Before we start…. Mitosis gif

Topic 1.3: How do living things sexually reproduce?

Concept 1: Male and reproductive cells combine to produce a zygote Sexual reproduction requires two parents, each contributing a sex cell called a gamete

Concept 1: Male and reproductive cells combine to produce a zygote Sexual reproduction requires two parents, each contributing a sex cell called a gamete The male contributes sperm cells

Concept 1: Male and reproductive cells combine to produce a zygote Sexual reproduction requires two parents, each contributing a sex cell called a gamete The male contributes sperm cells The female contributes an egg cell (also known as an ovum)

Concept 1: Male and reproductive cells combine to produce a zygote Sexual reproduction requires two parents, each contributing a sex cell called a gamete The male contributes sperm cells The female contributes an egg cell (also known as an ovum) When the male and female gametes combine, fertilization occurs.

Concept 1: Male and reproductive cells combine to produce a zygote Sexual reproduction requires two parents, each contributing a sex cell called a gamete The male contributes sperm cells The female contributes an egg cell (also known as an ovum) When the male and female gametes combine, fertilization occurs.

Concept 2: reproductive cells are formed by a cell-dividing process called meiosis Although human cells have 46 chromosomes, each chromosome is not unique

Concept 2: reproductive cells are formed by a cell-dividing process called meiosis Although human cells have 46 chromosomes, each chromosome is not unique Each chromosomes has a pair that carries almost identical information, called an homologous pair

Concept 2: reproductive cells are formed by a cell-dividing process called meiosis Although human cells have 46 chromosomes, each chromosome is not unique Each chromosomes has a pair that carries almost identical information, called an homologous pair One chromosome comes from the mother

Concept 2: reproductive cells are formed by a cell-dividing process called meiosis Although human cells have 46 chromosomes, each chromosome is not unique Each chromosomes has a pair that carries almost identical information, called an homologous pair One chromosome comes from the mother One chromosome comes from the father

Concept 2: reproductive cells are formed by a cell-dividing process called meiosis Although human cells have 46 chromosomes, each chromosome is not unique Each chromosomes has a pair that carries almost identical information, called an homologous pair One chromosome comes from the mother One chromosome comes from the father Human cells have 23 homologous pairs

Homologous pair

Down Syndrome

Diploid Haploid What is the goal of meiosis? Type of cell:   Type of cell: Number of chromosomes (in a human cell) Number of copies of each chromosome Formed through: Diploid Haploid What is the goal of meiosis?

Diploid Haploid What is the goal of meiosis? Type of cell:   Type of cell: Number of chromosomes (in a human cell) Number of copies of each chromosome Formed through: Diploid Haploid What is the goal of meiosis?

46 Diploid Haploid What is the goal of meiosis? Type of cell:   Type of cell: Number of chromosomes (in a human cell) Number of copies of each chromosome Formed through: Diploid 46 Haploid What is the goal of meiosis?

46 2 Diploid Haploid What is the goal of meiosis? Type of cell:   Type of cell: Number of chromosomes (in a human cell) Number of copies of each chromosome Formed through: Diploid 46 2 Haploid What is the goal of meiosis?

46 2 Mitosis Diploid Haploid What is the goal of meiosis?   Type of cell: Number of chromosomes (in a human cell) Number of copies of each chromosome Formed through: Diploid 46 2 Mitosis Haploid What is the goal of meiosis?

46 2 Mitosis Diploid Haploid What is the goal of meiosis?   Type of cell: Number of chromosomes (in a human cell) Number of copies of each chromosome Formed through: Diploid 46 2 Mitosis Haploid What is the goal of meiosis?

46 2 Mitosis 23 Diploid Haploid What is the goal of meiosis?   Type of cell: Number of chromosomes (in a human cell) Number of copies of each chromosome Formed through: Diploid 46 2 Mitosis Haploid 23 What is the goal of meiosis?

