DNA, Genes & Inheritance
DNA (deoxyribonucleic acid) stores the genetic instructions needed for an organism to grow, develop, and reproduce. Packaged into chromosomes inside the cell nucleus, genes code for specific proteins, while inherited combinations of alleles determine an organism's genotype and observable characteristics (phenotype).
- Chromosome
- A long, coiled molecule of DNA that carries genetic information in the form of genes.
- Gene
- A section of DNA that codes for a specific protein.
- Allele
- Different forms of the same gene.
DNA, Genes & Inheritance: 3D Molecular, Lattice, DNA & Vector Explorer
Drag directly on the 3D model to rotate it through any angle, or switch tabs to inspect VSEPR bond angles, crystal lattices, DNA base pairing, and 3D space diagonals.
Antiparallel Strands & Complementary Hydrogen Bonds
- Adenine (A) = Thymine (T): Joined by 2 hydrogen bonds (in RNA, Uracil replaces Thymine).
- Guanine (G) ≡ Cytosine (C): Joined by 3 hydrogen bonds, making G-C rich DNA more thermally stable.
- Backbone: Deoxyribose sugar and phosphate groups joined by strong covalent phosphodiester bondsin antiparallel 5'→3' and 3'→5' directions.
- Helicase slider (0%): DNA helicase breaks hydrogen bonds between bases so DNA polymerase can catalyse semi-conservative replication.
Key Concepts & Exam Definitions (7)
- Chromosome
- A long, coiled molecule of DNA that carries genetic information in the form of genes.
- Gene
- A section of DNA that codes for a specific protein.
- Allele
- Different forms of the same gene.
- Dominant
- An allele that is always expressed if present, represented by a capital letter.
- Recessive
- An allele that is only expressed if two copies are present, represented by a lowercase letter.
- Homozygous
- Having two identical alleles for a particular gene.
- Heterozygous
- Having two different alleles for a particular gene.
Quick-Fire Flashcards (5)
Click any card to check the answer, then mark it as Known to track your progress.
What structure does DNA have?
Where is DNA found in a eukaryotic cell?
What does it mean if an individual is heterozygous for a trait?
What is a phenotype?
How many chromosomes are in a normal human body cell?
Exam-Style Questions & Mark Schemes (3)
Write or think through your answer first, then click Check Mark Scheme to see the exact points examiners award marks for.
- Q1
Explain the relationship between chromosomes, DNA, and genes.
Click “Check Mark Scheme” to compare your answer, Chromosomes are made of long molecules of DNA. A gene is a small section of that DNA on a chromosome that codes for a protein.
- Q2
If brown eyes (B) are dominant and blue eyes (b) are recessive, what are the possible genotypes for a brown-eyed person?
Click “Check Mark Scheme” to compare your answer, BB or Bb.
- Q3
What is the purpose of meiosis?
Click “Check Mark Scheme” to compare your answer, To produce gametes (sex cells) with half the normal number of chromosomes, ensuring genetic variation.
Common Exam Questions (4)
What is DNA?
DNA is a polymer made of two strands coiled together to form a double helix. Its sequence of nucleotide bases carries the genetic instructions for building proteins in an organism.
What is a gene?
A gene is a short section of DNA on a chromosome that codes for a specific sequence of amino acids to make a particular protein.
What is an allele?
An allele is an alternative form of the same gene. For example, the gene for pea seed shape has a dominant allele for round seeds and a recessive allele for wrinkled seeds.
What is the difference between genotype and phenotype?
Genotype is the specific pair of alleles an organism carries for a gene (such as Bb or bb), whereas phenotype is the observable physical characteristic produced by that genotype and the environment (such as brown or blue eyes).
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Related study guides
Animal & Plant Cell Structure
All living organisms are composed of cells. Plant and animal cells are eukaryotic (containing a membrane-bound nucleus and organelles), whereas bacterial cells are prokaryotic and carry their DNA free in the cytoplasm as a single circular chromosomal loop and small rings called plasmids.
Evolution & Natural Selection
Evolution is a change in the inherited characteristics of a population over generations through natural selection. Genetic variation arises from random mutations, and individuals with phenotypes best suited to their environment are more likely to survive, reproduce, and pass on their advantageous alleles.
Mitosis vs Meiosis
Mitosis and meiosis are the two types of nuclear division in eukaryotic cells. Mitosis involves 1 division that produces 2 genetically identical diploid daughter cells for growth and tissue repair, whereas meiosis involves 2 divisions (meiosis I and II) that produce 4 genetically distinct haploid gametes for sexual reproduction.