Heredity and evolution

Question 1

define genetics

Answer 1

Genetics is the branch of biological sciences which deals with the study of genes, genetic variation, and heredity in living organisms.

Question 2

give phenotypic and gentoypic ratio for monohybrid dihbrid cross

Answer 2

monohybrid
genetic 1:2:1
phenotypic 3:1

dihybird
phenotypic 9:3:3:1

Question 3

name two human traits which have variation

Answer 3

free(d) and attached(r) ear lobes
black eye colour(d) and green colour(r)

Question 4

differentiate between genotype and phenotype

Answer 4

genotype:
-> it is the gene complement of an organism
->remains unchanged
->not easily observed

phenotype:
-> it is an expression of a charcater
->can change due to environmental effects
->easily seen

Question 5

3 ways of producing variant genotypes are:

Answer 5

->gene mutation
->crossing over
->hybiridization

Question 6

what did the reappearance of dwarf plant in f2 generation indicate?

Answer 6

Mendel proposed that something
was being stably passed down,
unchanged, from parent to offspring
through the gametes, over
successive generations. He called
these things as ‘factors’. Now we call
them as genes. Genes, therefore, are
the units of inheritance.

Question 7

mention the charcateristics of gene

Answer 7

-> functional units of heredity,evolution, variation and mutation
->they occupy a fixed position on a chromosome
-> they control the synthesis of a protein or enzyme to bring about a phenotype
->genes coding for contrasting traits are called alleles. they may exist in alternative forms

Question 8

what is a trait according to mendel?

Answer 8

traits are charcateristics that are controlled by factors now called as genes

Question 9

how are chromosome, gene and dna related to each other

Answer 9

genes are functional segments of dna on a chromosome

Question 10

are mendelian trait and gene same? explain giving reasons

Answer 10

they are the same. At mendel’s time, genes were not known. He called these traits or factors that are responsible for the inheritance of charcateristics. They show similarities
i)they exist in pairs
ii)they have definite, discrete, stable structure
iii) they segregate during gamete formation (meiosis)
iv) they restore their pairing condition during fertilisation

Question 11

how does a rare variation become a characteristic in a population? explain with example?

Answer 11

a population of red beetles living in a bush are frequently eaten by crows. By chance a few blue beetles are produced in the red beetle progeny but they too are eaten by crows. An elephant foot stamps the bushes killing most of the beetles. Some of the beetles survive and reproduce

Question 12

how can a variation occuring in a population give survival advantage?

Answer 12

In a population of red beetles, a few green beetles are produced. The red beetles are easily visible against the green bush and are eaten by the crows.
The grene beetles camouflaged with thte bush and are nto eaten. So their popoulation thrives

Question 13

How does a plant having Tt gene combination form a tall plant?

Answer 13

A gene produces an enzyme. The growth occurs by the hormone secreted by the enzyme. For example, the T gene produces an enzyme with secreted hormone and makes plant tall. if gene is altered the plant remains dwarf.

Question 14

Why do offsprings differ from parents

Answer 14

It is due to biparental percentage. The genes on the chromosome are partly derived from parents male and female. Hence when fertilisation occurs, a new combination of chromosomes enter the zygote leading to variations in the offspring

Question 15

What are causes of variations

Answer 15

Biparental percentage: offspring receive some characteristics from mother and some from father.
Gene mutations: mutation is gene or chromosomal paterns

Question 16

Mendel to genetics

Answer 16

He observed the occurrence of contrasting characteristics in the pea plant. On this basis he said that these contrasting characteristics are controlled by factors. These characteristics are called traits controlled by factors know known as genes

Question 17

Explain how gene expresses itself in a cell?

Answer 17

Genes are functional segments of DNA. They are units of heredity that gets passed on through reproduction from parents to progeny. It is the blue print of life. DNA expresses itself through synthesis of proteins. Proteins make structures in our body and also controls the functioning. In other words cells, tissues, organs and hence a living body expresses the traits inherited as genes/ DNA.

Question 18

Where are the genes located? What is the chemical nature of gene?

Answer 18

Genes are located on chromosomes in linear sequence and at fixed positions. Chemically, genes are acidic in nature since they are nucleic acids which constitute DNA. They are double helix of complementary nucleotides.

Question 19

Difference between dominant and recessive factors

Answer 19

dominant factor
it can express its effect even in the presence of a recessive factor
produces an efficient and complete proteins for showing effect

recessive factor
it can express its effect only in the presence of another recessive factor
produces defective and incomplete proteins

Question 20

how do traits get expressed

Answer 20

Factors/alleles are actually forms of genes which are functional segments of DNA are responsible for the expression of trait

They show the trait by controlling the synthesis of proteins/enzymes formed by them.

Synthesis of a fully functional protein or enzyme produces its physiological effect on organism and is known as dominant gene

Recessive genesare unable to prduce fully functional protein /enzyme. Since it is defective, it is unable to show its effect in the presence of a dominant gene.