Biology · Rung 2 of 4

Inheritance

In diploid organisms, chromosomes occur in pairs. Meiosis produces cells with one set, and fertilisation brings two sets together. Simple Mendelian models let us calculate inheritance probabilities. Those probabilities do not guarantee exact proportions in a small family.

Where this sits

Comes after
DNA & genes

Exercises from this rung

Generated by the app, from easiest to hardest

  1. A cell of the mouse with 40 chromosomes divides by mitosis. How many does each daughter cell have?

    Answer 40

    Why 40: mitosis copies and shares out, and each daughter comes out like the mother, with its 40. It is the division for growing and repairing; the one that halves the number is meiosis, and only to make gametes.

    easier

  2. At a locus in a diploid organism, genotype Aa means it is…

    • An organism without alleles
    • Homozygous
    • Heterozygous

    Why A diploid has two copies of each chromosome in a pair. At this locus, A and a represent different alleles, making Aa heterozygous. AA and aa are homozygous. A capital letter does not mean an allele is more common.

    in between

  3. Two individuals with tall stems have some offspring with dwarf stems. What are the parents' genotypes?

    • Both are Tt
    • Both are TT
    • Both are tt
    • One is TT and the other tt

    Why Both Tt. A tt child received one t from each parent, so each carries one hidden under their tall stems. That is the hallmark of a recessive trait: it skips a generation unseen.

    harder