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Questions and Answers

Meiosis occurs in haploid animals

True

Explain meiosis cell division

In this process the division of nucleus takes place twice and four new daughter cells are produced which contain half the number of chromosomes of the mother cell.

In meiosis chromosomes divide twice

False

Who first observed reductional division

Strasburger Signup and view all the answers

__ and Moore first named meiosis

Farmer Signup and view all the answers

Boveri first observed meiosis in the gonad of __

Round worm Signup and view all the answers

In lower haploid organisms, meiosis occurs in zygote (after/before) fertilization

After Signup and view all the answers

How many types of meiosis are there

3 Signup and view all the answers

Zygotic meiosis occurs in Humans

False Signup and view all the answers

In plant cell, leptotene phase looks like a bouquet of flowers

False Signup and view all the answers

What is synapsis?

Pair formation between homologous chromosomes in zygotene phase of meiosis Signup and view all the answers

What is bivalent

Each pair of homologous chromosome Signup and view all the answers

In which stage of meiosis centriole division starts

Zygotene Signup and view all the answers

What is tetrad?

In pachytene, each chromosome divide longitudinally except the centromere into two chromatids. This condition is called tetrad Signup and view all the answers

What is Chaisma?

Two nonsister chromatids of the bivalent break and re-pair with each other. This X shaped junction point of two nonsister chromatids is known as Chaisma Signup and view all the answers

The exchange of the segments of two nonsister chromatids is known as__

Crossing over Signup and view all the answers

Repulsion between chromosomes of bivalent starts in

Diplotene Signup and view all the answers

Loop is formed between midpoints of chaismata. The Chaisma then move towards the end of the chromosomes. This movement is called

Terminalization Signup and view all the answers

DNA replication takes place during interkinesis

False Signup and view all the answers

In which phase of meiosis-2 nucleolus and nuclear membrane disappear

Prophase Signup and view all the answers

Who first gave idea of crossing over in maize plant

Thomas Hunt Signup and view all the answers

In crossing over two nonsister chromatids breaks at the same place due to which enzyme

Endonuclease Signup and view all the answers

Which enzyme helps to rejoin segment of each chromatid to other

Ligase Signup and view all the answers

Study Notes

Meiosis

Meiosis is a specialized type of cell division that occurs in sexually reproducing organisms
It involves two rounds of division (Meiosis I and Meiosis II), resulting in four haploid daughter cells from a single diploid parent cell
This process ensures the genetic diversity of offspring

Stages of Meiosis

Meiosis I:
- Prophase I:
  - The chromosomes condense and become visible
  - Homologous chromosomes pair up, forming bivalents (tetrads)
  - Synapsis occurs, where homologous chromosomes align and exchange genetic material through crossing over
  - Chiasmata are formed, where the exchanged segments of chromatids are held together
  - Centriole division begins
- Metaphase I:
  - Bivalents align at the metaphase plate
  - Spindle fibers from opposing poles attach to the centromeres of each chromosome pair
- Anaphase I:
  - Homologous chromosomes separate and move towards opposite poles
  - Sister chromatids remain attached at the centromere
- Telophase I:
  - Chromosomes reach the poles and decondense
  - Nuclear membrane reforms, forming two haploid daughter cells
Meiosis II:
- This is similar to mitosis, but occurs with half the number of chromosomes
- Prophase II:
  - Nuclear membrane and nucleolus disappear
- Metaphase II:
  - Chromosomes align along the metaphase plate
- Anaphase II:
  - Sister chromatids separate and move to opposite poles
- Telophase II:
  - Chromosomes reach the poles, decondense, and nuclear membrane reforms
  - Four haploid daughter cells are formed

Key Facts

Reductional division: Meiosis is commonly referred to as reductional division because it reduces the chromosome number by half.
Discovery of Meiosis:
- Flemming first observed reductional division
- Farmer and Moore first named the process as "meiosis"
- Boveri observed it in the gonad of sea urchins
Zygotic Meiosis: In lower haploid organisms, meiosis occurs in the zygote before fertilization. This is known as zygotic meiosis.
Synapsis: Pairing of homologous chromosomes during Prophase I, forming bivalents.
Bivalent: A pair of homologous chromosomes that are joined together during synapsis.
Tetrad: A group of four chromatids (two pairs of sister chromatids) that forms during synapsis.
Chiasma: The site of crossing over between two non-sister chromatids.
Crossing Over: The exchange of genetic material between non-sister chromatids, leading to genetic diversity.
Repulsion: The process of homologous chromosomes moving apart from each other during the later stages of prophase I.
Terminalization: The movement of chiasmata towards the ends of the chromosomes.
Interkinesis: A short interphase period that occurs between Meiosis I and Meiosis II. DNA replication does not occur during this phase.
Crossing Over Mechanism:
- Two non-sister chromatids break at the same place due to an enzyme called endonuclease.
- The broken segments are then rejoined to the other chromatid, with the help of an enzyme called ligase.