Chapter 26 Reproduction and Development

Section 1 Animal Reproduction Distinguish between asexual and sexual reproduction. Explain the difference between external and internal fertilization. Identify the three types of mammalian reproduction.

Animal Reproduction If a species is to survive, its members must reproduce. 2 Types of Reproduction: Asexual-a single parent produces offspring that are genetically identical to the parent Sexual-sex cells from two parents unite to produce offspring that share traits from both parents

Asexual Reproduction Three types: Budding-occurs when part of the parent organism pinches off and forms a new organism Fragmentation-occurs when parts of an organism break off and then develop into a new individual that is identical to the original one Regeneration-occurs when an organism loses a body part that may develop into an entirely new organism

Budding in hydra

Fragmentation in planaria (flatworms)

Regeneration in sea stars

Sexual Reproduction The female parent produces sex cells called eggs. The male parent produces sex cells called sperm. When the nucleus of an egg and the nucleus of a sperm join, a fertilized egg called a zygote is created. This process is called fertilization.

Sexual Reproduction Human cells (except eggs, sperm, mature RBCs) contain 46 chromosomes. Eggs and sperm are formed by a process called meiosis. In humans, meiosis is the division of one cell that has 46 chromosomes into four cells that have 23 chromosomes each. When an egg and sperm join to form a zygote, the original number of 46 chromosomes is restored.

Types of Fertilization Fertilization can happen either outside or inside the female’s body. External fertilization occurs when the sperm fertilizes the eggs outside of the female’s body. (ex. frogs) Internal fertilization occurs when the egg and sperm join inside the female’s body; allows the female to protect the developing zygote inside her body. (ex. all mammals)

Mammalian Reproduction All mammals nurture their young with milk and reproduce in one of three ways: Monotremes are mammals that lay eggs. Ex. echidnas & platypuses Marsupials are mammals that give birth to partially developed young. Ex. opposums, koalas, wombats & Tasmasian devils Placental mammals are nourished inside their mother’s body before birth. Ex. armadillos, bat, & humans

Monotremes Echidna Platypus

Tasmanian Devil Wombat Marsupials Koala Opossum

Armadillo Bat Placental Mammals Human

Section 2 Human Reproduction Identify the structures and functions of the male and female reproductive systems. Describe two reproductive system problems.

The Male Reproductive System The male reproductive system produces sperm and delivers it to the female reproductive system. The testes are a pair of organs that make sperm and testosterone, the main male sex hormone. Testosterone helps regulate the production of sperm and the development of male characteristics.

The Male Reproductive System As sperm leave a testis, they are stored in a tube called the epididymis, where they mature. Another tube, the vas deferens, passes from the epididymis into the body and through the prostate gland. The mixture of sperm with fluids from several glands is called semen.

The Male Reproductive System To leave the body, semen passes through the vas deferens into the urethra The urethra is the tube that runs through the penis. The penis is the external organ that transfers semen into the female’s body.

The Male Reproductive System

The Female Reproductive System The female reproductive system produces eggs, nurtures fertilized eggs (zygotes), and gives birth. The two ovaries are the organs that make eggs. Ovaries also release estrogen and progesterone, the main female sex hormones that regulate the release of eggs and development of female characteristics.

The Female Reproductive System During ovulation, an egg is released from an ovary and passes into a fallopian tube. A fallopian tube leads from each ovary to the uterus. Fertilization usually happens in the fallopian tube. If the egg is fertilized, the resulting zygote enters the uterus. The uterus is the organ in which a zygote develops into a baby.

The Female Reproductive System When a baby is born, he or she passes from the uterus through the vagina and emerges outside the body. The vagina is the canal between the outside of the body and the uterus. The female reproductive system goes through monthly changes to prepare the body for pregnancy called the menstrual cycle.

The Female Reproductive System

The Menstrual Cycle

Multiple Births Twins are the most common multiple births. (30/1000) Fraternal twins (2/3) are more common than identical twins. (1/3) Triplets (2/1000) zygote split in two vs. two eggs are fertilized

Reproductive System Problems STDs (sexually transmitted diseases) can be passed from person to person via sexual contact. Ex. chlamydia, herpes, hepatitis B, HIV/AIDS, genital HPV, gonorrhea, syphilis Cancer-testicular or prostate cancer (males) - breast or cervical cancer (females) Infertility-unable to have children; problem can be with male, female, or both

Section 3 Growth & Development Summarize the processes of fertilization and implantation. Describe the development of the embryo and the fetus. Identify the stages of human development from birth to death.

From Fertilization to Embryo It takes the fertilized egg (zygote) 5 to 6 days to travel down the fallopian tube toward the uterus. During this time, the zygote undergoes cell division many times. 11 to 12 days after fertilization, the zygote has become a tiny ball of cells called an embryo. Implantation occurs when the embryo implants itself in the uterus.

From Fertilization to Embryo

From Embryo to Fetus After implantation, the placenta begins to grow. The placenta is a special two-way exchange organ with a network of blood vessels that provides the embryo with oxygen and nutrients from the mother’s blood and removes wastes produced by the embryo. A normal pregnancy lasts about 280 days, or 40 weeks. After week 10, the embryo is called a fetus.

From Embryo to Fetus

From Embryo to Fetus

End of week 2 Early weeks 5-8 weeks 3-4 weeks 9-16 weeks 17-24 Late weeks 5-8 weeks 25-36 Tiny fingers and toes Bones and bone marrow Sunlight affects sleeping pattern About 40 weeks Heart begins to form

embryo End of week 2 Early weeks 5-8 weeks 3-4 D implantation fertilization weeks 9-16 amnion fetus weeks 17-24 B, E, I A, J F, G Umbilical cord Late weeks 5-8 placenta weeks 25-36 C,H Tiny fingers and toes Bones and bone marrow Sunlight affects sleeping pattern birth About 40 weeks Heart begins to form

From Birth to Death Infancy-stage from birth to age 2 Childhood-stage from age 2 until puberty Adolescence-stage from puberty to adulthood Young adult-stage between ages 20 to 40 Middle age-stage between ages 40 to 65 Older adult-stage older than age 65