The mechanism by which the sex of an individual is determined is called sex-determination
Heredity (10)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.
- Why is a pair of sex chromosomes in human beings called a mismatched pair in terms of type and size ?
- 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 ?
- i. Name two animals whose sex is not genetically determined. Explain the process of their sex determination. OR
ii. With the help of a flowchart only, show how sex is genetically determined in human beings.
Answer
(a) XY; Y is shorter than X
(b) Mother / Female; Same kind
(c) i. Reptiles & Snails
In reptiles, the temperature at which fertilised eggs are kept determines whether the animal developing in the eggs would be a male or a female.
In snails, they can change their sex during their life time.
ii.
- The most obvious outcome of the reproductive process is the generation of individuals
- What is variation? List two main reasons that may lead to variation in a population
- How do Mendel’s experiments show that the
- Study Mendel’s cross between two plants with a pair of contrasting characters
- If the plants of F1 progeny are self-pollinated, then what would be observed in the plants of F2 progeny
- A cross between pea plant with white flowers (vv)