Question 1

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), which results in the sickle cell trait.

Question 2

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 individual is said to express the dominant gene because dominant alleles always exert their effect over recessive alleles when both are present.

Question 3

The probability of a certain event occurring is defined as: P = number of specific events/total number of events. If an event happens one out of every two times its probability is_________ _.

Accepted Answer

The probability is calculated as 1 (specific event occurrence) divided by 2 (total number of events), which equals 0.5 or 50%.

Question 4

The complement of chromosomes in an individual is called the_________ .

Accepted Answer

The karyotype refers to the complete set of chromosomes in an individual, including their number, form, and size. It is often used to study chromosomal abnormalities.

Question 5

Alleles are_________ .

Accepted Answer

Alleles are variations 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 genes themselves; rather, they are specific versions of a gene.

Question 6

You notice that both of your parents have a widow's peak that is determined by the dominant allele W. You however, have a straight hairline, which is a homozygous recessive condition (ww). What are the possible genotypes of your parents?

Accepted Answer

Since you have a straight hairline (ww), both of your parents must carry at least one recessive allele (w) to pass on to you. The only option that allows both parents to have a widow's peak (dominant trait) while still being able to pass on a recessive allele to you is if both are heterozygous (Ww).

Question 7

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 have the same expression regarding the trait they control.

Question 8

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

The genotype of the parents is TT, which means that they are both homozygous dominant for tallness. This means that they will only produce gametes with the T allele. Therefore, the offspring of these parents will all be heterozygous dominant (Tt), which means that they will all be tall.

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 heterozygous genotype is an intermediate of the phenotypes of the homozygous genotypes, as seen in the example where crossing white and red flowers results in pink flowers.

Question 10

Genes present only on the X chromosome are called __________ .

Accepted Answer

Genes located on the X chromosome are referred to as sex-linked genes because they are linked to the sex chromosomes, and their expression patterns can differ between males and females due to the presence of one or two X chromosomes.

Question 11

You observe that your friend has dimples. Dimples result from the presence of the dominant gene D; absence of dimples is a homozygous recessive condition (dd). What genotype or genotypes might your friend have?

Accepted Answer

Since dimples are a dominant trait, your friend could have either one or two copies of the dominant allele (D), making the possible genotypes DD or Dd.

Question 12

How many autosomes do humans have?

Accepted Answer

Humans have 22 pairs of autosomes, totaling 44 autosomes. These are the chromosomes not involved in determining sex.

Question 13

Incomplete dominance occurs when_________ .

Accepted Answer

In incomplete dominance, neither the dominant nor recessive allele is completely expressed, resulting in a phenotype that is a blend of both alleles. For example, in snapdragons, the alleles for flower color may be red (dominant) and white (recessive). However, plants with one red allele and one white allele will have pink flowers, indicating that neither allele is completely dominant over the other.

Question 14

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 are Ss (carrier of sickle cell trait) and ss (affected by sickle cell anemia). When these genotypes are crossed, the possible genotypes for the offspring are Ss (carrier of the trait) and ss (affected by anemia), each with a 50% probability.

Question 15

If the probability of an event occurring is 50%, what is the probability of that event occurring 5 times in a row?

Accepted Answer

The probability of an event occurring 5 times in a row, when each occurrence has a probability of 50% or 1/2, is calculated by multiplying the probability of the event occurring once by itself five times: (1/2)^5 = 1/32.

Question 16

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 more infrequently seen in women because it is a sex-linked recessive trait. For a woman to express the trait, she must inherit two copies of the gene (one from each parent), whereas a man only needs one copy (from his mother) since it is located on the X chromosome and men have only one X chromosome.

Question 17

What is true about the sex chromosomes?

Accepted Answer

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

Question 18

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

Heterozygous individuals have two different alleles for a specific gene, meaning the alleles differ in their expression.

Question 19

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 effect of the color blindness allele.

Question 20

Genotype is_________ .

Accepted Answer

Genotype refers to an individual's actual genetic makeup, including all of their genes, both expressed and not expressed.

Quiz 45: Principles of Heredity