Question 1

Peas are an appropriate choice for studies of genetic inheritance because

Accepted Answer

D

Question 2

The position of a gene on a chromosome is known as the

Accepted Answer

The position of a gene on a chromosome is referred to as the locus. This term is used to describe the specific physical location of a gene or other DNA sequence on a chromosome.

Question 3

Alternative forms (alleles) of a gene separate into gametes after meiosis with equal probability. This is known as

Accepted Answer

The Principle of Segregation, as described by Gregor Mendel, states that alleles for a trait separate during gamete formation, and each gamete receives one allele. This principle explains how offspring can inherit traits from both parents.

Question 4

The vinegar fly, Drosophila melanogaster, has a gene that controls the shape of the wings. The wild-type phenotype is flat wings, but a mutation in the gene produces curled wings. You would expect

Accepted Answer

The wild-type phenotype is usually dominant, so most individuals in a population will have the wild-type phenotype.

Question 5

In mice, a gene controlling coat colour has 2 alleles; B (black) and b (white). A pure breeding black mouse is crossed to a white mouse and all the offspring are black. The offspring are then crossed to white mice. The phenotypes of the offspring of this second cross are expected to be

Accepted Answer

Since the first cross between a pure breeding black mouse (BB) and a white mouse (bb) results in all black offspring, these offspring must be heterozygous (Bb). When these heterozygous black mice (Bb) are crossed with white mice (bb), the expected offspring ratio is 1/2 black (Bb) and 1/2 white (bb), following Mendelian inheritance principles.

Question 6

In dogs, length of hair is controlled by a gene with 2 alleles. Short hair is dominant to long hair. Two heterozygous short-haired dogs are crossed and they produce a short-haired puppy. What is the probability that the puppy is heterozygous?

Accepted Answer

The cross of two heterozygous short-haired dogs (Ss x Ss) results in a genotypic ratio of 1SS:2Ss:1ss. Since the puppy is short-haired, it can either be SS or Ss. Given this, the probability of the puppy being heterozygous (Ss) out of the short-haired possibilities (SS or Ss) is 2/3.

Question 7

The presence or absence of hair on the mid-digital region of a finger is determined by a single autosomal gene. The presence of hair is dominant to the absence of hair. In the pedigree below, shading represents the presence of mid-digital hair.
 If the parents have a 5th child, what is the probability that it will have mid-digital hair?

Accepted Answer

The answer of The presence or absence of hair on...

Question 8

The presence or absence of hair on the mid-digital region of a finger is determined by a single autosomal gene. The presence of hair is dominant to the absence of hair. In the pedigree below, shading represents the presence of mid-digital hair.
 If the parents have a 5th child, what is the probability that it will be female and have mid-digital hair?

Accepted Answer

The answer of The presence or absence of hair on...

Question 9

A gene controlling flower colour also controls the colour of the stem and seed coat. This phenomenon is known as

Accepted Answer

Pleiotropy occurs when one gene influences multiple, seemingly unrelated phenotypic traits, such as a gene affecting both flower color and the color of the stem and seed coat.

Question 10

The flowers of snapdragons are red, pink or white. Crossing homozygous red snapdragons with homozygous white snapdragons produces offspring that have pink flowers. Which of the following crosses would produce the highest percentage of white flowers?

Accepted Answer

Crossing a pink snapdragon (which is heterozygous, having one red allele and one white allele) with a white snapdragon (which is homozygous for the white allele) would produce the highest percentage of white flowers. This is because half of the offspring would receive a white allele from both parents, resulting in white flowers.

Question 11

Human ABO blood groups are determined by three alleles: IA, IB and i. A man with blood group AB has a number of children by a woman with blood group A. Their first child has blood group B. What is the probability that the second child will also have blood group B?

Accepted Answer

The man with blood group AB has genotype IAIB. The woman with blood group A can have genotype IAIA or IAi. For the first child to have blood group B, the woman must have genotype IAi. The possible genotypes for their children are IAIA, IAi, IBIA, and IBi. Only IBIA and IBi result in blood group B, giving a probability of 1/4.

Question 12

In tomatoes, the alleles for a gene controlling fruit shape assort independently of the alleles of a gene controlling fruit colour. Round-shaped fruit are dominant to oval-shaped fruit and red fruit are dominant to yellow fruit. A homozygous, red, round-fruit tomato plant is crossed to a tomato plant with yellow oval fruit to produce an F₁ generation. The F₁ plants are crossed to pure-breeding red oval plants. The phenotypic ratio for the offspring of this second cross would be expected to be

Accepted Answer

The answer of In tomatoes, the alleles for a gene...

