Mendelian and Chromosomal Inheritance Lecture Review

Comprehensive vocabulary flashcards covering basic genetics, Mendelian laws, blood groups, and the chromosome theory of inheritance based on provided lecture notes.

Pisum sativum

The scientific name for the garden pea plant selected by Gregor Mendel for his genetic studies.

Either-or features

Distinct, observable alternative traits in pea plants, such as purple or white flowers, which made them ideal for Mendel's research.

Short generation time

A practical reason for choosing pea plants, as they grow quickly from seed to maturity.

Large number of offspring

A feature of pea plant mating that allowed Mendel to collect statistically reliable data.

Strict control over mating

Enabled by pea plants' enclosed flowers, allowing Mendel to choose between self-pollination and manual cross-pollination.

Removing immature stamens

The manual method Mendel used to prevent self-pollination and facilitate controlled cross-pollination.

Character

A heritable feature that varies among individuals, representing a general category like flower position or eye color.

Trait (Variant)

Each specific state or version of a character, such as Axial flowers or White eyes.

Axial

A trait or variant for the character of flower position in pea plants.

Terminal

A trait or variant for the character of flower position in pea plants.

Red eye color

The wild type trait for eye color in fruit flies.

White eye color

The mutant trait for eye color in fruit flies.

Self-pollination

A process where pollen from the stamens lands on the carpel of the same flower or another flower on the same plant.

Cross-pollination

The transfer of pollen from one plant to the carpel of a completely different plant.

Blending Model

An incorrect historical hypothesis suggesting that inheritance works like mixing paint, where distinct traits merge permanently.

Intermediate seeds

The predicted, non-existent result of the blending model for crossing Round and Wrinkled seeds, where all offspring would be slightly wavy.

Pale pink flowers

The predicted, non-existent result of the blending model for a cross between Purple and White flowers.

Genotype

The underlying genetic makeup or specific set of alleles an organism carries, such as $BB$, $Bb$, or $bb$.

Phenotype

The organism's physical appearance or observable physiological traits, such as brown eyes.

Dominant Phenotype

A trait that is fully visible even if the organism carries only one copy of the corresponding allele.

Recessive Phenotype

A trait that remains physically hidden unless an organism carries two copies of the recessive allele.

Homozygous

Having two identical alleles for a given gene, such as $PP$ or $pp$.

Heterozygous

Having two different alleles for a given gene, such as $Pp$.

The Law of Segregation

States that the two alleles for a heritable character separate during gamete formation and end up in different gametes.

Monohybrid Cross

A cross between two individuals that are heterozygous for one specific character.

Phenotypic Ratio ($Pp \times Pp$)

$3$ Purple : $1$ White ($3/4$ dominant, $1/4$ recessive).

Genotypic Ratio ($Pp \times Pp$)

$1$ $PP$ : $2$ $Pp$ : $1$ $pp$ ($1:2:1$).

The Law of Independent Assortment

States that two or more genes assort independently, meaning each pair of alleles segregates independently of any other pair during gamete formation.

Dihybrid Cross

A cross involving two individuals that are heterozygous for two different characters.

Phenotypic Ratio ($YyRr \times YyRr$)

$9$ Yellow-Round : $3$ Yellow-wrinkled : $3$ green-Round : $1$ green-wrinkled ($9:3:3:1$).

Testcross

Breeding an individual with an unknown dominant phenotype with a homozygous recessive individual to determine the unknown genotype.

Homozygous Dominant Testcross Result

Produces offspring that are $100\%$ dominant phenotype and all have the $Pp$ genotype ($1:0$ ratio).

Heterozygous Testcross Result

Produces offspring in a $1:1$ phenotypic ratio ($1$ dominant : $1$ recessive).

Alleles

Alternative versions of a gene that account for variations in inherited characters.

Dominant Allele

The version of a gene that determines the organism's appearance when present.

Recessive Allele

The version of a gene that has no noticeable effect on appearance when a dominant allele is present.

Allele limit in individuals

An individual organism can inherit a maximum of only two alleles per gene (one from each parent).

Multiple Alleles

The phenomenon where a single gene can have dozens of alternative versions within a wide population.

Non-functional protein

The typical product of a recessive allele, which is often masked by the functional protein of a dominant allele.

Polydactyly

The condition of having extra fingers or toes, caused by a dominant allele that is rare in the human population.

Dominance (Definition)

Refers to how alleles interact when combined, not how frequently they appear in a population.

