(a) Define ‘speciation’. Explain how speciation occurs.
(b) Will geographical isolation be a major factor in the speciation of a self-pollinating plant species ? Give reason for your answer.
(a) The process by which new species develop from the existing species is known as speciation. New species are formed when the population of same species splits into two separate groups which then get isolated from each other geographically by the barriers such as mountain ranges, rivers or the sea. The geographical isolation of the two groups of population leads to their reproductive isolation due to which no genes are exchanged between them. However, breeding continues within the isolated populations producing more and more generations. Over the generations, the processes of genetic drift (random change in gene frequency), and natural selection operate in different ways in the two isolated groups of population and make them more and more different from each other. After thousands of years, the individuals of these isolated groups of population become so different that they will be incapable of reproducing with each other even if they happen to meet again. We then say that two new species have been formed.
(b) Geographical isolation will not be a major factor in the speciation of a self pollinating plant because it does not depend on other plants for its process of reproduction to be carried out.
Choose the one term from the following which includes the other three :
broccoli, wild cabbage, cauliflower, cabbage
”The sex of the children is determined by what they inherit from their father and not their mother.” Justify.
Which of the processes, sexual reproduction or asexual reproduction, brings about maximum variations in the offsprings ?
Define the term ‘evolution’. “Evolution cannot be equated with progress”. Justify this statement. [Delhi]
An individual cannot pass on to its progeny the experiences of its lifetime.” Justify the statement with the help of an example and also give reason for the same. [Foreign]
Name five varieties of vegetables which have been produced from ‘wild cabbage’ by the process of artificial selection.
Will geographical isolation be a major factor in the speciation of an organism that reproduces asexually ? Give reason for your answer.
Study the following cross and showing self-pollination in Flf fill in the blank and answer the question that follows
Explain the mechanism of sex determination in humans. [All India]
Or
With the help of a flow chart explain in brief how the sex of a newborn is genetically determined in human beings. Which of the two parents, the mother or the father, is responsible for determination of sex of a child? [Foreign]
State one characteristic which shows that the birds are very closely related to dinosaurs.
Mendel said that the characteristics or traits of organisms are carried from one generation to the next by internal factors which occur in pairs. What is the modern name for these factors ?
In human beings, the statistical probability of getting either a male or female child is 50 : 50. Give a suitable explanation.
The forelimbs of a frog, a bird and a man show the same basic design (or basic structure) of bones. What name is given to such organs ?
A man having blood group O marries a woman having blood group B and they have a daughter. What will be the blood group of the daughter ?
Why are human beings who look so different from each other in terms of size, colour and looks said to belong to the same species ?
Out of bacteria, spider, fish and chimpanzee, which organism has a better body design in evolutionary terms ? Give reason for your answer.
(a) Define ‘natural selection’.
(b) “Only variations that confer an advantage to an individual organism will survive in a population”. Do you agree with this statement ? Give reason for your answer.
Can the wing of butterfly and the wing of a bat be considered homologous organs ? Why or why not ?
In evolutionary terms, can we say which among bacteria, spiders, fish and chimpanzees have a ‘better body design’ why or why not ?
Gregor Mendel’s first law of genetics states “Of a pair of contrasted characters, only one can be represented in a gamete by its internal ‘factor’.
(a) Give the modern name for this ‘factor’.
(b) State where these factors are found in gametes.
Write the names of at least three inorganic molecules which helped in the origin of life on the earth.
(a) Explain the terms ‘analogous organs’ and ‘homologous organs’ with examples.
(b) In what way are analogous organs evidence for evolution ?
Will geographical isolation be a major factor in the speciation of an organism that reproduces asexually ? Why or why not ?
Give one example each of characters that are inherited and the ones that are acquired in humans. Mention the difference between the inherited and the acquired characters. [Delhi]
Give an example of body characteristics used to determine how close two species are in terms of evolution and explain it. [All India]
What are homologous organs? Can the wing of a butterfly and the wing of a bat be regarded as homologous? Why? [All India]
(a) What is the genotype of dwarf plants which always produced dwarf offspring ?
(b) What is the genotype of tall plants which always produced tall offspring ?
(c) What is the genotype of
Give an example of characteristics being used to determine how close two species are in evolutionary terms.
A woman has only daughters. Analyse the situation genetically and provide a suitable explanation.