Heredity and Evolution

"The sex of the children are determined by what they inherit from their father and not the mother." Justify.

"Variations that confer an advantage to an individual organism only will survive in a population." Justify.

For two statements are given- one labelled Assertion (A) and the other labelled Reason (R). Select the correct answer to these questions from the codes (a), (b), (c) and (d) as given below:

1. Both A and R are true, and R is correct explanation of the assertion.
2. Both A and R are true, but R is not the correct explanation of the assertion.
3. A is true but R is false.
4. A is false but R is true.

Assertion: A child which has inherited X chromosome from father will develop into a girl child.

Reason: Girl child inherits X chromosome from father and Y chromosome from mother.

List four tools used to study evolutionary relationships.

List any two factors that could lead to speciation.

Give one example of each of the characters that are inherited and the ones that are acquired in humans.

Mention the difference between the inherited and the acquired characters.

• What are chromosomes? Where are they seated?
• What is a sex chromosome?
• Explain the mechanism of sex determination in human beings.

In terms of evolution, what is the significance of homology between a human hand and a wing of a bird?

How do sexual and asexual reproduction lead to speciation? Give one point for each.

Read the following and answer any four questions from (i) to (v).

In human, the allele for brown eyes (B) is dominant over that for blue eyes (b). A brown eyed woman marries a blue-eyed man, and they have six children. Four of the children are brown eyed and two of them are blue eyed.

(i) What is the genotype of blue-eyed offspring?

1. BB
2. Bb
3. bb
4. Cannot be determined.

(ii) What is the woman's genotype?

1. BB
2. Bb
3. bb
4. Cannot be determined.

(iii) The ovum, produced by the mother carries the gene regarding eye colour is:

1. BB
2. Bb
3. B or b
4. B only.

(iii) The ratio of brown eyed children to blue eyed children in this family is 2 : I, which deviates from typical phenotypic ratios for monohybrid inheritance. What might be the reason?

1. Gametes carrying the brown eyed allele are more viable than those with the blue-eyed allele.
2. A different pattern of inheritance other than monohybrid inheritance is involved.
3. Not all of their babies survived childbirth, thus causing a distortion in the actual ratio.
4. The actual ratio differs from the expected ratio because the sample size is too small.

(iv) What is the gene carried by of the man's spenn regarding the eye colour?

1. BB
2. Bb
3. b only

d. b or B.

What is speciation?

Read the following and answer any four questions from (i) to (v).

Sex determination is the method by which distinction between males and females is established in a species. The sex of an individual is determined by specific chromosomes. These chromosomes are called sex chromosomes or allosomes. X and Y chromosomes are called sex chromosomes. The normal chromosomes other than the sex chromosomes of an individual are known as autosomes.

(i) ln XX-XO type of sex determination:

1. Females produce two different types of gametes.
2. Males produce two different types of gametes.
3. Females produce gametes with Y chromosome.
4. Males produce gametes with Y chromosome.

(ii) A couple has six daughters. What is the possibility of their having a girl next time?

1. 10%
2. 50%
3. 90%
4. 100%

(iii) Number of autosomes present in liver cells of a human female is:

1. 22 autosomes.
2. 22 pairs.
3. 23 autosomes.
4. 23 pairs.

(iv) XX-XO type of sex determination and XX-XY type of sex determination are the examples of:

1. Male heterogamety.
2. Female heterogamety.
3. Male homogamety.
4. Both (b) and (c).

(v) Select the incorrect statement.

1. ln male grasshoppers, 50% of sperms have no sex chromosome.
2. Female fruit fly is heterogametic.
3. Human male produces two types of sperms 50% having X chromosome and 50% having Y chromosomes.
4. In turtle, sex determination is regulated by environmental factors.

(a) Write foil form of DNA.

(b) Why are variations essential for the species ? (CCE 2011)

Describe briefly four ways in which individuals with a particular trait may increase in population.

For two statements are given- one labelled Assertion (A) and the other labelled Reason (R). Select the correct answer to these questions from the codes (a), (b), (c) and (d) as given below:

a. Both A and R are true, and R is correct explanation of the assertion.

b. Both A and R are true, but R is not the correct explanation of the assertion.

c. A is true but R is false.

d. A is false but R is true.

Assertion: ln grasshoppers, females are hetero gametic and males are homo gametic.

Reason: ln grasshoppers, male has only one sex chromosome (XO) whereas the female has sex chromosomes (XX).

(a) What is geographical isolation?

(b) Illustrate formation of a species with the help of an example where individuals are very different from each other and are capable of reproduction among themselves.

• What is genetics?
• Give the common name of the plant on which Mendel performed his experiments.
• What for did Mendel use the term factors and what are these factors called now?
• What are genes? Where are the genes located?

What is the function of genes in an organism?

What is gene?