19.1-.2

Mendelian Genetics

Principles of inheritance first described by Gregor Mendel, suggesting that traits are inherited via dominant and recessive alleles.

Incomplete Dominance

A form of inheritance in which the heterozygote phenotype is intermediate between the two homozygotes.

Codominance

A type of inheritance where both alleles in a heterozygote are fully expressed, resulting in a phenotype that displays characteristics of both alleles.

Multiple Alleles

A situation where more than two alleles exist for a given gene in a population.

Allelic Series

Hierarchy of dominance among multiple alleles of a gene, where some alleles dominate others.

Wild Type

The phenotype or genotype of the standard form found in a natural population, often considered the norm.

X-linked Traits

Traits associated with genes located on the X chromosome, often showing different patterns of inheritance in males and females.

Hemizygous

A condition in which an organism has only one allele for a gene, common in males for X-linked traits.

Reciprocal Cross

A genetic cross in which the sexes of the parents are reversed, which can lead to different offspring ratios.

Carriers

Individuals who carry a recessive allele for a trait but do not display the trait phenotypically.

Punnett Square

A diagram used to predict the genotype and phenotype combinations of a genetic cross.

Phenotype

The observable physical or biochemical characteristics of an organism, determined by both genetic makeup and environmental influences.

Genotype

The genetic constitution of an individual, represented by the alleles inherited for a particular gene.

Polygenic Inheritance

A type of inheritance where multiple genes contribute to a single trait, resulting in a range of phenotypes.

Epistasis

A form of gene interaction where one gene's expression is affected by the presence of one or more other genes.

Pleiotropy

A phenomenon where a single gene influences multiple phenotypic traits.

Linkage

The tendency of genes located close together on a chromosome to be inherited together during cell division.

F1 Generation

The first filial generation of offspring resulting from a cross between two parental (P) individuals.

F2 Generation

The second filial generation, which results from a cross of the F1 individuals.

Test Cross

A genetic cross between an individual with an unknown genotype and a homozygous recessive individual to determine the unknown genotype.

Autosomal Traits

Traits governed by genes located on non-sex chromosomes, affecting both males and females equally.

Dominant Allele

An allele that expresses its phenotype even in the presence of a recessive allele.

Recessive Allele

An allele that only expresses its phenotype when in a homozygous condition.

Homozygous

An organism with two identical alleles for a specific gene.

Heterozygous

An organism with two different alleles for a specific gene.

Lethal Alleles

Alleles that can lead to the death of an organism when expressed in certain genotypes.

Genetic Drift

A mechanism of evolution involving random changes in allele frequencies within a population.

Mutation

A change in the DNA sequence that can create new alleles in a population.

Natural Selection

The process by which organisms better adapted to their environment tend to survive and produce more offspring.

Founder Effect

A phenomenon where a small group of individuals establishes a new population, leading to reduced genetic variation.

Self-Pollination

The transfer of pollen from the anthers to the stigma of the same flower or to another flower on the same plant, leading to offspring that are genetically similar to the parent.

Cross-Pollination

The transfer of pollen from the anthers of one flower to the stigma of a different flower, promoting genetic variation among offspring.

Heterozygote Advantage

A phenomenon where individuals heterozygous for a particular trait have a higher fitness and adaptability compared to homozygous individuals.

Genetic Linkage Map

A representation of the relative positions of genes on a chromosome based on recombination frequencies used in genetic research.

Polygenic Trait

A trait that is influenced by multiple genes, often leading to a continuous range of phenotypes, such as skin color or height.

Quantitative Trait Locus (QTL)

A section of DNA that correlates with variation in a phenotype (trait) that is typically quantitatively measured.

Hybrid Vigor

The improved biological function observed in the offspring of genetically distinct parents, often resulting in increased survival and reproduction.

Sex-linked Traits

Traits that are controlled by genes located on sex chromosomes, commonly observed in X-linked inheritance patterns.

Chromosomal Aberrations

Structural changes in chromosomes that can lead to genetic disorders or abnormal traits.

Gene Pool

The total genetic diversity found within a population, encompassing all alleles present at all gene loci.