Theme 4A Flashcards
What is the problem with blending inheritance as a mechanism?
Variation will be reduced over time, and it does not explain the constant presence of variation observed in populations
Who was Gregor Mendel?
- Tested hypothesis of blending vs particulate inheritance
- Used true breeding peas (always give the same phenotype when self crossed)
Why were Mendel’s experiments successful?
- Used true breeding strains
- Focused on a single trait at a time
- Quantitative: counted the progeny
What is the difference between dominant and recessive?
Dominant alleles code for a functional protein whereas the recessive allele does not.
- ex: pea colour is determined by the presence of a functional enzyme that breaks down chlorophyll (recessive green peas won’t have as much chlorophyll breakdown)
What was the process of Mendel’s experiment?
- Parental generation: cross between two true breeding peas with different phenotype
- F1 generation self fertilize
- F2 generation have varieties in phenotype
How is the principle of segregation tested?
By predicting the outcome of crosses
What was Mendel’s hypothesis?
- Adult plants carry two versions of a gene that govern the inheritance of a character
- If an individuals pair of genes consists of different alleles, one allele is dominant over the other
- The pair of alleles that control a character separate as gametes. Half carry one allele, half carry the other (principle of segregation)
What is the product rule?
Probability of two independent events occurring in succession
- Independent probabilities are multiplied
What is the sum rule?
Probability of an outcome that can be achieved by two or more mutually exclusive events is the sum of their individual probabilities
- Individual probabilities are added
What is a monohybrid cross?
A cross between two heterozygotes for a single gene
- Probability of a gamete inheriting one of the two alleles is random
- Probability of genotype in a cross is determined by the product of the probabilities of acquiring each gamete from mother and father
What is the difference between homozygous and heterozygous?
- Homozygous: same two alleles, one type of gamete produced
- Heterozygous: two different alleles, two types of gametes produced
How do you determine if you have a heterozygote or homozygote?
A test cross: you mate an individual with a homozygous recessive genotype.
- Cross an individual with a dominant phenotype to the recessive homozygote. If there is a heterozygote, the recessive phenotype with show up
What is the chromosomal theory of inheritance?
- Chromosomes occur in pairs in diploid organisms
- Chromosomes of each pair are separated in gametes
- Separation of each pair of chromosomes is independent of other pairs
What is incomplete dominance?
- One allele not completely dominant to the other allele. Functional enzyme is produced, but not full amount
- Heterozygote has an intermediate phenotype
- Superscript used to label the alleles in lowercase letters
- 1:2:1 ratio
What is codominance?
- Codominant alleles have equal effects (both traits expressed)
What are complex traits?
There is not simply certain genres of traits (ex: people don’t just come in three sizes like small, medium, large. There is variation in size within those categories)
- Vary continuously
- Distribution of traits on a spectrum
- Polygenic
What influences continuous distribution?
Genetics and the environment
