Inheritance

Chapter 1: Basics of Inheritance

• Inheritance refers to the passing of genetic traits from parent organisms to their offspring.
• Every individual organism has two sets of chromosomes; one from the father and one from the mother.
• The combination of these sets result in variations in traits seen in the offspring.
• Sex determination in humans is controlled by one of the 23 pairs of chromosomes, known as the sex chromosomes (XX for females, XY for males).

Chapter 2: Genotype and Phenotype

• The genotype is the set of genes in an organism’s DNA responsible for a particular trait.
• The phenotype is the actual physical properties of the organism, like height, colour of eyes, etc.
• The phenotype is determined by an individual’s genotype and environmental factors, highlighting the concept of nature versus nurture.

Chapter 3: Dominant and Recessive Traits

• Traits are controlled by genes present on the chromosomes; a dominant gene will always express itself while a recessive gene will only express itself when its pair is also recessive or absent.
• Dominant genes override the characteristics that recessive genes would show.
• Homozygous dominant (both genes are dominant) or heterozygous (one dominant and one recessive gene) organisms will show the dominant trait.
• The recessive trait will only be visible in homozygous recessive (both genes are recessive) organisms.

Chapter 4: Genetic Crosses

• Genetic crosses can be represented using Punnett squares to predict the genotype and phenotype of the offspring.
• In a monohybrid cross, a single characteristic is worked out. For example, having blue or brown eyes.
• A dihybrid cross is when two characteristics are worked out at the same time.

Chapter 5: Genetic Disorders

• Genetic disorders are caused by changes, or mutations, in DNA. These changes can affect individual genes or chromosomes.
• Autosomal genetic disorders are caused by mutations in genes on the autosomes, while sex-linked genetic disorders are caused by mutations in genes on the sex chromosomes.
• Example of autosomal genetic disorders is cystic fibrosis, caused by a recessive allele on one of the non-sex chromosomes.
• An example of a sex-linked disorder is haemophilia, which is caused by a recessive allele on the X chromosome.

Chapter 6: Evolution and Natural Selection

• Evolution is the change in inherited characteristics of a species over time through the process of natural selection.
• Natural selection involves variations in the population, overproduction of offspring, and survival of the fittest.
• The individuals with the most favourable variations have a better chance of survival and are more likely to reproduce, passing these favourable traits onto their offspring.