2.14 : 遗传变异

Genetic variation stems from differences in DNA sequences among individuals, which are essential for species adaptation and evolution.

Genetic variations originate as ovaries produce eggs and testes produce sperm through a process called meiosis.

The ovaries release eggs that can potentially fertilize with sperm as they travel through the fallopian tubes to the uterus.

Each egg and sperm contribute 23 chromosomes, which are sequences of DNA that encode genes.

Alleles are the different versions of these genes which influence specific traits. For example, the gene determining eye color has various alleles, such as those for blue or brown eyes.

Fertilization results in a zygote with 46 chromosomes, combining genetic material from both parents.

Individuals with two identical alleles for a gene are called homozygous, while those with two different alleles are heterozygous.

For example, individuals with two mutated alleles of a globin gene develop a genetic disorder called sickle cell anemia, whereas heterozygous individuals who carry one healthy and one mutated allele do not exhibit severe disease symptoms.