Genetics: Genetic Diagrams

Genetics: Genetic Diagrams

  • Genetics is a branch of biology that studies genes, genetic variation, and heredity in organisms. In the context of revision, one should understand the role and application of genetic diagrams in genetics.

  • Genetic diagrams are helpful for predicting the possible outcomes of genetic crosses. They give probable combinations of genes in offspring based on the genes of the parents.

  • A mono-hybrid cross involves a single pair of contrasting characteristics. For example, focusing solely on the gene for eye colour.

  • In genetic diagrams, dominant alleles are shown in capital letters (e.g., T) while recessive alleles are shown in lowercase (e.g., t).

  • A Punnett square is a specific type of genetic diagram. It’s a two-by-two grid that displays the four possible combinations of alleles that could occur when the sperm and egg combine.

  • A Punnett square is set up by placing the alleles that one parent could contribute across the top and the alleles the other parent could contribute down the left side. The inside of the square shows the possible combinations.

  • Homozygous means that two alleles at a particular gene locus are the same whereas heterozygous means the two alleles at a gene locus are different.

  • To predict the genotype of the offspring, you need to know the genotype of the parents and understand how the alleles from the parents could combine.

  • Phenotype represents the physical characteristics of an organism that are determined by the genotype or the combination of alleles that an organism has.

  • Co-dominance is the phenomenon where the offspring inherits characteristics from both parents, for example, in some chickens, the feathers are both black and white.

  • Variations in traits are brought about by multiple alleles. This means that particular traits can be influenced by more than two forms of a particular gene.

  • Sex-linked traits are those traits where the genes responsible are present on the sex chromosomes, particularly the X chromosome.

  • Autosomal traits are those traits where genes responsible are present on any chromosome other than sex chromosomes.

  • A test cross can be used to determine the genotype of an individual with a dominant phenotype but unknown genotype. It involves crossing the individual with a homozygous recessive individual and examining the offspring.

  • Lastly, try to solve a variety of problem sets via genetic diagrams to practise applying these concepts as much as possible.