iPad 8:07 PM * 64%- Chapt L. Learning Objectives: Focus on these objectives as y

Question

iPad 8:07 PM * 64%- Chapt L. Learning Objectives: Focus on these objectives as you learn about the three main . Describe the main life cycles organisms may show 2. Explain the events in the stages of Meiosis I and Meiosis II 3. Evaluate the role of meiosis in sexual reproduction 4. Describe the events of meiosis responsible for genetic diversity . What is the very unique thing that happens between homologou:s chromosomes during prophase I? A. What is this exchange called? B. Why is this important? 2. In what part of your body does meiosis occur? . Clearly explain how meiosis results in genetic diversity 4. About independent assortment answer the following A. What is independent assortment? B. When does it occur? C. How does it increase genetic diversity? s. Explain briefly what happens during A. Meiosis I (4 points) a) Prophase I b) Metaphase I c) Anaphase I d) Telophase I B. Meiosis II (4 points) a) Prophase II b) Metaphase II c) Anaphase II d) Telophase II 6. Carefully compare and contrast mitosis and meiosis completing

Explanation / Answer

I 1 Basing upon the cell, an organism shows 2 types of life-cycle, namely, mitosis and meiosis. Mitosis occurs in the somatic cells, in which parent cell divides once to form 2 daughter cells. The chromosomal number remains same in the daughter cell as that of the parent cell. However, in meiosis parent divides twice to form 4 daughter cells or gametes. Gametes possess half chromosomal number as that of the parents. It occurs in the germinal cells.

I 2. Please consult Answer II 5 A and B for this. Meiosis II is similar to Mitosis.

I 3. Meiosis is quite helpful in the sexual reproduction because it helps in producing the gametes with haploid chromosomal number. When 2 haploid gametes are fused, a diploid zygote is formed which is equivalent to the ploidy level of the human beings. Meiosis helps in bringing the genetic diversity among populations beacuse of the crossing over process that occurs during the prophase I of meiiosis I

I 4 Crossing over: The pairing of the homologus chromosomes is known as synapsis. The synapsed chromosomes continue to become short and thick during the Pachytene stage of Prophase I. It is the third stage of Prophase I. A group of 4 chromosomes is known as tetrad. The 2 chromatids of the same chromosome are called sister chromatids and those of the 2 homologus chromosomes are known as non sister chromatids.

Crossing over involves mutual exchange of the corresponding segments of non sister chromatids of the homologus chromosomes. It takes place by breakage and reunion of chromatid segments. Breakage, also called nicking, is assisted by the enzyme, endonuclease and reunion also termed as annealing is done by the enzyme ligase.

II 1 Crossing over ( it is the characteristic feature of this phase) occurs during the prophase I of Meiosis I.

II 1 A The exchange is known as Crossing over, in which genes are exchanged between the homologus chromosomes.

II 1 B Variation which is a characteristic feature of meiosis is possible only due to the process of crossing over which allows exchange of genes between the 2 homologus chromosomes.

II 2 Meiosis occurs in the germinal cells of our body to form the gametes.

II 3 Meiosis helps in the genetic diversity, because new combination of genes are formed due to the crossing over which are different from the parental genes. This little change is possessed by every new offspring formed due to meiosis, accumulation of these changes for generations leads to genetic diversity.

II 4 A The genes of different characters located on different homologus chromosomes are independent to their segregation and assortment during gamete formation, this is independent assortment as per the Father of Genetics, Gregor Mendel.

II 4 B Independent assortment occurs during the gamete formation i.e. during the meiosis. It can be easily understood by reading the dihybrid cross given by Mendel.

II 4 C Independent assortment leads to genetic diversity, because new combnation of genes are formed or recombinants are formed due to this process. New combination of genes always lead to increase in genetic diversity.

5 A a. Prpophase I:

II 5 A b. Metaphase I:

II 5 A c Anaphase I:

II 5 A d. Telphase I:

II 5 B a Prophase II:

II 5 B b Metaphase II:

II 5 B c Anaphase II:

II 5 B d Telophase II:

II 6 Here is the able with the answer:

Mitosis Meiosis No. of divisions required 1 2 No. of daughter cells 2 4 Ploidy of the daughter cells n 2n Are daughter genetically identical Yes No(genetically dissimilar) How will the daughter cells used daughter cells will further divide to form new daughter cells daughter cells will act as gametes and will help in zygote formation

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