Tag: botany

Questions Related to botany

Drosophila has four homologous pairs of chromosomes. What is the number of linkage groups (homologous) in this animal?

botany chromosomal basis of inheritance linkage and crossing over linkage and recombination genetics: inheritance

  1. Four

  2. Two

  3. Eight

  4. Uncertain

Show answer
Correct Option: A
Explanation:
In the diploid nucleus, each chromosome is represented twice: by a homologous pair and there are same genes on homologous chromosomes.
In Drosophila, there are four pair of chromosomes: 2 pairs of large autosomes, (one slightly smaller than the other pair), 1 pair of very small autosomes, and a pair of sex chromosomes. Genes present on one chromosome form a linkage group. Homologous chromosomes carry same set of genes (the alleles may differ), hence same linkage group.
So, the correct answer is 'Four'.

Suppose that out of $1000$ offspring in the $F _2$ generation of a dihybrid cross, $748$ are tall and hairy, $6$ are tall and smooth, $4$ are short and hairy, $242$ are short and smooth. The reason is that the genes controlling these characters are.

botany chromosomal basis of inheritance linkage and crossing over linkage and recombination genetics: inheritance

  1. Lethal genes

  2. Complementary genes

  3. Linked genes

  4. Epistatic genes

Show answer
Correct Option: C

Association of parental combination of characters in offspring in excess of dihybrid cross is due to.

botany chromosomal basis of inheritance linkage and crossing over linkage and recombination genetics: inheritance

  1. Pseudoalleles

  2. Linkage

  3. Polygeny

  4. Codominance

Show answer
Correct Option: B
Explanation:
Linkage is the tendency of genes present close on the chromosomes to be inherited together and not to assort independently in the offspring. It gives only parental combinations in the offspring. Since, complete linkage is a rare phenomenon, the linked genes sometimes show tendency of independent assortment and results in production of new combinations in offspring in lower percentage. Hence, production of parental characters combinations in the offsprings of a dihybrid in excess to non-parental combinations is due to "linkage".

So, the correct answer is 'Linkage'.

Read (i) to (v) and find the correct option
(i) Nitrogen base is linked to pentose sugar through N-glycosidic linkage
(ii) Phosphate group is linked to 5 - OH of a nucleoside through phosphoester linkage
(iii) Two nucleosides are linked through 3' -5' N-glycosidic linkage
(iv) Negatively charged DNA is wrapped around positively charged histone octamer to form nucleosome
(v) Chromatin that is more densely packed and stains dark is called euchromatin

botany chromosomal basis of inheritance linkage and crossing over linkage and recombination genetics: inheritance

  1. i, ii, iii wrong

  2. iv alone is wrong

  3. iii and v are wrong

  4. i alone is wrong

  5. i, ii and iv are wrong

Show answer
Correct Option: C

Number of linkage in a polynucleotide would be __________________.

botany chromosomal basis of inheritance linkage and crossing over linkage and recombination genetics: inheritance

  1. Same as number of nucleotides

  2. Twice the number of nucleotides

  3. One less than the number of nucleotides

  4. One

Show answer
Correct Option: D

Which of the following is suitable for experiment on linkage ?

botany chromosomal basis of inheritance linkage and crossing over linkage and recombination genetics: inheritance

  1. aaBB $\times$ aaBB

  2. AABB $\times$ aabb

  3. AaBb $\times$ AaBb

  4. AAbb $\times$ AaBB

Show answer
Correct Option: B
Explanation:
AABB x aabb is suitable for the experiment on the linkage. Linkage is the tendency for certain genes tend to be inherited together because they are on the same chromosome. Thus, parental combinations of characters are found more frequently in offspring than non-parental.

So, the correct answer is 'AABB × aabb'.

Linkage decreases frequency of.

botany chromosomal basis of inheritance linkage and crossing over linkage and recombination genetics: inheritance

  1. Recessive allele

  2. Dominant allele

  3. Hybridisation

  4. Both B and C

Show answer
Correct Option: C
Explanation:
Distance between the linked genes is the major factor which controls the frequency of crossing over. Hence, greater is the linkage lesser will be the chances of crossing over or Hybridisation.

So, the correct answer is 'Hybridisation'.

Determination of percentage of crossing over between two linked genes is important in

botany chromosomal basis of inheritance linkage and crossing over linkage and recombination genetics: inheritance

  1. Maintaining heterozygosity in population

  2. Indicating relative position of genes in chromosomes

  3. Fixation of heterosis in organisms

  4. Explaining the phenomenon of coupling and repulsion

Show answer
Correct Option: B
Explanation:
If the distance between two linked genes is more then the frequency of crossing over will be more and vice versa.
Hence, percentage of crossing over may indicate the relative position of genes in chromosomes.
So, the correct answer is 'Indicating the relative position of genes in chromosomes'.

In a dihybrid cross between two heterozygotes, AaBb $\times$ AaBb, if we get a 3 : 1 ratio among offspring, the reason would be ___________.

botany chromosomal basis of inheritance linkage and crossing over linkage and recombination genetics: inheritance

  1. Polygenes

  2. Linked genes

  3. PIeiotropic genes

  4. Hypostatic genes.

Show answer
Correct Option: B
Explanation:

A.Polygenes – Inheritance is controlled by two or more genes in which the dominant alleles have cumulative effect, with each dominant allele expressing a part of functional polypeptide and full trait is shown when all the dominant alleles are present, is called Polygenic or Quantitative inheritance.

B.Linked genes – The tendency of some genes to inherit together is known as linkage, and the genes are linked genes.

C. Pseduoalleles - Genes are present together side by side and they produce related phenotypes are called pseudoalleles. These are distinguished from true alleles through rare crossing over.

D. Hypostatic gene – A gene whose effect are masked is by another gene is called Hypostatic gene. In the F2 generation 12:3:1 ratio.

In a dihybrid cross between two heterozygotes, AaBb x AaBb, if we get a 3:1 ratio among offspring, the reason would be Linked genes.

So, the correct option is ‘Linked genes’.

An exception to Mendel's principle/ Mendel did not include in his discoveries

botany chromosomal basis of inheritance linkage and crossing over linkage and recombination genetics: inheritance

  1. Dominance

  2. Purity of gametes/segregation

  3. Linkage

  4. Independent assortment

Show answer
Correct Option: C
Explanation:

A.Dominance - When two contrasting alleles for a character come together in an organism, only one is expressed and another one is not expressed. Expressed character is called Dominant character and the character which is not expressed is called Recessive character. It is the Mendel’s first principle.

B.Purity of gametes/segregation - In the living organisms, two alleles controlling each character maintains identity in the organism, but during the formation of gametes or spores, by meiosis move apart due to separation of the homologous chromosomes which bear them, so that each gametes or spore receives only one allele of each character on random basis. It is called Law of segregation. It is the Mendel’s second principle.

C.Linkage – The physical association of genes in a chromosome is called Linkgage. It is not the Mendel’s principle.

D.Indepedent assortment - When a cross is made between two individuals different from each other in two or more characters, then the inheritance of one character is independence of the inheritance of another character.

So, the correct option is ‘Linkage’.