10) Gregor Mendel Flashcards
What does looking at how DNA behaves at a genetic level mean?
Before: Looked at how DNA behaves at a molecular level
Now: Going to look at how DNA behaves at a genetic level e.g. its function: Transmission of the material of inheritance
It is the study of how and why offspring become the same ‘kind’ of organisms as their parents
What did natural selection require for inheritance to work?
Need offspring to inherit information (such as height, eye colour) from their parents
ALSO: Information needs to vary slightly from generation to generation= Variation to weed out the weakest
What is the theory of pangenesis?
Knew that reproductive cells were the material of inheritance BUT did not know how the offspring had inherited it
Theory: Information were made up of tiny bits of all cells in the body & blended into the reproductive cells
What was the problem with the theory of pangenesis?
Goes against natural selection= As it predicts the offspring will be a ‘blend’ of the parents
But doesn’t explain gender: Cant have a blend as you can be male or female
Also: Accumulation of information= Offspring will have twice as much information as its mother and father= Would get larger
Also: Generate too much variation
Why did Mendel use pure breeding plants?
Wanted to know what determined whether or not an organism had a particular trait (phenotype)
Problem: Most pairs of parents give rise to too much variation in their offspring= children can have lots of different heights etc..
Makes it hard to tell EXACTLY what information each parent is passing to its offspring
Solution: Use pure breeding plants= Will produce offspring just like them, the more similar the parents are, the easier it is to spot where the variation occurs in the offspring
Pure breeding plants= Inbred for several generations= Will produce strains that very little variation in phenotype.
2 types: Can be Smooth or Rough
What did Mendel do with the pure breeding plants?
Decided to cross breed the strains= Showed that the offspring only adopted one of the characteristics= Was either smooth OR rough
What did he showed?
Each plant gets one piece of information from its father, one piece of information from its mother= Compete in the offspring= Dominant ones determines phenotype
Suggested that each phenotype is determined by the genotype= Trait that you can see is determined by material of heredity that you can’t see
What is the principal of segregation?
Only one parental allele is given, at random, to each gamete the parent produces
Mendel showed this by crossing F1 generations (Tt)= F2 generation tall:short in 3:1 ratio
What do monohybrid crosses show?
A cross where you are only looking at one trait
Each allele has the same chance at going into the offspring= Random
What do dihybrid crosses show?
A cross where there are 2 traits of interest
What is the Principle of Independent Assortment?
The alleles of different genes are allocated to gametes independently of each other, represented by dihybrid crosses
What is a Test cross?
For a dominant phenotype, its phenotype can neither homozygous dominant (e.g. TT) or heterozygous (e.g. Tt)
Test Cross: To work out which genotype it is, cross it with a homozygous recessive strain
What are the assumptions of Mendelian genetics?
A trait is determined by one gene
Gene will have limited amount of alleles
Allele is either dominant or recessive
BUT: most genes do not obey this
