Biology 105 Chapter 51: Development Pages Chapter 51: Development Pages

Student Outcomes Describe the processes involved in fertilization Trace the generalized pattern of early development of the embryo from zygote through early cleavage Identify the significance of gastrulation in the developmental process Describe the processes involved in fertilization Trace the generalized pattern of early development of the embryo from zygote through early cleavage Identify the significance of gastrulation in the developmental process

Student Outcomes Define Organogenesis and the three germ layers

Fertilization Process of joining of egg and sperm to form a zygote. Known as conception. Spermatogenesis and oogenesis Involves 4 events: Process of joining of egg and sperm to form a zygote. Known as conception. Spermatogenesis and oogenesis Involves 4 events:

Fertilization events 1. sperm contacts the egg and recognition occurs 2. sperm or sperm nucleus enters the egg 3. egg becomes activated, beginning developmental changes 4. sperm and egg nuclei fuse. 1. sperm contacts the egg and recognition occurs 2. sperm or sperm nucleus enters the egg 3. egg becomes activated, beginning developmental changes 4. sperm and egg nuclei fuse.

Polyspermy the fertilization of the egg by more than one sperm. Results in extra chromosomes and is usually lethal.

Zygote Is totipotent Cleavage occurs shortly after fertilization Cell goes through 2 cell, 4 cell, 8 cell stages, etc. At the 32 cell stage – known as morula, and eventually a blastula Is totipotent Cleavage occurs shortly after fertilization Cell goes through 2 cell, 4 cell, 8 cell stages, etc. At the 32 cell stage – known as morula, and eventually a blastula

Morula-Blastula 32 cell stage – Usually at this stage when entering the uterus. These cells are known as blastomeres. Continued mitotic divisions (Cleavage) results in a Blastula (hollow ball of cells with a blastocoel)

Gastrulation Blastula becomes a gastrula which forms the 3 germ layers: –Ectoderm –Mesoderm –Endoderm –The three germ layers will give rise to organogenesis - the formation of organs. Notochord, brain and spinal cord are the first organs to develop Blastula becomes a gastrula which forms the 3 germ layers: –Ectoderm –Mesoderm –Endoderm –The three germ layers will give rise to organogenesis - the formation of organs. Notochord, brain and spinal cord are the first organs to develop

Ectoderm –Outer layer – Will give rise to: Nervous system and sense organs Outer layer of skin, nail and hair Pituitary –Outer layer – Will give rise to: Nervous system and sense organs Outer layer of skin, nail and hair Pituitary

Mesoderm Middle layer – Will give rise to skeleton muscles circulation excretory reproduction dermis Middle layer – Will give rise to skeleton muscles circulation excretory reproduction dermis

Endoderm Will give rise to: –Lining of the digestive tube –respiratory Will give rise to: –Lining of the digestive tube –respiratory

Implantation Occurs on about the 7 th day of embryo development. It imbeds in the endometrium of the uterus.

Human Development Timeline Fertilization 24 hours – 2 cell stage 3 days – Morula travels through fallopian tubes and reaches uterus 7 days – implantation 17 days – tissue that will give rise to heart is differentiating, neural plate is formed Fertilization 24 hours – 2 cell stage 3 days – Morula travels through fallopian tubes and reaches uterus 7 days – implantation 17 days – tissue that will give rise to heart is differentiating, neural plate is formed

Human development continued 25 days – primitive eye and ear visible, heart begins to beat 4 weeks – limb buds appear, brain division forming 8 weeks – muscles differentiation, embryo capable of movement, sex organs can be seen, bone is ossifying 25 days – primitive eye and ear visible, heart begins to beat 4 weeks – limb buds appear, brain division forming 8 weeks – muscles differentiation, embryo capable of movement, sex organs can be seen, bone is ossifying

Human development continued 3 months- sex can be determined 4 months – face takes on a ‘human’ form with eyes, ears and nose Third trimester – known as a fetus, tremendous growth of the body, cerebrum growth is rapid 266 days – Birth 3 months- sex can be determined 4 months – face takes on a ‘human’ form with eyes, ears and nose Third trimester – known as a fetus, tremendous growth of the body, cerebrum growth is rapid 266 days – Birth

All Development Stages Gametogenesis-Fertilization Embryo: Cleavage-Morula-Blastula- Implantation-Gastrula-Organogenesis Fetus: 2 month-Birth (organogenesis) Birth-Neonate-Infant-Child-Adolescent- Young adult-Middle aged adult-Elderly adult Death Gametogenesis-Fertilization Embryo: Cleavage-Morula-Blastula- Implantation-Gastrula-Organogenesis Fetus: 2 month-Birth (organogenesis) Birth-Neonate-Infant-Child-Adolescent- Young adult-Middle aged adult-Elderly adult Death

Multiple Births Twins –Identical - one egg, one sperm, seperation after the 2 cell stage or the inner cell mass divides into 2 separate masses (monozygotic) –Non identical - two eggs, two sperm (dizygotic) –Conjoined - Same as identical, seperation does not occur completely. Twins –Identical - one egg, one sperm, seperation after the 2 cell stage or the inner cell mass divides into 2 separate masses (monozygotic) –Non identical - two eggs, two sperm (dizygotic) –Conjoined - Same as identical, seperation does not occur completely.

Births cont. Triplets - –Identical - one egg, one sperm –Non identical - more than one egg and sperm Triplets - –Identical - one egg, one sperm –Non identical - more than one egg and sperm