Which of these sentences describe sources and preservation of genetic variation? Select all that apply.

A.) Antibiotic resistance in bacterial populations is caused by natural selection of bacteria that inherit mutations that make them resistant to the antibiotics.

B.)If a cell has two pairs of chromosomes, four kinds of gametes are possible as a result of reshuffling of chromosomes during meiosis.

C.) Crossing-over causes a shuffling of allele combinations during meiosis as the alleles from each parent form new combinations on homologous chromosomes.

D.) During mitosis in eukaryotes, the sister chromatids are separated and distributed to two daughter cells.

E.) When two bacteria are linked during conjugation, the donor cell passes DNA to the recipient cell which causes genetic recombination.

the correct answer is:

a population changes in response to a change in the environment.

estuaries are the partially enclosed coastal bodies of brackish water formed at the mouth of sea where river meets an ocean. it is a transition zone between river and sea water so estuaries are influenced to both marine environment such as tides, waves and to riverine such as flow of fresh water and sediments. the mixing of sea and fresh water provide high level of nutrients, making estuaries a high product habitats.

many estuaries suffers degradation from a variety of human activities like erosion from deforestation, overgrazing, overfishing, drainage and eutrophication.

so from the above statement answers will be

1. false as estuaries are formed due to both brackish and freshwater.

2.true, due to high productivity estuaries are breeding ground for many marine species.

3. direct and indirect activities of man that contribute to pollution and deposition of sediments.