Genetic Inheritance

Join now

If you're ready to pass your A-Level Biology exams, become a member now to get complete access to our entire library of revision materials.

Join over 22,000 learners who have passed their exams thanks to us!

Sign up below to get instant access!

Join now →

Or try a sample...

Not ready to purchase the revision kit yet? No problem. If you want to see what we offer before purchasing, we have a free membership with sample revision materials.

Signup as a free member below and you'll be brought back to this page to try the sample materials before you buy.

Download the samples →
  • Genetic inheritance is considered to be one of the basic principles of genetics which also describes the process of how characteristics are being passed on from generation to generation. Genetic inheritance takes place due to the passage of genetic material (DNA) from parents to their progeny.
  • During reproduction, the DNA that is being passed down from the parents contain all the necessary information for the survival, growth and reproduction of the next generation. Much of the insight we share regarding the inheritance began when Gregor Mendel, a monk, started experiments in this field. His ‘Laws of Inheritance’ and experiments lay the groundwork for modern genetics.
  • During sexual reproduction, genetic materials present in both parents combine and pass onto a single individual. Though the individual receives genetic materials from both parents, certain genes belonging to each parent will end up dominating the expression of various traits.

Alleles, Genotype and Phenotype

  • Genotypes and alleles are primary basics of genetics. An allele is referred to as a particular variety of a gene. The composition of two alleles each obtained from a parent is called the genotype. The physical expression of this is known as the phenotype. The two specific combination of alleles (genotype) have an impact on the physical expression (phenotype) of an organism.
  • Upon completing his experiments on pea plants, Gregor Mendel started crossing various traits of one characteristic like the colour of flowers. Genetically speaking, the variations in traits, for e.g., white or purple flowers occur due to different alleles.
  • In many instances within the world of plants and animals, individuals end up having two alleles for every gene, one from the paternal side and the other from the maternal side. An individual’s gene expression is dependent on the alleles received by them. For instance, if both parents have brown eyes and pass the brown-eye alleles to their offspring, their progeny will also receive the alleles for brown eyes.
  • Certain alleles are capable of dominating the expression of a specific gene. For e.g., if a baby has received a green-eye allele from his father and a brown-eye allele from his mother, the baby will have brown eyes since the green-eye allele is not dominant over the brown-eye allele. In this particular instance, the brown-eye allele is called the ‘dominant’ allele and the green-eye allele is called the ‘recessive’ allele.
  • The genetic blend of two alleles is called the genotype. For example, if a child receives one blue-eye allele represented by ‘B’ and one green-eye allele represented by ‘b’, then the genotype will be ‘Bb’. However, if the child receives two blue-eye alleles, ‘BB’ would be the genotype. If the child has two green-eye alleles, the genotype will be ‘bb’. As explained before, if the blue-eye allele is dominant over the green-eye allele, a child with the ‘Bb’ genotype would have blue eyes in theory rather than green or a mix of both green and blue. When two alleles are same in a genotype, i.e. ‘bb’ and ‘BB’, they are called homozygous genotypes. Genotypes that have two different alleles are called heterozygous genotypes.
  • The environment could also influence the phenotype allowing the expression of certain alleles in some environments only and not in others. As a result, two people living in different environments with the same genotype could exhibit different phenotypes.
  • Punnett squares are useful tools for identifying the possible outcomes of genotypes and phenotypes of the offspring of two adult individuals. This is also beneficial in recognizing the probability of the progeny’s expression with regard to certain traits. Punnett squares were discovered in the twentieth century and named after its creator, Reginald Punnett.