Human Development CH2

1. What is the difference between monozygotic and dizygotic twins?

Monozygotic (identical) twins develop from one fertilized egg that splits into two; dizygotic (fraternal) twins develop from two separate eggs fertilized by two separate sperm.

2. What is a zygote?

The single cell formed when a sperm and egg combine during fertilization.

3. What is a chromosome?

A structure made of DNA that carries genetic information.

4. What is an allele?

A specific version of a gene.

5. What is a genotype?

A person's genetic makeup—the genes or alleles they have.

6. What is a phenotype?

The observable characteristics or traits a person has.

7. What is the dominant-recessive pattern?

A dominant allele can determine a trait when only one copy is present; a recessive trait generally appears only when a person has two copies of the recessive allele.

8. What is a carrier?

A person who has one copy of a recessive allele but does not show the recessive trait.

9. What are the three periods of prenatal development?

Germinal period, embryonic period, and fetal period.

10. What happens during the germinal period?

From fertilization to about 2 weeks; the zygote divides, travels toward the uterus, and implants in the uterine wall.

11. What happens during the embryonic period?

About weeks 3-8; major organs and body structures begin to develop.

12. What happens during the fetal period?

About week 9 until birth; the fetus grows larger and body systems continue developing and becoming more functional.

13. What is the journey from sex cell to baby?

Sperm + egg → zygote → blastocyst → embryo → fetus → newborn.

14. What is a blastocyst?

A rapidly dividing ball of cells that develops from the zygote and implants in the uterus.

15. What is an embryo?

The developing human from about 2-8 weeks after fertilization.

16. What is a fetus?

The developing human from about 9 weeks after fertilization until birth.

17. What is a teratogen?

An environmental substance or condition that can harm prenatal development, such as alcohol, certain drugs, or some infections.

18. What is the Apgar scale?

A quick assessment of a newborn's physical condition, usually performed shortly after birth.

19. What does APGAR measure?

Appearance, Pulse, Grimace, Activity, and Respiration.

20. What are the stages of development in utero?

Germinal: fertilization-2 weeks; embryonic: weeks 3-8; fetal: week 9-birth. Major structures form during the embryonic period, while growth and maturation dominate the fetal period.