Part 2: Fertilization and Development

Unit 5 Topic 4

Figure 13.x1 SEM of sea urchin sperm fertilizing egg

Monozygotic 2 amniotic

sacsMonozygotic 1 amniotic sac

Monozygotic 2 amniotic

sacs, 2 placentas

Dizygotic 2 sperm, 2

eggs

TWINS

IDENTICAL: 1 egg, 1 sperm

Fraternal

If fertilization occurs…

Cleavage

Gastrulation

Starts 9 days post-fertilization

Extraembryonic membranes:

• Develop within the 1st month • Chorion

– Outermost membrane– Becomes part of placenta– Functions in gas

exchange– Makes HCG hormone

• Amnion– Encloses embryo– Filled with fluid cushion

• Yolk sac– In mammals, produces

first blood cells and gamete germ cells

• Allantois– Forms part of umbilical

cord– Functions in waste

removal

• Placenta– Grows out of chorion– Lots of villi– Bathed in mother's blood for nutrient,

gas, waste exchange

1st month

2nd month

3rd month 4th month

5th month

6th month

7th month 8th month

Birth

Contraception - Barrier methodsSuccess measured as # of pregnancies per 100 women per year

Used perfectly: 3 Typical: 14

Used perfectly: 0.2 Typical: 0.5 Used perfectly: 0.1 Typical: 0.15

Used perfectly: 6 Typical: 20

Other birth control methods• Birth control pill

– Used perfectly: 0.1 Typical: 5– Injections, rings, patches

• Rhythm method– Used perfectly 1-9 Typical: 20

• Withdrawal– Used perfectly: 4 Typical: 19

• Spermicide– Used perfectly: 6 Typical: 26

• Abstinence– 0

Twins…

• List the following in order of genetic relatedness (most closely related first, least closely related last):– Mom and Dad– Monozygotic twins– Sister and Brother (non-twins)– Mom and Daughter– Dizygotic twins

Twins… Did you say…

Monozygotic twins (100%)

Sister and Brother (50%)Dizygotic twins (50%)

Mom and Daughter (50%)

Mom and Dad (0%)

Two Little Miracles

These are Twins

monozygotic or dizygotic?

egg

Fertilization

What process is this? Cleavage

What process is this?

Blastocyst