What is the genotype in a Punnett square?
The two things a Punnett square can tell you are the genotypes and phenotypes of the offspring. A genotype is the genetic makeup of the organism. This is shown by the three genetic conditions described earlier (BB, Bb, bb). The phenotype is the trait those genes express.
.~ An organism can be thought' of as a large collection of phenotypes. A phenotype is the appearance of a traitand is determined by pairs of genes. The pairs of genes represent the genotype for the trait. However, if a trait is determined by incomplete dominance, you can tell if you are homozygous or heterozygous.
- Genotype. Genotype is the genetic make-up of an individual organism. Your genotype functions as a set of instructions for the growth and development of your body. The word 'genotype' is usually used when talking about the genetics of a particular trait (like eye colour).
- There are three primary sources of genetic variation, which we will learn more about:
- Mutations are changes in the DNA.
- Gene flow is any movement of genes from one population to another and is an important source of genetic variation.
- Sex can introduce new gene combinations into a population.
- Variation is all the differences which exist between members of the same species. There are two kinds of variation; continuous and discontinuous.You should be able to give some examples of each. Continuous variation is variation that has no limit on the value that can occur within a population.
Supplement. The genotypic ratio describes the number of times a genotype would appear in the offspring after a test cross. For example, a test cross between two organisms with same genotype, Rr, for a heterozygous dominant trait will result in offspring with genotypes: RR, Rr, and rr.
- The expected genotype ratio when two heterozygotes are crossed is 1 (homozygous dominant) : 2 (heterozygous) : 1 (homozygous recessive). When a phenotypic ratio of 2 : 1 is observed, there is probably a lethal allele.
- Definition of trihybrid. : an individual or strain that is heterozygous for three pairs of genes.
- The example below is for phenotypic distribution when the parents are heterozygous at three unlinked traits in peas. 27:9:9:9:3:3:3:1 ratio: As can be seen in the forked line diagram above, a trihybrid cross yields a phenotypic ratio of 27:9:9:9:3:3:3:1.
The Genotype of a Carrier. If a trait is recessive, two copies of the allele are required for the physical appearance of the trait in the organism. This means only those with a homozygous recessive genotype, such as bb, will exhibit a recessive trait.
- The Genotype of a Carrier. If a trait is recessive, two copies of the allele are required for the physical appearance of the trait in the organism. This means only those with a homozygous recessive genotype, such as bb, will exhibit a recessive trait.
- The O allele is recessive and the A and B alleles are co-dominant. A homozygous individual will have one of the following genotypes, AA, BB, or OO. A heterozygous individual will have an AO, BO, or AB genotype.
- Red/green colour blindness is passed from mother to son on the 23rd chromosome, which is known as the sex chromosome because it also determines sex. For a female to be colour blind it must be present on both of her X chromosomes.
Updated: 21st November 2019