Question 1

How many autosomes pairs do humans have?

Accepted Answer

Humans have 22 pairs of autosomes and 1 pair of sex chromosomes, making a total of 23 pairs of chromosomes.

Question 2

Incomplete dominance occurs when .

Accepted Answer

Incomplete dominance is a form of inheritance in which neither allele is completely dominant over the other, leading to a phenotype that is a blend or intermediate of the two parental traits.

Question 3

Autosomes are pairs of chromosomes that contain genes for determining .

Accepted Answer

Autosomes are chromosomes that contain genes for determining body characteristics, excluding those that determine the sex of an individual, which are found on sex chromosomes.

Question 4

What is true about the sex chromosomes?

Accepted Answer

Possession of the Y chromosome is what typically determines maleness in humans. Normal males have one X and one Y chromosome (XY), while normal females have two X chromosomes (XX).

Question 5

ABO blood types are determined by three alleles designated IA, IB, and i. A person with alleles IA and i will have the blood type .

Accepted Answer

The presence of the IA allele determines the A blood type, and since i is a recessive allele, it does not affect the A phenotype.

Question 6

Genotype is _.

Accepted Answer

Genotype refers to the genetic makeup of an individual, including all of its genes, not just those that are expressed. It is the underlying genetic code that can influence traits, which are then influenced by environmental factors to produce the phenotype, or the observable characteristics.

Question 7

The genes for color blindness are sex-linked and recessive. What is not true about the expression of color blindness?

Accepted Answer

Color blindness is less common in women because it is a sex-linked recessive trait. Women have two X chromosomes, so they would need two copies of the recessive allele to express color blindness. Men, having only one X chromosome, express color blindness if they inherit one recessive allele. Therefore, it is not frequently seen in women.

Question 8

Inheritance of ABO blood types is an example of .

Accepted Answer

ABO blood types are an example of codominance because both A and B alleles are expressed in the phenotype of AB blood type individuals.

Question 9

If white flowers are crossed with red flowers and the resulting plants have pink flowers, that condition is known as .

Accepted Answer

Incomplete dominance occurs when the phenotype of the heterozygotes is intermediate between the phenotypes of the homozygotes, as seen in the crossing of white and red flowers to produce pink flowers.

Question 10

If the parental genotypes for sickle cell anemia/trait are Ss and ss, what is the probability of offspring having the sickle cell trait? If there is some probability of offspring having sickle cell anemia, what is that probability?

Accepted Answer

The parental genotypes Ss (carrier of sickle cell trait) and ss (affected by sickle cell anemia) can produce offspring with genotypes Ss (sickle cell trait) and ss (sickle cell anemia) in a 1:1 ratio, meaning there is a 50% chance for the offspring to inherit the sickle cell trait and a 50% chance to inherit sickle cell anemia.

Question 11

If the genotype of an individual contains alleles for a particular trait that differ in their expression, the individual is said to be for that trait.

Accepted Answer

When an individual has two different alleles for a specific trait, they are considered heterozygous for that trait. This means the alleles differ in their expression, with one typically being dominant over the other.

Question 12

A complement of an individual's chromosomes displayed as homologous pairs is called the .

Accepted Answer

A karyotype is a complete set of chromosomes in an individual, displayed as homologous pairs. It is used to look for chromosomal abnormalities.

Question 13

If a person is homozygous for a particular trait, the alleles for that trait .

Accepted Answer

Homozygous individuals have two identical alleles for a particular gene, meaning the alleles will have the same expression for that trait.

Question 14

Predict the phenotype of a particular individual if the genotype of both parents is TT (T determines tallness, it is dominant; t determines dwarfism, it is recessive).

Accepted Answer

Since both parents have the genotype TT, which is homozygous dominant for tallness, their offspring will also inherit a dominant allele T from each parent, ensuring the phenotype is tall.

Question 15

Genes present only on the X chromosome are called _.

Accepted Answer

Sex-linked genes are those located on the sex chromosomes, specifically the X chromosome in this context. These genes can be responsible for certain traits or disorders that are inherited in a sex-linked manner.

Question 16

What is the probability of a male having color blindness if his X chromosome carries the c allele? (He is Xc. XC determines normal color vision, it is dominant. Xc determines color blindness.)

Accepted Answer

Since males have only one X chromosome, if it carries the allele for color blindness (Xc), they will express the trait because they do not have a second X chromosome that could potentially carry a normal vision allele (XC) to mask the color blindness allele.

Question 17

If an individual has alleles for a particular trait that differ in their expression, and one of the alleles always exerts its effect, the individual is said to express the _ gene.

Accepted Answer

The allele that always exerts its effect, regardless of the other allele present, is referred to as the dominant allele. This is a fundamental concept in genetics where dominant alleles mask the expression of recessive alleles in heterozygous individuals.

Question 18

A pair of chromosomes, one from the egg and one from the sperm, that carry complete (or nearly complete) genetic instructions for the same traits are called _.

Accepted Answer

A homologous pair refers to a pair of chromosomes, one inherited from each parent, that have the same genes at the same loci, but possibly different alleles. These chromosomes are crucial for sexual reproduction and genetic diversity.

Question 19

Alleles are _.

Accepted Answer

Alleles are different versions of a gene that code for the same trait on a pair of homologous chromosomes. They can be dominant or recessive, but they are not chromosomes themselves nor are they exclusively dominant or recessive genes.

Question 20

The inheritance of sickle cell anemia involves incomplete dominance. (S determines normal hemoglobin, it is dominant; s is the sickle cell gene). A homozygous recessive person has sickle cell anemia. A heterozygous person has the sickle cell trait. If parental genotypes are SS and ss, what is the probability of offspring having the sickle cell trait?

Accepted Answer

In this cross, one parent is SS (normal) and the other is ss (sickle cell anemia). All offspring will inherit one S allele from the SS parent and one s allele from the ss parent, making them all heterozygous (Ss) and thus having the sickle cell trait.

Quiz 45: Principles of Heredity