class 10 chapter 8 science notes

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Heredity refers to the passing of traits from parents to offspring.
The characteristics or traits (such as eye color, height, etc.) are controlled by genes.
Genes are segments of DNA located on chromosomes.
Genotype refers to the genetic makeup of an organism, while phenotype refers to the physical expression of these traits.

Gregor Mendel is the father of genetics.
Mendel's work with pea plants led him to propose two main laws of inheritance:
- Law of Dominance: States that in a pair of factors (alleles), one is dominant and the other is recessive. The dominant allele determines the organism's trait.
- Law of Segregation: States that pairs of alleles separate during gamete formation, and each gamete carries only one allele for each trait.
- Law of Independent Assortment: States that genes for different traits are inherited independently of each other (this applies when genes are on different chromosomes).

Mendel conducted experiments with pea plants, observing traits such as flower color, seed shape, and plant height.
Monohybrid Cross: Cross involving a single trait.
Dihybrid Cross: Cross involving two traits.

Alleles are different forms of the same gene.
Dominant allele: Expressed when present (represented by uppercase letters, e.g., T for tall).
Recessive allele: Expressed only when two copies are present (represented by lowercase letters, e.g., t for short).
A heterozygous organism has one dominant and one recessive allele (Tt), while a homozygous organism has two identical alleles (TT or tt).

In humans, sex is determined by the X and Y chromosomes.
- Females have two X chromosomes (XX).
- Males have one X and one Y chromosome (XY).
The father’s sperm determines the sex of the offspring.

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