Chapter 7 Meiosis and Sexual Reproduction This picture shows gametes ___________ There are many small sperm cells competing to _____________ a larger egg cell uniting fertilize

Chapter 7 Objectives Summarize the events that occur during meiosis. Section 1 Meiosis Objectives Summarize the events that occur during meiosis. Relate crossing-over, independent assortment, and random fertilization to genetic variation. Compare spermatogenesis and oogenesis.

7.1 Vocabulary Meiosis Crossing over Independent assortment Spermatogenesis Sperm Oogenesis ovum

Formation of Haploid Cells Chapter 7 Formation of Haploid Cells Meiosis is a form of cell division that __________ the number of chromosomes when forming specialized reproductive cells, such as __________ or _____________ These specialized cells are _______________ Since the chromosome number is being ______________ by half, this process is often called cell __________________ halves gametes spores haploids reduced reduction

What are the two types of human gametes? What do gametes do? Why is it important that they contain half the number of chromosomes as found in a diploid cell? Sperm and egg cells They fuse to create a fertilized zygote So that they create a diploid cell when they fuse

Meiosis involves two divisions of the nucleus called… _________________ These divisions are very similar to the process of _________________, but with a few changes Before meiosis begins, the DNA of the original cell must be copied during _______________ This original cell is a _________________ cell Meiosis I Meiosis II mitosis interphase diploid

Meiosis I includes…. Prophase ___ Metaphase ___ Anaphase ___ Telophase ___ Meiosis II includes Prophase ____ Metaphase ____ Anaphase ____ Telophase ____ I I I I II II II II

Chapter 7 Prophase I Nuclear ______________ and _______________ break down _____________ is arranged __________________ become visible How many chromosomes are in the cell? How many chromatids? membrane nucleolus Spindle Chromosomes 4 8

Chapter 7 Prophase I Meiosis This stage differs from mitosis because the homologous chromosomes ________ up in a process called ___________ pair synapsis Mitosis

structure traits mom dad identical tall short Review...what are homologous chromosomes? They are a pair of chromosomes that are similar in ________________ and that also contain genes for the same ____________ You inherit one from ______ and one from ______ They are not ________________ For example…dad’s chromosome may have a _________ gene while mom’s has a __________ gene structure traits mom dad identical tall short

Since they are not identical, the homologous chromosomes are ______________ differently However, the identical copies within each chromosome are colored the same…what are they called? colored sister chromatids

The homologous structures pair up so ____________ that they form a four part structure called a ________ Within a tetrad, a process called ________________ may occur tightly tetrad crossing over

During crossing over, areas on _______________ chromatids may exchange genetic material This picture shows a ___________ cross over nonsister single Letters = genes

Before crossing over, how many different gene combinations existed? After crossing over, how many different gene combinations exist? 2 4

Chapter 7 Metaphase I Meiosis The __________ of homologous chromosomes line up along the _______________ This arrangement is also _____________ to meiosis pairs equator unique Mitosis

Chapter 7 Anaphase I Homologous _______________ are pulled apart by spindle fibers and moved towards ______________ poles of the cell chromosomes opposite

Telophase I and Cytokinesis Chapter 7 Telophase I and Cytokinesis Prophase I Opposite of ______________ Cytokinesis splits the __________________ and separates the ______ new cells How many chromosomes are in each new cell? The chromosome number has been reduced by _______ and the cells are now _____________ cytoplasm 2 2 half haploid

After Meiosis I After Mitosis 4 chromosomes per cell 2 chromosomes per cell

VERY IMPORTANT!!!!!!!! These two cells do NOT enter ________________ again and do NOT copy their ________ again! They both proceed with meiosis ____. interphase DNA II

Chapter 7 Prophase II In each cell, the nuclear membrane and nucleolus ___________ _____________ is arranged dissolve Spindle

Chapter 7 Metaphase II individual Now, _______________ chromosomes line up along the equator in each cell

Chapter 7 Anaphase II Sister _____________ are pulled towards the opposite poles of each cell After the chromatids separate, what are they called? chromatids chromosomes

Telophase II and Cytokinesis Chapter 7 Telophase II and Cytokinesis In each cell, the nuclear membrane and nucleolus ___________ The spindle ______________ Chromosomes will ____________ Cytokinesis splits the cells into ______ unique haploid cells reform dissolves uncoil 4

Meiosis and Genetic Variation Chapter 7 Meiosis and Genetic Variation Meiosis is an important process that allows for the rapid generation of new genetic ________________. Three mechanisms make key contributions to this genetic variation: _________________________ combinations Independent Assortment Random fertilization Crossing over

Independent Assortment Chapter 7 Independent Assortment Refers to the _____________ distribution of homologous chromosomes during meoisis I random

Chapter 7 In ____________________, the homologous chromosomes may pair and line up randomly on either side Metaphase I

Chapter 7 segregate gametes This affects how the chromosomes ________________ and are passed along to the ________________ gametes

Since humans have 23 pairs of homologous chromosomes…each pair has ____ ways it may face while lining up Mathematically, the total number of possible gametes formed is… 2n or 223 = 8,388,608 gametes 2

Random fertilization fuse offspring variation Each of the possible gametes (223) must _______ with another one of the possible gametes (223) during fertilization Mathematically, the total number of possible zygotes is… 223 x 223 = 70,368,744,000,000 zygotes So many different ________________ with great _________________ may result fuse offspring variation

Crossing over Since homologous chromosomes may __________ genetic information within a tetrad, the number of possible gametes and zygotes is actually ___________________ exchange unlimited

Chapter 7 Importance of Genetic Variation Meiosis and the joining of gametes are essential to __________________ The pace of evolution is sped up by genetic _______________. Each offspring contains a combination of genes that is ________________ from each parent evolution recombination different

Gamete Formation in Males and Females Chapter 7 Gamete Formation in Males and Females Meiosis in Males The process by which sperm are produced in male animals is called _______________________ Spermatogenesis occurs in the male reproductive organ, called the _______________ spermatogenesis testes

First, an immature diploid cell, called a ___________ cell, begins to grow After meiosis, four _____________ haploid cells are formed germ unique

These haploid cells must ______________, meaning they must change slightly in form and develop _________, to become sperm cells differentiate flagella

Chapter 7 Meiosis in Females The process by which gametes are produced in female animals is called ____________________ Oogenesis occurs in the female reproductive organs, called _______________ and produces female gametes called eggs or ________ (ovum – singular) oogenesis ovaries ova

equally one nutrients 3 polar bodies In oogenesis, the cytoplasm does not divide ____________, resulting in… _____ large egg cell that contains more cytoplasm and ______________ and ______ smaller cells called second _________ ___________, which will all die equally one nutrients 3 polar bodies

Chapter 7 Objective 1 pair tetrads synapsis Crossing haploid Summarize the events that occur during meiosis. At the beginning of Meiosis I, homologous chromosomes ________ tightly to form ___________ in a process called _____________. ____________ over may occur. When the homologous chromosomes separate, two ____________ cells are formed During Meiosis II, the sister ______________ separate, forming _____ different gametes. pair tetrads synapsis Crossing haploid chromatids 4

Chapter 7 Objective 2 Relate crossing-over, independent assortment, and random fertilization to genetic variation. Crossing over – Independent Assortment – Random fertilization - Changes gene combinations on Non-sister chromatids of homologous chromosomes The homologous chromosomes line up and segregate randomly during Meiosis I. The possible gametes fuse randomly

Chapter 7 Objective 3 Compare spermatogenesis and oogenesis. Creates one large egg cell and three smaller polar bodies Creates four motile sperm cells