Heredity

Notes

1. Heredity

Definition: Heredity is the transmission of characters (traits) from parents to offspring through genes.

Examples Eye colour Hair type Blood group Height (partly hereditary) 2. Variation

Variation means differences among individuals of the same species.

Causes of Variation DNA copying errors Sexual reproduction Environmental factors Importance Helps organisms adapt. Essential for survival. Basis of evolution. 3. Why Do Offspring Resemble Their Parents?

Because hereditary information is stored in DNA.

During reproduction, DNA from both parents is passed to the offspring.

4. DNA

DNA (Deoxyribonucleic Acid)

Functions:

Stores hereditary information Controls body characteristics Passes genetic information to the next generation 5. Gene

A gene is the functional unit of heredity.

Located on chromosomes Controls one specific trait

Example: Gene for tallness

6. Chromosome

Chromosomes are thread-like structures found inside the nucleus.

They contain DNA and genes.

Human Chromosomes 46 chromosomes 23 pairs 7. Mendel – Father of Genetics

Gregor Johann Mendel performed experiments on pea plants.

Reasons for choosing pea plants:

Short life cycle Easy pollination Contrasting characters Many offspring 8. Mendel's Monohybrid Cross Parents

Tall (TT)

×

Dwarf (tt)

↓

F₁ Generation

All Tall (Tt)

↓

F₂ Generation

Tall × Tall

Result:

Genotype Ratio

1 TT : 2 Tt : 1 tt

Phenotype Ratio

3 Tall : 1 Dwarf

Important Conclusions Dominant trait appears first. Recessive trait remains hidden. Recessive trait appears in F₂ generation. 9. Dominant and Recessive Traits Dominant Trait

Expresses itself even when only one dominant allele is present.

Example: Tallness (T)

Recessive Trait

Expresses only when both alleles are recessive.

Example: Dwarfness (t)

10. Alleles

Alternative forms of a gene are called alleles.

Example

T = Tall

t = Dwarf

11. Acquired and Inherited Traits Acquired Traits

Develop during life.

Not inherited.

Examples:

Muscles by exercise Pierced ears Inherited Traits

Passed from parents.

Examples:

Eye colour Hair colour 12. Sex Determination in Human Beings

Female Chromosomes

XX

Male Chromosomes

XY

Female Gamete

Always X

Male Gamete

X or Y

Female Egg Male Sperm Child X X Girl (XX) X Y Boy (XY)

Therefore,

Father determines the sex of the child.

Important Definitions