Genetic analysis 1+2 Flashcards
What was Mendel’s experiment with smooth and wrinkled phenotypes of peas?
1) Cross-bred 2 true breeding pea varieties (smooth seeds, wrinkled seeds)
2) F1 progeny all had smooth seeds
3) Self fertilise F1 progeny
4) Wrinkled seeds reamerged in a definite proportion
What is co-dominance?
- Simultaneous expression of 2 phenotypes determined by a gene having more than 2 alleles
- Eg. blood groups
What is Mendel’s first law?
- 2 alleles segregate during gamete formation
- Half of gametes carry one allele and half the gametes carry the other
- No blending, only dominant or recessive phenotypes
Which one of Mendel’s laws did Hunt Morgnan violate?
Mendel’s second law
What did Mendel do?
- Grew pea plants
- Set up an experimentsal system of breeding different strains of pea plant
What were Gregor Mendel’s ideas?
- Genes were discrete, physical entities which function independantly of each other and determine specific characteristics (distinct phenotypes)
What is genetic recombination?
- Crossovers occurring between chromosomes during gamete formation, producing non-parental recombinant combinations of alleles
- Every chromosome involved in at least one crossover during meiosis
- Occurs at the ends of chromosomes
What is Mendel’s second law?
- Un-linked genes controlling different characteristics are assorted INDEPENDANTLY into gametes
- Different genes R/r Y/y lie on different chromosomes
What did Mendel miss in his experiments?
- Some genes have more than 2 alleles
- Some alleles are not completely recessive or dominant
- Many genes don’t show independent assortment as they lie on the same chromosome
- In-complete dominance
- co-dominance
What is a ‘true breeding’ organism?
An organism which always passes down certain phenotypic traits to offspring
What did Thomas Hunt Morgan discover?
- Backcross grey-normal winged drospohila with a mutant ebony-vestigal winged parents
- Expected 4 phenotypes in EQUAL proportions
- BUT there were 4 phenotypes in UNEQUAL proportions
What were Huntt Morgans conclusions?
- Both genes are on the same chromosome so they are linked and inherited together
- Carry both dominant genes on one chromosome and both recessive genes on a different chromosome
What were Mendel’s conclusions?
- In the gametes there is one allele of each gene
- The gamete combine randomly to form the progeny
What was Mendel’s 2nd experiment?
- Looked at yellow/green and wrinkled/smooth
- Breed heterozygotes plants for both traits with homozygous recessive parents - this is a backcross
- Observes phenotypes in 4 equal proportion
(rY Ry RY ry) not (Rr rr yY yy)
What can measuring the recombination frequencies allow?
Allows genetic maps before genome sequencing
