Biology Test 261

Statement (d) is correct about reproduction in honeybees. Fertilised eggs hatch into female worker bees, while unfertilised eggs become drones or males.

Tubuli recti in male testis are formed by end to end fusion of seminiferous tubules.

Double fertilisation is a characteristic feature of angiosperms. In these plants, one male gamete fuses with egg cell to form the zygote, while second male gamete fuses with secondary nucleus and gives rise to triploid endosperm.

In an angiospermic embryo sac; n, 2n and 3n conditions are found respectively in egg, zygote and endosperm.

The appearance of ancestral characters in new-borns like tail, etc. are atavistic. It is the sudden reappearance or refunctioning of some ancestral organs, which have either completely disappeared or are present as vestigial organs.

Darwin’s finches are evidences in favour of organic evolution. It is the process by which changes in the genetic composition of populations of organisms occurs in response to environmental changes.

A constitutive gene is a gene that is transcribed continually. A housekeeping gene is typically a constitutive gene that is transcribed at a relatively constant level.

When gene migration happens multiple times, it is called gene flow. When new genes or alleles are added to new population and are lost from old population in turn changing the gene frequencies is called gene migration. Genetic drift refers to a random gene frequency change and occurs only by chance.

Mendel’s law of dominance states that in F1-generation only dominant trait appears and in F2-generation dominant and recessive traits appear in the ratio of 3 : 1.

In homozygous condition, deletion of any chromosomal part will be the most harmful change. The deletion is the absence of a chromosomal portion resulting into loss of genes or a gene.