(c) gametogenesis

(C) Gametogenesis

Process by which gametes are produced in the gonads

Two types:

- Spermatogenesis

- Oogenesis

OogenesisThe primary oocyte goes through first meiotic division and the cytoplasm of the cell is divided unequallyThe larger daughter cell is called the secondary oocyte and the smaller daughter cell is called the polar bodyDuring second meiotic division, 1 mature ovum is produced and 3 polar bodies

SpermatogenesisPrimary spermatocyte goes through first meiotic division and form two daughter cells of equal sizeEach daughter cell (secondary spermatocyte) goes through the second meiotic division forming four motile sperm cells of equal size

Comparison of Ova and Sperm

Egg cells contain stored food in the form of yolk

Egg cells are larger than sperm

Sperm are motile, egg cells are not

(B) Fertilization

The fusion of the nuclei of one sperm with one ova (egg)

to produce a zygote

Sperm (n) + Ovum (n) =2n

Sperm (23) + Ovum (23) = 46

Parthenogenesis•An embryo develops from an unfertilized egg•typically involves the development of eggs into viable offspring from females without fertilization by sperm..

• Parthenogenesis is no longer only for lower invertebrates, such as aphids, mites and nematode worms--it's also been found in fish, bees, birds and lizards.

the second polar body -- the daughter cell produced along with the egg in the second stage of meiosis -- acts like a sperm and re-enters the egg. Essentially the egg fertilizes itself! As this polar body contains identical genetic material to the egg, having been produced by normal division of an already haploid cell, the resulting diploid cell has only half the genetic diversity of the female's original cells. Thus fewer bands appear in the DNA fingerprint of the offspring.

Parthenogenesis

FertilizationUnion of a haploid sperm nucleus with a haploid egg nucleusThis results in a

diploid zygote with the full number of chromosomes

n

n

2n

FertilizationUnion of a haploid sperm nucleus with a haploid egg nucleus

This results in a diploid zygote with the full number of chromosomes

Fertilization and the Stages of Mitosis

Two types of Fertilization

External Fertilization

Internal Fertilization

**Parthenogenesis**

•Eggs are fertilized outside the Eggs are fertilized outside the body of the femalebody of the female

•Large number of eggs are Large number of eggs are requiredrequired

•This type of fertilization is This type of fertilization is found in an aquatic environmentfound in an aquatic environment

ExEx: fish and frogs: fish and frogs

External FertilizationExternal Fertilization

Spawning???

http://www.umces.edu/2002Session/oyster.html

External Fertilization

External Fertilization

External Fertilization

External Fertilization

What are some differences between External and Internal

Fertilization?

Provide examples!!!

External Fertilization

External Fertilization

External Fertilization

External Fertilization

Internal Fertilization

Takes place inside the body of the female

Less eggs are required

Ex: mammals, birds and reptiles

Internal Fertilization

The embryo arrives in the uterus 5-10 days after fertilizationThe embryo implants into the uterine wall and establishes pregnancyPlacenta- nourishes the embryoUmbilical cord- attaches the embryo to the placentaAmnion- embryo develops inside the amniotic sac which contains amniotic fluid that serves as a shock absorberGestation Period- length of pregnancy (approximately nine months)

Fertilization

Good Review Webpage

http://regentsprep.org/Regents/biology/biology.cfm

Implantation of blastocyst

Day 7 Fertilization

Day 4

Day 3 Day 2

Day 1

Day 0

Egg released by ovary

Fertilization and Implantation

Section 39-4

Uterine wall

Blastocyst

Morula

4 cells 2 cells Zygote

Ovary

Fallopian tube

http://regentsprep.org/Regents/biology/units/reproduction/index.cfmhttp://regentsprep.org/Regents/biology/biology.cfm

Development

The zygote, which is a fertilized egg consisting of one cell, will begin to divide rapidly by mitosis forming the early developing human embryo.   Fertilization and the initial stages of this mitotic cell division occur in the oviduct.  The early embryo is migrates down the fallopian tube and completes most of its development in the wall of the uterus.

Do NowDo Now

Looking at the diagram above. Hypothesize the systems that will develop from these three layers.

