Ch. 12 - Genetics And Evolution Flashcards
Penetrance
The proportion of individuals in the population carrying an allele who actually express the phenotype of the allele
Expressivity
Varying phenotypes despite identical genotypes
Mendel’s First Law: Law of Segregation
1) genes exist in ___
2) an organism has ___ alleles for each gene
3) how alleles separate
4) what happens if an organism possesses two different alleles for the same gene
1) alternative forms (alleles)
2) two
3) the 2 alleles segregate during meiosis resulting in gametes that carry only 1 allele for any inherited trait
4) if 2 alleles are different one will be completely expressed (dominant) one will be silent (recessive)
NOTE: #4 now proven to not be 100% true due to existence of codominance (if more than 1 dominant form of gene exists and individual inherits 2 dominant forms they will both be expressed as Co dominant traits) and incomplete dominance (a person can have a dominant and recessive allele and express a phenotype that is of varying degree between the 2)
Mendel’s second law: law of independent assortment
The inheritance of 1 gene does not affect the inheritance of another gene
NOTE: this is known to be not 100% true either, there are linked genes that are inherited together
Genetic leakage
Flow of genes between species via mating between 2 different species to produce a hybrid offspring.
Genetic drift
Changes in composition of gene pool due to chance. Tends to be more common in small populations
Founder effect
Severe case of genetic drift where a small population finds itself in reproductive isolation from other populations as a result of natural barriers, catastrophic events or other factors that suddenly reduce the size of population available for breeding
If two complete dominance heterozygotes are crossed (ex: Pp and Pp) what will the the ratio of genotypes? Of phenotypes?
Genotypes are 1:2:1 (1 homo dominant, 2 complete dominance hetero, 1 homo recessive)
Phenotypes are 3:1 (3 express the dominant trait, 1 expresses the recessive trait)
In a dihybrid cross (PpTt x PpTt) of 2 complete dominance heterozygotes for 2 different genes, what is the ratio of phenotypes?
9:3:3:1
9 will display dominant traits P and T
3 will display P and t
3 will display p and T
1 will display t and p
What conditions must be met for hardy Weinberg equilibrium? (5)
1) population is very large
2) there are no mutations that affect the gene pool
3) mating between individuals in the population is random
4) there is no migration of individuals in or out of the population
5) the genes in the population are all equally successful at reproducing
What are the 2 equations that describe hardy Weinberg equilibrium and what do they represent?
1) p^2 + 2pq + q^2 = 1
Represents the frequency of dominant phenotype and genotype in population
2) p + q = 1
Represents frequency of alleles in a population
