Mendelian Genetics and Inheritance Patterns

Law of Segregation

two 'factors' control each trait

Principle of Dominance

one 'factor' will dominate the other

Law of Independent Assortment

factors controlling different characteristics are inherited independently of each other

F1 Phenotype Ratio

3:1

F2 Phenotype Ratio

9:3:3:1 phenotype ratio

Sex-Linked Traits

Traits controlled by genes on sex chromosomes

X-linked Traits

traits on the X chromosome

Males (XY)

have only one X chromosome = only 1 allele for any X-linked trait

Recessive X-linked Allele

is ALWAYS expressed in MALES; X-linked recessive alleles are less common in females

Codominance

both alleles expressed EQUALLY in a heterozygote

Incomplete Dominance

a completely dominant allele; the heterozygous phenotype is somewhere in between the two parental phenotypes

Multiple Alleles

Many genes have more than two alleles

Human Blood Type

is controlled by three alleles

Mendelian Genetics

the study of how traits are inherited from parents to offspring based on the principles discovered by Gregor Mendel.

Trait

a genetically determined characteristic

Phenotype

the trait or characteristic determined by the organism

Physical Phenotype

the observable physical traits or characteristics of an organism, resulting from the interaction of its genotype (genetic makeup) with the environment

Genotype

the combinations of alleles

Punnett Square

Diagram that shows the cross between parents and the potential offspring genotypes, Read the diagram and report expected genotypes and phenotypes as a percentage

Probability

how likely something is to happen

Ratio

shows how many times one number contains another

Genotype Ratio

number of homozygous dominant: number of heterozygous: number of Homozygous Recessive - pp

Phenotype Ratio

9 - 3 - 3 - 1

Homozygous Dominant

PP

Heterozygous

Pp

Dominant

will be expressed even if only one copy is present

Recessive

has to have two copies to be present

Monohybrid Cross

shows the expected inheritance pattern of one trait

Allele

versions of the same gene

Gene

a segment of DNA that carries the instructions for building proteins

Dihybrid Cross

shows the expected inheritance of TWO characteristics, Use 'FOIL' to determine the parents' gametes