Reproductive

Muscles,

Skeleton

Digestive

Nervous

ETC

Ectoderm

MesodermEndoderm

It is the three germ layers that give rise to all the tissues and organs of an animal

Ectoderm Mesoderm EndodermNervous system

Digestive System

lining of mouth, nostrils, and anus

epidermis of skin, sweat glands, hair, and nails

bones and muscles

blood and blood vessels

reproductive and excretory system

dermis layer of skin

lining of digestive tract

lining of trachea, bronchi, and

lungs

liver, pancreas

thyroid, parathyroid

urinary bladder

The Three germ layers

Do Now

Identify what is the purpose of the following:

The placenta:

The umbilical cord:.  

The amniotic fluid:

Do Now answers

The placenta is a combination of maternal and fetal tissue which allows for the exchange of materials with the fetus and mother.   Needed materials such as food and oxygen diffuse through the placenta to the fetus, while wastes from the fetus diffuse to the mother.   The umbilical cord is a fetal structure containing blood vessels which allows materials to be carried between the fetus and placenta in both directions.   The amniotic fluid surrounds the fetus and helps to provide a shock absorber to protect the fetus against mechanical injury in the event the mother is shaken or injured in some manner.

Human Development

Fetal Development

Development is a highly regulated process   After this small cluster of cells called the gastrula forms in humans, tissues begin to form. In humans, the embryonic development of essential organs occurs in early stages of pregnancy.  During the first three months of human development, organs begin to form.  The human embryo is usually referred to as a fetus when human like features become visible in its structure.    All organs and body features are developed by the end of the sixth month.   During the last three months of pregnancy, organs and features develop well enough to function after birth.

What are some things that could affect What are some things that could affect fetal development? fetal development?

6 weeks 4 months

What are some things that could affect What are some things that could affect fetal development? fetal development?

The embryo (or fetus) may encounter risks from faults in its genes and from its mother's exposure to environmental factors such as: inadequate dietuse of alcohol (Fetal alcohol syndrome)TobaccoDrugsother toxins infections   

Reproductive TechnologiesReproductive technology has medical, agricultural, and ecological applications.  In many instances, these technologies have progressed at a faster rate than the ethical considerations resulting from these technologies.  Some of these techniques include birth control methods used to block the process of fertilization.   Many technologies now exist to enhance the process of fertilization and development in humans and other organisms. Amniocentesis Hormone therapy can cause increased egg production.  Surgery can open blocked fallopian tubes in females and the vas

deferens in males. In vitro fertilization (test-tube babies) is a widely used technique to

aid infertile couples, allowing them to have children where this otherwise would not be possible.

Amniocentesis

Fetal cells are removed and surveyed for genetic disorders

Reproductive Technologies

(IV) Multiple Births 1. Identical twins- Develops from one

zygote separating into two during cleavage. One sperm and one egg is involved and therefore the babies will look identical and must be of same sex

(IV) Multiple Births 1. Identical twins- Develops from one

zygote separating into two during cleavage. One sperm and one egg is involved and therefore the babies will look identical and must be of same sex

Identical twins do not have identical fingerprints. They are a product of their environment.

Conjoined Twins

Conjoined “Siamese” Twins Chang and Eng

Eng Bunker---Chang BunkerBorn: May 11, 1811 Died: January 11, 1874

The developing embryo begins to split into identical twins but then

stops part way leaving the partially separated egg to mature

into a conjoined fetus.

They are more often female than male (ratio of 3:1)

They occur as often as once in every 40,000 births but only once

in every 200,000 live births.

40% are still born

70% are female - even though monozygotic twins are more frequently male than female.

75% are still born or die within 24 hours.

Cephalophagus

Dicephalus

This refers to one body with two heads.

Ischophagus

Anterior union of the lower half of the body

http://www.conjoined-twins.i-p.com/

Conjoined twins

Parasitic twins: Asymmetrical conjoined twins, one twin being small,

less formed, and dependent upon the other.

Fetus in fetu: Situation in which an imperfect fetus is contained

completely within the body of its sibling.

(V) Multiple Births

Fraternal twins- Develop from two separate eggs, each fertilized by separate sperm cells. Therefore, the babies may not look identical and could be of different sex. Simply ciblings!

(V) Multiple Births

Fertility drugs often cause production of more than one ovum during ovulation. Septuplets = 7 ova + 7 sperm (7 zygotes)

(V) Multiple Births