Chapter 2: Mendelian Genetics and Monohybrid Crosses

Characters

Observable traits controlled by genes. (color, shape, length, position, etc)

Traits

Different forms of a character.

Monohybrid Cross

Cross studying one character's contrasting traits.

Punnett Square

Diagram predicting offspring genotypes from crosses.

Test Cross

Cross to determine genotype of dominant phenotype.

1:1

Dihybrid Cross

Cross studying two independent characters simultaneously. Most often when both parents are heterozygous for both characteristics.

Independent Assortment

Genes segregate independently during gamete formation. Characters controlled by loci on separate chromosomes, and the events that occur in metaphase and anaphase of meiosis I

Branch Diagram

Visual tool for calculating phenotypic ratios from a dyhybird cross.

Trihybrid Cross

Cross studying three characters simultaneously.

Meiosis

Cell division producing gametes with half chromosomes.

Gregor Mendel

Father of genetics, studied pea plant inheritance.

Unit Factors

Genes that determine traits, exist in pairs.

Dominant Trait

Trait expressed when at least one allele is present.

Recessive Trait

Trait expressed only when two alleles are present.

Homozygous

Individual with two identical alleles for a gene.

Heterozygous

Individual with two different alleles for a gene.

Phenotype

Physical expression of an organism's genotype.

Genotype

Genetic makeup of an individual.

Alleles

Different versions of a gene.

Locus

Specific location of a gene on a chromosome.

Segregation

Separation of alleles during gamete formation to each receive equal likelihood.

Mendelian Ratios

Expected ratios of phenotypes from genetic crosses.

Mendelian phenotypic ratio for the test-cross will be 1:1

F1 Generation

First filial generation from parental cross.

F2 Generation

Second filial generation from F1 self-cross.

Mendel's Postulates

Fundamental principles of inheritance proposed by Mendel.

Chromosomal Theory of Heredity

Genes are located on chromosomes, inherited in pairs.

Gametes

Reproductive cells that carry alleles.

Cross-Fertilization

Mating between different individuals to combine traits.

Polymorphic

Genes with multiple alleles in a population.

true-breeding

term used to describe organisms that produce offspring identical to themselves if allowed to self-pollinate (garden pea plants)

polymorphic

genes and loci with multiple versions

Mendel's law of segregation

unit factors (alleles) are segregated when the paired homologous chromosomes are separated during anaphase 1 of meiosis

product rule

two independent events occur simultaneously, the combined probability of the two outcomes is equal to the product of their individual probabilities of occurrence