CHAPTER 10 SEXUAL REPRODUCTION AND GENETICS SECTION 1- MEIOSIS

CHAPTER 10SEXUAL REPRODUCTION

AND GENETICS

SECTION 1- MEIOSIS

Human body cells have 46 chromosomes.

Sexual Reproduction and Genetics

Each parent contributes 23 chromosomes.

Section 1 - Meiosis

Homologous chromosomes—one of two paired chromosomes, one from each parent.

Chromosomes and Chromosome Number

Chromosomes and Chromosome Number


Homologous Chromosomes: Same length. Same centromere

position. Carry genes that control

the same inherited traits.

Section 1 - Meiosis

Haploid and Diploid Cells

Human gametes contain 23 chromosomes.


A cell with n chromosomes is called a haploid cell.

A cell that contains 2n chromosomes is called a diploid cell.

An organism produces gametes to maintain the same number of chromosomes from generation to generation.

Section 1 - Meiosis

Meiosis

The sexual life cycle in animals involves meiosis.

Meiosis produces gametes.

When gametes combine in fertilization, the number of chromosomes is restored (back to 2n – diploid).

Sexual Reproduction and GeneticsSection 1 - Meiosis

Meiosis Meiosis is a reduction division.

In other words, it reduces the chromosome number by half through the separation of homologous chromosomes.

In humans - from 46 chromosomes to 23.

Meiosis involves two consecutive cell divisions called meiosis I and meiosis II.


Meiosis I


Interphase

Chromosomes replicate. Synthesis of proteins.

Section 1 - Meiosis

Meiosis I


Prophase I

Chromosomes coil and condense.

Pairing of homologous chromosomes occurs.

Each chromosome consists of two chromatids.

The nuclear envelope breaks down.

Centrioles moves toward poles.

Spindles form and bind to centromeres.

Section 1 - Meiosis

Meiosis I


Prophase I Crossing over produces exchange of genetic

information. Crossing over—chromosomal segments are

exchanged between a pair of homologous chromosomes.

Section 1 - Meiosis

Meiosis I


Metaphase I

Homologous chromosomes line up at the equator ofthe cell.

Section 1 - Meiosis

Meiosis I


Anaphase I Homologous chromosomes separate and move to opposite poles of the cells.

Chromosome # is reduced from 2n to n when homologous chromosomes separate.

Section 1 - Meiosis

Meiosis I


Telophase I The spindles break down. Chromosomes uncoil and

form two nuclei. The cell divides.

Section 1 - Meiosis

Meiosis II Prophase II

A second set of phases begins as the spindle apparatus forms and the chromosomes condense.

Sexual Reproduction and GeneticsSection 1 – Meiosis

Meiosis II

Metaphase II A haploid number of chromosomes line up at the equator.


Meiosis II


Anaphase II The sister chromatids are pulled apart at the centromere by spindle fibers and and move toward the opposite poles of the cell.

Section 1 - Meiosis


Meiosis II

Section 1 - Meiosis

Telophase II The chromosomes reach the poles, and the nuclear membrane and nuclei reform.

Meiosis II


Cytokinesis results in four haploid cells, each with n number of chromosomes.

Section 1 - Meiosis

MEIOSIS VIDEOShttps://www.youtube.com/watch?v=rqPMp0U0HOA

https://www.youtube.com/watch?v=1-RKH5eVJVM

https://www.youtube.com/watch?v=Gvjz9k19J1M

The Importance of Meiosis

Meiosis consists of two sets of divisions.

Produces four haploid daughter cells that are not identical.

Results in genetic variation.



Meiosis Provides Variation

Depending on how the chromosomes line up at the equator, four gametes with four different combinations of chromosomes can result.

Genetic variation also is produced during crossing over and during fertilization, when gametes randomly combine.

Section 1 - Meiosis


Law of Independent Assortment

Random distribution of alleles occurs during gamete formation.

Genes on separate chromosomes sort independently during meiosis.

Each allele combination is equally likely to occur.

Section 2 - Meiosis


Law of Independent Assortment

Two pairs of homologous chromosomes can be arranged in two different ways at meiosis I of meiosis.

These arrangements occur randomly, with approximately half the meiotic cells oriented one way and the other half oriented the opposite way.

Section 2 - Meiosis


Independent Assortment

Section 2 – Mendelian Genetics


Crossing Over

Section 2 - Meiosis

During prophase I, nonsister chromatids of homologous chromosomes exchange pieces of genetic material.

As a result each homologue no longer entirely represents a single parent.


Crossing Over

Section 2 - Meiosis

Free ends of one maternal and one paternal chromatid wrap around each other at one or more points.

Crossover allows the paired maternal and paternal chromosomes to exchange genetic material.

Sexual Reproduction and GeneticsMitosis vs. Meiosis


Mitosis vs. Meiosis

Take out your book and copy Table 1 from page 275.

Mitosis vs. Meiosis

Mitosis Meiosis

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CHAPTER 10 SEXUAL REPRODUCTION AND GENETICS SECTION 1- MEIOSIS