A pea plant with purple flowers is heterozygous for flower color. Its genotype is Pp. The P and p alleles in the pea plant’scells are located

next to each other on the same chromosome.
at the same location on homologous chromosomes.
on the X and Y chromosomes.
some distance apart on the same chromosome.

Solution

Genes coding for the same trait are located at the same locus on homologous chromosomes.

Some dogs bark while trailing; others are silent. The barkergene is dominant, the silent gene recessive. These genes are not linked. The gene for normal tail is dominant over the gene for screw (curly) tail. A barker dog with a normal tail that is heterozygous for both traits is mated to another dog of the same genotype. What fraction of their offspring will be barkers with screw tails.

3/4
9/16
3/16
1/4

Solution

BbNn × BbNn is expected to produce a ratio of 9 expressing both dominants to 3 expressing one combination of dominant trait and recessive trait to 3 expressing the other combination of dominant and recessive trait to 1 expressing both recessives.

Which of the following illustrates pleiotropy?

In fruit flies, the genes for scarlet eyes and hairy body are located on the same chromosome.
Matings between earless sheep and long-eared sheep always result in short-eared offspring.
Wheat kernels can range from white to red in color, a trait controlled by several genes.
The human cystic fibrosis gene causes many symptoms, from respiratory distress to digestive problems.

Solution

Pleiotropic genes have multiple effects on the phenotype.

A fruit fly has two genes for eye color, but each of its sperm cells has only one. This illustrates

independent assortment
linked genes
pleiotropy
segregation

Solution

The principle of segregation, a consequence of the behaviour of chromosomes during meiosis, states that gametes receive only one of two possible homologous chromosomes.

What contribute to the success of Mendel ?

Qualitative analysis of data
Observation of distinct inherited traits
His knowledge of biology
Consideration of one character at one time

There are three genes a, b, c. Percentage of crossing over between a and b is 20%, b and c is 28% an a and c is 8%. What is the sequence of genes on chromosome?

b, a, c
a, b, c
a, c, b
None of these

Solution

Percent crossing over between two genes is proportional to the distance between them.

Lack of independent assortment of two genes Aand B in fruit fly Drosophila is due to

repulsion
recombination
linkage
crossing over

Solution

The lack of independent assortment in sweet pea and Drosophila is due to linkage.

Originally, genetic inheritance was thought to be a function of the blending of traits from the two parents.Which exception to Mendel’s rules is an example of blending ?

Polygenic inheritance
Incomplete dominance
Codominance
Pleiotropism

Solution

Incomplete dominance results in the progeny’s expressing an intermediate form of the two parental alleles. (In a cross between red-flowered plants and white-flowered plants,the expression of pink-flowered plants would be a “blend” of the parental traits). Codominance is not an example of blending because both alleles are fully expressed in the individual.

The piechart shows the results of a survey of the incidence of blood groups A, B, AB and O amongst people in Britain.

biology-screen-3

Which of the following conculsions can be deduced from the diagram ?

Only 5% of individuals are heterozygous for blood group alleles.
Group O is the most common as it is the homozygous recessive group.
The alleles for blood group A and B are dominant to the allele for blood group O.
Any individual, selected at random from the sample population, has a 1 in 20 chance of being blood group AB.

Solution

5% of the population are of blood group AB, i.e. 1 out of every 20 individuals is AB.

A red-flowered plant crossed with a white-flowered plant of the same species, produced F₁ plants which all had pink flowers.

Self-pollination of the F₁ plants produced and F₂ generation in which 39 plants had red flowers, 83 had pink flowers and 40 had white flowers. What does this experiment demonstrate?

Codominance
Continuous variation
A dihybrid cross
Linkage

Solution

The alleles for red and white flowers are co-dominant, resulting in pink flowers when both are present in the genotype.

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