46 2 Mitosis 23 1 Diploid Haploid What is the goal of meiosis?   Type of cell: Number of chromosomes (in a human cell) Number of copies of each chromosome Formed through: Diploid 46 2 Mitosis Haploid 23 1 What is the goal of meiosis?

46 2 Mitosis 23 1 Meiosis Diploid Haploid What is the goal of meiosis?   Type of cell: Number of chromosomes (in a human cell) Number of copies of each chromosome Formed through: Diploid 46 2 Mitosis Haploid 23 1 Meiosis What is the goal of meiosis?

46 2 Mitosis 23 1 Meiosis Diploid Haploid What is the goal of meiosis?   Type of cell: Number of chromosomes (in a human cell) Number of copies of each chromosome Formed through: Diploid 46 2 Mitosis Haploid 23 1 Meiosis What is the goal of meiosis?  To turn diploid cells into haploid cells.

Meiosis Watch meiosis video

Interphase DNA is replicated Organelles are replicated Cell grows

Interphase DNA is replicated Organelles are replicated Cell grows Prepare to divide

Enter Meiosis I….

Prophase I Nuclear membrane disappears DNA condenses into chromosomes Homologous chromosomes pair up

Prophase I Nuclear membrane disappears DNA condenses into chromosomes Homologous chromosomes pair up One diploid cell Duplicated DNA

Metaphase I Spindle fibers attach to chromosomes Chromosomes line up along the middle of the cell

Metaphase I Spindle fibers attach to chromosomes Chromosomes line up along the middle of the cell One diploid cell Duplicated DNA

Anaphase I Homologous chromosomes separate and move to each end of the cell

Anaphase I Homologous chromosomes separate and move to each end of the cell One diploid cell Duplicated DNA

Telophase I Two nuclei form and each nucleus contains a complete copy of the cell’s DNA Cell is ready to divide

Telophase I Two nuclei form and each nucleus contains a complete copy of the cell’s DNA Cell is ready to divide One diploid cell Duplicated DNA

Cytokinesis Cell divides into two cells

Cytokinesis Cell divides into two cells Two haploid cells Duplicated DNA

Enter meiosis II…

Prophase II Nuclear membranes disappear

Prophase II Nuclear membranes disappear Two haploid cells Duplicated DNA

Metaphase II Chromosomes line up single file along the middle of the cell

Metaphase II Chromosomes line up single file along the middle of the cell Two haploid cells Duplicated DNA

Anaphase II Duplicated chromosomes are pulled apart and one copy moves to each end of the cell

Anaphase II Duplicated chromosomes are pulled apart and one copy moves to each end of the cell Two haploid cells Duplicated DNA is separated

Telophase II Four nuclei form Cell prepares to divide

Telophase II Four nuclei form Cell prepares to divide Two haploid cells Duplicated DNA is separated

Cytokinesis Two cells divide into four cells

Cytokinesis Two cells divide into four cells Four haploid cells One copy of DNA

Variation and Diversity Sexual reproduction introduces diversity during meiosis in two main ways

Variation and Diversity Sexual reproduction introduces diversity during meiosis in two main ways Crossing over: occurs during prophase I when the legs of two homologous chromosomes cross over and exchange genetic material

Crossing over

Variation and Diversity Sexual reproduction introduces diversity during meiosis in two main ways Crossing over: occurs during prophase I when the legs of two homologous chromosomes cross over and exchange genetic material

Variation and Diversity Sexual reproduction introduces diversity during meiosis in two main ways Crossing over: occurs during prophase I when the legs of two homologous chromosomes cross over and exchange genetic material Independent assortment: during metaphase I the homologous pairs line up randomly, resulting in a random combination of chromosomes in each gamete cell

Variation and Diversity Sexual reproduction introduces diversity during meiosis in two main ways Crossing over: occurs during prophase I when the legs of two homologous chromosomes cross over and exchange genetic material Independent assortment: during metaphase I the homologous pairs line up randomly, resulting in a random combination of chromosomes in each gamete cell

Independent assortment

Meiosis versus Mitosis