Bihar Board - Class 12 Biology - Chapter 5: Principles Of Inheritance And Variation Long Answer Question
LONG ANSWER TYPE
Q.1. What are the criteria for selecting organisms to perform crosses to study the inheritance of a few traits?
A.1. The following criteria are adopted for selecting organisms:
The traits should be easily visible.
The organisms should have different traits.
They should have a short life span
They must be true breeds
The pollination procedure should be simple.
The traits can be manipulated easily
Random mating of gametes should take place
Q.2. Why is Drosophila used extensively for genetic studies?
A.2. Drosophila is extensively for genetic studies because it has the following characteristics:
They have a life span of two weeks.
They can be grown in the laboratory on simple synthetic mediums.
A large number of progenies are produced by a single mating.
The male and the female Drosophila can be differentiated easily.
It has many variations easily visible under a simple microscope.
Q3.List out the characteristics of the chromosome theory of Inheritance.
A3 The important characteristics of the chromosome theory of Inheritance are:
Fertilization restores diploid condition.
Chromosomes segregate and assort independently.
Homologous chromosomes separate at the time of meiosis.
Both chromosomes, as well as genes, exist in pairs within the diploid cells.
Gamete contains only one chromosome of a particular type and only one of the two alleles of a character.
Q4.Define autosome, hemizygous, homozygous, and heterozygous?
A4.
Autosome– All chromosomes apart from the sex chromosomes are called the Autosomes. The number of autosomes differs from one organism to another. Humans have 44 numbers or 22 pairs of autosomes.
Hemizygous– It is a condition in which an organism has only one copy of a gene or DNA sequence present in diploid cells.
Homozygous— It is a condition in which an organism has two similar alleles of a given gene (XX).
Heterozygous–It is a condition in which an organism has two different alleles of a given gene (XY).
Q5.Why did scientists select fruit flies for his genetics experiments?
A5. Drosophila melanogaster is a small common fly species, which belongs to the family Drosophilidae. This species is generally known as the vinegar fly or a fruit fly.
In the year 1830, Drosophila melanogaster was established as a key model organism for biomedical science and it is due to the considerable biological similarity to mammals and an abundance of available genetic tools.
Like humans, these fruit flies species have a similar distribution of chromosomes. An individual with a pair of X chromosomes is female fruit fly and an individual with one X and one Y chromosome is male.
Describe the individuals with the following chromosomal abnormalities:
6. Trisomy at chromosome 21
7. XXY
8. XO
A.
6) Trisomy– Trisomy results in an autosomal linked genetic diorder known as Down’s syndrome. The individuals exhibit the following characteristics:
Protruding tongue
Roundhead
Slanting eyes
Short height
Open mouth
Short neck
Mental retardation
Under-developed genitalia and gonads
7) XXY– The presence of an additional copy of an X-chromosome results in inklienfeltor syndrome. The patient exhibits the following characteristics:
The male individual possesses feminine characteristics.
Development of breasts in males
Male is sterile
Poor beard growth
Feminine voice
8) XO– Loss of X-chromosome results in Turner’s syndrome. Characteristics:
The female is sterile.
The ovaries are immature.
Webbed neck
Thorax is shield-shaped
Under-developed breasts.
Puffy fingers
Short height
Uterus is small
Q.9. What are the criteria for selecting organisms to perform crosses to study the inheritance of a few traits?
A.9. The following criteria are adopted for selecting organisms:
The traits should be easily visible.
The organisms should have different traits.
They should have a short life span
They must be true breeds
The pollination procedure should be simple.
The traits can be manipulated easily
Random mating of gametes should take place
Q.10. What is recombination? Mention its applications with reference to genetic engineering.
A.10. Recombination is the process of producing a new combination of genes by crossing over during meiosis.
Applications:
It is a means of introducing new traits.
Variability is increased, which is necessary for natural selection.
It is used for preparing linkage chromosome maps.
The desired recombinants produced as a result of crossing over are selected by the plant breeders to produce new crop varieties
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