Part 2: Fertilization and Development Unit 5 Topic 4

Figure 13.x1 SEM of sea urchin sperm fertilizing egg

Monozygotic 2 amniotic sacs Monozygotic 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 1 st 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 methods Success measured as # of pregnancies per 100 women per year Used perfectly: 3 Typical: 14 Used perfectly: 0.2 Typical: 0.5Used 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