Solving Pedigree Analysis in 3 steps

The information from a pedigree makes it possible to determine how certain alleles are inherited: whether they are dominant, recessive, autosomal, or sex-linked. To start reading a pedigree: Determine whether the trait is dominant or recessive. If the trait is dominant, one of the parents must have the trait.

Pedigrees can show someone is a carrier for diseases by determining which parent, if not both, is either dominant or recessive. Each child must have a letter from their parent then that will determine if someone gets a disease or not then it goes on from generation to generation.

​Pedigree. A pedigree is a genetic representation of a family tree that diagrams the inheritance of a trait or disease though several generations. The pedigree shows the relationships between family members and indicates which individuals express or silently carry the trait in question.

Pedigrees are normally used to represent simple dominant and recessive traits. For example, having a widow’s peak hairline is dominant. However, they can be carriers of the trait, and if they are carriers, their male children will be colorblind.

1. First: Look for Mitochondrial Inheritance.
2. Second: Look if the gene is Dominant, Recessive.
3. Third: Look if the disease is X-linked or Autosomal or Y-linked.
4. Codominant Inheritiance.

Crude penetrance estimates can be derived by dividing the observed number of diseased (penetrant) individuals by the number of obligate carriers (penetrant as well as obligate non-penetrant, that is, normal individuals with several affected offspring or normal individuals with affected parent and child).

In an ideal world, the right way to estimate penetrance would be to ascertain, from birth, a large cohort of people with a particular genotype, follow them until all have died of something or other, and then ask how many ever developed the disease before they died.

Genetic interaction is the set of functional association between genes. One such relationship is epistasis, which is the interaction of non-allelic genes where the effect of one gene is masked by another gene to result either in the suppression of the effect or they both combine to produce a new trait (character).

Penetrance measures the proportion of individuals in a population who carry a specific gene and express the related trait.

If the syndrome is 70% penetrant, what does this mean? a) on average, people who have this syndrome will develop 70% of the hallmarks that characterize the syndrome. b) each child of an affected parent has a 70% chance of also developing the syndrome.

Penetrance refers to the probability of a gene or trait being expressed. In some cases, despite the presence of a dominant allele, a phenotype may not be present. One example of this is polydactyly in humans (extra fingers and/or toes).

Mutation type and penetrance. Incomplete penetrance may be due to the effect of the type of mutation. Some mutations of a given disease may exhibit complete penetrance, where as others in the same gene show incomplete or very low penetrance.

Penetrance in genetics is the proportion of individuals carrying a particular variant (or allele) of a gene (the genotype) that also express an associated trait (the phenotype). The penetrance is 100%.

Penetrance refers to the proportion of people with a particular genetic change (such as a mutation in a specific gene) who exhibit signs and symptoms of a genetic disorder. If some people with the mutation do not develop features of the disorder, the condition is said to have reduced (or incomplete) penetrance.

Expressivity is the degree to which trait expression differs among individuals. Unlike penetrance, expressivity describes individual variability, not statistical variability among a population of genotypes.

Penetrance is used to describe whether or not there is a clinical expression of the genotype in the individual. Expressivity is the term that describes the differences observed in the clinical phenotype between two individuals with the same genotype.

Modifier genes can affect penetrance, dominance, and expressivity….Nonetheless, research has shown that variable phenotypes can be caused by a number of factors, including the following:

• Modifier genes.
• Environmental factors.
• Allelic variation.
• Complex genetic and environmental interactions.

Phenotype is the observable physical or biochemical characteristics of an individual organism, determined by both genetic make-up and environmental influences, for example, height, weight and skin colour.

So, if you have a patient, whose genotype is SS, we will transplant cells that are AA from a normal person; the cells in the person will start producing AA. In this unit, you can change the genotype of a child or an individual from sickle cell to AA.

AS and SS shouldn’t think of marrying. And definitely, SS and SS must not marry since there’s absolutely no chance of escaping having a child with the sickle cell disease. The only thing that can change the genotype is the bone marrow transplant (BMT).

A homozygous dominant (AA) individual has a normal phenotype and no risk of abnormal offspring. A homozygous recessive individual has an abnormal phenotype and is guaranteed to pass the abnormal gene onto offspring.

AB negative