Chapter 12

Asexual vs Sexual reproduction

Asexual reproduction- a single individual gives rise to offspring that are identical to itself and others

Sexual reproduction- when two individuals mix their genetic material

Sexual reproduction takes place during Meiosis

Meiosis

The process and stages of sexual reproduction

Has eight stages

Prophase I

Prophase I is the first stage of Meiosis I

Nucleus begins to break apart

Centrioles distribute microtibules to the two pairs of homologous chromosomes

Metaphase I

The microtubles grab one of each pair of homologous chromosomes and pull them

The chromosomes line up in the middle of the cell

Anaphase I

The chromosomes are further pulled part and two pairs of sister chromatids form

The cell begins to separate

The cytoplasm begins to divide

Telophase I

The pairs of sister chromatids are at the opposite sides of the cell and a new nucleus forms around them

Than through the process of cytokinesis the cytoplasm divides and two cells form

Prophase II

There are now two different cells and the microtubules grab the chromosomes of each cell

The nucleus also breaks up in each cell

Metaphase II

microtubules start to pull and move the chromosomes in each cell

The chromosomes are lined up in the middle of the cell in each cell

Anaphase II

The microtubles pull apart the chromosomes to form two pairs of sister chromatids in each cell

The the cells start to separate

The cytoplasm begins to divide

Cytokinesis starts in Anaphase and ends in telophase

Telophase II

The sister chromatids are pulled to the ends of each cell

a nucleus is formed in each cell because cytokinesis ends during telophase

Last stage of Meiosis

Four cells are formed

Homologous Chromosomes

Homologous Chromosomes are contained in somatic body cells of sexually reproducing eukaryotes

Homologous chromosomes are chromosomes that carry the same genes of the the same characteristics

They carry one gene from the mother and one from the father

Genes

A gene is hereditary material that is transferred from the parents to the offspring and determines some characteristics of the offspring

Genes occur in pairs on homologous chromosomes

Allele

Alleles are different forms of the same genes

Paired genes on homologous chromosomes may vary in alleles

These arise by mutation and are the the basis of differences in shared traits

Offspring of sexual reproducers inherit new combinations of parental alleles

Results in new combinations of traits

Haploid

A haploid is a single set of unpaired chromosomes

People have haploid cells that each contain 23 sets of chromosomes

The variable for haploid is n

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