Phases of meiosis Prophase I a) DNA coils tightly to form visible chromosomes which appear rod-shaped. Each chromosome is made up of two strands of DNA. One strand of a double-stranded chromosome is known as a chromatid. The sister chromatids are held together by a region called the centromere. b) Nuclear membrane dissolves. c) In animal cells, a pair of centrioles (not visible on these slides) separate and with their newly formed asters (visible) move to each pole. d) Homologous chromosomes pair up. These pairs are called tetrads because there are two chromosomes, but four DNA molecules. Crossing-over occurs.
Oogenesis
The formation of the ovum (mature female gamete) from undifferentiated germ cells is called oogenesis. This process takes place in the ovaries (female gonads). Oogenesis consists of three stages known as the multiplication phase, growth phase, and maturation phase.
Cell Division
Cell division involves the formation of new daughter cells from the parent cells. It is a part of the cell cycle that takes place in both prokaryotic and eukaryotic organisms. Cell division is required for three main reasons:
Phases of meiosis
Prophase I
a) DNA coils tightly to form visible chromosomes which appear rod-shaped. Each chromosome is made up of two strands of DNA. One strand of a double-stranded chromosome is known as a chromatid. The sister chromatids are held together by a region called the centromere.
b) Nuclear membrane dissolves.
c) In animal cells, a pair of centrioles (not visible on these slides) separate and with their newly formed asters (visible) move to each pole.
d) Homologous chromosomes pair up. These pairs are called tetrads because there are two chromosomes, but four DNA molecules. Crossing-over occurs.
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