Basic Principles of Hereditary

Phenotype

An organism’s physical traits

Genotype

The genetic makeup of an organism.

Alleles

An alternate version of genes that represent genetic diversity in the population.

Locus (loci)

The location of an allele on a chromosome. If changed, the gene will change. 

Homozygous

Alleles that are the same

Heterozygous

Alleles that are for the same trait but different.

Dominate allele

Needs one or two copies to be expressed.

Recessive allele

Must have both copies to be expressed.

Cross

When two individuals are mated with each other

Monohybrid cross

Cross between parents that differ in only one trait.

Dihybrid cross

Cross between parents that differ in only two traits.

Test cross

Cross between two unknown individuals and homozygous recessive individual. 

True breeding parents

Can only pass one allele to their offspring and are either homozygous dominant or homozygous recessive.

Genetic disorders

Disorders that result from certain combinations of alleles passed from parent to offspring and are mostly recessive.

Autosomal chromosomes

Not involved with sex determination in the offspring. (we have 22)

Sex chromosomes

Directly involved w/ sex determination in the offspring

XXY (Klinefelter syn)

Individual looks male but cannot reproduce

XO (Turners syn)

Individual looks like a pre-pubescent female and cannot reproduce.

YO

Organism will die

X-linked genes

Genes located on the sex chromosome that don’t determine sex but are linked to recessive disorders. 

Barr body

Forms on a random X chromosome in females that inactivates it to even out genetic activity between males and females.

Incomplete dominance

One allele is dominant, but the other isn’t recessive, when present both influence the phenotype. 

Multiple alleles (codominance)

Some genes have more than two alleles. Ex. blood type

Polygenic inheritance

Traits are controlled by more than one gene and greatly increases genetic variability.