Question 1

At birth we inherit

Accepted Answer

At birth, humans inherit 23 pairs of chromosomes, totaling 46 chromosomes. Each parent contributes one chromosome to each pair, so we inherit 23 chromosomes from our mother and 23 from our father.

Question 2

__________ are chromosomes that do NOT contain the instructions for the development of sexual characteristics.

Accepted Answer

Autosomes are chromosomes that do not determine sex in organisms that have sex chromosomes. They carry the genetic information for the other traits of an organism.

Question 3

Sperm and ova

Accepted Answer

Sperm and ova are produced through meiosis, which reduces the chromosome number by half, resulting in gametes that contain a single set of chromosomes (haploid), unlike other body cells which are diploid.

Question 4

Each sperm or ova contains __________ chromosomes.

Accepted Answer

Sperm and ova, being haploid cells, each contain 23 chromosomes, which is half the number found in somatic (body) cells, making them ready for fertilization where they combine to form a full set of 46 chromosomes.

Question 5

Identical twins occur when

Accepted Answer

Identical twins occur when a single fertilized egg (ovum) splits into two, creating two genetically identical organisms. This is different from fraternal twins, where two separate eggs are fertilized by two separate sperm.

Question 6

Fraternal twins occur when

Accepted Answer

Fraternal twins occur when two different sperm fertilize two different ova, resulting in two genetically unique siblings born at the same time.

Question 7

The sex of a child is determined by

Accepted Answer

The sex of a child is determined by the type of sperm that fertilizes the ovum. Sperm can carry either an X or a Y chromosome, while ova always carry an X chromosome. If an X-carrying sperm fertilizes the ovum, the result is a female (XX). If a Y-carrying sperm fertilizes the ovum, the result is a male (XY).

Question 8

Homozygous is to __________ as heterozygous is to __________.

Accepted Answer

Homozygous refers to having two identical alleles for a particular gene, while heterozygous refers to having two different alleles for a gene.

Question 9

A recessive allele will influence the expression of a trait only when it

Accepted Answer

A recessive allele influences the expression of a trait only when it is paired with another recessive allele, forming a homozygous recessive genotype. Dominant alleles mask the expression of recessive alleles in heterozygous combinations.

Question 10

Suppose that one parent's contribution to eye colour are alleles that are homozygous for brown and the other parent's contribution are alleles that are homozygous for blue. What will be the eye colour of their children?

Accepted Answer

Brown eye color is typically dominant over blue eye color. If one parent contributes two brown alleles (homozygous dominant) and the other contributes two blue alleles (homozygous recessive), all their children will inherit one brown allele and one blue allele, resulting in brown eyes due to the dominance of the brown allele.

Question 11

A person who is heterozygous for blue eyes has

Accepted Answer

In genetics, eye color is often an example of simple Mendelian inheritance where brown eye color is typically dominant over blue eye color. Therefore, a person who is heterozygous for blue eyes carries one allele for blue eyes and one allele for brown eyes, but will exhibit the dominant brown eye phenotype.

Question 12

One parent is homozygous for blue eyes and the other parent is heterozygous for brown eyes. Which of the following is NOT a possible outcome for their children?

Accepted Answer

Homozygous brown eyes are not possible because one parent is homozygous for blue eyes, meaning they can only pass on alleles for blue eyes.

Question 13

Natural selection has favoured species that reproduce sexually because sexual reproduction

Accepted Answer

Sexual reproduction introduces genetic variation within a species, which increases the chances of survival under changing environmental conditions, making it an adaptive advantage.

Question 14

If the environment in which a genetically diverse species lives suddenly changes, we might reasonably expect that

Accepted Answer

Genetic diversity within a species increases the likelihood that some individuals will possess traits that allow them to survive in changing environments. This diversity acts as a buffer against extinction since different individuals may be adapted to cope with new conditions.

Question 15

Fruit fly larvae with "rover"phenotypes were more likely to survive under __________ conditions, whereas fruit fly larvae with "sitter"genes were more likely to survive under __________ conditions.

Accepted Answer

Rover phenotypes are advantageous in crowded conditions as they move more to find food, while sitter phenotypes are better in low-density conditions where movement is less necessary.

Question 16

Sokolowski and colleagues showed that fruit flies with either "rover"or "sitter"behavioural phenotypes were differently selected depending on the crowdedness of the environment. This study provided support for the idea that

Accepted Answer

Sexual reproduction may increase a species ability to adapt to environmental changes.

Question 17

Hemophilia is caused by a __________ gene on the __________ chromosome.

Accepted Answer

Hemophilia is caused by a recessive gene located on the X chromosome. Since males have only one X chromosome, a single recessive gene on their X chromosome will result in the disease. Females, having two X chromosomes, must have the gene on both chromosomes to exhibit the disease, making it much rarer in females.

Question 18

Although eamily carries the gene for hemophilia, she does not suffer from the disorder. This is because

Accepted Answer

Hemophilia is a sex-linked disorder carried on the X chromosome. Since females have two X chromosomes, a female with one allele for hemophilia and one allele for normal blood clotting will not exhibit the disorder because the normal allele is dominant over the allele for hemophilia.

Question 19

John has hemophilia and his wife carries the recessive gene but does not have the condition. If they were to have children, what is the probability that any male child would also carry the recessive gene but NOT have the condition?

Accepted Answer

Hemophilia is a sex-linked recessive disorder carried on the X chromosome. A male child inherits his X chromosome from his mother and Y chromosome from his father. Since John has hemophilia, he has an X chromosome with the hemophilia gene. His wife, being a carrier, has one normal X chromosome and one X chromosome with the hemophilia gene. A male child will inherit the Y chromosome from John and one of the X chromosomes from his mother. Therefore, he cannot be a carrier without having the condition, as males with the hemophilia gene on their single X chromosome will express the condition.

Question 20

The gene for hemophilia is carried on the sex chromosomes, which makes the disorder an example of a __________ gene

Accepted Answer

Hemophilia is an example of a sex-linked disorder because the gene responsible for hemophilia is located on the X chromosome. This means that males, with one X and one Y chromosome, are more likely to express the disorder when they inherit a single affected X chromosome, whereas females, with two X chromosomes, are typically carriers unless they inherit affected X chromosomes from both parents.

Quiz 3: Evolution, Heredity, and Behaviour