please help asap!!! 18. 13.3, U_LO4 Crossing over occurs during a. prophase of m
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please help asap!!!
18. 13.3, U_LO4 Crossing over occurs during a. prophase of mitosis b. prophase I of meiosis c. prophase II of meiosis d. metaphase I of mciosis c. metaphase II of meiosis 19. 13.2, U LO4 All of the following are characteristics of meiosis EXCEPT a. involves two divisions b. reduces the number of chromosomes c. results in genetically identical cells d. produces haploid cells e. occurs in the ovaries and testes 20. 13.1, U LO4 Consider an organism whose karyotype shows it to have a total of 60 chromosomes. How many chromosomes would be contained in the sperm of this organism? a. 23 b. 30 ?. 46 d. 60 e, 90 21. 13.3, U LO4 During which stage of meiosis do the homologous chromosomes separate? a. prophase I b. metaphase II c. anaphase II d. prophase II e. anaphase I 22. 15.4,R LO4 Occasionally, chromosomes fail to separate during meiosis, leading to daughter cells abnormal number of chromosomes. This phenomenon is called a. epistasis. b. crossing over c. nondisjunction. d. pleiotropy e chromosome inactivation. that have an 23. 19, U LO4 What is the function of reverse transcriptase in retroviruses? a. it converts host cell RNA into viral DNA. b. it uses viral RNA as a template for DNA synthesis. c. it uses viral RNA as a template for making complementary RNA strands. it translates viral RNA into proteins. It uses viral DNA to make complementary RNA. d. e. 4Explanation / Answer
18) Option b: Cross over or homologous recombination occurs during pachytene stage of prophase I. At each point of crossing over a chiasma is formed between non-sister chromatids of homologous chromosomes.
19) Option c: Unlike mitosis which generates genetically identical cells, meiosis produces at the end of division four cells that are unique and non-identical. The four cells are haploids containing only one set of chromosomes. The production of non-identical cells in meiosis results in genetic diversity and variability.
20) Option b: A karyotype is the number and appearance of chromosomes in the nucleus of a eukaryotic cell. A diploid organism whose karyotype shows 60 chromosomes will have a total of 30 chromosomes in the haploid sperm.
21) Option e: The homologous chromosomes separate during the anaphase I of meiosis I. The homologous chromosomes align up at the equatorial plate in metaphase I and then separate in the subsequent anaphase I. Cohesin which holds the two homologous chromosomes together is released by enzyme seperase which leads to the separation of homologous chromosomes.
22) Option c: Non-disjunction is the failure of homologous chromosomes or sister chromatids to separate at anaphase of cell division. In the resulting cells, one has the two copies of identical chromosomes which other have none. This condition is referred to as aneuploidy.
23) Option b: Reverse transcriptase of viruses carries out RNA dependent DNA synthesis. The viral RNA of retrovirus is used to make complementary DNA (cDNA) which then propagates the infection.
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