High School Biology : Genetics and Evolution

Study concepts, example questions & explanations for High School Biology

varsity tutors app store varsity tutors android store

Example Questions

Example Question #12 : Understanding Dominant/Recessive

Sharon has blonde hair. Her husband is heterozygous for brown hair, with brown being the dominant autosomal trait. What percent chance will their daughter have blonde hair?

Possible Answers:

100%

0%

25%

75%

50%

Correct answer:

50%

Explanation:

The genotype for Sharon is rr, because blonde is a recessive trait therefore in order to have blonde hair she must be homozygous recessive. Her husband is Rr, because it states that he has brown hair, which is dominant, in addition to being heterozygous. When drawing out a punnet square, you will find the offspring will be Rr, Rr, rr and rr. Therefore, their daughter has 50% chance of having brown hair and 50% chance of having blonde hair.

Example Question #62 : Genetics And Evolution

Sickle cell disease can be terrible and painful; however, the sickle cell trait (heterozygous for the sickle cell gene) is protective against malaria. 

Molly is married to Fred. Molly has the recessive disorder of sickle cell anemia. Fred does not have the disease and is also not a carrier. What is the chance that Molly and Fred's children are all carriers of the disease?

Possible Answers:

25%

100%

50%

75%

0%

Correct answer:

100%

Explanation:

Since Molly is autosomal recessive (ss) and Fred is autosomal dominant (SS), all their children will be heterozygotes, or carriers and they will thus all be protected against malaria.

Example Question #61 : Genetics And Evolution

The eye color brown is superior to blue. Linda has brown eyes and marries someone with blue eyes. Linda's father has blue eyes and her mother is homozygous dominant. What is the percent chance of Linda's children having blue eyes? 

Possible Answers:

0.75

1.0

0.25

0.50

Correct answer:

0.50

Explanation:

Linda's mother has brown eyes: BB

Linda's father has blue eyes: bb

Using the pedigree (BB x bb), Linda has to be Bb (100%). Linda is marrying someone with blue eyes (bb). Doing the pedigree of Linda (Bb) and her partner (bb) gives you 0.50 Bb (brown eyes) and 0.50 bb (blue eyes). 

Example Question #27 : Genetics Principles

Consider a rare plant that exhibits the phenotype of dark blue leaves (BB) as its dominant trait and and light blue leaves (bb) as its recessive trait. It flowers a bright yellow flower (YY) when dominant, and an orange flower (yy) when recessive. 

When two dihybrid plants of the same species are crossed, what will be the expected phenotypic ratio of offspring that exhibit light blue leaves and yellow flowers? 

Possible Answers:

Correct answer:

Explanation:

Dihybridcross

Once you properly set up your punnet square of a dihybrid cross, you should obtain a phenotypic ratio of 9:3:3:1. There will be 9 plants with dark blue leaves/yellow flowers, 3 plants with light blue leaves/yellow flowers, 3 plants with dark blue leaves/orange flowers, and 1 plant with light blue leaves/orange flowers.

Example Question #62 : Genetics And Evolution

Traits (alleles) are separated from one another during formation of gametes and are transmitted independently of one another according to __________.

Possible Answers:

the law of independent assortment

the law of the Mendelian genome

the law of mitotic inheritance

the law of segregation

Correct answer:

the law of independent assortment

Explanation:

During metaphase of meiosis, chromosomes form tetrads at the center of the cell. These tetrads are formed from pairs of homologous chromosomes. One chromosomes came from the organism's mother and the other from its father. During alignment, these chromosomes are arranged randomly, such that each gamete will have a combination of maternal and paternal DNA from the organism. This random mixing of DNA during gamete formation is known as the law of independent assortment, and plays a key role in diversifying the genetic background of offspring that form from the gamete.

Example Question #1 : Understanding Chromosomes

In a dihybrid cross (AaBb x AaBb), how many total genotypes are possible in the offspring?

Possible Answers:

Correct answer:

Explanation:

The alleles for gene A assort independently from the alleles of gene B, meaning that the genotype for one does not affect the genotype of the other. Even though there are two genes, we can solve this problem by answering the question separately for the two genes.

