Principles of Inheritance and Variation Mind Map

Mendel's laws describe the regular patterns by which contrasting traits are inherited through discrete hereditary units called alleles, as shown by pea plant crosses.

When explaining a Mendelian law, connect the statement to gamete formation and support it with a ratio or cross, rather than only naming the law.

Inheritance of one gene studies how a single character controlled by one gene pair passes from parents to offspring, producing predictable genotypic and phenotypic ratios.

Always write both genotypic and phenotypic ratios. In incomplete dominance and codominance, do not force the 3:1 ratio.

A dihybrid cross follows the inheritance of two gene pairs at the same time and tests whether their alleles assort independently or show linkage.

Before writing the ratio, check whether the question suggests independent assortment or linkage. Morgan-based questions usually expect linkage and recombination reasoning.

Polygenic inheritance occurs when one trait is controlled by many genes, while pleiotropy occurs when one gene influences more than one phenotypic effect.

Use a short arrow in answers: polygenic means many genes to one character; pleiotropy means one gene to many phenotypic effects.

Sex determination is the biological mechanism by which chromosomal constitution or ploidy decides whether an organism develops as male or female.

Write the organism and system before explaining. XX-XY, XX-XO, ZW-ZZ, and haplodiploidy should not be mixed.

A mutation is a sudden, heritable change in genetic material that may alter a nucleotide sequence, gene function, chromosome structure, or chromosome number.

For mutation answers, mention the level of change: gene-level point mutation, frameshift due to insertion or deletion, or chromosomal structural change.

Pedigree analysis is the study of inheritance of a trait across generations using standard symbols to infer whether a disorder is dominant, recessive, autosomal, or sex-linked.

First decide dominant or recessive from generation pattern, then decide autosomal or sex-linked from male-female distribution and father-to-son transmission.

Chromosomal disorders are conditions caused by abnormal chromosome number or structure, often due to errors during cell division such as nondisjunction.

For each syndrome, write the chromosomal cause first, then give one or two key features if asked. Do not list features without the chromosome basis.