Question 1

The ________ of an organism refers to the alleles that are present.

Accepted Answer

Genotype refers to the specific combination of alleles that an organism has. Karyotype refers to the number and appearance of an organism's chromosomes. Pedigree refers to a diagram that shows the inheritance of a particular trait or disorder through multiple generations of a family. Phenotype refers to the physical or observable characteristics of an organism. Pleiotropy refers to a single gene having multiple effects on an organism's phenotype.

Question 2

In rabbits,there is a gene that controls ear length,with a dominant allele "T" for long ears and a recessive allele "t" for short ears.At another gene locus,there are alleles "B" for black coat and "W" for white coat.Neither the B or W allele is dominant,and BW produces a gray coat.These two allele pairs assort independently.If a gray rabbit that is heterozygous at the gene locus controlling ear length is mated with a white rabbit that is also heterozygous at the gene locus controlling ear length,what proportion of the long-eared offspring will be homozygous for the long-eared trait?

Accepted Answer

The gray rabbit has the genotype B/W T/t, and the white rabbit has the genotype W/W T/t. When considering only the ear length gene, the possible genotypes for the offspring are TT, Tt, and tt. Since we're only interested in long-eared offspring (TT or Tt), the TT genotype represents 1/3 of the long-eared offspring (TT or Tt), as the possible combinations are TT, Tt, and Tt, with TT being the only homozygous long-eared genotype.

Question 3

A scientist has an uncharacterized pea plant.She wants to determine the plant's genotype for seed color.In order to be certain that she will get conclusive results from a single cross,with what plant could she cross it? Check all that apply.

Accepted Answer

The answer of A scientist has an uncharacterized pea plant.She...

Question 4

The observable expression of the genes present is called

Accepted Answer

The observable expression of genes present is called phenotype. Genotype refers to the genetic makeup of an organism while karyotype is a visual representation of an organism's chromosomes. Epistasis refers to the interaction between different genes that affect the expression of a trait.

Question 5

In mice,the allele for black fur is dominant to the allele for brown fur.If a male heterozygous black mouse is crossed with a female brown mouse,what percentage of the F₁ offspring do you predict will be homozygous? (Enter the number only without the percent sign.For example,enter 100% as 100 and enter 12.5% as 12.5)

Accepted Answer

The answer of In mice,the allele for black fur is...

Question 6

A diploid individual carrying two different alleles at a given gene locus is called

Accepted Answer

Heterozygous individuals carry two different alleles at a given gene locus, whereas homozygous individuals carry two copies of the same allele. Homologous refers to having the same structure or relationship, and polygenic refers to traits that are influenced by multiple genes.

Question 7

Mendel performed reciprocal crosses in which he used pollen from a white-flowered plant to fertilize a purple-flowered plant and pollen from a purple-flowered plant to fertilize a white-flowered plant.What did these reciprocal crosses demonstrate?

Accepted Answer

Reciprocal crosses involve reversing the sexes of the parents in a cross. In Mendel's reciprocal crosses, he found that in both cases, the resulting offspring had the same phenotype. This demonstrates that each parent makes an equal genetic contribution to the offspring, as the male and female gametes each contribute half of the offspring's genetic material.

Question 8

In humans,the sickle-cell trait is caused by a single defective allele,but sickle-cell disease only occurs in individuals that are homozygous for the sickle-cell allele.A man and woman each carry the trait,but do not have sickle-cell disease.What is the probability that their first two children will both have sickle-cell disease?

Accepted Answer

Since both parents are carriers (heterozygous) for the sickle-cell trait, each child has a 1/4 chance of being homozygous for the sickle-cell allele and thus having sickle-cell disease. The probability that both of two children will have the disease is (1/4) * (1/4) = 1/16.

Question 9

A male fruit fly has the genotype PpYYrrTt.In terms of these 4 allele pairs,how many different types of gametes can he form?

Accepted Answer

The male fruit fly can form 4 different types of gametes because the alleles for Y and r are homozygous (YY and rr), so they do not provide any variation in gametes. The alleles Pp and Tt are heterozygous, each providing two possibilities (P or p, T or t), leading to 2 x 2 = 4 different combinations.

Question 10

A diploid individual carrying two identical alleles at a given gene locus is called

Accepted Answer

Homozygous refers to an individual carrying two identical alleles at a given gene locus.

Question 11

As a genetic counselor,you are constructing a human pedigree for a particular disease.You note that every generation shows the trait,suggesting that the trait is

Accepted Answer

If every generation shows the trait, it suggests that the trait is dominant. This means that an affected person must have inherited the dominant mutation from at least one affected parent, and every affected person has a 50% chance of passing the trait on to their offspring.

Question 12

Pedigrees are useful to geneticists because they can help determine: Check all that apply.

Accepted Answer

The answer of Pedigrees are useful to geneticists because they...

Question 13

Before Mendel's experiments with pea plants,which ideas formed the basis for most thinking about heredity? Check all that apply.

