Chapter 10 Sexual Reproduction and Genetics Now: Section 1: Meiosis Later: Section 2: Mendelian Genetics Section 3: Gene Linkage and Polyploidy

Meiosis Objective Questions 1. What is meiosis? 2. What is the purpose of meiosis? 3. How is meiosis different from mitosis?

BIG IDEA The purpose of meiosis is to produce 4 gametes (Sperm or Egg) containing only 1 copy of each chromosome.

Question 1: What is meiosis? Meiosis Video

Meiosis is one of 2 types of cell division. What is meiosis? Meiosis is one of 2 types of cell division. Cell Division Mitosis Meiosis We did this one already

And.. That’s The Point … Meiosis is just another type of cell division!

What is the purpose of meiosis? Question 2: What is the purpose of meiosis?

What is the purpose of meiosis? Meiosis is a process to create 4 haploid daughter cells (gametes) each with ½ the normal number of chromosomes. (That’s called “haploid”)

What is the purpose of meiosis? Chapter 10 Sexual Reproduction and Genetics What is the purpose of meiosis? Let’s take a look at humans… This is called a karyotype Human body cells have 46 chromosomes, 23 HOMOLOGOUS pairs…

What is the purpose of meiosis? Each parent contributes 23 chromosomes 23 from Dad 23 from Mom

What is the purpose of meiosis? Homologous chromosomes— two paired chromosomes, one from each parent

“Why are gametes haploid?” you may ask.

Why is it important to reduce the chromosome #? What is the purpose of meiosis? Why is it important to reduce the chromosome #? 1st generation 46 2nd generation 92 3rd generation 184 4th generation 368

The point is: Meiosis is a reduction division… Only ½ the number of chromosomes will be given to the offspring from each parent

Question 3: How is Meiosis different from Mitosis?

Chromosomes and Chromosome Number Chapter 10 Sexual Reproduction and Genetics 10.1 Meiosis Chromosomes and Chromosome Number Same length Same centromere position Carry genes that control the same inherited traits

How is Meiosis different from Mitosis? Purpose is to create two identical daughter cells Purpose is to create 4 haploid gametes Mother cell goes through 1 cell cycle…produces 2 daughter cells…which will become 2 new mother cells. Mother cell goes through 1 cell cycle…produces 2 daughter cells…each of which will go through another cell cycle, creating 2 gametes Sister chromatids become visible at prophase, line up randomly at metaphase Sister chromatids attached as TETRADS(4 chromatids together) appear at prophase, stay together at metaphase line No genetic variation Genetic variation

Haploid and Diploid Cells Chapter 10 Sexual Reproduction and Genetics 10.1 Meiosis Haploid and Diploid Cells An organism produces gametes to maintain the same number of chromosomes from generation to generation. 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.

The sexual life cycle in animals involves meiosis. Chapter 10 Sexual Reproduction and Genetics 10.1 Meiosis Meiosis I The sexual life cycle in animals involves meiosis. Meiosis produces gametes. When gametes combine in fertilization, the number of chromosomes is restored.

Chapter 10 Sexual Reproduction and Genetics 10.1 Meiosis Stages of Meiosis I Reduces the chromosome number by half through the separation of homologous chromosomes Involves two consecutive cell divisions called meiosis I and meiosis II

Chromosomes replicate. Chapter 10 Sexual Reproduction and Genetics 10.1 Meiosis Meiosis I Interphase Chromosomes replicate. Chromatin condenses. Interphase

Pairing of homologous chromosomes occurs. Chapter 10 Sexual Reproduction and Genetics 10.1 Meiosis Meiosis I Prophase I Pairing of homologous chromosomes occurs. Each chromosome consists of two chromatids. Prophase I The nuclear envelope breaks down. Spindles form.

Crossing over produces exchange of genetic information. Chapter 10 Sexual Reproduction and Genetics 10.1 Meiosis Meiosis I Prophase I Crossing over produces exchange of genetic information. Crossing over—chromosomal segments are exchanged between a pair of homologous chromosomes.

Chromosome centromeres attach to spindle fibers. Chapter 10 Sexual Reproduction and Genetics 10.1 Meiosis Meiosis I Metaphase I Chromosome centromeres attach to spindle fibers. Metaphase I Homologous chromosomes line up at the equator.

Homologous chromosomes separate and move Chapter 10 Sexual Reproduction and Genetics 10.1 Meiosis Meiosis I Anaphase I Homologous chromosomes separate and move to opposite poles of the cell. Anaphase I

The spindles break down. Chapter 10 Sexual Reproduction and Genetics 10.1 Meiosis Meiosis I Telophase I The spindles break down. Telophase I Chromosomes uncoil and form two nuclei. The cell divides.

A second set of phases begins Chapter 10 Sexual Reproduction and Genetics 10.1 Meiosis Meiosis II Prophase II A second set of phases begins as the spindle apparatus forms and the chromosomes condense. Prophase II

A haploid number of chromosomes Chapter 10 Sexual Reproduction and Genetics 10.1 Meiosis Meiosis II Metaphase II A haploid number of chromosomes line up at the equator. Metaphase II

The sister chromatids are Chapter 10 Sexual Reproduction and Genetics 10.1 Meiosis Meiosis II Anaphase II The sister chromatids are pulled apart at the centromere by spindle fibers and move toward the opposite poles of the cell. Anaphase II

The chromosomes reach the poles, and Chapter 10 Sexual Reproduction and Genetics 10.1 Meiosis Meiosis II Telophase II The chromosomes reach the poles, and the nuclear membrane and nuclei reform. Telophase II

Chapter 10 Sexual Reproduction and Genetics 10.1 Meiosis Meiosis II Cytokinesis results in four haploid cells, each with n number of chromosomes. Cytokinesis Visualizing Meiosis I and Meiosis II

The Importance of Meiosis Chapter 10 Sexual Reproduction and Genetics 10.1 Meiosis The Importance of Meiosis Meiosis consists of two sets of divisions Produces four haploid daughter cells that are not identical Results in genetic variation Mitosis and Meiosis

Meiosis Provides Variation Chapter 10 Sexual Reproduction and Genetics 10.1 Meiosis 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.

Sexual Reproduction v. Asexual Reproduction Chapter 10 Sexual Reproduction and Genetics 10.1 Meiosis Sexual Reproduction v. Asexual Reproduction Asexual reproduction The organism inherits all of its chromosomes from a single parent. The new individual is genetically identical to its parent. Sexual reproduction Beneficial genes multiply faster over time.