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Blue Eyes Secret behind blue eyes: Take a tour of heredity Have you ever wondered why people resemble their parents? The answer to this and other questions about inheritance lies in a specialized branch of biology called Heredity. Understanding the role of heredity in disease has become a central part of medical research. Gaining knowledge towards heredity and its concepts will provide an unparalleled insight into the factors which control all heritable aspects of human biology.

Learning Objectives

After completing the topic, the student will be able to:

  • Discover and discuss how we share some genes and physical traits with our parents and our other relatives.
  • Define and discuss the term heredity and understand the principles behind it.
  • Contrast haploid and diploid chromosome number in humans.
  • Define and discuss the terms: allele, gene, genotype, phenotype, P, F1, F2 generation , homozygous and heterozygous condition.
  • Discriminate asexual reproduction and sexual reproduction and their impact on genetic variation.
  • Define and differentiate the terms mitosis and meiosis.
  • Explore the significance of meiosis.
  • Understand and explore the molecular details of meiosis and how it reduces the number of chromosomes in the parent cell by half and produces four gamete cells.
  • Inspect what happens if meiosis goes wrong and predict the consequences if meiosis does not occur in the organisms.
Heredity Heredity - Passing of traits from parent to offspring In humans, eye color is an inherited characteristic. The traits such as brown, blue or grey eyes; black, brown or blond hair are transmitted from parents to offspring through discrete heritable units called "genes" which can be sorted and passed along, generation after generation, in undiluted form.

The most fundamental property of all living things is the ability to reproduce. All organisms inherit the genetic information specifying their structure and function from their parents. How genetic information is replicated and transmitted from cell to cell and organism to organism thus represents a question that is central to all of biology.

It has long been noted that offspring resemble their parents in many ways, and that many traits are passed from one generation to the next. This is evident in the physical similarities of siblings, and in offspring and their parents.

Although there are definite similarities between parents and offspring (and between offspring), there is also variation. After all, children never look entirely like either of their parents, because they have inherited traits from both parents.

Variation is the phenomenon where offspring differ somewhat in appearance from parents and siblings. The transmission of traits from one generation to the next is called inheritance, or heredity. Genetics is the scientific study of heredity and hereditary variation.

For example, in humans, eye color is an inherited characteristic and an individual might inherit the "brown–eye trait" from one of the parents. Inherited traits are controlled by genes and the complete set of genes within an organism's genome is called its genotype. A phenotype is the composite of an organism's observable characteristics or traits, such as its morphology.

Structure of a gene Structure of a gene A gene is a locatable region of genomic sequence, corresponding to a unit of inheritance, which is associated with regulatory regions, transcribed regions and/or other functional sequence regions. This stylistic diagram shows a gene in relation to the double helix structure of DNA and to a chromosome (right). The chromosome is X–shaped because it is dividing. Introns are regions often found in eukaryote genes that are removed in the splicing process (after the DNA is transcribed into RNA). Only the exons encode the protein. This diagram labels a region of only 50 or so bases as a gene. In reality, most genes are hundreds of times larger.
Genes control our lives

Offspring acquire genes from parents by inheriting chromosomes. In next chapters, we will examine how chromosomes are passed from parents to offspring, and how this process gives rise to genetic variation in offspring.

Dawkins defines the word 'gene' to mean "an inheritable unit" instead of the generally accepted definition of "a section of DNA coding for a particular protein". In River Out of Eden, Dawkins further refined the idea of gene–centric selection by describing life as a river of compatible genes flowing through geological time.

Scoop up a bucket of genes from the river of genes, and we have an organism serving as temporary bodies or survival machines. A river of genes may fork into two branches representing two non–interbreeding species as a result of geographical separation. The concept of the gene has changed considerably from "unit of inheritance" to a DNA–based unit that can exert its effects on the organism through RNA or protein products.

It was also previously believed that one gene makes one protein; this concept has been overthrown by the discovery of alternative splicing and trans–splicing where in a single gene can contribute to formation of multiple proteins. Evidence is also accumulating that the control regions of a gene do not necessarily have to be close to the coding sequence on the linear molecule or even on the same chromosome.

The concept that genes are clearly delimited is also being eroded. There is evidence for fused proteins stemming from two adjacent genes that can produce two separate protein products. Even more ground–breaking than the discovery of fused genes is the observation that some proteins can be composed of exons (nucleic acid sequence in DNA which actually codes for a specific portion of the complete protein) from far away regions and even different chromosomes.

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