NIOS Class 12 Biology Chapter 22 Solution – Principles of Genetics
NIOS Class 12 Biology Solution Chapter 22 Principles of Genetics . NIOS Class 12 Biology Chapter 22 Question Answers Download PDF. NIOS Class 12 Biology Notes.
Board |
NIOS |
Class |
12th (Higher Secondary) |
Subject |
Biology |
Topic |
Question Answer, Solution, Notes |
INTEXT 22.1
1.) Name the founder of genetics and state why he is called so.
Ans: Gregor John Mendel is called founder of genetics , because he was the first to suggest principles underlying heredity
2.) State one difference between
i) homozygous and heterozygous individuals – Homozygous bears identical alleles controlling a trait, while heterozygous bears dissimilar alleles controlling a trait.
ii) dominant and recessive traits – the one which expresses itself in a heterogygous organism in the F1 hybrid is called the dominant trait (dominant allele) and the one that remains masked in F1 individual but gets expressed in the next generation (F2), is called recessive.
iii) genotype and phenotype – Genotype is genetic constitution of an individual, represented with the help of symbols and phenotype is class of individuals recognised based on externally or internally visible characters.
iv) monohybrid and dihybrid crosses. – monohybrid is the cross between two parents differing in a single pair of contrasting character whereas dihybrid corss is the cross of two parents differing in two pairs of contrasting characters.
3.) Define heredity and Genetics.
Ans: Heredity is the study of transmission of characters from one generation to next generation. Variation and differences between individuals of same species.
4.) Give the monohybrid and dihybrid phenotypic ratios for Mendelian inheritancce.
Ans: Monohybrid ratio = 3 : 1 and Dihybrid ratio = 9 : 3 : 3 : 1 are the ratios .
5.) Mention two sources of variation.
Ans: Differences between parents and their children, between children of the same parents, or between individuals within the same group are considered variations. Mutation, Recombination are the sources of variations.
INTEXT 22.2
1.) Define : (i) An allele .- Alleles are diffrerent forms of a gene
(ii) Codominance..
(iii) Polygenes …
(iv) Lethal genes .
2.) Name the kind of inheritance in terms of expression of
(i) blood groups of human- Codominance and multiple alleles
(ii) wheat kernel colour .- Incomplete dominance
(iii) human skin colour? – Polygenic inheritance
3.) State the phenotypic monohybrid ratio in case of incomplete dominance.
Ans: In case of incomplete dominance the phenotypic monohybrid ratio is 1 : 2 : 1
INTEXT 22.3
1.) What are genes and where are they located?
Ans: Genes are segments of DNA which have genetic information in it.Genes are located linearly on the chromosomes. All the genes present on the same pair of chromosomes and with a tendency to be inherited together forms a linkage group
2.) State the names of the scientists who proposed the chromosomal theory of inheritance.
Ans: The scientists who proposed the chromosomal theory of inheritance are Sutton and Boveri
3.) Define
(i) linkage – Genes present on the same chromosome tend to be inherited together and are said to be linked. This phenomenon is called linkage
(ii) crossing over- The physical exchange of non-sister chromatids from a homologous pair of chromosomes is known as crossing over.
4.) When does gene exchange through chiasma formation occur between homologous chromosomes?
Ans:The gene exchange through chiasma formation occur between homologous chromosomes during prophase I of meiosis
5.) Why is the human female called the homogametic sex?
Ans: sex chromosomes are morphologically similar (i.e. XX) in an individual, the female human is termed as homogametic. They produce only one kind of gametes (containing X)
6.) A colour blind man married a normal woman whose father and mother both had normal colour vision. Will any of their sons be colour blind? If not why not.
Ans: No. Because gene for color blindness on X chromocomes is a recessive gene so it gets marked by renual gene from mother
7.) With the help of flow chart explain the difference in sex determination in birds and mammals.
Ans:
8.) Name an insect in which all males are produced parthenogenetically.
Ans: Ants and bees are the insect in which all males are produced parthenogenetically
9.) In honey bees “males have no father and cannot have sons but have a grandfather”. Justify the statement.
Ans: “Males have no father and cannot have sons but have a grandfather” Because males develop from unfertilised or haploid eggs and females from fertilised or diploid eggs
10.) Which sex in birds is heterogametic?
Ans: The females are heterogametic and produce two types of eggs , because s the female has the heteromorphic morphologically different sex chromosomes (ZW).
11.) Why is sex determination in honeybees called haplodiploidy
Ans: When determining sex, honey bees use a special technique. Unfertilized eggs develop into males in honey bees, while fertilised eggs become females. Males and females are haploid and unfertilized eggs are diploid, respectively, hence sex is determined by these two factors. Therefore, haplodiploidy refers to the determination in honey bees.
INTEXT 21.4
1.) Why is mitochondrial inheritance treated as a case of maternal inheritance?
Ans: Since mitochondria enter the zygote from the egg, mitochondrial DNA inheritance is thought to be an example of maternal inheritance. certain diseases and therefore the genes responsible for them are due to defects in mitochondrial DNA and can be traced to the mother’s family
2.) Into how many groups have human chromosomes been grouped in the human karyotype?
