Question 1

Different ratios occur in crosses with single gene pairs or two gene pairs. What types of ratios are likely to occur in crosses dealing with a single gene pair?

Accepted Answer

Crosses dealing with a single gene pair typically result in two types of ratios - 3:1 for a dominant/recessive relationship and 1:1 for a heterozygous cross. Therefore, option C is the correct answer as it includes both ratios - 3:1 and 1:1. Option A includes the 9:3:3:1 ratio which is typically observed in a dihybrid cross with two gene pairs, and Option B includes the 1:4:6:4:1 ratio which is observed in a cross involving two heterozygous individuals. Option D is incorrect as it does not include the typical ratios observed in a single gene pair cross.

Question 2

Mendel studies seven different traits in the garden pea. What genetic term is used to describe an observable trait, such as those studied by Mendel?

Accepted Answer

The term used to describe an observable trait is phenotype. Genotype refers to the genetic makeup of an organism, haplotype refers to a specific set of genetic variations on one chromosome, appearance and category are not specific genetic terms.

Question 3

In tigers, a recessive allele causes a white tiger (absence of fur pigmentation). If one phenotypically normal tiger that is heterozygous is mated to another that is phenotypically white, what percentage of their offspring is expected to be white?

Accepted Answer

The normal tiger is heterozygous, meaning it has one normal allele and one allele for whiteness (Nw). The white tiger has two recessive alleles (ww). When crossed (Nw x ww), 50% of the offspring are expected to be white (ww).

Question 4

A sexually reproducing animal has two unlinked genes, one for head shape (H) and one for tail length (T). Its genotype is HhTt. Which of the following genotypes is possible in a gamete from this organism?

Accepted Answer

Gametes contain only one allele from each gene due to meiosis, which separates alleles into different gametes. Thus, a gamete from an HhTt organism could have an HT genotype, combining one allele from each gene.

Question 5

When Mendel crossed yellow-seeded and green-seeded pea plants, all the offspring were yellow seeded. When he took these F1 yellow-seeded plants and crossed them to green-seeded plants, what genotypic ratio was expected?

Accepted Answer

In this cross, the F1 yellow-seeded plants (heterozygous, Yy) are crossed with green-seeded plants (homozygous recessive, yy). This results in a 1:1 genotypic ratio of Yy (yellow-seeded) to yy (green-seeded) offspring.

Question 6

Albinism is an autosomal (not sex-linked) recessive trait. A man and woman are both of normal pigmentation, but both have one parent who is albino (without melanin pigmentation). What is the probability that their first female child will have albinism?

Accepted Answer

Since both parents are heterozygous carriers of the recessive allele for albinism, they each have a 1/2 chance of passing on the recessive allele to their offspring. The probability of both parents passing the recessive allele to their first female child would be (1/2) x (1/2) = 1/4. Therefore, the probability of their first female child having albinism is 1/4, or D.

Question 7

Albinism is an autosomal (not sex-linked) recessive trait. A man and woman are both of normal pigmentation, but both have one parent who is albino (without melanin pigmentation). What is the probability that their first child will be an albino?

Accepted Answer

Both parents are carriers of the albino allele, meaning they each have a 1/2 chance of passing it on to their offspring. To determine the probability of their first child being an albino, we need to use a Punnett square.

Punnett square:

|   | A    | a    |
|---|------|------|
| A | AA   | Aa   |
| a | Aa   | aa   |

Each box represents a 1/4 chance of that particular genotype occurring in their offspring. The only way for their child to be albino (aa) is if both parents pass on the recessive allele (a). Therefore, the probability of their first child being albino is 1/4 or 0.25 or 25%. Thus, the best choice is D, 1/4.

Question 8

A man has extra digits (six fingers on each hand and six toes on each foot). His wife and their daughter have a normal number of digits. Having extra digits is a dominant trait. The couple's second child has extra digits. What is the probability that their next (third) child will have extra digits?

Accepted Answer

Since having extra digits is a dominant trait and the man has extra digits while his wife does not, the man must be heterozygous (Hh) to have produced a child with a normal number of digits with his wife, who must be homozygous recessive (hh). Therefore, each child has a 1/2 chance of inheriting the dominant allele (H) from the father and thus having extra digits.

Question 9

Gray seed color in peas is dominant to white. Assume that Mendel conducted a series of experiments where plants with gray seeds were crossed among themselves, and the following progeny were produced: 302 gray and 98 white.
(a) What is the most probable genotype of each parent?
(b) Based on your answer in (a) above, what genotypic and phenotypic ratios are expected in these progeny? (Assume the following symbols: G = gray and g = white.)

Accepted Answer

The correct answer is (a) Gg × Gg; (b) genotypic = 1:2:1, phenotypic = 3:1. This is because when two heterozygous (Gg) individuals are crossed, the genotypic ratio of their offspring is expected to be 1 GG : 2 Gg : 1 gg, which corresponds to a phenotypic ratio of 3 gray : 1 white, matching the observed outcome.

Question 10

Albinism is an autosomal (not sex-linked) recessive trait. A man and woman are both of normal pigmentation and have one child out of three who is albino (without melanin pigmentation). What are the genotypes of the albino's parents?

Accepted Answer

Since albinism is an autosomal recessive trait and they have an albino child, both parents must carry one copy of the recessive allele, making them heterozygous.

Question 11

Use the figure and the following description to answer the question(s) below.
-Which of the boxes marked 1-4 correspond to plants with dark leaves?

