Mendelian Gentics and patterns of inheritance

Phenotype

Physical appearance of an organism

Genotype

Genetic makeup for that organism

Locus

The specific site a gene occupies in the chromosome

Alleles

Different forms or versions of a particular gene

Dominant

Stronger version of a pair of alleles that shows its effect even if there is only one copy in the genome

Recessive

The allele of a gene shows its effect only if there are two copies in the genome

Homozygous

An individual that carries two identical alleles for a locus

Heterozygous

Two alleles for a locus are different

True-breeding

Offspring produced from self-fertilization remained uniform from one generation to the next

F1 generation

Offspring that resembled one of the parents in all cases

F2 generation

Exhibits a 3:1 ratio of both traits

Mendelian ratio

The 3:1 ratio observed in the F2 generation for a monohybrid cross

Testcross

To determine genotype of dominant trait by crossing an individual with unknown genotype with a homozygous recessive genotype

Principle of segregation

Alternative alleles for a character segregate during gamete formation and are joined at random during fertilization

Dihybrid crosses

Mating between individuals with different alleles at two loci

Principle of independent assortment

Two or more genes assort independently during gamete formation

Punnett square

Predicts the ratios of the various offspring of a cross

Pedigree

A consistent graphical representation of matings and offspring over multiple generations for a particular trait

Carriers

Heterozygotes (normal phenotype) that may transmit the recessive allele to their offspring

Hardy-Weinberg Principle

Mathematically predicts allele and genotype frequencies for a population that is not evolving

Genetic equilibrium

Population with no net change in allele or genotype frequencies over time

Hardy-Weinberg equation

p + q = 1, where p is the frequency of the dominant allele and q is the frequency of the recessive allele

Genotype frequencies

Described by the relationship: p2 + 2pq + q2 = 1

Conditions for Hardy-Weinberg equilibrium

Not-evolving population and ideal situations that seldom occur in the natural world

Multifactorial

Many factors, both genetic and environmental, collectively influence phenotype

Dominant inheritable disorders

Juvenile glaucoma, dwarfism, Huntington's Disease

Recessive inheritable disorders

Albinism, cystic fibrosis, sickle-cell disease, dwarfism, Huntington's Disease