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Saturday, 10 October 2015

HEREDITY and evolution notes and HOT Questions

HEREDITY and evolution  notes  and HOT Questions
1. The similarities between parents and their offspring are accounted for by ‘heredity’ and   the dissimilarities by ‘variation’. Both heredity and variation are accounted for when we study genetics’.

2. Asexual reproduction tends to produce ‘clones’, i.e., organisms which are genetically 
identical. Chances of variations are higher in organisms showing sexual reproduction.

3. The differences or dissimilarities between parents and children as individuals of a species 
are called variations. Hereditary variations refer to the differences which are inherited by the progeny from their parents. The inheritance of such heritable variations is determined by the genetic constitution of an individual. Examples of inheritable variations are blood type, skin colour, hair colour, height, etc.
   HEREDITY and evolution  notes  and HOT Questions

4. Environmental variations are caused due to differences in sunlight, water, soil, nutrients 
and other factors of environment.

5. The type of variation in which individuals can be arranged in a definite increasing order of 
gradation with respect to particular characteristics, like height, is called continuous variation. On the other hand, where no gradation between the distinct features can be seen is called discontinuous variation.

6. Causes of variation are — (i) reshuffling of genes during meiosis, (ii) errors in DNA copying, (iii) environment.

7. Gregor Johann Mendel is considered the ‘father of genetics’.Mendel attributed contrasting ‘factors’coming from the parents and their random combinations, as the cause of ‘variation’. 
Mendel’s ‘factors’ were termed ‘genes’ by Johannsen. It was observed that the paired condition of the ‘factors’ is present in the diploid state. But when haploid gametes are formed, the factors ‘segregate’. Since chromosomes are paired in its diploid state but separate during gametic meiosis, it is fair enough to judge that the ‘factors’ are placed on the ‘chromosomes’.

8. Chromosomes are made of giant DNA molecules. A DNA molecule consists of two polynucleotide strands forming a double helix. DNA is the genetic material throughout the living world except in a few viruses where RNA serves as the genetic material (e.g., HIV). 

9. Each chromosome has two arms called chromatids’ joined at the centre called ‘centrosome’. Eukaryotic chromosomes have basic proteins mixed with DNA and are usually more complex in structure than prokaryotic chromosomes. 

10. A gene is the functional unit of DNA that serves as hereditary unit. It is possible to insert a segment of a foreign DNA into the original DNA of a species to make a transgenic 
organism commonly called GOMs, i.e., Genetically Modified Organisms.

11. Each human nucleus has 23 pairs of chromosomes out of which 22 are same in male and female and are known as ‘autosomes’. The 23rd pair is different in male and female and are known as ‘sex chromosomes’. Females have ‘XX’ sex chromosomes and males have sex chromosomes ‘XY’ type

12. Evolution is a set of changes brought about  by the forces of natural selection on the variation within a population, so that resultant organisms are better adapted to their surroundings.

14. Evidences of evolution can be summarised as follows :

A. Paleontological or fossil evidence Fossils are remains or impressions of the organisms of the past. Archaeopteryx is a fossil that has both reptilian and avian features, proving that birds have evolved from the reptiles.

B. Embryological evidence All the vertebrate embryo up to 6 weeks stage look similar. Hence, the ‘biogenetic law’ or the ‘law of recapitulation’ was suggested by Haeckel which states that an organism during the course of its development repeats the developmental history of its race.

C. Morphological and anatomical evidence

(i) Homologous organs : Organs which are similar in structure and origin but different in function and appearance are called homologous organs, e.g., forearm of man, wing of a bat, flipper of a seal, etc.
(ii) Analogous organs : Organ which are similar in appearance and function but different in structure and origin are known as ‘analogous organs’, e.g., wings of a bird and the wings of a butterfly.
(iii) Vestigial organs are the functionless remnants of the organs, functional in the ancestral forms, e.g., vermiform appendix is the remnant of the caecum (an organ of digestion in the herbivorous ancestors).

15. The most accepted theory of evolution comes from Charles Darwin, whose theory is known as ‘Origin of Species by natural selection’. Its tenets are as follows :

(a) Organisms have a far higher capacity to reproduce that can be sustained by nature, thereby creating ‘competition’ or ‘struggle for existence’.
(b) Offspring vary from one another and from the parents.
(c) Those with ‘favourable variations’ are fit for the ‘struggle for existence’.
(d) The favourable variations are accumulated over a long time period creating a new species. The weak point of Darwinism is that it could not explain how variations arise.

16. Certain fossils show features which are intermediate between two groups. Such fossils

form the connecting links and clearly demonstrate stages during the evolutionary process. A very well known example of an extinct animal is dinosaur that, existed long ago in large numbers.
1. What decides that humans give rise to humans?
2. What are hereditary characteristics?
3. Are the variations created by sexual reproduction heritable or non-heritable?
4. What determines the functional property of a gene?
5. What is the basis of sex determination in most plants and animals?
6. Who is known as ‘the father of genetics’?
7. Who coined the term ‘gene’?8. What is centrosome?
9. What is haploid?
10. What do you mean by the term palaeontology?
11. Name the most accepted theory of evolution.
12. Define the term ‘evolution’.
13. Give an example of homologous organ from the plant kingdom.
14. Whose theory influenced Darwin? What did Darwin fail to explain?
1. What is a gene? [2007, 2006]
2. Write the scientific term used for ‘science of heredity and variation’. [2005]
3. What is the function of genes in an organism? [2005]
4. Who proposed the theory of inheritance of acquired characters? [2004]
5. Give an example of a vestigial organ present in the human. [2004]
6. In terms of evolution what is the significance of homology between a human hand and wing of a bird?
7. Name the scientist who established the laws of inheritance. [2004]
8. Define inheritance. [2004]
9. One of the examples of two analogous organs can be the wing of parrot and
(a) flipper of whale
(b) foreleg of horse
(c) front leg of frog
(d) wings of housefly [2003)

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