inheritance variation and evolution

DNA

"Deoxyribonucleic acid; contains genetic instructions for development and function."

Chromosome

"Coiled DNA molecule found in the nucleus; humans have 46 (23 pairs)."

Gene

"Section of DNA coding for a specific protein."

Allele

"Different form of a gene (e.g.

Homozygous

"Two identical alleles for a gene."

Heterozygous

"Two different alleles for a gene."

Dominant allele

"Allele that is expressed if present (capital letter)."

Recessive allele

"Allele that is expressed only if two copies are present (lowercase letter)."

Genotype

"Genetic makeup of an organism (allele combination)."

Phenotype

"Physical expression of genes."

Monohybrid cross

"Cross involving one gene with two alleles."

Punnett square

"Diagram used to predict genotype and phenotype ratios."

Probability in genetics

"Chance of a particular genotype or phenotype occurring."

Sex determination

"Females XX

Autosomal gene

"Gene located on non-sex chromosomes."

Sex-linked gene

"Gene located on X or Y chromosome; can show different inheritance patterns in males and females."

Variation

"Differences between individuals."

Continuous variation

"Range of small differences (e.g.

Discontinuous variation

"Distinct categories (e.g.

Causes of variation

"Genetic factors

Mutation

"Random change in DNA sequence; may be beneficial

Selective breeding

"Humans breed organisms with desirable traits to produce offspring with those traits."

Advantages of selective breeding

"Improves yield

Disadvantages of selective breeding

"Reduces genetic diversity; can unintentionally pass on disease."

Genetic engineering

"Changing an organism’s genome to produce desired traits."

Examples of genetic engineering

"Insulin production

Concerns with genetic engineering

"Ethics

Evolution

"Gradual change in species over time through natural selection."

Natural selection

"Organisms with beneficial traits survive and reproduce; traits passed to next generation."

Evidence for evolution

"Fossils

Speciation

"Formation of a new species when populations are reproductively isolated."

Reproductive isolation

"Populations cannot interbreed due to behavioural

Extinction

"Permanent loss of a species due to environmental change

Genetic disorders

"Caused by inherited alleles (e.g.

Cystic fibrosis

"Recessive disorder affecting cell membranes; causes thick mucus in lungs and digestive issues."

Sickle cell anaemia

"Recessive disorder causing abnormal haemoglobin and sickle-shaped red blood cells."

Carrier

"Individual with one recessive allele for a disorder but does not show symptoms."

Pedigree charts

"Diagram showing inheritance of traits across generations."

How to identify carriers

"Individuals with normal phenotype but pass on recessive allele to offspring."

Cloning

"Producing genetically identical organisms."

Natural cloning examples

"Bacteria (binary fission)

Artificial cloning

"Embryo splitting

Fossil formation

"Hard parts of organisms preserved in rock; sometimes replaced by minerals."

Limitations of fossil record

"Incomplete; soft tissues rarely preserved; some species never fossilised."

Antibiotic resistance as evolution example

"Bacteria with resistance survive antibiotics → reproduce → population changes."