Hello all, I have a question that I\'m working on for a college biology assignme

Question

Hello all,

I have a question that I'm working on for a college biology assignment. My dad's mom and dad both have brown eyes, but all 3 of their children have blue eyes. I have no information on my great grandparents. I need to know what the genotype would be for each individual so it would be:

my dad's dad: brown eyes
my dad's mom: brown eyes
my dad: blue eyes
my aunt: blue eyes
my uncle: blue eyes

Here is the the specific wording on my assignment:
-If an individual in the family shows a recessive trait but the parents both show the dominant trait, what would be the genotypes of each individual?

I have done so much research and I am just not finding any info on this. Most of the sites I go to say it is impossbile for 2 parents to have brown eyes and the children all have blue eyes. If anyone could help me on this, I would greatly appreciate it!!!!!

Thank you & have a good day!!!

Explanation / Answer

The genotype is the specific genetic makeup (the specific genome) of an individual, in the form of DNA. Together with the environmental variation that influences the individual, it codes for the phenotype of that individual. Non-hereditary mutations are not classically understood as representing the individuals' genotype. Hence, scientists and doctors sometimes talk for example about the (geno)type of a particular cancer, thus separating the disease from the diseased. While codons for different amino acids may change in a random mutation (changing the sequence coding a gene), this doesn't necessarily alter the phenotype.

Typically, one refers to an individual's genotype with regard to a particular gene of interest and, in polyploid individuals, it refers to what combination of alleles the individual carries (see homozygous, heterozygous). Any given gene will usually cause an observable change in an organism, known as the phenotype. The terms genotype and phenotype are distinct for at least two reasons:

1. To distinguish the source of an observer's knowledge (one can know about genotype by observing DNA; one can know about phenotype by observing outward appearance of an organism).
2. Genotype and phenotype are not always directly correlated. Some genes only express a given phenotype in certain environmental conditions. Conversely, some phenotypes could be the result of multiple genotypes.

The distinction between genotype and phenotype is commonly experienced when studying family patterns for certain hereditary diseases or conditions, for example, hemophilia. Sometimes people who do not have hemophilia can have children with the disease, because the parents each "carried" hemophilia genes in their body, even though these genes have no effect on the parents health. The parents in this case are called carriers. Healthy people who are not carriers and healthy people who are carriers of the hemophilia gene have the same outer appearance (ie they do not have the disease), therefore they are said to have the same phenotype. However, the carriers have the gene and the other healthy people do not (they have different genotypes).

With careful experimental design, one can use statistical methods to correlate differences in the genotypes of populations with differences in their observed phenotype. These association studies can be used to determine the genetic risk factors associated with a disease. They may even be able to differentiate between populations who may or may not respond favorably to a particular drug treatment. Such an approach is known as personalized medicine.

Inspired by the biological concept and usefulness of genotypes, computer science employs simulated genotypes in genetic programming and evolutionary algorithms. Such techniques can help evolve mathematical solutions to certain types of otherwise difficult problems.

and

The phenotype of an individual organism is either its total physical appearance and constitution or a specific manifestation of a trait, such as size, eye color, or behavior that varies between individuals. Phenotype is determined to some extent by genotype, or by the identity of the alleles that an individual carries at one or more positions on the chromosomes. Many phenotypes are determined by multiple genes and influenced by environmental factors. Thus, the identity of one or a few known alleles does not always enable prediction of the phenotype.

Nevertheless, because phenotypes are much easier to observe than genotypes (it doesn't take chemistry or sequencing to determine a person's eye color), classical genetics uses phenotypes to deduce the functions of genes. Breeding experiments can then check these inferences. In this way, early geneticists were able to trace inheritance patterns without any knowledge of molecular biology.

Phenotypic variation (due to underlying heritable genetic variation) is a fundamental prerequisite for evolution by natural selection. The fitness of an organism is a high-level phenotype determined by the contributions of thousands of more specific phenotypes. Without phenotypic variation, individual organisms would all have the same fitness, and changes in phenotypic frequency would proceed without any selection (randomly).

The interaction between genotype and phenotype has often been conceptualized by the following relationship:

genotype + environment phenotype

A slightly more nuanced version of the relationships is:

genotype + environment + random-variation phenotype

An example of the importance of random variation in phenotypic expression is Drosophila flies in which number of eyes may vary (randomly) between left and right sides in a single individual as much as they do between different genotypes overall, or between clones raised in different environments.

A phenotype is any detectable characteristic of an organism (i.e., structural, biochemical, physiological and behavioral) determined by an interaction between its genotype and environment (see genotype-phenotype distinction and phenotypic plasticity for a further elaboration of this distinction).

According to the autopoietic notion of living systems by Humberto Maturana, the phenotype is epigenetically being constructed throughout ontogeny, and we as observers do the distinctions that define any particular trait at any particular state of the organism's life cycle.

The idea of the phenotype has been also generalized by Richard Dawkins to include effects on other organisms or the environment in The Extended Phenotype.

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