USC Bridge Nurs 500 3.2 Meiosis Compared to Mitosis

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1

mRNA carries instructions from DNA for building proteins

DNA directs its own division and serves as the blueprint for protein synthesis. Genes are a segment of a DNA molecule that carries instructions for creating one polypeptide chain. The 4 nucleotide bases - ATGC are the letters and information of DNA.

Three forms of RNA typically act together to carry out DNAs instructions for polypeptide synthesis.

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Gamete formation involves meiosis, which differs from mitosis

Human produce eggs and sperm through the process of meiosis.

Involves two consecutive cell divisions (meiosis I and II), but only one round of DNA replication • Produces four daughter cells

Two of the 46 chromosomes are sex chromosomes XY or XX

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Functions of meiosis

– Number of chromosomes are cut in half (2n to n)

– Introduces genetic diversity, as all daughter cells are genetically different from original cell

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Interphase of meiosis

Genetic information (chromosomes) is stored in the nucleus. Human cells are diploid- two sets of chromosomes one from the mother and one from the father. These matched pairs are called homologous chromosomes.

Chromosomes are duplicated into two identical copies of DNA protein sister chromatids coiled into tight helical fiber strands.

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diploid number of chromosomes

The nuclei of all human cells except gametes contain the diploid number of chromosomes - 46, consisting of 23 pairs of homologous chromosomes.

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Homolougous chromosomes

pairs of chromosomes- one from the father (sperm) and one from the mother (egg), that carry genes for the same traits.

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Phrophase 1 of meiosis

As Meiosis begins, spindles form and duplicated centrisomes start to migrate toward opposite poles of the cell.

In the Nucleus the chromosomes are condensing.

Homologous chromosomes stick together in pairs.

After the spindle forms and the nuclear envelope breaks down microtubules from opposite poles attach to each chromosome of the homologous pair resulting in a tug of war.

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Metaphase 1 of meiosis

The chormosome pairs are positioned in the middle of the cell.

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Anaphase 1

Homologous chromosomes seperate from each other and move toward opposite poles.

Each chromosome still consits of two sister chromotids.

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Telophase 1 and Cytokinesis

Cells begin meiosis with 46 chromosomes, but each daughter cell now has only 23 chromosomes.

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Meiosis 2

Microtubules from oppostie poles attach to the chromosomes which then move to the center of the cell.

The sister chromatids seperate becoming full fledged chromosomes that move to opposite poles.

Nuclear envelopes re-form and each daughter cell divides into two cells.

Completing meiosis with 4 haploid cells ( cells with a single set of chromosomes) that mature into gametes that can contribute to the next generation.

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After Meiosis how many copies of each chromosome does a cell have?

one.