Genetics and Heredity Concepts

Essentials of Genetics

• Genetics is the study of heredity, which is the transmission of traits from parents to offspring.
• Gregor Mendel is considered the founder of genetics, and he published a paper on the topic in 1866.
• A trait is a variant of a character found within a population, such as purple or white flowers in pea plants.

Key Concepts

• An allele is a different variation of the same gene.
• Genes found on sex chromosomes display unique patterns of inheritance.
• Heredity patterns are more complex than Mendel's laws suggest.
• Chromosome behavior helps predict heredity.

Types of Fertilization

• Self-fertilization occurs when sperm-carrying pollen grains released from the stamens land on the egg-containing carpel of the same flower.
• Cross-fertilization occurs when fertilization of one plant is done by pollen from a different plant.

Generations and Breeding

• The P generation refers to the parent individuals from which offspring are derived in studies of inheritance.
• The F1 generation is the offspring of the two parental individuals.
• The F2 generation is the offspring of the F1 generation.
• True breeding refers to organisms for which sexual reproduction produces offspring with inherited traits identical to those of the parents.
• Hybrids are offspring that result from the mating of individuals from two different species or from two true-breeding varieties of the same species.

Gregor Mendel

• Gregor Mendel was a monk from Brunn, Austria.
• He discovered that heritable factors, or genes, are passed down from generation to generation.
• His work in a pea garden led to the foundation of the field of genetics.

Laws of Inheritance

• The law of segregation states that individuals have two alleles for each gene and that when gametes form by meiosis, the two alleles separate, each resulting gamete ending up with only one allele of each gene.
• The law of independent assortment states that when gametes form during meiosis, each pair of alleles for a particular character segregates independently of other pairs.

Garden Pea Flower Anatomy Experiment

• Genotype determines phenotype.

Punnett Square

• A Punnett square is a tool used to show all of the possible allele combinations that parents can pass on to their children for a specific trait.
• It was developed by Reginald C. Punnett in the early 1900's as a tabular tool to predict genetic outcomes.

Crosses

• A monohybrid cross is an experimental mating of individuals that are heterozygous for the character being followed (or the self-pollination of a heterozygous plant).
• A dihybrid cross is an experimental mating of individuals that are each heterozygous for both of two characters (or the self-pollination of a plant that is heterozygous for two characters).