concept of alleles.

Question 19

Genes provide the cell with a specific set of instructions. What kind of instructions are they?

Accepted Answer

Genes provide biochemical instructions to the cell, which determine the structure and function of proteins and other molecules that are necessary for cellular activities. These instructions are encoded in the DNA sequence of genes and are transcribed into RNA, which is then translated into proteins. The specific sequence of nucleotides in a gene determines the specific sequence of amino acids in the protein, which in turn determines the protein's three-dimensional shape and function in the cell.

Question 20

If tallness is dominant and designated as "T," and shortness is recessive and designated as "s," who would likely be short?

Accepted Answer

Since shortness is recessive and designated as "s", someone who is "ss" would likely be short.

Quiz 2: Biological Foundations