Meiosis

MEIOSIS

▪Human body cells have 46 chromosomes

Meiosis - General Overview

Sexual Reproduction and Genetics

▪Each parent contributes 23 chromosomes

▪Meiosis takes place in sex cells called gametes:

○ Egg from Female and sperm from Male

▪One cell becomes 4 NON-IDENTICAL cells

Multiple Choice

What is the scientific term that refers to sex cells?

• autosome

• gamete

• karyotype

• chromosome

Multiple Choice

The process that creates genetically unique sex cells

• Mitosis

• Reproduction

• Meiosis

• Budding

Multiple Choice

The process that creates genetically identical daughter cells

• Meiosis

• Mitosis

• Sexual Reproduction

• Krebs Cycle

What are:
● Chromosomes
● Homologous chromosomes
● Centromeres
● Sister Chromatids

○ Identify on board as a

class

Chromosomes and Chromosome Number

Meiosis – Homologous Chromosomes

Sexual Reproduction and Genetics

▪Same length

▪Same centromere position

▪Carry genes that control the

same inherited traits

▪One is from mother, one is
from father = a matching set

Multiple Choice

These are two pairs of chromosomes at the same location

• Chromatin

• Sister Chromatids

• Homologous Chromosomes

• Twin DNA

Haploid and Diploid Cells

▪Human gametes contain 23 chromosomes.

Sexual Reproduction and Genetics

▪A cell with n chromosomes is called a haploid cell.

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

Meiosis

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

Multiple Choice

The term that refers to a cell that has its full or complete number of chromosomes is

• N

• gamete

• haploid

• Diploid

Multiple Choice

This term refers to half the normal chromosome number

• haploid

• 2N

• diploid

• 3N

Meiosis I

▪The sexual life cycle in
animals involves
meiosis.

Sexual Reproduction and Genetics

▪Meiosis produces
gametes.

Meiosis

● When gametes combine in fertilization, a zygote is

formed and the number of chromosomes is restored.

Meiosis I

Sexual Reproduction and Genetics

Meiosis

▪Interphase

▪Chromosomes replicate.

▪Chromatin condenses.

Interphase

Meiosis I

Sexual Reproduction and Genetics

Meiosis

▪Prophase I

▪Pairing of homologous
chromosomes occurs.

▪Each chromosome consists of two chromatids.

▪The nuclear membrane breaks down.

▪Spindles form.

Prophase I

Meiosis I

Sexual Reproduction and Genetics

Meiosis

▪Prophase I continued...

▪Crossing over produces exchange of genetic info. (Tetrad)
▪Crossing over—chromosomal segments are
exchanged between a pair of homologous
chromosomes. (aka recombination)

​When Crossing over occurs, we get an exchange of genetic material. Parts of each chromosome actually switch places.



We call this process Recombination

Multiple Choice

The process of trading genetic information from one chromosome to another during Prophase 1

• Crossing Over

• Trade off

• Switcharoo

• Genetic displacement

Multiple Choice

Crossing over happens when part of the genetic information of one chromosome switches places with the genetic information from another chromosome. Another term for this process is known as

• genetic recombination

• genetic reduction

• a mutation

• nondisjunction

Meiosis I

Sexual Reproduction and Genetics

Meiosis

▪Metaphase I

▪Chromosome
centromeres attach to
spindle fibers.

▪Homologous chromosomes line up in the
middle of the cell.

Metaphase I

Meiosis I

Sexual Reproduction and Genetics

Meiosis

▪Anaphase I

Anaphase I

▪Homologous chromosomes
separate and move

to opposite sides of the cell.

​Mendel's law of independent assortment states that the alleles of two (or more) different genes get sorted into gametes independently of one another. In other words, the allele a gamete receives for one gene does not influence the allele received for another gene.

​The Law of Independent Assortment

Multiple Choice

Each trait is individual; gene that determines one trait does not determine the others

• Monohybrid

• Dominant

• Homozygous

• Law of Independent Assortment

Multiple Choice

This law describes how each homologous pair separates independently of any other pairs during Anaphase I of meiosis

• Law of Segregation

• Law of Independent Assortment

• Law of Gravity

• Law of Mathematical Order

Meiosis I

Sexual Reproduction and Genetics

Meiosis

▪Telophase I

▪The spindles break down.

▪Chromosomes uncoil and form two nuclei.

▪The cell divides.

○ This is called cytokinesis

Telophase I

Meiosis II

▪Prophase II

Sexual Reproduction and Genetics

Meiosis

A second set of phases (Meiosis II) begins
as the spindle apparatus forms and the
chromosomes condense.

Prophase II

Meiosis II

▪Metaphase II

Sexual Reproduction and Genetics

Meiosis

Chromosomes line up
in the middle of the
cells.

Metaphase II

Meiosis II

Sexual Reproduction and Genetics

Meiosis

▪Anaphase II

Anaphase II
▪The sister chromatids are

pulled apart at the centromere by spindle
fibers and move toward the opposite poles of the cell.

Sexual Reproduction and Genetics

Meiosis

Meiosis II

▪Telophase II

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

Telophase II

Meiosis II

Sexual Reproduction and Genetics

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

Meiosis

Cytokinesis

The Importance of Meiosis

▪Meiosis consists of two sets of divisions

Sexual Reproduction and Genetics

▪Produces four haploid daughter cells that are not identical

Meiosis

▪Results in genetic variation

Sexual Reproduction and Genetics

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.

Meiosis

MITOSISVS MEIOSIS

- 4 genetically different Sperm cells, all of which could

be used to fertilize an egg

Or

- 4 genetically different Egg cells, only 1 of which can

fully develop and be fertilized, the other three are called Polar Bodies and are used as nutrients and support for the single egg cell.

End Product of Meiosis

Multiple Choice

At the end of meiosis, how many complete/operational sex cells are created for each original cell?

• 2 for males; 2 for females

• 1 for males; 4 for females

• 4 for males; one for females

• 1 for males; 1 for females

Multiple Choice

Sperm and egg cells are

• Somatic

• Diploid

• Gametes

• Body cells

Multiple Choice

This type of reproduction creates genetic diversity

• Sexual

• Asexual

• Solo

• Polyp

Multiple Choice

The stage of meiosis where crossing over or the exchange of genetic information happens between pairs of chromosomes

• Prophase II

• Telophase I

• Metaphase II

• Prophase I

Multiple Choice

The end result of mitosis is _______________

• 2 identical diploid cells

• 2 genetically unique diploid cells

• 4 identical haploid cells

• 4 different haploid cells

Multiple Choice

The alleles for different traits are sorted separately and don't affect one another.

• Law of Dominance

• Law of Independent Assortment

• Law of Conservation of Matter

• Law of Segregation

Multiple Choice

What is another term for body cells?

• somatic cells

• gamete

• stem cell

• neural cell

Multiple Choice

The end result of meiosis is ______________

• 2 identical diploid cells

• 2 unique diploid cells

• 4 identical haploid cells

• 4 unique haploid cells

Multiple Choice

The exchange of genetic information that insures that every gamete is unique is referred to as

• mitosis

• meiosis

• reduction division

• crossing over

Multiple Choice

Sea turtles have 56 chromosome in their somatic cells. How many chromosomes are in their gametes?

• 28

• 56

• 112

• 46