Q3—MEIOSIS PROCESS

Meiosis

• a process that is important in sexual reproduction and involves combining the genetic information of one parent with that of the other parent to produce a genetically distinct individual.

Meiosis

• a division of the nucleus that reduces chromosome number by half.

Meiosis

• takes place in the ovaries and testes of animals, humans.

Meiosis

• form of cell division that produces a haploid sex cells or gametes.

  • involves DNA replication followed by two successive nuclear and cellular divisions.

Diploid

• signifies the presence of two complete sets of homologous chromosomes within the cells.

Homologous Chromosomes

• pairs of chromosomes (not identical), yet are identical in position and size to the centromere.

Homologous Chromosomes

• have the same sequence of gene loci (the position of genes in chromosomes).

Diploid Cells

• one of the cells that the human body is made up of.

Gametes (sex cells)

• what the formed daughter cells from cell division become.

Synapsis

PROPHASE I

• when homologous chromosomes pair with each other, forming a tetrad.

Tetrad

PROPHASE I

• composed of four chromatids.

Crossing Over

• when chromatids of tetrad exchange parts.

Crossing Over

• (…of homologous chromosomes) may happen, leads to the exchange of genetic material.

Nuclear Envelope

• what breaks down during PROPHASE I.

Haploid

• cells with a single set of chromosomes.

Diploid

• two sets of chromosomes (2n), in humans 26 pairs or 46 total.

Haploid

• one set of chromosomes (n), gametes or sex cells, in humans 23 chromosomes.

Homologous Pair

• each chromosome in pair are identical to the other (carry genes for same trait).

Homologous Pair

• only one pair differs—sex chromosomes X or Y.

Somatic Cells

• are “body” cells and contain the number of chromosomes; called the “Diploid” number (2n).

  • Ex: skin cells, brain cells, etc.

Gametes

• are the “sex” cells and contain only ½ the normal number of chromosomes; called the “Haploid” number (n)

  • Ex: sperm cells and ova.

Male Gamete

• is the Sperm and is produced in the male gonad the Testes.

Female Gamete

• is the Ovum (ova = pl.) and is produced in the female gonad the Ovaries.

Ovulation

• when the ovum is released from the ovary and transported to an area where fertilization, the joining can occur.

Fertilization

• in humans, this occurs in the Fallopian tube.

Fertilization

• results in the formation of the Zygote (fertilized egg).

Fertilization

• the fusion of a sperm and egg to form a zygote.

Zygote

• a fertilized egg.

Homologous Chromosomes

• pair of chromosomes (maternal and paternal) that are similar in shape and size.

Tetrads

• carry genes controlling the same inherited traits.

Autosomes

• code for most of the offspring’s traits

Prophase I

• when chromosomes condense,

• homologous chromosomes pair each other,

• each pair contains four sister chromatids; a tetrad.

Prophase I

• when the nuclear envelope breaks down,

• chromosomes duplicate,

• synapsis occurs,

• crossing over happens

Metaphase I

• when tetrads or homologous chromosomes move to the center of the cell.

Metaphase I

• when chromosomes align,

• spindle fibers attach,

  • and there is random arrangement.

Anaphase I

• when there is the separation of homologous chromosomes,

• independent assortment (key source for genetic variation),

• sister chromatids remain together.

Anaphase I

• when homologous chromosomes are pulled to opposite poles.

Telophase I

• when two daughter cells are produced,

  • the resulting daughter cells have a haploid chromosome number.

Telophase I

• when daughter nuclei are formed (haploid, 1n).

Meiosis II

• when daughter cells undergo a second division, much like mitosis.

• no additional replication occurs.

Prophase II

• the step following cell division in telophase I.

Prophase II

• when sister chromatids are still attached,

  • nuclear membrane dissolves again.

Prophase II

• when spindle fibers form again.

Metaphase II

• when sister chromatids move to the center.

Anaphase II

• when centromeres split, 

  • individual chromosomes are pulled to poles.

Telophase II & Cytokinesis

• when four haploid daughter cells results from one original diploid cell.

Daughter Cells

• are produced by meiosis and are not genetically identical to one another.

Variation

• differences between members of a population.

Variation

• causes diverse populations that over time can be stronger for survival.

Meiosis

• results in random separation of chromosomes in gametes.