Inheritance

For mitosis or meiosis, writing "cell division" and stopping scores nothing. Give all three: number of cells (two vs four), chromosome number (diploid/same vs haploid/half) and genetic outcome (identical vs different). Meiosis is used ONLY to make gametes — never for growth or repair. Spell the two words distinctly.

On genetic-cross questions, put exactly ONE allele in each gamete (not two). Use clearly distinct upper/lower-case letters — H/h or T/t, not C/c or S/s, which look alike in handwriting. Complete the 2×2 grid, then state the offspring PHENOTYPES and their ratio or probability — that is where the mark is, not the genotype grid alone.

Sex-linked inheritance is beyond 4BI1 and earns no credit — invoking it on a pedigree or Punnett question loses marks (only error-carried-forward is available). Deduce parental genotypes from the phenotypes given and use the exact allele letters stated in the question, not letters you introduce yourself.

Natural-selection marks need precise language. Mutation makes a new ALLELE (not a "characteristic" or "trait"); the advantaged REPRODUCE MORE (not just "survive" or "numbers increase"); the ALLELE is passed on and its frequency rises. "The trait is inherited" or "numbers go up" loses the marks, and mutation must be named.

"Dominant" describes an allele expressed when only one copy is present (heterozygote) — it does NOT mean the allele is the most common in the population. A recessive allele can be far more common yet stay masked whenever a dominant allele is present. Keep genotype (alleles carried, e.g. Aa) separate from phenotype (what is observed).

Many mutations have no phenotypic effect, for several reasons: the changed base may still code for the SAME amino acid; the mutation may lie in NON-CODING DNA; it may produce a RECESSIVE allele masked by a dominant one; or it may not affect the protein's ACTIVE SITE. Give at least two distinct reasons — "it does nothing" is not enough.