Genetic VocabularyGenetic Vocabulary

Genotype:Genotype: The types of the genes of The types of the genes of an organisman organism

Phenotype:Phenotype: The observable The observable characteristics of an organismcharacteristics of an organism

Dominant Gene:Dominant Gene: A gene which, when A gene which, when present on a chromosome, passes on present on a chromosome, passes on a certain physical characteristic.a certain physical characteristic.

Recessive Gene:Recessive Gene: A gene that is A gene that is inferior to another gene that controls inferior to another gene that controls the same trait (the dominant gene). the same trait (the dominant gene). The inferior gene does not get The inferior gene does not get expressed in the presence of a expressed in the presence of a dominant gene. dominant gene.

AlleleAllele: Location of a gene on a : Location of a gene on a chromosomechromosome

HomozygousHomozygous: The state of having two : The state of having two identical alleles of a particular gene (eg identical alleles of a particular gene (eg AA, aa). AA, aa).

HeterozygousHeterozygous: The state of having two : The state of having two different alleles of a particular gene (eg different alleles of a particular gene (eg Aa)Aa)

The Fundamental Question

What is the relationship between genes (genotype) and observable characteristics (phenotype)?

The answer?

Phenotype = Genotype + Environment.

Genes and Environment Determine Characters

Genetically identical hydrangeas growing in soils of different acidity (different environments).

The phenotype = genotype + environment principle applies equally to human traits.

Genes, Alleles, and Chromosomes

Consistency is Good

Characters investigated by Mendel

No matter what the character, Mendel observed a 3:1 ratio of characters in the F2.

Monohybrid Crosses Yielded Consistent Results

Therefore, the Principle of Segregation indeed is a general principle of genetics.

What Works for Peas Also Works for Humans

An albino woman

In the cross Aa x Aa, where A is a dominant allele for wild type (standard) pigmentation and a is a recessive allele for no pigmentation (albinism), ¾ of offspring will be wild type and ¼ will be albino.

Are Different Characters Like Color and Shape Inherited Together or Inherited Independently?

Mendel performed dihybrid crosses to find out.

Mendel’s conclusion: Different characters are inherited independently.

Simple Dominance Inheritance – When one trait is determined by one type of gene.

List of Simple Dominance Genes:Tongue Rolling Blue vs. Brown EyesEar-Lobes Arm CrossingHand Folding PTC

Multi-Gene Inheritance – When one trait is determined by many genes.

List of Multi-gene Inheritances:Height Skin pigmentationWeight Metabolism

Incomplete Dominance – two different alleles both possess dominance, resulting in a mixture of the alleles’ traits.

Examples:Green Eyes Wavy HairPink Roses

Co-Dominance – Two different alleles both possess dominance, but the resulting trait features both phenotypes

Examples:Type AB Blood Spots

Sample problems:

A Brown-eyed man whose mom was blue-eyed marries a woman with blue eyes. What is the probability of have a daughter with blue eyes?

What two types of eye color could you cross, that could produce offspring with the 3 types of eye colors?

A black dog marries a white dog what are the chances that they will produce a puppy with spots?