Principles of Inheritance and Variation

Question 1

define:
i) inheritance
ii) variation
iii) genetics

Answer 1

i)Inheritance is the process by which charcaters are passed down from parent to progeny
ii) Variation is the degree by which progeny differ from their parents.
iii) Genetics is the branch of biology that deals with inheritance as well as variation of characters from parents to progeny.

Question 2

explain how genetic material exists in the nucleus

Answer 2

i) In interphase nucleus, genetic material exists as a network of chromatin. There are long thin threads with single centromere.

ii) IN the S phase of cell division, there is a replication of genetic material. It is still present as chromatin network but with two thin strands attached to 1 centromere.

iii) In the prophase of cell division, the chromatin materials undergoes condensation(lose water) and form compact chromosomes. They have 2 chromatids attached to 1 centromere. The condensation is completed by metaphase.

Question 3

each chromosome has 2 copies. what do you mean by this statement

Answer 3

A diploid organism has 2 copies of each chromosome, one that is coming from the mother and one that is coming from the father.
A particular no of chromosome, say chromosome 1, coming from the mother and father are alike, for a given species.

This means that these chromosomes have same length, position of centromere, and have information carried by genes and same position of genes on the chromosome.

Chromosomes need no be alike within the same parents. Chromosome 1 and chromosome 2 of the mother may not be similar.

Question 4

what is locus of a gene

Answer 4

The fixed position of a gene on a chromosome is called as locus (pl. loci).

Question 5

what are autosomes and what are sex chromosomes

Answer 5

autosomes are chromosomes which carry information for al features of the body except sex.

sex chromosomes carry information ofr sex of the offpsring as well as certain features of the body.

humans of 23 chromosomes of which 22 are autosomes and the last pair is the sex chr,

Question 6

what are homologus chromosomes

Answer 6

ALike genes of 2 parents are homologous chromsomes.
They have same shape, structure( length+posn of centromere), same information carried by genes, same genes and same sequence of genes of the chr.

Question 7

what do genes decide

Answer 7

In a diploid organisms, there are 2 genes for each charcater( one in each parental chrosmomes). Each chromsomes will posses a single gene copy(allele) for each trait

Question 8

what is fixed in a species.

Answer 8

No of chromosomes or chromosome no is fixed in a species. Size shape of info of chromsomes are also the same.

Question 9

why cant diploid organisms of different spiecies interbreed freely with one another?

Answer 9

This is because, if such a fertilisation happens, then the formed zygote will not be a proper diploid( b/c each chromosome will not have a proper pair). The offspring will not be able to live or even if it lives, then it will be sterile due to inability to form gemetes by meisosis ( b/c not all its chromosomes are paired to be seperated in meisosi).

Question 10

what do homologous chromosomes have

Answer 10

Homologous chromsomes have gens conding for the same character. They may contain infor for diff traits.

Question 11

what are traits

Answer 11

characters manifests itself in different forms called traits.
There are 2 traits for each character as given by mendel. These are contrasting traits of which one is dominant and one is recessive

Question 12

what are alleles

Answer 12

Alternate form of a gene are called alleles.
When alleles for a gene are same- homozygous
when alleles for a gene are different- heterozygous

Question 13

what is crossing over

Answer 13

Crossing over is the exchange of genetic material between homolgous chromsoeoms.

Question 14

what are parental combination and new combination

Answer 14

parental gene combination refers to the same gene combination as present in the parents and non parental gene combination refers to gene combination formed after recombination i.e different combination of genes than present in parents.’

also c/a parental type and recombinant type.

Question 15

does percentage of variation remain the same in different organisms

Answer 15

The percentage of variation among offpsrings vary from one organism to the other. There will be different amounts of parental/ new combinations. This depends on the no of cells undergoing crossing over and the distance between 2 genes on chromosomes.

Question 16

What it is a test cross

Answer 16

The cross used to determine the genotype of an organism exhibiting a dominant trait is called test cross. IN this cross, the organism whose genotype is unknown is crossed with a double recessive organism.

If the offpsrings all have dominant trait , then the unknown organism has homozygous dominant

If the offpsrings have 50% dominant trait and 50% recessive trait, then the uknown organism has heterozygous dominant.