Accepted Answer

Before Mendel, it was believed that traits from both parents blended in offspring (B), heredity occurred within species (C), and traits were directly transmitted from parents to offspring (E).

Question 14

In watermelons,the gene for green color is dominant over its allele for striped color.At another gene locus,the gene for short shape is dominant over its allele for long shape.These two allele pairs assort independently.If a plant with long,striped fruit is crossed with a plant that is heterozygous for both of these traits,what percentage of the offspring do you expect will be short and green? (Enter the number only without the percent sign.For example,enter 100% as 100 and enter 12.5% as 12.5)

Accepted Answer

The answer of In watermelons,the gene for green color is...

Question 15

Achondroplasia is a common form of dwarfism caused by an autosomal dominant mutation in the fibroblast growth factor receptor 3 (FGFR3)gene.Two copies of the mutant gene are invariably fatal before or shortly after birth.If a person with achondroplasia marries a person of normal height,what is the probability that both their first child and second child will have achondroplasia?

Accepted Answer

Since achondroplasia is caused by an autosomal dominant mutation, the affected person must have at least one copy of the mutant gene. Therefore, the affected person must be heterozygous with one mutant allele and one normal allele. 
When the affected person's normal height spouse is added to the equation, we can create a Punnett square to determine the probability of their offspring inheriting achondroplasia:

|   | A | a | <- Parent 1 (A = mutant allele, a = normal allele)
|---|---|---|
| a | Aa| aa|
| a | Aa| aa|

There is a 50% chance that the affected person will pass on the mutant allele (A) to each of their offspring, since they are heterozygous. There is also a 50% chance that the unaffected spouse will pass on a normal allele (a) to each of their offspring. Therefore, the probability that both children will have achondroplasia is:
0.5 (chance of inheriting mutant allele from affected parent) x 0.5 (chance of inheriting normal allele from unaffected parent) x 0.5 (chance of inheriting mutant allele from affected parent again) x 0.5 (chance of inheriting normal allele from unaffected parent again) = 0.125 or 1/4. So the answer is B) 1/4.

Question 16

In rabbits,there is a gene that controls ear length,with a dominant allele "T" for long ears and a recessive allele "t" for short ears.At another gene locus,there are alleles "B" for black coat and "W" for white coat.Neither the B or W allele is dominant,and BW produces a gray coat.These two allele pairs assort independently.If a gray rabbit that is heterozygous at the gene locus controlling ear length is mated with a white rabbit that is also heterozygous at the gene locus controlling ear length,what is the probability that their first offspring will be gray with long ears?

Accepted Answer

The gray rabbit has the genotype B/W T/t, and the white rabbit has the genotype W/W T/t. When these genotypes are crossed, the probability of getting a gray (BW) offspring is 1/2 (since the gray rabbit can pass either B or W, but the white rabbit can only pass W, so the only way to get gray is if the gray rabbit passes B). The probability of getting an offspring with long ears (T/_ where _ can be either T or t) is 3/4, since there are three combinations that result in long ears (TT, Tt, tT) out of four possible combinations (TT, Tt, tT, tt). Multiplying these probabilities gives 1/2 * 3/4 = 3/8.

Question 17

Let R = red pigment and r = no pigment.In carnations,RR offspring make a lot of red pigment,rr offspring make no pigment and Rr offspring make a small amount of red pigment,thus appearing pink.Pink carnations are therefore an example of

Accepted Answer

Incomplete dominance occurs when the heterozygous phenotype is intermediate between the two homozygous phenotypes. In this case, the Rr offspring have a phenotype that is intermediate between the RR and rr homozygotes, appearing pink due to a small amount of red pigment. This is different from codominance, where both alleles are expressed equally in the phenotype, and epistasis and pleiotropy, which involve more complex interactions between genes.

Question 18

A Punnett square is generally used to

Accepted Answer

A Punnett square is a tool used to predict the genotypic ratio among the offspring of two parents with known genotypes. The Punnett square allows for the combination of alleles from each parent to be depicted and the resulting genotypes of the offspring to be determined. Therefore, choice C is the best answer as it accurately describes the primary use of a Punnett square.

Question 19

You toss a coin twice.Because the outcome of the first toss does not affect the outcome of the second toss,these 2 events are called

Accepted Answer

The events are independent because the outcome of one does not affect the outcome of the other.

Question 20

If you are tossing a six-sided die,what is the probability of getting either a 1 or a 2 on your first toss AND a 1 or a 2 on your second toss?

Accepted Answer

The probability of getting either a 1 or 2 on the first toss is 2/6 or 1/3. The probability of getting either a 1 or 2 on the second toss, given that you got a 1 or 2 on the first toss, is also 2/6 or 1/3. To find the probability of both events happening together (getting a 1 or 2 on both tosses), you multiply the probabilities: 1/3 x 1/3 = 1/9. Therefore, the answer is B: 1/9.

Quiz 12: Patterns of Inheritance