There are three possible genotypes with respect to the A gene (AA, Aa, aa) and three possible genotypes with respect to the B gene (BB, Bb, bb). Since genes A and B assort independently, the possible offspring will be the product of the possibilities for each separate gene.

Listed out, these genotypes are: AABB, AABb, AaBB, AAbb, AaBb, aaBB, Aabb, aaBb, aabb.

Example Question #2 : Understanding Chromosomes

If a somatic cell of a diploid organism contains eight chromosomes during interphase, which of the following must be true?

Possible Answers:

A gamete will contain eight chromosomes

A gamete will contain four chromosomes

A germ cell in metaphase I will contain four chromosomes

A somatic cell in metaphase will contain eight chromatids

Correct answer:

A gamete will contain four chromosomes

Explanation:

A somatic cell is a non-sex cell. During interphase (i.e. not during mitosis), a somatic cell of a diploid organism will be in its 2n state with two copies of each chromosome. A diploid somatic cell with eight chromosomes indicates that 2n=8.

When a somatic cell undergoes mitosis it first replicates its chromosomes, so in metaphase it will have sixteen chromatids. At this point, each of the eight chromosomes will be composed of two identical chromatids, for a total of sixteen.

When a germ cell begins meiosis, it also replicates the chromosomes and has sixteen chromatids until meiosis I is complete. During meiosis II, the two daughter cells from meiosis I each contain four chromosomes, each with two chromatids, for a total of eight chromatids. These chromatids are split during meiosis II, giving you four gametes that each have four chromosomes, each made of only one chromatid. This means that the gametes are haploid, since they contain only half of the original genetic material (n=4).

The transition from diploid to haploid occurs after meiosis I, since the first daughter cells only contain one copy of each chromosome after the tetrads are separated.

Example Question #63 : Genetics And Evolution

What are chromosomes made of?

Possible Answers:

DNA coils into circular grains to make up chromatids, which are organized into chromatin. The choromatins are held together at the centrosome to make up a chromosome.

DNA that is coiled into histone proteins make up chromatin, which is organized into chromatids. The chromatids are held together at the centrosome to make a chromosome.

DNA and RNA interact to make a chromatid, which are organized into centrosomes. Two centrosomes are held together at the chromatin to make a chromosome.

DNA that is coiled into histone proteins make up a centrosome, which are organized into chromatids. The chromatids are held together at the centriole to make a chromosome.

Correct answer:

DNA that is coiled into histone proteins make up chromatin, which is organized into chromatids. The chromatids are held together at the centrosome to make a chromosome.

Explanation:

Strings of DNA coiled around histone proteins make up chromatin. Chromatin condenses into chromatids. Two chromatids line up at the centrosome during cell replication, which results in X-shaped chromosomes.

Example Question #64 : Genetics And Evolution

A collection of an individual’s genes—inherited alleles—is defined as which of the following?

Possible Answers:

Locus of alleles 

Morphology 

Genotype

Phenotype 

Correct answer:

Genotype

Explanation:

Genotype is defined as the sequence of genetic makeup that determines specific characteristics and traits—phenotypes—of an individual. The genome is defined as the collection of an individual’s genes and consists of DNA. A genotype is expressed when information in DNA makes RNA and protein molecules, which determine the structure and function of cells; however, a genotype can also refer to genes carried by an individual, which includes mutations. Last, phenotype refers to observable physical characteristics within an individual. Some phenotypical traits are determined by the genotype, while others are shaped by environmental factors. 

Example Question #1 : Understanding Codominance And Incomplete Dominance

A plant with red flowers is crossed with a plant with white flowers. The resulting offspring have pink flowers. What term describes the dominance of this trait?

Possible Answers:

Incomplete dominance

Codominance

Dominance

Recessiveness

Correct answer:

Incomplete dominance

Explanation:

A phenotypic "blending" of two traits is referred to as incomplete dominance, indicating that neither trait is truly dominant over the other. Instead of one color overpowering expression of the other, both colors are expressed simultaneously.

Codominance suggests that both phenotypes are dominant, but cannot be expressed at the same time. The result of codominance would be regions of dominant red expression and regions of dominant white expression, resulting in spots rather than blending.

Learning Tools by Varsity Tutors