B13 variation and evolution Flashcards
what is variation
in a population differences in the characteristics
give examples of what variation may be due to
the genes they have inherited (genetic causes)
the conditions in which they have developed (environmental
causes)
a combination of genes and the environment.
what is evolution
a change in the inherited characteristics of a population over time through a process of natural selection which may result in the formation of a new species
what is natural selection
all species of living things have evolved from simple life forms that first developed more than three billion years ago
how does natural selection occur
within a particular species more individuals are born than can survive
due to differences in their genes individuals may show variation in their phenotypes
individuals with characters best suited to their environment are more likely to survive
how are new species formed
If two populations of one species become so different in phenotype that they can no longer interbreed to produce fertile offspring they
have formed two new species
what are fossils
the remains of organisms that lived billions of years ago that are found in rocks
how can fossils be formed
from parts of organisms that have not decayed because one
or more of the conditions needed for decay are absent
when parts of the organism are replaced by minerals as they
decay
as preserved traces of organisms, such as footprints, burrows
and rootlet traces.
why are there gaps in the fossil record
Many early forms of life were soft-bodied, which means that they
have left few traces behind. What traces there were have been
mainly destroyed by geological activity. This is why scientists
cannot be certain about how life began on Earth.
what is selective breeding used to produce
food crops from wild plants
domesticated animals from wild animals
what is selcetive breeding
the process by which humans breed plants and animals for particular genetic
characteristics
what are the steps of selective breeding
choose parents that best show the desired characteristic
breed them together
from the offspring, again choose those with the desired characteristic and breed
continue over many generations
name some of the types of characteristics that could be affected
Disease resistance in food crops.
Animals which produce more meat or milk.
Domestic dogs with a gentle nature.
Large or unusual flowers.
what can selective breeding lead to
inbreeding where some breeds are particularly prone to disease or inherited defects
what is genetic engineering
a process which involves modifying the genome of an organism by introducing a gene from another organism to give a desired
characteristic
