HER - Heredity [OVERVIEW]

Heredity

Introduction

heredityYou may have noticed in your lifetime that traits run in families. For instance, members of a family may share similar facial features, hair color (like the mother and daughter to the right), or a predisposition to health problems such as diabetes. Characteristics that run in families often have a genetic basis, meaning that they depend on genetic information a person inherits from his or her parents. What if you wanted to figure out how genetic information is transmitted between generations? For instance, you might be curious how traits can "skip" a generation, or why one child in a family may suffer from a genetic disease while another does not. How could you go about asking these kinds of questions scientifically? Gregor Mendel first asked these questions in the nineteenth century. Since then, we have acquired a vast array of knowledge surrounding the process of creating gametes, mixing up genes, and attempting to predict phenotypes of offspring based on the alleles of the parents. In this lesson, we will discuss all of the above and add a mathematical analysis to help answer the question of how different two data sets are from each other.

List of Lessons

In this module, we will study the following topics:

    1. Reproduction and Meiosis – this lesson will cover the two major types of reproduction, the phases of meiosis, and processes that occur during meiosis to ensure genetic variety is maximized.
    2. Errors in Meiosis – this lesson discusses common errors in meiosis – both nondisjunction and chromosomal level.
    3. Mendelian Inheritance – this lesson discusses Gregor Mendel’s contribution to the study of heredity and Punnett squares based on these methods.
    4. Non-Mendelian Inheritance – this lesson covers deviations from Mendel’s model such as polygenic inheritance, multiple alleles, codominance, sex-linked inheritance, incomplete dominance, and pleiotropy.
    5. Genetic Linkage – this lesson covers the violation of the law of independent assortment that occurs when genes are located on the same chromosome pair.
    6. MATH Chi-square Statistics – this lesson covers the major statistical test of AP Biology to allow comparison of a data set to an expected data set.
    7. Environmental Effects – this lesson discusses the effect the environment can have on gene expression and phenotypes.

Module Objectives

By the end of this module, students will be able to:

  • Explain how meiosis results in the transmission of chromosomes from one generation to the next.
  • Describe similarities and/ or differences between the phases and outcomes of mitosis and meiosis.
  • Explain how the process of meiosis generates genetic diversity.
  • Explain the inheritance of genes and traits as described by Mendel’s laws.
  • Explain deviations from Mendel’s model of the inheritance of traits.
  • Explain how the same genotype can result in multiple phenotypes under different environmental conditions.
  • Explain how chromosomal inheritance generates genetic variation in sexual reproduction.

Key Terms

Allele -­ one of two or more forms of a gene.

Codominance - occurrence when both alleles are visible in the phenotype.

Complete Dominance - occurrence when if both the dominant and recessive alleles are present in the genotype, only the dominant allele will be visible in the phenotype. The recessive condition is only evident when the dominant allele is absent.

Dihybrid - cross between individuals of two traits of interest.

Epistasis - occurrence where the effect of one gene are modified by one or several other genes.

Homologous Chromosomes - pair of maternal and paternal chromosomes carrying the genes for the same traits; same length, centromere position, and staining patterns.

Incomplete Dominance - occurrence when phenotype represents an intermediate condition of the two alleles.

Law of Independent Assortment - during meiosis, alleles segregate into cells regardless of the movement of alleles for other traits.

Law of Segregation - during meiosis, maternal and paternal alleles separate in the formation of gametes.

Linked Genes - genes that tend to be inherited together based on their relative distance to each other on the same chromosome.

Monohybrid - cross between individuals of one trait of interest.

Multiple alleles - a specific trait has more than two alleles that contribute to the genotype and phenotypic condition.

Pleiotropy - occurrence when one gene influences the phenotype of many traits.

Polygenic inheritance - multifactoral inheritance; when a single trait is controlled by two or more alleles.

Principle of dominance - Mendel's observation that traits have variations where one may mask the effect of the other.

Probability - mathematical study of possible outcomes given specific events.

Sex linked traits - the expression of an allele is related to sex of an individual as the genes of interest are located on the X chromosome.

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