12/10/23: Development I

Vocabulary:

Zygote - (lasts 2 weeks) egg cell fertilized by a sperm cell, contains 23 PAIRS of chromosomes (half from mom + half from dad)

Chromosomes - each contains thousands of genes

Genes - hereditary info, half from mom + half from dad

Heterozygous - dif. gene pairs (ex. brown eye gene + blue eye gene)

Homozygous - gene pairs are the same (ex. brown hair + brown hair)

Sex-Limited Genes - genes present in males + females but, activated more in one sex due to hormones (facial hair, breasts)

Notes:

• Types of Genes - dominant or recessive

  • Dominant Gene - when paired w/ a recessive, you take on its trait

• 23rd Pair of Chromosomes - sex chromosomes

  • X - female sex chromosome

  • Y - male sex chromosome

  • Determines the sex of the baby - males

• Types of twins - identical + fraternal

  • Identical Twins (Rarest) - monozygotic twins; occur when one egg is fertilized by one sperm, then divides into two; must be the same sex

  • Fraternal Twins (Most common)- dizygotic twins; occur when two eggs are released and fertilized by two separate sperm; can be same/opposite sex, hereditary via the mother