Ans:Into Seven groups the human chromosomes have been grouped in the human karyotype
3.) State the chromosomal abnormality in Klinefelters, Turners syndrome and in Mongolism
Ans: Any change from the normal number or structure of chromosomes causes abnormalities
Kline felter : 2n = 47; XXY Turner : 2n = 45; XO Mongolism : 2n = 47; Trisomy of chromosome 21
TERMINAL EXERCISE
1.) State the three Mendel’s laws of inheritance. Which one of these laws is universal?
Ans: 1. Law of segregation or purity of gametes.
The two Heredity chromosomes of each pair separate (segregate) into two distinct cells to create the gametes at the time of ovulation. Each gamete receives one member of a pair of factors and the gametes are pure
2.) Law of dominance : According to the second law of inheritance, when a pair of genes reflect two conflicting personalities, one gene’s expression will always outweigh the other.
3.) Law of independent assortment, which states that when two features are inherited, the genes corresponding to the two distinct features are independently passed down to the offspring.
2.) Consider a hypothetical case of a cross between a tall plant (TT) and a dwarf plant (tt). Work out the phenotypic and genotypic ratios of the F2 progeny if the cross were to show
(a) dominance (b) incomplete dominance
3.) What will be the blood group of the progeny of parents with AB and O groups.
Ans : The progeny will either have A blood group or B blood group.
4.) Write notes on :
(a) recessive lethal genes : Recessive gene is the opposite of dominant gene. Only in the homozygous state (tt) where both genes of an allele are present does the recessive trait manifest.
(b) pleiotropy : A gene may affect several phenotypes even though it may have multiple alleles and hence produce multiple genotypes.
(c) linkage groups : A linkage group is made up of all the genes that are found on the same pair of chromosomes and have a tendency to be passed down together due to heredity.
(d) mitochondrial inheritance:
(e) human karyotype : The organisation of human chromosomes into seven groups based on chromosome type and size is known as the human karyotype.
(f) human genome: All the genes found in the haploid set of human chromosomes can be referred to as the human genome.
5.) Why do we find so many different complexions among humans?
Ans: Human have different complexion because they have melanocye which produce different type of melanin in different amount, which indicates different skin tone in human.
6.) State the chromosome theory of inheritance.
Ans: (i) The chromosome theory have following feature:
The body cells, or somatic cells, of an organism are produced by the repetitive Zygotes that have been divided have two identical sets of chromosomes, making them diploid. One set of chromosomes (maternal) is obtained from the mother out of these.
and one pair from the father (paternal chromosomes), respectively. A homologous pair is made up of two chromosomes of the same kind that carry the same genes for the same set of features. There are 23 pairs of chromosomes in humans.
(ii) At the period of gamete creation, meiosis occurs during which homologous pairs of chromosomes separate.
(iii) Mendelian components or genes are thought to be placed linearly on the chromosomes based on the behaviour of chromosomes during meiosis. As molecular biology has advanced, it is now understood that the genes are distinct collections of DNA segments that make up a chromosome.7. Work out the following crosses and mention the phenotypic ratio of their progeny.(a) A colour blind man marries a carrier womam(b) A man with normal colour vision marries a carrier woman.
8.) Why is X-linked inheritance termed cris-cross inheritance?
Ans: Crisscross inheritance, sex linked or X-linked inheritance are terms used to describe the inheritance of a recessive sex-linked trait from a father to a daughter and then from the daughter to her sons.
9.) Give an account of genetic disorders caused by abnormal chromosomal number.
Ans: 1.) Down syndrome or mongolism
Due to trisomy of chromosome 21, the person has 47 chromosomes rather than the normal 46. The following traits or characteristics result from this flaw:
have a thick tongue, are intellectually disabled, and have drooping faces.
2.) Klinefelter syndrome
Male with 47 chromosomes and an additional X chromosome. (XXY plus 44 autosomes). Klinefelter’s syndrome is characterised by tall, mentally retarded men who are sterile and have breast growth or gynecomastia.
3.) Thalassemia
Because of this autosomal condition, normal haemoglobin cannot be synthesised. As a result, regular blood transfusions are necessary for survival.
The faulty gene is autosomal recessive and is present in heterozygous individuals.
The disorder might not be visible to parents. Thalassemia affects the child who inherits the faulty genes from both parents (homozygous recessive).
10.) What is amniocentesis? How and for what is it carried out?
Ans: Amniocentesis is a method for identifying genetic diseases brought on by faulty genes.
It can be carried out by
(i) a tiny amount of the amniotic fluid that surrounds the foetus is drawn out using a syringe.
(ii) This fluid contains cells that separate from the foetus’ skin.
(iii) Cultured foetal cells are collected.
(iv) The dividing cells’ chromosomes are examined for genetic flaws.
11.) In what way is chromosomal sex determination of humans different from that of birds?
Ans: In human, males are heterogametic while in birds, female are heterogametic.
12.) From which kind of eggs do males and females of honeybees emerge.
Ans: They emerge from unfertilized egg,