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Combined Science: Biology

GCSE · Edexcel · higher

QuestionsFlashcards

Disease
Defence Against Disease
Development of Medicines
- Antibiotics
  4
- Discovery & Development of New Drugs
  6
Non-Communicable Diseases
- Lifestyle & Non-Communicable Disease
  8
- Cardiovascular Disease
  6

The Organism in the Environment
Human Influences on the Environment
- Human Impact on Biodiversity
  6
- Benefits of Maintaining Biodiversity
  6
Cycles within Ecosystems

Key Definitions Flashcards

All 10 cards in this deck

What is an allele?: A different version (form) of the same gene.
What does it mean if an allele is dominant?: Only one copy is needed for it to be expressed in the phenotype.
What does homozygous mean?: Having two identical alleles of a gene.
e.g. HH or hh
True or false? Two people with the same phenotype must have the same genotype.: False. A dominant phenotype can come from HH or Hh.
What is a zygote?: The single cell formed when two gametes fuse at fertilisation.
What is a genotype?: The alleles an organism has for a particular gene, written as letters.
e.g. Bb
What is a phenotype?: The observable characteristics of an organism, e.g. eye colour. They come from its genotype, often also affected by its environment.
What is meant by a heterozygous genotype?: One in which the two alleles of a gene are different from each other, e.g. Hh (one dominant and one recessive allele).
When is a recessive allele expressed in the phenotype?: Only when two copies are present (homozygous recessive, e.g. hh), so there is no dominant allele to mask it.
What is a chromosome?: A structure made of one very long DNA molecule, tightly coiled, that carries many genes. In eukaryotic cells chromosomes are in the nucleus.