Accepted Answer

Without the figure or description, it's impossible to accurately determine which boxes correspond to plants with dark leaves. However, the correct answer is based on the hypothetical scenario provided in the question.

Question 12

In certain plants, tall is dominant to short. If a heterozygous plant is crossed with a homozygous tall plant, what is the probability that the offspring will be short?

Accepted Answer

Since the homozygous tall plant can only contribute alleles for tallness and the heterozygous plant has one allele for tallness, all offspring will receive at least one allele for tallness, making it impossible for any to be short.

Question 13

Use the figure and the following description to answer the question(s) below.
-Which of the boxes marked 1-4 correspond to plants with a heterozygous genotype?

Accepted Answer

In order to have a heterozygous genotype, an individual must have two different alleles for a particular gene. In this figure, only boxes 2 and 3 show two different color alleles for the gene in question, whereas boxes 1 and 4 have the same color alleles, indicating a homozygous genotype. Therefore, the correct answer is D) 2 and 3.

Question 14

Two plants are crossed, resulting in offspring with a 3:1 ratio for a particular trait. This ratio suggests that ________.

Accepted Answer

A 3:1 ratio is indicative of a Mendelian inheritance pattern for a single trait, which shows that both parents were heterozygous for the particular trait.

Question 15

Mendel accounted for the observation that traits which had disappeared in the F1 generation reappeared in the F2 generation by proposing that ________.

Accepted Answer

Mendel proposed that traits can be dominant or recessive, and the recessive traits were obscured by the dominant ones in the F1 generation. This explains why the traits disappeared in the F1 generation but reappeared in the F2 generation when both dominant and recessive alleles were present.

Question 16

A black guinea pig crossed with an albino guinea pig produced twelve black offspring. When the albino was crossed with a second black animal, six blacks and six albinos were obtained. What is the best explanation for this genetic situation?

Accepted Answer

The fact that the first cross between a black guinea pig and an albino guinea pig produced only black offspring suggests that black is the dominant trait and albino is recessive. This is further supported by the second cross between the albino guinea pig and a black animal, which produced both black and albino offspring in a 1:1 ratio, indicating that the black parent was heterozygous for the black trait (Bb) and the albino parent was homozygous recessive (bb). Therefore, the best explanation for this genetic situation is that albino is recessive and black is dominant.

Question 17

Use the figure and the following description to answer the question(s) below.
-Which of the boxes marked 1-4 correspond to plants that will be true-breeding?

Accepted Answer

Boxes 1 and 4 represent true-breeding plants because they are homozygous for the dominant and recessive alleles, respectively.

Question 18

When crossing an organism that is homozygous recessive for a single trait with a heterozygote, what is the chance of producing an offspring with the homozygous recessive phenotype?

Accepted Answer

In a cross between a homozygous recessive (aa) and a heterozygote (Aa), there is a 50% chance of producing an offspring with the homozygous recessive phenotype (aa), as one allele comes from each parent.

Question 19

Why did the F1 offspring of Mendel's classic pea cross always look like one of the two parental varieties?

Accepted Answer

The F1 offspring of Mendel's classic pea cross always looked like one of the two parental varieties because one allele was dominant. This means that the dominant allele was expressed over the recessive allele, leading to the visible expression of only one of the two possible phenotypes.

Question 20

The work of Gregor Mendel provided an answer to two prevailing hypotheses popular at the time. What were these two hypotheses?

Accepted Answer

The two prevailing hypotheses at the time were blending inheritance, which proposed that the traits of the parents would blend together in the offspring, and inheritance of acquired characteristics, which suggested that traits acquired during an organism's lifetime could be passed down to their offspring. Mendel's work showed that neither of these hypotheses was completely accurate, and instead proposed the idea of discrete inherited factors (now known as genes) that follow specific patterns of inheritance.

Quiz 14: Mendel and the Gene

Different ratios occur in crosses with single gene pairs or two gene pairs. What types of ratios are likely to occur in crosses dealing with a single gene pair?

Mendel studies seven different traits in the garden pea. What genetic term is used to describe an observable trait, such as those studied by Mendel?

In tigers, a recessive allele causes a white tiger (absence of fur pigmentation) . If one phenotypically normal tiger that is heterozygous is mated to another that is phenotypically white, what percentage of their offspring is expected to be white?

A sexually reproducing animal has two unlinked genes, one for head shape (H) and one for tail length (T) . Its genotype is HhTt. Which of the following genotypes is possible in a gamete from this organism?

When Mendel crossed yellow-seeded and green-seeded pea plants, all the offspring were yellow seeded. When he took these F1 yellow-seeded plants and crossed them to green-seeded plants, what genotypic ratio was expected?

Albinism is an autosomal (not sex-linked) recessive trait. A man and woman are both of normal pigmentation, but both have one parent who is albino (without melanin pigmentation) . What is the probability that their first female child will have albinism?

Albinism is an autosomal (not sex-linked) recessive trait. A man and woman are both of normal pigmentation, but both have one parent who is albino (without melanin pigmentation) . What is the probability that their first child will be an albino?

A man has extra digits (six fingers on each hand and six toes on each foot) . His wife and their daughter have a normal number of digits. Having extra digits is a dominant trait. The couple's second child has extra digits. What is the probability that their next (third) child will have extra digits?

Albinism is an autosomal (not sex-linked) recessive trait. A man and woman are both of normal pigmentation and have one child out of three who is albino (without melanin pigmentation) . What are the genotypes of the albino's parents?

Use the figure and the following description to answer the question(s) below. -Which of the boxes marked 1-4 correspond to plants with dark leaves?