Flashcards · 8461 · Topic 6

Inheritance, variation and evolution flashcards

20 cards on Topic 6, subtopics 4.6.1 to 4.6.4. Pick a subtopic or study them all.

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Sexual vs asexual reproduction: Sexual: two parents; gametes made by meiosis fuse; offspring varied. Asexual: one parent; mitosis only; no fusion of gametes; offspring are identical clones.
Meiosis: what it produces: Genetic information is copied, the cell divides twice, forming four gametes, each with a single set of chromosomes, all genetically different. Fertilisation restores the full number (23 + 23 = 46 in humans).
DNA, gene and genome: DNA: a polymer of two strands forming a double helix, in chromosomes. Gene: a small section of DNA coding for a sequence of amino acids, making a specific protein. Genome: all the genetic material of an organism.
How many amino acids are coded for by 300 bases?: Three bases code for one amino acid, so 300 ÷ 3 = 100.
Complementary base pairs, and how a protein is madeHigher: A pairs with T, C with G. Proteins are made on ribosomes from a template; carrier molecules bring amino acids in the right order; the chain folds into a unique shape (an enzyme, hormone or collagen).
Aa × Aa: genotypes and phenotype ratio: 1 AA : 2 Aa : 1 aa, so 3 dominant : 1 recessive. As probabilities: 3/4 and 1/4. With 20 offspring, expect 15 and 5.
Polydactyly and cystic fibrosis: dominant or recessive?: Polydactyly: dominant allele. Cystic fibrosis (a disorder of cell membranes): recessive allele. Two carriers have a 1/4 chance of an affected child.

Natural selection, and when a new species has formed: Variation exists from mutation; individuals better suited to the environment are more likely to survive and breed, passing on their alleles, which become more common over many generations. A new species: populations can no longer interbreed to produce fertile offspring.
Selective breeding: steps and risk: Choose parents with the desired characteristic, breed them, select the best offspring and repeat over many generations. Risk: inbreeding, making some breeds prone to disease or inherited defects.
Genetic engineering: the stepsHigher: Enzymes isolate the required gene; it is inserted into a vector, usually a bacterial plasmid or a virus; the vector carries the gene into the required cells, at an early stage of development.
Variation: causes, and how mutations affect it: Differences in characteristics are caused by genes, the environment, or both. Mutations occur continuously; most have no effect on the phenotype, a few influence it, and very rarely a new phenotype suits a change in the environment, leading to rapid change in the species.
Methods of cloning plants and animals: Plants: cuttings, and tissue culture (small groups of cells grown into new plants). Animals: embryo transplants (an embryo split into cells, each implanted in a host mother) and adult cell cloning (a body cell nucleus put into an enucleated egg cell, stimulated by an electric shock).

How do antibiotic-resistant bacteria develop, and how can it be slowed?: A mutation gives a resistant strain; the antibiotic kills non-resistant bacteria; resistant ones survive, reproduce and spread. Slow it by not using antibiotics for viral or non-serious infections, finishing the course, and restricting farm use.
Darwin vs Lamarck, and Woese's three domains: Darwin: evolution by natural selection (On the Origin of Species, 1859). Lamarck: changes during a lifetime are inherited, now known not to happen in most cases. Woese: archaea, bacteria, eukaryota.
How do fossils form?: From parts of organisms that have not decayed because conditions for decay were absent; when parts are replaced by minerals as they decay; or as preserved traces such as footprints, burrows and root pathways.
Why is the fossil record incomplete?: Many early forms of life were soft-bodied and left few traces, and many fossils have been destroyed by geological activity.
Factors that may cause extinction: New predators, new diseases, more successful competitors, changes to the environment over geological time, and single catastrophic events such as massive volcanic eruptions or asteroid collisions.

Linnaean classification: the ranks, largest first: Kingdom, phylum, class, order, family, genus, species. Organisms are named by the binomial system of genus and species, for example Homo sapiens.
The three-domain system: Proposed by Carl Woese, using evidence from chemical analysis. Archaea: primitive bacteria, often in extreme environments. Bacteria: true bacteria. Eukaryota: protists, fungi, plants and animals.
Evolutionary trees: Diagrams showing how closely related organisms are thought to be. They use current classification data for living organisms and fossil data for extinct organisms.