CBSE Questions for Class 10 Biology Heredity And Evolution Quiz 2 - MCQExams.com

• A dihybrid cross considers two pairs of contrasting characters. TtRr genotype is obtained from the dihybrid cross of TTRR and ttrr which are true-breeding homozygous dominant and homozygous recessive breeding lines. 
• TtRr genotype consists of both dominant and recessive alleles for two different traits. Hence, it's a dihybrid genotype.
• On the other hand, other genotypes given in the questions contain heterozygous alleles for either one of the two traits or none at all.

• A dihybrid cross is a cross between F$$_1$$ offspring (first-generation offspring) of two individuals that differ in two traits of particular interest.
• For example : RRyy/rrYY or RRYY/rryy parents result in F$$_1$$ offspring that are heterozygous for both R and Y (RrYy). Thus, Mendel's dihybrid ratio is depicted by 9:3:3:1.
• So, the correct answer is option B.

Homologous organs are those that have similar structures and share common ancestors but have different functions e.g., the wings of a bat for flight, the lateral fin of a whale for swimming, and the human arm to hold or lift any object. Thus, the correct answer is option C.

• A Large number of human fossils have been discovered from Africa. This led to the "Out of Africa hypothesis" according to which modern humans evolved only in Africa and then traveled to Asia, Europe, and other places to replace the indigenous populations. 
• Most probably, Homo erectus was the first hominid to move out of Africa, and colonize Asia, Europe, and other parts of the earth.
• So, the correct answer is option B.

• The evolutionary process by which new biological species arise is called speciation. 
• The speciation not only brings phenotypic changes but also genotypic changes which causes a variation in the gene pool.
• Isolation is the segregation of different populations into smaller units by a certain mechanism so as to prevent interbreeding among them.
• Genetic variation is the difference in DNA among individuals or the differences between populations.

• Analogous organs are those organs which are evolved from different origins but perform same function.
• Whereas homologous organs are those organs which are evolved from same origin but have different functions. 
• Wings of butterfly, housefly and bat are examples of analogous organs. 
• Thus, the correct answer is option A.

• Organisms belonging to different groups but living in the same habitat have organs that are modified and adapted to their requirements. 
• This gives rise to organs that may have a different origin with dissimilar structures but will perform similar functions. These types of structures or organs are called analogous organs. 
• For example, the wings of a bat and an insect. Bats and insects have different embryonic origins; bat is a mammal whereas, an insect is an arthropod. Their wings are structurally different. 
• The wings of bats have bones but, insects' wings are membranous folds composed of cuticles. But both these types of wings perform a similar function, i.e. of flying. 

• The wings of an insect are analogous to the wings of a bird and bat. It is because the structure of the wings of the insect is different from the wings of birds and bats. However, their function is similar.
• Flippers of penguins and dolphins have a similar function (helps in swimming) but different origins so, they are analogous organs.
• The wings of bat and pigeon are analogous organs, as both use wings for flying.
• Hence, the correct answer is option C.

Solution:
Correct answer is option D
Explanation for correct option: