MEIOSIS

Use the Nelson text, "Biology 11", pp. 103-107 to complete the blanks.


Introduction

Meiosis is the process by which ________ cells, or _____________, are formed. In humans, this takes place in the _______________ and _________________. It involves _______ (#) stages of cell division that have some similarities to _______________. In mitosis, the chromosome number of _________________ cells is the same as in the ________________ cell. In meiosis, the chromosome number is _________ that of the parent cell. A human cell containing ___________ chromosomes will undergo meiosis and produce ______________ that have _________ chromosomes. The number of ____________________ in a gamete is called the ________________ chromosome number, or ______. The number of chromosomes in all other cells (called body cells) is twice the haploid number and is called the _______________ number, or ______. In humans, the haploid number is ________ and the diploid number is _________.

Offspring carry genetic information from each of the ________________. Each of the _______ (#) chromosomes from your father is matched by ________ (#) chromosomes from your mother. The paired chromosomes are called _____________________ chromosomes because they are similar in _____________, ______________, and _________________ arrangement. The genes in the _________________ chromosomes deal with the same _______________. Each cell in your body except __________ cells contains __________ pairs of homologous chromosomes, or ________ chromosomes in total. These chromosomes interact during _____________. Your characteristics are determined by the manner in which _____________ from homologous chromosomes interact.

Draw Fig. 1 on pg. 104 (homologous chromosomes)















Stages of Meiosis

Meiosis involves ________ (#) nuclear divisions that produce ______ (#) _______________ cells. Meiosis I is often called ________________ division because the _______________ number is reduced to the ______________ number of chromosomes. The second phase, ____________________, is marked by separation of the two _________________. As in mitosis, the DNA replicates before meiosis.

Draw Fig. 2 on pg. 104 (mitosis vs. meiosis)















Meiosis I (see Fig. 4 on pg. 105)

During _______________ I, the ________________ membrane begins to dissolve, the _______________ splits, and its parts move to opposite poles within the cell, and ______________ __________________ are formed. The chromosomes come together in ____________________ pairs. Each chromosome of the pair is a homologue and is composed of a pair of ________________ chromatids. The whole structure (2 homologous chromosomes) is called a ____________ because there are 4 chromatids.

This process (pairing up of homologues) is called ____________________ and as the chromosomes synapse (pair up), the ______________ often intertwine. Sometimes the intertwined chromatids from different homologues break and exchange segments or undergo ________________________ (see Fig. 3 and 4 on pg. 105). Crossing over permits the exchange of __________________ material.

_________________ I follows Prophase I. The ______________________ chromosomes attach themselves to the _______________ _______________ and line up along the ___________________ plate.

During _________________ I, the homologous chromosomes move toward opposite ____________. The process is known as ___________________. At this point of meiosis, _____________________ division occurs. One member of each ___________________ pair will be found in each of the new ___________. Each chromosome consists of ______ (#) _______________ chromatids.

During _________________ I, a ____________________ begins to form around each _________________. Unlike in mitosis, the __________________ in the two ________________ are not __________________ and do not carry exactly the same information.

Draw Fig. 3 on pg. 105 (crossing over)















Meiosis II (see Fig. 5 on pg. 106)

During Meiosis II, pairs of _________________ will separate and move to opposite ____________. There is no __________________ of the chromosomes prior to meiosis II.

___________________ II signals the beginning of the second division. During this stage, the ___________________ membrane dissolves and _________________ fibres begin to form.

___________________ II follows prophase II. The chromosomes, each with two ______________, are arranged along the __________________ plate. The chromatids remain pinned together by the ___________________.

___________________ II can be identified by the __________________ of the attachment between the two _______________ and by their __________________ to the opposite poles. This stage ends when the ___________________ membrane begins to form around the chromatids, now referred to as (daughter) _____________________.

The cell then enters its final stage of meiosis: ______________________ II. During this stage, the ________________ nuclear division is completed and the second division of ____________________ (cytokinesis) occurs. ___________ (#) ______________ daughter cells are produced from each meiotic division.

Examine telophase II in Fig. 5 on pg. 106. Note that each cell has only 2 daughter chromosomes (haploid) compared to 4 homologous chromosomes during prophase I (Fig. 4 on pg. 105). Also note that each cell is genetically different (indicated by different sizes and colours). This is what makes all sex cells (gametes) genetically different and leads to GENETIC DIVERSITY in the offspring, an advantage of sexual reproduction.