Question 13

In tomatoes, the alleles for a gene controlling fruit shape assort independently of the alleles of a gene controlling fruit colour. Round-shaped fruit are dominant to oval-shaped fruit and red fruit are dominant to yellow fruit. A homozygous, red, round-fruit tomato plant is crossed to a tomato plant with yellow oval fruit to produce an F₁ generation. F₁ plants were crossed to plants that were homozygous red and heterozygous round. You would expect the offspring to be

Accepted Answer

The F1 generation will be heterozygous for both traits (RrYy) and when crossed with a homozygous red, heterozygous round plant (RRYy), the expected phenotypic ratio is 3 round red: 1 oval red.

Question 14

In a testcross involving tomatoes, one tomato plant has the genotype O/o ; R/r. The genotype of the other plant is

Accepted Answer

A testcross involves crossing an individual with a homozygous recessive individual to determine the genotype of the first individual. The correct choice is o/o; r/r, which is homozygous recessive for both traits.

Question 15

Stem length, seed shape and flower colour in pea plants are determined by three independently assorting genes. Each trait has a dominant and a recessive phenotype. If a plant that is heterozygous for the three traits is allowed to self-fertilise, you would expect 3/8 of the offspring to be

Accepted Answer

For each trait, the heterozygous parent (Aa) can produce two types of gametes (A and a) with equal probability. When self-fertilizing, the probability for each trait to be heterozygous in the offspring is 1/2 (Aa x Aa = 1/4 AA, 1/2 Aa, 1/4 aa). Since the traits assort independently, the probability that all three traits are heterozygous in the offspring is (1/2)^3 = 1/8, not 3/8 as stated in the question. Therefore, none of the options perfectly match the expected outcome based on Mendelian genetics principles. However, the closest option in the context given, considering a possible misunderstanding in the question's phrasing, would be D, as it directly refers to being heterozygous for all three traits, which aligns with the scenario of a heterozygous parent self-fertilizing.

Question 16

Which of the following statements about sex-linked traits in humans is true?

Accepted Answer

Females have two X chromosomes, allowing them to be carriers of X-linked traits. They can pass these traits to their offspring without expressing the trait themselves if it is recessive. This is because females can inherit and carry a recessive gene on one of their X chromosomes without it being expressed, as the dominant gene on the other X chromosome can mask the effect of the recessive gene.

Question 17

Haemophilia is a defect in blood clotting. It is a recessive trait that has arisen from a mutation of a gene on the X-chromosome. A boy with haemophilia has parents who have normal blood clotting. If the parents have another child what is the probability it will be normal?

Accepted Answer

The mother must be a carrier (X^HX^h) and the father is normal (X^HY). The possible genotypes for their children are: X^HX^H (normal girl), X^HX^h (carrier girl), X^HY (normal boy), and X^hY (haemophilic boy). Thus, 3 out of 4 children will be normal.

Question 18

Red-green colour-blindness in humans is a recessive X-linked trait. A man and a woman with normal vision have a colour-blind son. What is the probability that their next child will also be a colour-blind son?

Accepted Answer

Given that red-green color blindness is a recessive X-linked trait, and the parents have normal vision but have a color-blind son, it means the mother is a carrier (X^NX^c) and the father is normal (X^NY). For their next child to be a color-blind son, the child must inherit the X^c from the mother and the Y from the father. The probability of inheriting X^c from the mother is 1/2, and the probability of being a son (inheriting Y from the father) is also 1/2. Multiplying these probabilities gives 1/2 * 1/2 = 1/4.

Question 19

When two genes are linked, most of the phenotypes of the parental traits will be inherited together. For example, eye colour and bristle form in the vinegar fly, Drosophila, are linked. The alleles for white eyes and crooked bristles occur on one chromosome in a fly while the alleles for red eyes and straight bristles occur together on another chromosome. Gametes produced by the fly that contain a chromosome with both the white-eye allele and the straight-bristle allele are referred to as

Accepted Answer

Recombinants are the result of crossing over during meiosis in linked genes, leading to new combinations of alleles different from those found in the parent organisms.

Question 20

In tomato plants, a gene controlling fruit shape has 2 alleles: O (round) and o (oval). A gene controlling inflorescence (position of the flowers) has two alleles: S (simple) and s (compound). A pure-breeding plant with oval fruit and simple inflorescence is crossed to a pure-breeding plant with round fruit and compound inflorescence. All the offspring have round fruit and simple inflorescence. The offspring are then crossed to plants with oval fruit and compound inflorescence. The phenotypes of this second generation are
Oval simple 200
Round compound 190
Oval compound 50
Round simple 60.
Which statement about the genes is true?

Accepted Answer

The observed phenotypes and their ratios suggest linkage between the genes controlling fruit shape and inflorescence, as the parental phenotypes are more common than the recombinant types, indicating that the genes do not assort independently and are likely on the same chromosome with a recombination frequency less than 50%.

Quiz 9: Inheritance