Variation and evolution Flashcards
The development of understanding of genetics and evolution
Our current understanding of genetics has…
… developed over time.
Describe the development of our understanding of genetics (aka the history run-down) - Late 1800s
Late 1800s - scientists discovered chromosomes and observed how they behaved during cell division
In the early 1900s, scientists discovered similarities in the way that chromosomes and Mendel’s ‘hereditary units’ acted.
What was proposed as a result?
That the ‘hereditary units’ (now known as genes) are located on chromosomes.
Who was Gregor Mendel?
Mendel was an Austrian scientist and monk who lived in the 1800s.
He is referred to as the ‘founding father of modern genetics’.
Briefly describe the work of Mendel
Mendel carried out breeding experiments on plants in the mid 1800s/19th Century.
One of his observations was that the inheritance of each characteristic is determined by ‘units’ that are passed on to descendants, unchanged.
Describe the development of our understanding of genetics (aka the history run-down) - Early 1900s
Early 1900s - scientists discovered similarities in the way that chromosomes and Mendel’s ‘hereditary units’ behaved.
Describe the development of our understanding of genetics (aka the history run-down) - 1953
1953 - The structure of DNA (e.g. double helix) was determined and the mechanism of gene function worked out.
This scientific work led to the gene theory being developed.
Which three traits of the pea plant (the species he used) did Mendel study?
Colour of peas
Colour of flowers
Height
What did Mendel study?
The inheritance of different characteristics: He devised the laws of inheritance!
What was the pattern in characteristics found by Mendel?
First cross- all offspring had the dominant ‘hereditary unit’ (Tt for height)
Second cross - 1/4 had hereditary units that were both recessive. (tt for height).
They expressed a different characteristic to the other pea plants e.g. were dwarfs/green.
What were the three conclusions made by Mendel?
-Characteristics in plants are determined by ‘hereditary units’ (genes)
-Hereditary units are passed on to offspring unchanged, with one unit from each parent
-Hereditary units can only be dominant or recessive - if an individual has both the dominant and recessive unit for a characteristic, then the dominant characteristic will be expressed
Variation
Differences in the characteristics of individuals in a population.
What might cause variation?
-the genes that individuals in a population have inherited (genetic causes)
-the conditions in which the individuals in a population have developed (environmental causes)
-a combination of genes and the environment
What usually exists within a population of a species?
There is usually extensive genetic variation within a population of a species.
What is the effect of a mutation on an individual’s phenotype?
-Most have no effect on the phenotype
-Some influence phenotype
-Very few determine phenotype
What does the variation within a population of a species arise from?
Mutations.
Mutations occur _______.
Continuously
How often will a mutation will lead to a new phenotype?
Very rarely.
However, if there IS a new phenotype, and it’s suited to an environmental change, it can lead to a relatively rapid change in the species.
What are the two types of variation?
-Genetic variation
-Environmental variation
What causes genetic variation?
(linked to how the genome influences the development of the phenotype of an organism).
-The mixing of genetic information
-When gametes fuse
-You inherit some genes from your mother, and some genes from your father
Name some characteristics in animals determined only by genes:
-eye colour
-blood group
-inherited disorders
What is haemophilia?
An inherited disorder where you bleed more than other people.
(not in spec but interesting x)
Genome
All of the genetic material in an organism.
How does the genome’s interaction with the environment influence the development of the phenotype of organisms?
The environment, including all of the conditions that the organisms live and grow in, cause differences between members of the same species.
This is called environmental variation.
e.g. A plant grown in lots of sunlight would be luscious and green vs one grown in darkness which would be tall and spindly with yellow leaves.
A twin may go on holiday and get tanned so look physically different to the other, or gain weight through a diet high in saturated fat.