10th Class Science Heredity and Evolution Sex Determination

       Sex Determination

Genetic inheritance determines the sex of an individual. The genes inherited from the parents determines the sex of the child, whether it is a boy or the girl. The sex chromosomes carries two types of genes X and Y. There are total number of 46 chromosomes in an individual; half of them comes from mother and half of them comes from father. Out of these 46 chromosomes, 44 are autosomes and 2 are sex chromosomes. In female the sex chromosomes are XX and in male the sex chromosomes are XY. During gametes formation the number of chromosomes is halved and is called haploid. It is 22 + X chromosomes from female and 22+X or Y chromosomes from male. If the X chromosomes of male fertilized with X chromosomes of female then the new born baby is female and if the Y chromosomes of male combines with the X chromosomes of female then the new born baby is male.

         Acquired and Inherited Traits

        Acquired Traits

We know that new species arise from pre existing species with modifications. The favorable changes appear due to the use or disuse of organs, over a long period of time. The traits which develop in an organism due to external environment is called acquired traits. The acquired traits of an organism cannot be passed on to their future generations. Only those traits can be transmitted from one generation to the next, in which, changes have occurred in the genes present in the reproductive cells of parents. The changes which occur in non reproductive cells of an organism cannot be inherited from one generation to the next,

            Inherited Traits

The traits which are transmitted from one generation to the next, due to the change in its gens, is called inherited traits. For example, the colour of red beetles changes from red to green during reproduction. This change of colour in the beetles has been due to change in the genes of the reproductive cell.

         The transmission of traits from one generation to the next is called:

(a) Variations

(b) Characters

(c) Heredity

(d) All of these

(e) None of these

Answer: (c)

         Which factor determines the appearances of an organisms:

(a) Chromosomes

(b) Genes

(c) DNA

(d) Ribosomes

(e) None of these

Answer: (b)

              Which plant did Mendel's chose for his experiment to study the laws in inheritance?

(a) Mango plant

(b) Papaya

(c) Grams

(d) Pea Plant

(e) None of these

Answer: (d)

         Which one is the ratio of each phenotype of the seeds in F₂ generation?

(a) 1 : 3 : 3 : 9

(b) 1 : 9 : 3 : 1

(c) 3 : 1: 1 : 3

(d) 1 : 3 : 1 : 3

(e) None of these

Answer: (a)

         Read the statement given below regarding the results of Mendel's experiment and identify which one of the following is correct?

Statement 1: Whenever two traits of a character crossed, the \[{{F}_{1}}\] plants showed only one of the traits and the other traits never appeared.

Statement 2: The traits that did not appeared in \[{{F}_{1}}\] reappeared in \[{{F}_{2}}\], but only on 25% of cases.

(a) Statements 1 and 2 both are true

(b) Statements 1 is true and 2 is false

(c) Statements 1 is false and 2 is true

(d) Statements 1 and 2 both are false

(e) None of these

Answer: (a)