Which one of the following traits of garden pea studied by Mendel was a recessive feature ?

Round seed shape
Axial flower position
Green seed colour
Green pod colour

The genes controlling the seven pea characters studied by Mendel are now known to be located on how many different chromosomes ?

Four
Seven
Six
Five

Solution

The seven traits are now known to be present on 4 chromosome. But they do not show linkage, because of large distances between them on the chromosome.

In a certain plant, red fruit (R) is dominant over yellow fruit (r) and tallness (T) is dominant over shortness (t). If a plant with RRTt genotype is crossed with a plant rrtt genotype, what will be the percentage of tall plants with red fruits in the progeny ?

50%
100%
75%
25%

Solution

Independent assortment of genes does not take place when

genes are located on homologous chromosomes
genesare linked and located on same chromosomes
genes are located on non homologous chromosomes
All the above

Solution

Independent assortment of genes takes place only when they are located on separate non-homologus chromosomes.Where two or more than two genes are located on same chromosome, independent assortment will not be possible.

When dominant and recessive alleles express itself together it is called

codominance
dominance
amphidominace
pseudodominance

Solution

According to principle of dominance, out of the two factors of alleles representing different traits of a character, only one expresses itself. But when both express themselves it is codominance.

A gene is said to be dominant if

it expresses its effect only in homozygous state
it expresses its effect only in heterozygous condition
it expresses its effect both in homozygous and heterozygous condition
it never expresses its effect in any conditions

Solution

A dominant gene would lead to the expression of its phenotype irrespective of the fact whether its allelic gene is dominant or recessive.

Harmful mutations does not get eliminated from gene pool because

they are recessive and carried by homozygous individuals.
they are recessive and carried by heterozygous individuals.
they are formed repeatedly.
they show genetic drift.

Suppose that in sheep, a dominant allele (B) produces blackhair and a recessive allele (b) produces white hair. If you sawa black sheep, you would be able to identify

its phenotype for hair colour.
its genotype for hair colour.
the genotypes for only one of its parents.
the genotypes for both of its parents.

Solution

Black is the phenotype of the sheep. Without further information, you cannot identify the genotype of a black sheep because it could be either BB or Bb. The possible genotypes of the parents of a black sheep could be BB × BB, BB × Bb, Bb × bb, or Bb × Bb. Thus, there is no one single genotype for either parent.

What is the probability that a cross between a true-breeding pea plant with smooth seeds and a true-breeding pea plant with wrinkled seeds will produce F₁ progeny with smooth seeds ?

1/2
1/4
zero
1

Solution

This is an example of a mono hybrid cross. All of the F₁ progeny would have smooth seeds. (The F₁ generation would all have the genotype Ss, producing the phenotype of smooth seeds because the smooth allele, S, is dominant to the wrinkled allele, s).

Two organisms that are true-breeding for a certain genetic characteristic are mated and their offspring analysed. Which of the following statements about this situation is true?

Both parents are homozygotes.
The offspring are either all homozygotes or all heterozygotes.
The offspring represent the F1generation and the gametes produced by the offspring will carry only one allele for this gene.
All of the above

Solution

Given that both parents are true-breeding, the cross must be either AA × AA, AA × aa, or aa × aa. If you work out these crosses, you will see that all of the possible answers are true for each possible situation.

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