S1 Mendel

Allele

Mutations produce alternative forms (alleles) of

a gene

Diploidy

diploid cells (written as 2n) contain pairs of homologous chromosomes. For example, in humans, somatic (body) cells are diploid with 46 chromosomes (23 pairs).

This contrasts with haploid (n) cells, like sperm and egg cells, which contain only one set of chromosomes.

Genotype vs Phenotype

Genotype

– The allele (or set of alleles if diploid) for a given

trait

• Phenotype

– Observed effect, or “expression” of the genotype

Dominant vs Recessive 

• Dominant allele: Expressed even if only one copy is present (heterozygous). Represented with a capital letter (e.g., A).

• Recessive allele: Expressed only when two copies are present (homozygous recessive). Represented with a lowercase letter (e.g., a).

• Example: In pea plants, A = purple flowers (dominant) and a = white flowers (recessive).
    - AA or Aa → purple
    - aa → white

Describe the differences in function and structure between DNA

and RNA

 D N A

– Antiparallel

– Double-stranded helix

– Made of nucleotides

RNA is similar to DNA, except that

– It is usually single-stranded

– It has uracil (U) in place of thymine (T)

– The sugar in RNA nucleotides is ribose instead of deoxyribose

Describe the different roles of DNA, RNA, and proteins

• DNA (Deoxyribonucleic Acid): Stores and transmits genetic information. It contains the instructions for building all the proteins an organism needs.

• RNA (Ribonucleic Acid): Acts as the messenger and worker — carries DNA’s instructions to the ribosome and helps assemble proteins.
    - mRNA (messenger): copies DNA’s code
    - tRNA (transfer): brings amino acids
    - rRNA (ribosomal): makes up ribosomes

• Proteins: Carry out most cellular functions — they form structures, enzymes, and signaling molecules that determine traits and control biological processes

Distinguish Mitosis from Meiosis

• Mitosis:

  • Produces 2 identical diploid cells

  • Used for growth, repair, and asexual reproduction

  • 1 division

  • Daughter cells are genetically identical to the parent cell

• Meiosis:

  • Produces 4 non-identical haploid cells (gametes)

  • Used for sexual reproduction

  • 2 divisions (Meiosis I and II)