The nucleus is the genetic control center

DNA is the main genetic material

A chromosome usually contains one DNA molecule

A DNA molecule contains many genes

Nucleus → Chromosome → DNA → Gene (determining traits) [→ means "includes"]

Traits: morphology, structure, physiological characteristics and behavior

relative shape. Example: Height of pea stems: tall stems and short stems

genetically determined traits

AA and Aa are dominant traits. aa is a recessive trait

Recessive traits that create something out of nothing

Human body cells have 23 pairs of chromosomes, of which the pair that determines gender are "sex chromosomes"

Female sex chromosomes are "XX". The number of chromosomes in normal female somatic cells is 22 pairs XX

Male sex chromosomes are "XY". The number of chromosomes in normal male somatic cells is 22 pairs XY

The probability of having a boy or girl is equal

Concept: The phenomenon of differences between offspring and parents and between individual offspring

Example: Parents have double eyelids, children have single eyelids

:Differences in skin color between twin brothers

Factors causing variation ① Environmental factors (no genetic material changes, not heritable)

②Changes in genetic material (heritable)

Variations are divided into favorable variations and unfavorable variations

①Effective measures: Prohibiting marriage between close relatives🚫

②Dangers of incest marriage: high probability of genetic diseases