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Chapter 7 Meiosis and Sexual Reproduction
This picture shows gametes ___________ There are many small sperm cells competing to _____________ a larger egg cell uniting fertilize
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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.
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7.1 Vocabulary Meiosis Crossing over Independent assortment
Spermatogenesis Sperm Oogenesis ovum
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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
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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
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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
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Meiosis I includes…. Prophase ___ Metaphase ___ Anaphase ___ Telophase ___ Meiosis II includes Prophase ____ Metaphase ____ Anaphase ____ Telophase ____ I I I I II II II II
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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
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Chapter 7 Prophase I Meiosis
This stage differs from mitosis because the homologous chromosomes ________ up in a process called ___________ pair synapsis Mitosis
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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
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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
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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
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During crossing over, areas on _______________ chromatids may exchange genetic material
This picture shows a ___________ cross over nonsister single Letters = genes
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Before crossing over, how many different gene combinations existed?
After crossing over, how many different gene combinations exist? 2 4
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Chapter 7 Metaphase I Meiosis
The __________ of homologous chromosomes line up along the _______________ This arrangement is also _____________ to meiosis pairs equator unique Mitosis
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Chapter 7 Anaphase I Homologous _______________ are pulled apart by spindle fibers and moved towards ______________ poles of the cell chromosomes opposite
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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
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After Meiosis I After Mitosis 4 chromosomes per cell 2 chromosomes per cell
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VERY IMPORTANT!!!!!!!! These two cells do NOT enter ________________ again and do NOT copy their ________ again! They both proceed with meiosis ____. interphase DNA II
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Chapter 7 Prophase II In each cell, the nuclear membrane and nucleolus ___________ _____________ is arranged dissolve Spindle
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Chapter 7 Metaphase II individual
Now, _______________ chromosomes line up along the equator in each cell
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Chapter 7 Anaphase II Sister _____________ are pulled towards the opposite poles of each cell After the chromatids separate, what are they called? chromatids chromosomes
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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
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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
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Independent Assortment
Chapter 7 Independent Assortment Refers to the _____________ distribution of homologous chromosomes during meoisis I random
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Chapter 7 In ____________________, the homologous chromosomes may pair and line up randomly on either side Metaphase I
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Chapter 7 segregate gametes
This affects how the chromosomes ________________ and are passed along to the ________________ gametes
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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 = ,388,608 gametes 2
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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… x = 70,368,744,000,000 zygotes So many different ________________ with great _________________ may result fuse offspring variation
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Crossing over Since homologous chromosomes may __________ genetic information within a tetrad, the number of possible gametes and zygotes is actually ___________________ exchange unlimited
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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
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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
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First, an immature diploid cell, called a ___________ cell, begins to grow
After meiosis, four _____________ haploid cells are formed germ unique
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These haploid cells must ______________, meaning they must change slightly in form and develop _________, to become sperm cells differentiate flagella
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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
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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
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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
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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
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Chapter 7 Objective 3 Compare spermatogenesis and oogenesis.
Creates one large egg cell and three smaller polar bodies Creates four motile sperm cells
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