CH 12 Flashcards
What two concepts were the basis for ideas about heredity?
1) Heredity occurs within species
2) Traits are transmitted directly from parent to offspring
What did Josef Kolreuter do?
crossed tobacco strains to produce hybrids
What did Josef Kolreuter observe?
-Hybrid offspring differed from both parents
-Additional variation observed in 2nd generation offspring contradicts direct transmission
What did T.A. Knight do?
crossed two varieties of garden pea, Pisum sativa
What did T.A. Knight observe?
Crossed two true-breeding strains: self fertilization produces one type
1st generation resembled only 1 parent strain
2nd generation resembled both
Pea plants were optimal because:
- Other research showed that pea hybrids could be produced
- Many pea varieties were available
- Peas are small plants and easy to grow
- Peas can self-fertilize or be cross-fertilzed
What were the three stages of Mendel’s experimental method?
- Produce true breeding strains for each trait he was studying
- Cross-fertilize true breeding strains having alternate forms of a trait
(also perform reciprocal crosses to ensure source of pollen is from both types (for ex white and purple) - Allow the hybrid offspring to self fertilize for several generations and count the number of offspring showing each form of the trait
monohybrid cross
used to study only two variations of a single trait
F1
first filial generation
In the F1 generation, offspring is produced by…
crossing two true-breeding strains
For every trait Mendel studied, all F1 plants resembled…
the same parent
dominant
expressed
recessive
hidden by a dominant allele
F2
-second filial generation
-produced from the self-fertilization of F1 plants
Although masked in the F1 generation the ____ _____ reappeared among some F2 individuals
recessive trait
F2 generation ratio
3:1
In F2 plants,
__ plants with the dominant form
___ plants with the recessive form
The dominant recessive ratio was ___
3/4; 1/4; 3:1
Mendel discovered the ratio is actually
__ true breeding dominant plant
__ not true-breeding dominant plants
__ true breeding recessive plant
1; 2; 1
Mendel’s conclusions
-each trait was _____, _____
-for each pair, one trait was ______, the other ______
-pairs of alternative traits examined were segregated among the progeny of a particular cross
-alternative traits were expressed in the F2 generation in the ratio of 3/4 dominant to 1/4 recessive
intact, discrete
dominant, recessive
Mendel’s five-element model
- Parents transmit discrete factors (genes)
- Each individual receives one copy of a gene from each parent
- Not all copies of a gene are identical
- Alleles remain discrete - no blending
- Presence of allele does not guarantee expression
allele
alternative form of a gene
homozygous
two of the same allele
heterozygous
different alleles
genotype
an individual’s complete set of alleles
phenotype
an individual’s physical appearance
principle of segregation
two alleles for a gene segregate during gamete formation (one from each parent) and are rejoined at random during fertilization
dihybrid cross
used to study two variations of two traits in a single cross
Dihybrid cross ratio
9:3:3:1
Principle of Independent Assortment
In a dihybrid cross, the alleles of each gene assort independently
The segregation of different allele pairs is ____ - for ex, seed shape is independent of seed color
independent
Independent alignment of different homologous chromosome pairs during metaphase 1 leads to the _____ ______ of the different allele pairs
independent segregation
testcross
used to determine the genotype of an individual with an unknown phenotype
Cross the unknown genotype with a homozygous recessive
