High School Biology : Genetics Principles

Study concepts, example questions & explanations for High School Biology

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Example Questions

Example Question #21 : Genetics Principles

In a fictional rabbit there is a gene allele that controls whether its tongue is keratinized—K—or not—k. A rabbit with the genotype of either KK or Kk has a keratinized tongue. A rabbit with the genotype of kk has a non-keratinized tongue. If a heterozygous male and female rabbit mate, then what is the probability that their offspring will be heterozygous for the gene that controls for tongue keratinization?

Possible Answers:

Correct answer:

Explanation:

Both of the parent's genotypes are Kk. This means that the offspring can be either KK, Kk, or kk.

Parental genotype: 

Offspring probability:

Example Question #22 : 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:

5:16

1:2

1:8

3:16 

1:4

Correct answer:

3:16 

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 #11 : Understanding Dominant/Recessive

For a monohybrid cross of a gene that exhibits complete dominance, what will be the expected ratios for the phenotype and genotype?

Possible Answers:

Phenotype - 1

Genotype - 1:1:1:1

Phenotype - 3:1

Genotype - 3:1

Phenotype - 3:1

Genotype - 1:1:1:1

Phenotype - 3:1

Genotype - 1:2:1

There is not enough information given to determine an answer. 

Correct answer:

Phenotype - 3:1

Genotype - 1:2:1

Explanation:

For better visualization of this explanation we can use eye color as an example. BB and BB will be brown eyes and bb will be blue eyes. 

In a monohybrid cross you are dealing with only one gene. We can use "Bb" as an example for the gene as it is a hybrid of two alleles. BB & Bb are dominant and bb is recessive. 

Setting up a punnet square of Bb x Bb we will get 4 results: BB, Bb, Bb, and bb

The phenotype is what we see: eye color. Phenotype will be expressed the same for BB and Bb, therefore we have 3 that will express the dominant phenotype and 1 that will express the recessive phenotype; 3:1.

The genotype is the actual gene that creates the phenotype. So for this we have 3 different genes that arise from the monohybrid cross: BB, Bb, and bb. We get 1 homozygous dominant, 2 heterozygous, and 1 homozygous recessive; 1:2:1.

Example Question #61 : Genetics And Evolution

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:

25%

75%

0%

50%

100%

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 #21 : Inheritance Patterns

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:

0%

75%

50%

100%

25%

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 #21 : Inheritance Patterns

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:

0.25

0.50

1.0

0.75

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 #23 : 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 #21 : Inheritance Patterns

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 the Mendelian genome

the law of segregation

the law of mitotic inheritance

the law of independent assortment

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 #71 : Genetics And Evolution

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 somatic cell in metaphase will contain eight chromatids

A germ cell in metaphase I will contain four chromosomes

A gamete will contain four chromosomes

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.

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