Human Growth and Development

Cell Division Process

Function

Key Features

Possible Errors

Mitosis

Cell division for growth and repair

Produces two identical daughter cells. Ensures each new cell has 46 chromosomes. Produces four non-identical cells. Each gamete has 23 chromosomes. Crossing over (gene recombination) increases genetic diversity.

Mistakes can cause genetic mutations, leading to diseases, cancer or cell death.

Meiosis

Creates sex cells (gametes) for reproduction

Errors can lead to genetic disorders: ●​ Down Syndrome (extra chromosome 21). ●​ Cat’s Cry Syndrome

(missing part of chromosome 5).

Genetic Codes Genetic information is stored in DNA (deoxyribonucleic acid), which is made of sugar (deoxyribose), phosphates, and four bases :

●​ Adenine (A) pairs with Thymine (T) . ●​ Guanine (G) pairs with Cytosine (C) .

Genes are the basic units of heredity, stored in chromosomes. Humans have around 20,000 genes, each carrying inherited traits. The 23rd pair of chromosomes are the sex chromosomes, thus determining biological sex: ●​ Females: XX. ●​ Males: XY (Y chromosome triggers male traits). Alleles and Trait Inheritance

Alleles are different versions of a gene. Each person inherits two alleles per gene (one from each parent). Alleles can be dominant or recessive , affecting traits like eye color or blood type. Dominant alleles are expressed with just one copy. Recessive alleles are only expressed if both copies are recessive.

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