Sexual Reproduction

Cellular Reproduction There are 2 types of reproduction: Asexual Reproduction Asexual Reproduction Sexual Reproduction Sexual Reproduction

Cellular Reproduction 1. Asexual Reproduction (5 phases) 1 mother cell divides into 2 daughter cells 1 mother cell divides into 2 daughter cells Daughter cell is identical to its mother Daughter cell is identical to its mother Interphase + Mitosis Interphase + Mitosis All cells have 46 chromosomes called “DIPLOID cells” All cells have 46 chromosomes called “DIPLOID cells” Produce SOMATIC cells (not sexual cells) Produce SOMATIC cells (not sexual cells)

Cellular Reproduction 2. Sexual Reproduction (9 phases) 1 mother cell divides into 4 daughter cells 1 mother cell divides into 4 daughter cells Daughter cells have ½ the chromosomes of their mother (23) “HAPLOID cells ” Daughter cells have ½ the chromosomes of their mother (23) “HAPLOID cells ” Interphase + Meiosis I + Meiosis II Interphase + Meiosis I + Meiosis II Crossing over of genetic material often occurs. Crossing over of genetic material often occurs. SEXUAL cells (egg and sperm) known as “gametes” SEXUAL cells (egg and sperm) known as “gametes”

Asexual Reproduction Sexual Reproduction Produces __ daughter cells Produces cells which are _____ to their mother cell Mother:__chromosomes Daughter :__chromo

Asexual Reproduction Sexual Reproduction Crossing over? YES NO Crossing over? YES NO _______ cells DIPLOID HAPLOID __ phases:

Gametes…don’t forget!! ~ Another name for eggs and sperm ~ They are haploid (23 chromosomes) ~ They are sexual cells ~ They are produced by sexual reproduction

The “n” value n = the basic (smallest) number of chromosomes Interphase of Meiosis (4n = 92) After Telophase I (2n = 46) Gametes at the end of Meiosis ~ after Telophase II ~ (n = 23)

There are 3 major steps: There are 3 major steps: ~ Interphase ~ Meiosis I ~ Meiosis I ~ Meiosis II ~ Meiosis II Sexual Reproduction

Homologous Chromosomes A pair of chromosomes (maternal and paternal) that have similar/identical shapes and sizes. A pair of chromosomes (maternal and paternal) that have similar/identical shapes and sizes. Have genes for the same characteristics (ie: eye color). Have genes for the same characteristics (ie: eye color). Each locus (gene position) controls the same trait and is in the same place on homologous chromosomes. Each locus (gene position) controls the same trait and is in the same place on homologous chromosomes.

Vocabulary Homologous Chromosomes chromatids tetrad

Vocabulary Sperm + egg = zygote

Homologous Chromosomes PaternalMaternal Eye color Hair color Locus

Remember!! Remember!! InterphaseProphaseMetaphaseAnaphaseTelophase

Interphase Prophase I Metaphase I Anaphase I Telophase I Prophase II Metaphase II Anaphase II Telophase II

Meiosis 4n=92 2n=46 meiosis I n=23 meiosis II 4 haploid gamètes (n) After Interphase diploid (2n)

tent/animations/content/meiosis.htm l tent/animations/content/meiosis.htm l

Interphase (4n = 92) Same as Interphase in Mitosis Same as Interphase in Mitosis Chromosome replication, growth and preparation (chromatin rolls etc) Chromosome replication, growth and preparation (chromatin rolls etc) Each of the replicated chromosomes possesses 2 chromatides which are attached at their centromere. Each of the replicated chromosomes possesses 2 chromatides which are attached at their centromere.

Interphase (4n = 92) We can see the nucleolus and the nuclear membrane. We can see the nucleolus and the nuclear membrane. Nuclear membrane Nucleolus Cell membrane Chromatine There are 92 chromosomes (46 pairs!!)

Meiosis I (4 phases) ~ Prophase I ~ Metaphase I ~ Anaphase I ~ Telophase I

Prophase I (4n = 92) 2 homologous chromosomes combine. This combination is called a TETRAD XX 2 homologous chromosomes combine. This combination is called a TETRAD XX Spindle fibers grow, and attach to each side of the tetrad Spindle fibers grow, and attach to each side of the tetrad The nuclear membrane and the nucleolus both disappear The nuclear membrane and the nucleolus both disappear

Prophase I (4n = 92) centrioles Spindle fibers

Crossing Over During Prophase I During Prophase I One chromatid of each chromosome crosses over with the chromatid of the other chromosome. One chromatid of each chromosome crosses over with the chromatid of the other chromosome. The result is an exchange of their genetic material The result is an exchange of their genetic material

Crossing Over The exchange of sections of homologous chromosomes in a TETRAD. Maternal chromo Paternal chromo

Metaphase I (4n = 92) Spindle fibers pull on the tetrads, and align them in the centre of the cell. Spindle fibers pull on the tetrads, and align them in the centre of the cell.

Metaphase I (4n = 92)

Anaphase I (4n = 92) The tetrads separate and homologous chromosomes travel to the poles. The tetrads separate and homologous chromosomes travel to the poles. Homologues chromosomes are still attached by their centromeres. Homologues chromosomes are still attached by their centromeres.

Anaphase I (4n = 92)

Telophase I/Cytokenisis (2n = 46) Each pole has a diploid number of chromosomes. Each pole has a diploid number of chromosomes. Cytokenisis - 2 diploids cells are formed. Cytokenisis - 2 diploids cells are formed. Spindle fibers and centrioles disappear. Spindle fibers and centrioles disappear. The nuclear membrane sometimes reforms, and the nucleolus does not reform at this point. The nuclear membrane sometimes reforms, and the nucleolus does not reform at this point.

Telophase I (2n = 46) Cell division

Meiosis II (4 phases) ~ Prophase II ~ Metaphase II ~ Anaphase II ~ Telophase II

Meiosis II Interphase II – does not exist ** Don’t forget!! This process is occuring in both daughter cells created during Meiosis I **

Prophase II (2n = 46) Same as Prophase in Mitosis Same as Prophase in Mitosis

Metaphase II (n = 46) Same as Metaphase in Mitosis Same as Metaphase in Mitosis

Anaphase II (2n = 46) Same as Anaphase in Mitosis Same as Anaphase in Mitosis DON’T FORGET! Chromosomes are separated into chromatids. DON’T FORGET! Chromosomes are separated into chromatids.

Télophase II/Cytokenisis (n = 23) Same as Telophase in Mitosis Same as Telophase in Mitosis EXCEPT n = 23 The nucleolus and nuclear membrane reform The nucleolus and nuclear membrane reform Cytokenisis Cytokenisis Important: 4 haploid gametes are formed.

Telophase II/Cytokenisis (n = 23)

Meiosis– hill.com/sites/ /student_view0/chapter28/animation __how_meiosis_works.html

Attention!!!!!!!!!!!!! Female meiosis is somewhat different. 4 gametes are initially created, but Cytokenisis is UNEQUAL. In this case, ONE GAMETE survives, and the other 3 are not viable. Female meiosis is somewhat different. 4 gametes are initially created, but Cytokenisis is UNEQUAL. In this case, ONE GAMETE survives, and the other 3 are not viable.

Mitosis vs Meiosis Mitosis Meiosis Result 2 diploid cells (2n) 4 haploid cells (n) The cells are identical different Occurs in somatic cellules (all cells in the body) sexual Cellules (sperm and egg)

Meiosis– United Streaming

Visual Representations 7/animations/meiosis.html 7/animations/meiosis.html ent/animations/content/meiosis.html ent/animations/content/meiosis.html Mitosis vs. Meiosis