cell reproduction. lesson objectives –meiosis describe asexual reproduction; explain the genetic...
TRANSCRIPT
CELL REPRODUCTIONCELL REPRODUCTION
MEIOSIS MEIOSIS
Lesson Objectives –Meiosis
• Describe asexual reproduction; explain the genetic relationship between parent and offspring.
• Describe sexual reproduction; explain the genetic relationship between parent and offspring.
• Describe gametogenesis and identify the key differences between oogenesis and spermatogenesis.
• Identify and describe the main steps of meiosis, distinguishing between the quantity of genetic material in the parent and resulting cells.
ASEXUAL REPRODUCTION
• One parent
• Offspring genetically identical to parent
• Does not happen through MEIOSIS!!!
• Some modes of reproduction:– Binary fission– Budding– Spore formation
SEXUAL REPRODUCTION
• Two parents
• Offspring NOT genetically identical to parents
• Happens through MEIOSIS..
SEXUAL REPRODUCTION AND GAMETES
• Two different cells join together to form a new organism• Gametes (sexual reproduction cells) only have one-half
of the chromosomes found in body cells• Two types of gametes
– Sperm (male)– Eggs or ova (female)
• The union of these two is called fertilization• New diploid cell formed from two haploid cells is called a zygote
• Number of chromosomes present in each gamete called haploid number (n)
• Number of chromosomes present in each body cell called diploid number (2n)
GAMETOGENEIS: SPERMATOGENESIS AND OOGENESIS
• Spermatogenesis produces four haploid sperm cells
• Oogenesis produces one mature ovum or egg cell
CROSSING_OVER
http://youtu.be/CCqAri4wtjQ
BACK
Formation of homologous chromosomes called a tetrad
MEIOSIS
• Form of cell division that produces daughter cells having half the number of chromosomes of the parent cell
• Phases of meiosis similar to mitosis– Mitosis produces two genetically identical diploid cells from
one diploid cell• Four phases
• Cell divides once
– Meiosis creates four genetically different haploid cells from one diploid cell
• Eight phases
• Cell divides twice
PHASES OF MEIOSIS• Meiosis I
1. Prophase I 2. Metaphase I 3. Anaphase I 4. Telophase I and Cytokinesis I• Meiosis II 5. Prophase II 6. Metaphase II 7. Anaphase II 8. Telophase II and Cytokinesis II
MEIOSIS I• Prophase I crossing-over occurs (genetic variation)
NEXT
• Metaphase I independent assortment VIEW
• Anaphase I homologous chromosomes separated
• Telophase I & Cytokinesis I two daughter cells formed
CONTINUE
INDEPENDENT ASSORTMENTRETURN
MEIOSIS II• Prophase II• Metaphase II• Anaphase II• Telophase II & Cytokinesis II
Note: DNA is not replicated again between Meiosis Iand Meiosis II
Summary: At the end of meiosis, 4 daughter cells are formed = eggs or sperm. Each contains half as many chromosomes as the parent cell (n); each cell is genetically different from its parents and from its "siblings". Fertilization of an egg by a sperm restores the chromosome number to 2n.
GENETIC VARIABILITY OF FOUR HAPLOID CELLS
Lesson Summary—Meiosis
• Asexual reproduction produces a clone, an organism that is genetically identical to its parent.• Asexual reproduction includes binary fission, budding, and spore formation.• Sexual reproduction involves haploid gametes and produces a diploid zygote through fertilization.• Meiosis is a type of cell division that halves the number of chromosomes. There are eight stages of meiosis, divided into meiosis I and meiosis II. DNA is not replicated between meiosis I and meiosis II.• Crossing-over, the independent assortment of chromosomes during anaphase I, and random fertilization result in genetic variation.• Meiosis is a step during spermatogenesis and oogenesis. Spermatogenesis produces four haploid sperm cells, while oogenesis produces one mature ovum.• Eukaryotes have three different versions of the sexual life cycle: a haploid life cycle, a diploid life cycle, and a life cycle known as the alternation of generations. The sexual life cycle depends on when meiosis occurs and the type of cell that undergoes meiosis.