Meiosis and Inheritance

Meiosis and Inheritance

Meiosis and Genetic Variation

  • Meiosis is a type of cell division that produces four genetically distinct haploid gametes.
  • The process involves two rounds of division, meiosis I and meiosis II.
  • Prior to meiosis I, DNA in the parent cell is replicated to form chromatids.
  • In meiosis I, homologous chromosomes separate. Each resulting cell carries a mix of maternal and paternal genes, resulting in genetic variation.
  • In meiosis II, the sister chromatids separate, producing four gametes, each with a unique set of chromosomes.
  • Additional variation arises due to crossing over during prophase I of meiosis, where parts of non-sister chromatids exchange places.
  • As a result of these processes, each gamete is genetically unique, providing the basis for genetic variation within species.

Inheritance Patterns

  • Genes are inherited in pairs, one from each parental gamete.
  • A gene variant is called an allele, and individuals have two alleles (one from each parent) for each gene.
  • The manifestation of a gene’s effect – observable characteristics or phenotypes – depends on the two alleles possessed and how they interact.
  • The types of inheritance pattern include: complete dominance, incomplete dominance, codominance, and sex-linked inheritance.
  • Complete dominance happens when the phenotype of the heterozygote is identical to the dominant homozygote.
  • In incomplete dominance, a heterozygote expresses an intermediate phenotype.
  • In codominance, both alleles express their phenotype fully, without blending.
  • Sex-linked genes are located on sex chromosomes. In humans, most sex-linked genes are on the X chromosome.

Genetic Disorders

  • Inherited disorders are caused by faulty alleles. They may be recessive, requiring two copies of the faulty allele, or dominant, requiring only one.
  • Some genetic disorders include cystic fibrosis, sickle cell anaemia, and haemophilia.
  • Carriers are people who carry one copy of the faulty allele but do not express the associated disorder. They can, however, pass the allele on to offspring.

Punnett Squares

  • A Punnett Square is a diagram used to predict the outcome of a particular cross or breeding experiment.
  • It depicts all possible genetic combinations for the offspring, and probabilities of each.
  • Biologists use Punnett Squares to understand inheritance patterns, predict genetic disorders in offspring, and conduct breeding experiments.