Mendelian Patterns of Inheritance

Genotype

The genetic composition of an individual for a particular gene (TT, Tt, tt)

Homozygous

Both alleles are the same (TT, tt)

Homozygous Recessive

Both alleles are recessive (tt)

Homozygous Dominant

Both alleles are dominant (TT)

Heterozygous

One dominant and one recessive allele (Tt)

Phenotype

Characteristics of an organism that are a result of the expression of the genotype

Locus

The physical location of a gene on a chromosome

Koltreuter’s Blending Inheritance

Inheritance hypothesis that suggests that parental genetic material blends together to make offspring (WRONG)

Inheritance

The acquisition of traits by their transmission from parent to offspring

Lamarkian Inheritance

Inheritance hypothesis that states that traits of the parent obtained during their lifetime would pass on to offspring (WRONG)

Mendel’s Particulate Inheritance

Inheritance hypothesis that states that traits are passed on in discrete particulate units (CORRECT)

True Breeding

A strain that exhibits the same traits after several generations of self-fertilization

Hybridization

When two individuals of the same species with different characteristics are bred with each other through cross fertilization

Single Factor Cross

A cross between individuals that differ in one trait (i.e. height of pea plant)

P Generation

Parental, The true breeding generation for tall and short plants

F1 Generation

Filial 1, The offspring of the P generation

F2 Generation

Filial 2, The offspring of the F1 generation

Monohybrids

Single trait hybrids

1. Traits may exist in two forms: Dominant and recessive

2. An individual carries two genes for a given character, and genes have variant forms (alleles)

3. The two alleles of a gene separate during the process that gives rise to haploid cells and gametes (meiosis), so each sperm and eggs receives only one allele

Mendel’s Law of Segregation (3)

Dominant

The trait that is displayed

Recessive

The trait that is masked by the dominant trait

Test Crosses

A method to determine genotype when all that is known is the phenotype

Chromosome Theory of Inheritance (Law of Segregation)

The law of segregation describes how two homologous chromosomes separate (segregate) during meiosis I to make haploid gametes.

Two Factor Cross

A cross between individuals that differ in two traits (i.e. seed color and shape), making an F1 generation of dihybrids

Dihybrids

Two trait hybrids

Linked Assortment, Independent Assortment

Two possible hypotheses for two factor crosses

Linked Assortment

Two factor cross hypothesis that states that different traits are linked together and the combination doesn’t change from the P generation

Independent Assortment

Two factor cross hypothesis that states that different traits are not linked together and the combination of traits can differ from the P generation

Chromosome Theory of Inheritance (Law of Independent Assortment)

Describes the random distribution of chromosomes between haploid cells

Pedigrees

Diagrams that show trait inheritance over several generations

Autosomal Recessive

The kind of disorder Cystic Fibrosis is, Two unaffected individuals can produce affected offspring and two affected individuals will result in all offspring being affected

Autosomal Dominant

The kind of disorder Huntington Disease is, All affected individuals have at least one affected parent

Hemophilia

Caused by a mutation on the X chromosome (recessive)

Hemizygous

Having one copy of the X chromosome

Since males are hemizygous, they are disproportionately affected

Females with one mutated gene are considered carriers but do not exhibit the affected phenotype

Affected males cannot pass the mutated gene to their male offspring

Characteristics of X-linked recessive inheritance (3)

Vitamin D Resistant Rickets

Caused by a mutation on the X chromosome (dominant)

Females have double the change to inherit a mutated chromosome

Affected males pass the mutated gene to ALL daughters

Homozygote females pass mutates gene to ALL offspring

Heterozygote females have a 50% chance to pass the mutated gene to each of their offspring

Characteristics of X-linked dominant inheritance (4)

Wild Type Allele

The prevalent allele in a given population

Mutant Allele

Alleles that have been altered in some way, either by amount of protein produced or functionality of the protein

Dominant Traits

Tend to have functional/productive proteins that they encode for

Recessive Traits

Tend to have loss-of-function, alternative function, or decreased production

Incomplete Dominance

Heterozygotes that exhibit an intermediate phenotype between the dominant and recessive traits

Co-Dominance

Multiple alleles are expressed simultaneously

Polygenic

Multiple genes with different variations of alleles may interact together to affect one particular characteristic

Epistatic Gene Interaction

The alleles of one gene mask the phenotypic affects of another gene

Discrete Traits

Traits that can be categorized (Eye color, hair color, blood type, etc)

Quantitative/Continuous Traits

Traits that show continuous variation (Height, weight, skin color, metabolic rate)

Probability

The chance that an event will have a particular outcome