Unit X: The Life Process of Reproduction

Cell Division Definition: the process by which a cell divides Nuclear and Cytoplasmic Division Mitosis: process by which the nucleus divides during cell division -when the nucleus divides, each daughter nucleus receives a complete copy of the genetic material Cytokinesis: the cytoplasm and organelles of the old cell are divided between the daughter cells.

Structure of the Chromosome Composed of DNA (deoxyribonucleic acid) Chromatin: the material of the chromosomes in the form of long, thin threads, form when the cell is not going to divide Each chromosome contains a number of genes (units of hereditary material)

Stages of Cell Division Interphase: Phase between divisions growth of the cell replication of the DNA

Prophase Thickening of chromatin material in the nucleus to form chromosomes chromosomes can be seen and are rod-like in shape nuclear membrane breaks apart centrioles begin to move towards opposite ends(poles) of the cell spindle fibers appear and extend between centrioles

metaphase Chromosomes line up along the equator (middle) of the cell Each chromosome is attached to a spindle fiber at the centromere

Anaphase Separation of the chromatids from each other each chromatid moves away from the equator and moves toward the poles

Telophase Tightly coiled chromosomes unfold and lengthen (become chromatin) 2 new nuclear membranes form around chromatids spindle fibers disappear Cytokinesis takes place: -in animals: by pinching in of the cell membrane -in plants: by the formation of the cell plate

Cell Division Occurs in cell growth and asexual reproduction Each daughter cell gets an exact copy of the genetic information from the parent cell Daughter cells are clones of the parent cell

Chromosome number Diploid (2n) number: the full number of chromosomes characteristic of the species (humans =46) Haploid (n) number: having half the diploid number of chromosomes, also called monoploid (humans=23) Cancer: uncontrolled mitosis of cells

Asexual reproduction Definition: a type of reproduction in which there is only one parent and all offspring are genetically identical to the parent (clones) A. Types of Asexual reproduction 1. Binary Fission 2. Budding 3. Regeneration 4. Sporulation 5. Vegetative Propagation

Meiosis Definition: formation of a gamete with the haploid (monoploid) number of chromosomes also called reduction division Parent cell will divide twice to yield 4 daughter cells

Stage I Interphase I: the DNA replicates itself Prophase I: a) fine threads of chromatin shorten and thicken b) chromosomes appear c) homologous chromosomes come together in pairs

Stage I since the chromosomes are so close, they can exchange parts (crossing over) -this leads to variety in the offspring

Metaphase I: chromosome pairs line up down the middle of the cell

Stage I Anaphase I: 2 chromosomes from each tetrad move toward the opposite poles and separate of a tetrad

Stage I Telophase I: 2 daughter cells are produced with the haploid number of chromosomes

stage II No DNA replication, phases are exactly like mitosis division of the cytoplasm and separation of chromatids of each chromosome produces 4 daughter cells each with the haploid number of chromosomes (sex cells)

More on Meiosis A. occurs in the production of sex cells (gametes) B. 2 cell divisions C. daughter cells contain one-half the number of the chromosomes the parent possesses

A Comparison of Mitosis and Meiosis Point of Comparing Mitosis Meiosis # of Divisions One Two Recombination (crossover) No Yes Number of daughter cells Four Genetic makeup Clones Much different Function Growth,repair, & asexual reproduction Sperm and egg for sexual reproduction

Gametogenesis Definition: process by which gametes (sex cells) develop in gonads -gametes: cells that provide the nuclear material for sexual reproduction Oogenesis: production of eggs (ovum) in the ovaries -During meiosis, 3 polar bodies and 1 mature ovum (egg) are produced -polar bodies disintegrate and die

Spermatogenesis Definition: production of sperm in the testes -in 1 meiotic division, 4 haploid pre-sperm are produced -Pre-sperm then undergo hormonal changes to become flagellated and motile

Fertilization Definition: union of egg and sperm -results in a diploid zygote zygote: diploid cell resulting from fertilization, restores the species number of chromosomes

Types of Fertilization 1. External Fertilization: gametes fuse outside the body of the female -limited to aquatic organisms -fertilization occurs in the water once each parent has released its sex cells Many hazards: -egg and sperm may not meet -eggs may be eaten -eggs may die due to a changing environment -a large number of eggs and sperm are released to overcome these hazards -example: fish

Internal Fertilization Definition: gametes fuse inside the body of a female -limited to terrestrial animals -chances of fertilization of the egg increases -requires specialized sex organs to transfer the sperm into the female’s body -fewer eggs are produced, but still a large number of sperm are released to ensure fertilization

Development Definition: complex series of changes that occur after fertilization and give rise to the adult organism -embryo: organism in the early stages of development Cleavage: fertilized egg divides into 2 cells, then 4 and so on -no cell growth during cleavages -converts a single, large fertilized egg into many small cells -cells then undergo a rearrangement into a hollow ball of cells (blastula)

Types of Development External development in water -nourishment is provided by the yolk -oxygen diffuses into the organism -wastes diffuse from the embryo into the water -little or no care of the young -small number of young survive and mature

Reproduction in Humans A. Humans 1. Testes are the gonads a) sperm cells (male gametes) are produced in the testes b) secrete testosterone 2. Testes are held in the scrotum a) keeps the temperature of the testes slightly lower than the rest of the body -necessary for normal sperm production 3. Semen: mixture of fluids from glands and sperm

Female Reproductive System 1. Ovaries are the gonads a) produce eggs (female gametes) b) secrete estrogen, progesterone 2. Eggs develop in follicles 3. Ovulation: an egg matures in a follicle and is released from the ovary -first occurs at puberty -ends at menopause 4. Oviduct (Fallopian Tube): tube connected to the ovary containing ciliated cells that create a current that draws the released egg down the oviduct -where fertilization occurs

female reproductive system 5. Uterus: thick-walled, muscular, pear-shaped organ -where development of the embryo occurs 6. Cervix: narrow neck of the uterus 7. Vagina (birth canal): leads to the outside of the body

Fertilization Fertilization normally occurs in the upper end of the oviduct, generally within 24 hours of ovulation. - If Fertilization does not occur, the egg will deteriorate and be shed with the menstrual flow. -- If fertilization is successful, the resulting zygote undergoes the first of several cleavage divisions it will experience over the next 6 to 10 days as it continues down the Oviduct to the Uterus.

Fertilization - If two eggs are fertilized  Fraternal Twins --- When (the Embryo) reaches the Uterus, it implants itself into the blood-vessel rich lining and begins to establish the placental connection. - If two eggs are fertilized  Fraternal Twins --If one egg is fertilized and the zygote separates during cleavage  Identical Twins

Development Prenatal Development – All the processes of embryonic development that occur before birth. - Tissues of the embryo and the mother grow together to form the Placenta. This allows nutrients and oxygen to pass from mother to embryo. - The Amnion is a membrane that surrounds the embryo and is filled with Amniotic Fluid (this shields the embryo from mechanical shock).

Development - Umbilical Cord contains blood vessels that carry blood between the Embryo and the Placenta. Nutrients and Oxygen  Embryo Wastes and Carbon Dioxide  Mom

Development Birth – Occurs after a period of development known as the Gestation Period. (In humans this is about 9 months) - Strong Contractions of the Uterus force the baby through the Cervix and Birth Canal (Vagina) to the outside of the body. -The baby begins to breath, eat, and excrete waste on its own.