Organisms have tens of thousands of genes - Genes determine traits- Genes are lined up on chromosomes- 1 chromosome can contain a thousand or more genes

Each species of organisms contains a different number of chromosomes

The chromosome numbers of a species is not related to the complexity of the organism

The Chromosomes in most plants and animals occur in pairs

• 1 chromosome comes from the male parent

• 1 chromosome comes from the female parent

Diploid – A cell with two of each kind of chromosome (1 from each parent)

We say the cell is a diploid cell or 2n*Supports Mendel’s conclusion that organisms have two factors (alleles) for each trait

Haploid – A cell with one of each kind of chromosome (gametes)

We say the cell is a haploid or n

*Supports Mendel’s conclusion that parents give 1 allele for each trait to their offspring

Homologous Chromosomes – Paired chromosomes

Each pair of homologous chromosomes has genes for the same traits

Ex. Pod shape

On homologous chromosomes, the genes are arranged in the same order

Because there are different possible alleles for the same gene, the two chromosomes in the homologous pairs are not always identical to each other.

Meiosis – cell division .-produces haploid gametes

Meiosis occurs in the body cells that produce gametes(Male and Female reproductive organs)

The process of meiosis produces:male gametes (sperm) - n, haploidfemale gametes (eggs) – n, haploid

When the sperm fertilizes the egg, the resulting cell is a Zygote – 2n diploid

The zygote then can develop by mitosis into a multicellular organism

This process is called Sexual ReproductionTwo parents produce an offspring that is not identical to either parent

What are the benefits to sexual reproduction?

Gamete ProductionGamete Production

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Meiosis Square Dance •Write down the phases and what is taking place as you watch the video.

MeiosisMeiosisSimilarSimilar to to mitosismitosisHowever, several However, several differences:differences:Meiosis occurs in 2 phases Meiosis occurs in 2 phases (2 cell divisions: (2 cell divisions: Meiosis Meiosis II & & Meiosis IIMeiosis II

Results in Results in 4 cells4 cellsVocabulary:Vocabulary:

Diploid (2N) Diploid (2N) ––

Haploid (N)Haploid (N) - - 10

Normal amount of genetic Normal amount of genetic materialmaterial1/2 the genetic 1/2 the genetic material.material.

MeiosisMeiosisMeiosis Meiosis forms haploid cellsforms haploid cells..

Example In Humans: Example In Humans: OvaOva (egg) (egg) and and spermsperm..

OvaOva produced in produced in ovariesovaries (females)(females)

Process is called Process is called oogenesisoogenesisSpermSperm produced in produced in testestestes (males)(males)

Process is called Process is called spermatogenesisspermatogenesis

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Spermatogenesis & Spermatogenesis & OogenesisOogenesis

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Sperm Sperm formatiformati

onon

Egg Egg formatiformati

onon

Overview of MeiosisOverview of Meiosis

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Meiosis IMeiosis IPrior to division (Prior to division (S phaseS phase), amount of ), amount of DNA doublesDNA doubles

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Metaphase IMetaphase IDuring Metaphase Metaphase II homologous homologous chromosomes chromosomes line-up along the EQUATOR EQUATOR of of the cellthe cell

Areas of homologous chromosomes connectconnect at areas called CHIASMATACHIASMATA

Genes are Genes are exchanged at exchanged at these these connectionsconnections

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Crossing OverCrossing OverSegments of Segments of homologous homologous chromosomes breakchromosomes break and reattach at and reattach at similar locations.similar locations.

Results in Results in new new genetic genetic combinations combinations of of offspring.offspring.

This is the main This is the main advantage of advantage of sexual sexual reproductionreproduction

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Anaphase IAnaphase IDuring Anaphase I, each During Anaphase I, each HOMOLOGOUS CHROMOSOMEHOMOLOGOUS CHROMOSOME is is pulled to opposite sides pulled to opposite sides of the cell.of the cell.

Unlike mitosis, the Unlike mitosis, the CENTROMERES DO NOT CENTROMERES DO NOT BREAKBREAK..

Nuclei MAY OR MAY NOT Nuclei MAY OR MAY NOT reform following reform following division.division.

CYTOKENESISCYTOKENESIS may or may may or may not occur.not occur.

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Meiosis IIMeiosis IIDNA DNA DOES NOT DOES NOT doubledoubleChromosomes randomly line-Chromosomes randomly line-up along metaphase plate up along metaphase plate like regular mitosis.like regular mitosis.

During During Anaphase II, Anaphase II, CENTROMERES BREAK CENTROMERES BREAK and each and each SISTER CHROMATID SISTER CHROMATID is pulled is pulled to opposite sides of the to opposite sides of the cell.cell.

Nuclei reform Nuclei reform and and cytokinesiscytokinesis usually occurs usually occurs (although it is often (although it is often unequal).unequal).

Sister chromatids19

Overview of MeiosisOverview of Meiosis

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