What are homologous structures? Give an example. Is it necessary that homologous structures always have a common ancestor?
Homologous organs are those organs which have the same basic structural design and developmental origin but have different functions and appearance. Example: The forelimb of a frog, a lizard, a bird and a man seem to be built from the same basic design of bones, but they perform different functions.
Yes, it is necessary that homologous structures always have a common ancestor in order to carry out the different activities. Otherwise there cannot be any similarity in basic plan, internal structure, development or origin.
(a) If a normal human cell has 46 chromosomes, how many chromosomes will be there in a human (;) sperm cell, and (ii) zygote ?
(b) What sizes of plants are produced if both parents have genes Tt ?
a) Name the scientist who gave the theory of origin of life on earth. What is this theory ?
(b) How are those species which are now ‘extinct’ studied ?
Will geographical isolation be a major factor in the speciation of an organism that reproduces asexually ? Why or why not ?
How are fossils formed? Describe, in brief, two methods of determining the age of fossils. [All India]
A woman has only daughters. Analyse the situation genetically and provide a suitable explanation.
What do you understand by the double helical structure of DNA? Who proposed this structure?
Define variation in relation to a species. Why is variation beneficial to the species? [Delhi]
Give an example of body characteristics used to determine how close two species are in terms of evolution and explain it. [All India]
If the trait A exists in 10% of a population of an asexually reproducing species and a trait B exists in 60% of the same population, which trait is likely to have arisen earlier ?
State whether the following statement is true or false :
The sex of an infant is not a case of inheritance of characteristics.
(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
Does genetic combination of mother play a significant role in determining the sex of a new born baby ?
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 ?
Name the various tools of tracing evolutionary relationships which have been used for studying human evolution.
Does the occurrence of diversity of animals on earth suggest their diverse ancestry also? Discuss this point in the light of evolution.
A man with blood group A marries a woman with blood O and their daughter has blood group O. Is this information enough to tell you which of the traits blood group A or O is dominant ? Why or why not ?
Give an example of characteristics being used to determine how close two species am in evolutionary terms ?
A study found that children with light-coloured eyes are likely to have parents with light-coloured eyes. On this basis, can we say anything about whether the light eye colour trait is dominant or recessive? Why or why not?
Only variations that confer an advantage to an individual organism will survive in a population. Do you agree with this statement ? Why or why not ?
”The sex of the children is determined by what they inherit from their father and not their mother.” Justify.
Distinguish between acquired and inherited traits by giving one example of each. Why are traits acquired during the lifetime of an individual not inherited? [Delhi(C)]
How is the equal genetic contribution of male and female parents ensured in the progeny? [Delhi]
Explain with examples how the following are evidences in favour of evolution in organisms. (i) Homologous organs (ii) Analogous organs (iii) Fossils [Delhi]
What is meant by the term speciation? List four factors which could lead to speciation. [Delhi]
State the meaning of inherited traits and acquired traits. Which of the two is not passed on to the next generation? Explain with the help of an example.
Name the first scientist who studied the inheritance of traits from one generation to the next.
The gene for red hair is recessive to the gene for black hair. What will be the hair colour of a person if he inherits a gene for red hair from his mother and a gene for black hair from his father ?
Fill in the following blanks with suitable words :Fill in the following blanks with suitable words :
(a) Genes always work in …………………
(b) In pea plants, the gene for dwarfness is………………… whereas that for tallness is…………………
(c) Most people have………………… earlobes but some have………………… earlobes.
(d) A human gamete contains………………… chromosomes whereas a normal body cell has………………… chromosomes in it.
(e) All races of man have………………… blood groups.
(f) The………………… chromosomes for a………………… are XX whereas that for a………………… are XY.
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 ?
(a)What is meant by ‘heredity’ ? What are the units of heredity.
(b) State Mendel’s first law of inheritance.
