testcross
100 percent.
Given those conditions, the offspring have a 50% chance of demonstrating the dominant phenotype and a 50% chance of demonstrating the recessive phenotype.
The homozygous dominant individual can only pass on the dominant allele and the homozygous recessive individual can only pass on the recessive allele, therefore all offspring will be heterozygous and have the dominant phenotype.
Straight thumbs, hitch hiker's thumb is recessive...so the F1 generation in this example would be heterozygous and have the dominant (straight thumbed) phenotype.
Phenotype: Black Bear x Brown Bear Genotype: BB x bb Possible gametes: B B b b Possible B B crosses: b Bb Bb b Bb Bb Phenotype of offspring: Only Black bears
To determine the genotype of an individual that shows the dominant phenotype you would cross that individual with one that is homozygous recessive. A monohybrid cross of two individuals that are heterozygous for a trait exhibiting complete dominance would probably result in a phenotype ratio is 3 dominant 1 recessive.
Homozygous recessive.
100 percent.
To perform a testcross, you cross an individual with a dominant phenotype (but unknown genotype) with a homozygous recessive individual. By examining the offspring's phenotypes, you can determine the genotype of the unknown individual through the principles of Mendelian genetics. This allows you to determine if the individual is homozygous dominant or heterozygous for a specific trait.
Given those conditions, the offspring have a 50% chance of demonstrating the dominant phenotype and a 50% chance of demonstrating the recessive phenotype.
The phenotype pairings which the genotypes of individuals be directly known are homozygous recessive.
In a test cross, one individual with a dominant phenotype but unknown genotype is crossed with a homozygous recessive individual. The genotype of the individual with the dominant phenotype can then be inferred based on the phenotypic ratios of the offspring.
It is easier to analyze genotype by observing phenotype in organisms with incomplete dominance (also known as codominance), because in incomplete dominance the individual will show a specific phenotype for each situation, whether it is homozygous dominant, heterozygous, or homozygous recessive. For example, in flowers, such as the ones that Mendel studied, a homozygous dominant flower will be red, a homozygous recessive flower will be white, and a heterozygous flower will be pink. In complete dominance, a heterozygous will only express the dominant phenotype, as opposed to incomplete dominance, in which a heterozygous individual will express a phenotype that is representative of both of the dominant and recessive traits. Because heterozygous individuals in complete dominance express the dominant phenotype, it is hard to determine whether the genotype is homozygous dominant or heterozygous for the trait. Hope this helps!
The homozygous recessive individual is used in a test cross to determine the genotype of an individual with a dominant phenotype but unknown genotype. When crossed with a homozygous recessive individual, if any offspring display the recessive trait, it indicates that the unknown individual is heterozygous for that trait.
Phenotype
The genotype ratio is 1:2:1 (1 homozygous dominant, 2 heterozygous, 1 homozygous recessive) and the phenotype ratio is 3:1 (3 individuals showing the dominant trait, 1 individual showing the recessive trait).
The homozygous dominant individual can only pass on the dominant allele and the homozygous recessive individual can only pass on the recessive allele, therefore all offspring will be heterozygous and have the dominant phenotype.