Biology π | Variation & Selection | 18 Flashcards
(39 cards)
Define variation
Differences between
individuals of the same species
Define phenotypic variation
The difference in features between individuals of the same species
What is continuous variation?
When there are very many small degrees of difference for a particular characteristic between individuals and they are arranged in order and can usually be measured on a scale
What is discontinuous variation?
When there are distinct differences for a characteristic
Discontinous variation is caused by __
genes only
Continuous variation is caused by __
both genes and environment
What are examples of discontinuous variation?
ABO blood groups, seed shape in peas and seed colour in peas
What is a mutation?
A random genetic change
What are the two ways phenotypic variation is caused?
By genetics or the environment
What is gene mutation?
A random change in the base sequence of DNA
Why do most mutations not have an effect on the phenotype?
The protein that a mutated gene
produces may work just as well as the protein from the non-mutated gene
How are new alleles formed?
By mutations that affect the phenotype
What can increase rate of mutation?
- Ionising radiation: gamma rays, x rays, UV rays
- Chemicals such as tar in tobacco
What are the different sources of genetic variation in offspring?
Mutation, meiosis, random mating and random fertilisation
Define adaptive feature
An inherited feature that helps an organism to survive and reproduce in its environment
Define fitness
The probability of an organism surviving and reproducing in the environment in which it is found
What are hydrophytes?
Plants adapted to live in extremely wet conditions
What are some adaptations of hydrophytes?
- Large air spaces in their leaves
- Small roots
- Stomata usually open all the time and mainly found on the upper epidermis of the leaf
Why do hydrophytes have large air spaces?
To keep them close to the surface of the water where there is more light for photosynthesis
Why do hydrophytes have small roots?
So they can also extract nutrients from the surrounding water through their tissues
Why is the stomata of hydrophytes on the upper epidermis and always open?
So they can exchange gases much more easily with the air
(proximity)
What are xerophytes?
Plants adapted to live in extremely dry conditions
What are some adaptations of xerophytes?
- Thick waxy cuticle
- Sunken stomata
- Leaf rolled with stomata inside and an inner surface covered in hairs
- Small leaves
- Extensive shallow roots
- Thickened leaves or stems
Why do xerophytes have a thich waxy cuticle?
The cuticle cuts down water loss in two ways: it acts as a barrier to evaporation and also the shiny surface reflects heat and so lowers temperature