22. Paleozoic era startedmillion years ago A) 65.5 B)4000 C)542 D) 251 23. Plant

Question

22. Paleozoic era startedmillion years ago A) 65.5 B)4000 C)542 D) 251 23. Plant species A has 10 and plant species B has 12 chromosomes. A new species C is formed by allopolyploidy from species A and B. The diploid number of species C is likely to be A) 24 B) 22 C) 28 D) 26 24. After separation from chimpanzee line first hominin in human phylogeny is A) Australopithecus africanus B) Australopithecus afarensis C)Ardipithecus ramidus D) Homo habilis 25. What is not a source of variations A) recombination B) gene flow C)mutation D)jindependent assortment 26. The smallest cells without cell walls are present in A) cyanobacteria B) mycoplasmas C) chlamydias Match the terms: Each question 2 marks D) actinomycetes

Explanation / Answer

22. The paleozoic era is started from 542 million years ago.

Explanation

The paleozoic era is started from 542 million years ago with the emergence of complex life forms and ended 251 million years ago with the largest mass extinction.

The cenozoic era was started 66 million years ago and precambrian era was started 4600 million years ago.

23. The answer is B. 22.

Explanation

When species A with 10 and species B with 12 chromosomes combine, it will form species C with 22 chromosomes.

Species A 2n = 10 ------ n = 5

Species B 2n = 12 ------ n = 6

Therefore, n + n = 5 + 6 = 11 ---- sterile F1 hybrid.

2n + 2n = 10 + 12 = 22 ---- fertile amphidiploid species C.

24. The answer is D. Homo habilis.

Explanation

The chronological order of evolution of humans after chimpanzees is as follows:

Homo habilis ------> A. rabidus ------> A. afarensis ------> A. Africanus.

24. The answer is A. Recombination

Explanation

Recombination by itself does not produce variations until alleles are segregating already at different loci.

25. The answer is B. Mycoplasma.

Explanation

The mycoplasma are the smallest self replicating organisms having only 500 - 1000 genes. It is a genus of bacteria which lack a cell wall around the cell membrane.

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