If pea plants with round and green seeds (RRyy) are crossed with pea plants having wrinkled and yellow seeds (rrYY), the seeds developed by the plants of $F_{1}$ generation will be :
[1 marks]
Assertion (A): A human child bears all the basic features of human beings.
Reason (R): It looks exactly like its parents, showing very little variations.
[1 marks]
| (a) | What are chromosomes? |
| (b) | Explain in brief how stability of DNA content of a species is ensured in sexually reproducing organisms? |
[3 marks]
Consider the following statements:
(i) The sex of a child is determined by what it inherits from the mother.
(ii) The sex of a child is determined by what it inherits from the father.
(iii) The probability of having a male child is more than that of a female child.
(iv) The sex of a child is determined at the time of fertilisation when male and female gametes fuse to form a zygote.
The correct statements are:
[1 marks]
Chromosomes:
(i) carry hereditary information from parents to the next generation.
(ii) are thread like structures located inside the nucleus of an animal cell.
(iii) always exist in pairs in human reproductive cells.
(iv) are involved in the process of cell division.
The correct statements are:
[1 marks]
Mendel worked out the rules of heredity by working on garden pea using a number of visible contrasting characters. He conducted several experiments by making a cross with one or two pairs of contrasting characters of pea plant. On the basis of his observations he gave some interpretations which helped to study the mechanism of inheritance.
(i) When Mendel crossed pea plants with pure tall and pure short characteristics to produce $F_{1}$ progeny, which two observations were made by him in $F_{1}$ plants?
(ii) Write one difference between dominant and recessive trait.
(iii) (A) In a cross with two pairs of contrasting characters
RRYY X rryy
(Round Yellow) (Wrinkled Green)
Mendel observed 4 types of combinations in $F_{2}$ generation. By which method did he obtain $F_{2}$ generation? Write the ratio of the parental combinations obtained and what conclusions were drawn from this experiment.
OR
(iii) (B) Justify the statement: "It is possible that a trait is inherited but may not be expressed."
[4 marks]
The statement that correctly describes the characteristic(s) of a gene is:
[1 mark]
Assertion (A): Genes inherited from the parents decide the sex of a child.
Reason (R): X chromosome in a male child is inherited from his father.
[1 mark]
In order to trace the inheritance of traits Mendel crossed pea plants having one contrasting character or a pair of contrasting characters. When he crossed pea plants having round and yellow seeds with pea plants having wrinkled and green seeds, he observed that no plants with wrinkled and green seeds were obtained in the \( F_{1} \) generation. When the \( F_{1} \) generation pea plants were cross-bred by self-pollination, the \( F_{2} \) generation had seeds with different combinations of shape and colour also.
(a) Write any two pairs of contrasting characteristics of pea plant used by Mendel other than those mentioned above.
(b) Differentiate between dominant and recessive traits.
(c) State the ratio of the combinations observed in the seeds of \( F_{2} \) generation (in the above case). What do you interpret from this result?
OR
(c) Given below is a cross between a pure violet flowered pea plant (V) and a pure white flowered pea plant (v). Diagrammatically explain what type of progeny is obtained in \( F_{1} \) generation and \( F_{2} \) generation:
Pure violet flowered plant (VV) x Pure white flowered plant (vv)
[4 marks]
| (a) |
What is variation? List two main reasons that may lead to variation in a population. |
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OR |
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| (b) |
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[2 marks]
The mechanism by which the sex of an individual is determined is called sex-determination. In human beings, sex of a newborn is genetically determined, whereas in some others it is not. There are 46 (23 pairs) chromosomes in human beings. Out of these, 44 (22 pairs) control the body characters and 2 (one pair) are known as sex chromosomes. The sex chromosomes are of two types X chromosome and Y chromosome. At the time of fertilisation, depending upon which type of male gamete fuses with the female gamete, the sex of the newborn child is decided.
| (a) |
Why is a pair of sex chromosomes in human beings called mismatched pair in terms of type and size ? |
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| (b) |
Out of male or female, which of them has a perfect pair of sex chromosomes ? In case of a perfect pair, will the gametes produced be of the same kind or of a different kind? |
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| (c) |
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[4 marks]