DNA & Genetics - Year 10

DNA (Deoxyribonucleic Acid)

Molecule found in every cell that contains genetic information and acts as a blueprint for growth, development, and reproduction.

Watson-Crick Model (1953)

Model of DNA structure described by James Watson and Francis Crick.

Gene

A section of DNA that determines a specific trait.

Allele

Different forms of the same gene (e.g. B = brown eyes, b = blue eyes).

Punnett Square

A diagram used to predict possible genotypes and phenotypes of offspring from a genetic cross.

Genotype

The genetic makeup of an organism (combination of alleles, e.g. BB, Bb, or bb).

Phenotype

The physical expression of the genotype (e.g. brown eyes, blue eyes)

Dominant Allele

Represented by a capital letter; masks the recessive trait (e.g. B).

Recessive Allele

Represented by a lowercase letter; only shown if both alleles are recessive (e.g. b).

Homozygous Dominant

Both alleles are dominant (BB).

Homozygous Recessive

Both alleles are recessive (bb).

Heterozygous 

One dominant and one recessive allele (Bb)

Genotype Ratio

Proportion of genetic combinations (e.g. 1 BB : 2 Bb : 1 bb).

Phenotype Ratio

Proportion of observable traits (e.g. 3 brown eyes : 1 blue eyes).

Pedigree

A chart showing the genetic history of a family over several generations.

Sex Chromosome

One of the two chromosomes that determine biological sex (X and Y).

Autosome

A chromosome that is not a sex chromosome.

Sex-Linked Gene 

A gene located on one of the two sex chromosomes

Carrier

A heterozygous individual who carries a recessive allele but does not show symptoms.

Autosomal Trait

A trait located on a non-sex chromosome; affects males and females equally.

Sex-Linked Trait

A trait located on a sex chromosome; usually affects males more (e.g. colour blindness).

Sex-Linked Punnett Square

A Punnett square showing inheritance of traits on the X or Y chromosome.

Mutation

A change in the DNA base sequence that can affect the production of proteins.

Mutagen

A factor that causes mutations (can be natural or spontaneous).

Chromosomal Mutation

A large-scale change affecting many genes (e.g. extra or missing chromosome).

Genic Mutation

A small-scale change affecting a single gene.

Down Syndrome

A chromosomal mutation where an individual has an extra chromosome 21 (47 chromosomes total).

Klinefelter Syndrome

A chromosomal condition in males caused by an extra X chromosome (XXY).

Missense Mutation

A base change that alters the protein but doesn’t stop its production.

Insertion Mutation

An extra base is added, changing all information after it.

Deletion Mutation

A base is removed, changing all information after it.

Mitosis

Cell division that produces two identical diploid cells for growth and repair.

Meiosis

Cell division that produces four unique haploid sex cells (gametes) for reproduction.

Chromosome

Structure made of DNA that carries genetic information.

Diploid (2n)

Cell containing two sets of chromosomes (body cells).

Haploid (n)

Cell containing one set of chromosomes (gametes).

Gametes

Sex cells (sperm and egg).

Somatic Cells

Body cells such as skin, muscle, or blood cells.

Interphase (Mitosis Step 1)

Stage where DNA is copied before cell division.

Prophase (Mitosis Step 2)

Chromosomes appear; nuclear membrane breaks down.

Metaphase (Mitosis Step 3)

Chromosomes line up in the middle of the cell.

Anaphase (Mitosis Step 4)

Chromatids are pulled apart to opposite sides of the cell.

Telophase & Cytokinesis (Mitosis Step 5 & 6)

Two identical cells form at the end of mitosis.

Result of Mitosis

2 identical diploid cells.

Result of Meiosis

4 unique haploid cells with half the DNA of the original cell.

Genetic Variation (Meiosis)

Differences in offspring caused by meiosis (none in mitosis).

Biotechnology

Use of living organisms or biological systems to make useful products and solve problems in medicine, agriculture, or the environment. E.g. IVF

Genetic Engineering

Changing or inserting genes into an organism’s DNA.

Transgenic Organism

An organism that contains genes from another species.

Cloning

Creating exact genetic copies of an organism or cell.

Enzyme

A protein that speeds up chemical reactions; used in biotechnology.

Genetically Modified Organism (GMO)

Organism whose DNA has been modified artificially (e.g. crops with pest resistance).

Genetically Modified Food

Food made from organisms whose DNA has been altered by inserting genes from another organism.

Selective Breeding

Choosing parents with desired traits to produce offspring with those traits.

Medical Biotechnology

Use of living cells to improve health (e.g. vaccines, antibiotics, stem cell therapy). 

Environmental Biotechnology

Use of organisms to reduce pollution or produce biofuels (e.g. bacteria cleaning oil spills).

Advantages of Biotechnology

Improves food production, cures diseases, reduces pollution, increases crop resistance.

Disadvantages of Biotechnology

May reduce biodiversity, raises ethical issues, expensive, unknown long-term effects.

Phosphate Group

The part of a nucleotide that links to the sugar of the next nucleotide, forming the DNA backbone.

Deoxyribose Sugar

The five-carbon sugar in DNA that connects to both the phosphate group and nitrogen base.

Nitrogen Base

The part of a nucleotide that stores genetic information through base pairing.

Adenine (A)

A nitrogen base that always pairs with Thymine (T).

Thymine (T)

A nitrogen base that always pairs with Adenine (A)

Guanine (G)

A nitrogen base that always pairs with Cytosine (C).

Cytosine (C)

A nitrogen base that always pairs with Guanine (G).

Base Pairing Rule

Adenine pairs with Thymine (A-T) and Guanine pairs with Cytosine (G-C).

Complementary Base Pairing

The way nitrogen bases match up across the two DNA strands (A with T, G with C).

Double Helix

The twisted-ladder shape of DNA formed by two complementary strands.

Steps for a Punnett Square

Write one parent’s alleles across the top and the other parent’s down the side, then fill in the boxes to show possible offspring combinations.