Biology by Bradford
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The subtopic in the middle and ten tasks round it: label three diagrams, complete a table, put a process in order and fill 50 gaps. Every standard level statement has a box; the four boxes for higher level only are dashed and badged HL, and drop off for an SL class. Type into the blanks and check them, or print it on A4, Letter or A3 with an answer key.
Living things produce more than can survive, because food, water, space and other resources run short: a population cannot grow beyond its . Abiotic factors such as a hard frost or a drought select too. They are , killing a similar share of a population whatever its size, and the individuals best able to the extremes are the ones that go on to breed.
Endler let guppies breed in ponds, then added a strong predator, a weak one or none. Several generations later, males living with the strong predator had spots: conspicuous males were more often. Elsewhere the spots increased, because females brightly spotted males: . By controlling the selection , Endler could model evolution in action.
If 9% of a population show the recessive phenotype, q = , p = and the carriers make up . Genotype frequencies that do not fit the prediction show a condition is not being met: mating may not be , or some genotypes may survive better than others.
Breeders choose the individuals with the traits they want and breed only from them: . Dairy cattle bred for milk yield, and kale, broccoli and cauliflower bred from wild cabbage, are the result. When bacteria become resistant to an antibiotic, nobody chose them: the drug killed the cells and the resistant ones multiplied. That is , an consequence of human action.
Many in Darwin's day accepted that species evolve; what they lacked was a convincing . Lamarck had argued that characteristics during life are passed on, yet a muscle built by exercise leaves the of its genes unchanged, so only traits can evolve. Natural selection replaced Lamarck's idea, a , and over billions of years has produced all of Earth's biodiversity.
| Natural selection | Sexual selection | |
|---|---|---|
| Favours traits that | help an individual | help it win a |
| Who or what selects | the environment: food supply, disease, climate | the opposite sex, usually , choosing a mate |
| Example | a thicker coat where winters are hard | the long, bright plumage of male |
| Price paid | none: the trait itself aids survival | showy males are easier for to find |
Dashed curves show the population before selection. Selection against both extremes leaves the where it was; selection for both extremes can split a population into groups. Every pattern changes the in the gene pool.
Only a change in the base sequence of a gene makes a brand-new . Sexual reproduction makes none, but gives every new individual a new of the alleles already present. Natural selection acts on the that results.
Number the steps in order.
Competition between members of the same species is . How well a genotype survives and reproduces is its .
All the genes in a population, with every version of each, make up its . As individuals with different heritable traits survive and breed at different rates, natural selection shifts the in it. Joining Darwin's theory to genetics gave . Populations that are evolve apart: allele databases show that the allele for blood group O is almost universal in many Indigenous peoples of South America, while elsewhere the alleles for groups A and B are common too.
Many in Darwin's day accepted that species evolve; what they lacked was a convincing mechanism. Lamarck had argued that characteristics acquired during life are passed on, yet a muscle built by exercise leaves the base sequence of its genes unchanged, so only heritable traits can evolve. Natural selection replaced Lamarck's idea, a paradigm shift, and over billions of years has produced all of Earth's biodiversity.
Only a change in the base sequence of a gene makes a brand-new allele. Sexual reproduction makes none, but gives every new individual a new combination of the alleles already present. Natural selection acts on the variation that results.
Living things produce more offspring than can survive, because food, water, space and other resources run short: a population cannot grow beyond its carrying capacity. Abiotic factors such as a hard frost or a drought select too. They are density-independent, killing a similar share of a population whatever its size, and the individuals best able to tolerate the extremes are the ones that go on to breed.
Competition between members of the same species is intraspecific. How well a genotype survives and reproduces is its fitness.
| Natural selection | Sexual selection | |
|---|---|---|
| Favours traits that | help an individual survive | help it win a mate |
| Who or what selects | the environment: food supply, disease, climate | the opposite sex, usually females, choosing a mate |
| Example | a thicker coat where winters are hard | the long, bright plumage of male birds of paradise |
| Price paid | none: the trait itself aids survival | showy males are easier for predators to find |
Endler let guppies breed in ponds, then added a strong predator, a weak one or none. Several generations later, males living with the strong predator had fewer spots: conspicuous males were eaten more often. Elsewhere the spots increased, because females prefer brightly spotted males: sexual selection. By controlling the selection pressures, Endler could model evolution in action.
All the genes in a population, with every version of each, make up its gene pool. As individuals with different heritable traits survive and breed at different rates, natural selection shifts the allele frequencies in it. Joining Darwin's theory to genetics gave neo-Darwinism. Populations that are geographically isolated evolve apart: allele databases show that the allele for blood group O is almost universal in many Indigenous peoples of South America, while elsewhere the alleles for groups A and B are common too.
Dashed curves show the population before selection. Selection against both extremes leaves the mean where it was; selection for both extremes can split a population into two groups. Every pattern changes the allele frequencies in the gene pool.
If 9% of a population show the recessive phenotype, q = 0.3, p = 0.7 and the carriers make up 0.42. Genotype frequencies that do not fit the prediction show a condition is not being met: mating may not be random, or some genotypes may survive better than others.
Breeders choose the individuals with the traits they want and breed only from them: artificial selection. Dairy cattle bred for milk yield, and kale, broccoli and cauliflower bred from wild cabbage, are the result. When bacteria become resistant to an antibiotic, nobody chose them: the drug killed the susceptible cells and the resistant ones multiplied. That is natural selection, an unintended consequence of human action.