Complete Dominance

The phenotypes of the heterozygote ($Pp$) and the dominant homozygote ($PP$) are indistinguishable.

Incomplete Dominance

Neither allele is completely dominant, resulting in an $F_1$ hybrid with an intermediate, blended phenotype.

Snapdragons

Plants that exhibit incomplete dominance, where Red ($C^RC^R$) and White ($C^WC^W$) parents produce Pink ($C^RC^W$) offspring.

Codominance

Two dominant alleles both alter the phenotype in separate, distinguishable ways, and both are fully expressed simultaneously.

MN blood group

An example of codominance where both alleles are fully expressed in the heterozygote.

Roan coat color

An example of codominance in cattle where white and red hairs grow side-by-side.

Indistinguishable heterozygote

In complete dominance, the $Pp$ individual looks exactly like the $PP$ parent.

Intermediate mixture

The appearance of a heterozygote in incomplete dominance, appearing as a quantitative blend of the parents.

ABO Blood Group Alleles

There are three alleles in the human population for this trait: $I^A$, $I^B$, and $i$.

Type A Genotypes

$I^AI^A$ or $I^Ai$.

Type B Genotypes

$I^BI^B$ or $I^Bi$.

Type AB Genotype

$I^AI^B$.

Type O Genotype

$ii$.

Relationship between $I^A$ and $i$

$I^A$ is completely dominant over $i$.

Relationship between $I^B$ and $i$

$I^B$ is completely dominant over $i$.

Relationship between $I^A$ and $I^B$

These alleles are codominant to one another.

Polygenic Inheritance

Occurs when two or more distinct genes work together to dictate a single phenotypic character.

Pleiotropy

The opposite of polygenic inheritance; it is not the focus of this lecture but is mentioned for contrast.

Continuous gradient

A bell-curve distribution of traits in a population, characteristic of polygenic inheritance.

Polygenic examples

Human skin color, height, and eye color.

Wild Type

The phenotype most commonly observed in natural populations, often denoted with a "$\text{+}$" sign.

Mutant

Phenotypes that represent alternatives to the wild type due to changes or mutations in the allele.

Huntington's disease

A condition in humans caused by a dominant mutation, illustrating that mutants are not always recessive.

Chromosome Theory of Inheritance

States that Mendelian genes have specific loci on chromosomes, which undergo segregation and independent assortment.

Loci

Specific positions along chromosomes where genes are located.

Sex-linked gene

A gene located on either the $X$ chromosome or the $Y$ chromosome.

X-linked

Genes specifically located on the $X$ sex chromosome.

Y-linked

Genes specifically located on the $Y$ sex chromosome.

Carrier female

A heterozygous female ($X^NX^n$) who possesses a recessive allele but does not display its phenotype.

Hemizygous dominant

A male with a normal phenotype on his single $X$ chromosome ($X^NY$).

Hemizygous recessive

A male with the recessive or affected phenotype on his single $X$ chromosome ($X^nY$).

X-linked cross ratio (Carrier Female $\times$ Dominant Male)

A $1$ Male : $1$ Female ratio, where $1/2$ of males are affected ($X^nY$).

Thomas Hunt Morgan

The scientist who challenged genetic theories to obtain white-eyed female fruit flies.

Morgan's Proposed Cross

Heterozygous carrier female ($X^{w^+}X^w$) mated with a white-eyed mutant male ($X^wY$).

Morgan's F3 Fruit Fly Ratio

$1$ Red-eyed Female : $1$ White-eyed Female : $1$ Red-eyed Male : $1$ White-eyed Male ($1:1:1:1$).

Linked Genes

Genes located close together on the same chromosome that tend to be passed down together.

Physical vehicle of inheritance

A reference to chromosomes, upon which linked genes reside and travel together into gametes.

Unlinked Gene Ratio

In a dihybrid testcross ($AaBb \times aabb$), the phenotypic ratio is an equal $1:1:1:1$.

Linked Gene Ratio (No crossing over)

In a dihybrid testcross, this results in a $1:1$ ratio of parental phenotypes only.

Recombinants

Offspring with novel combinations of phenotypes that differ from either parent.

Crossing Over

The physical breakage and exchange of segments between homologous chromosomes during Prophase I of meiosis.

Homologous chromosomes

The pairs of chromosomes that exchange genetic material during crossing over.

Prophase I

The stage of meiosis where crossing over occurs between linked genes.

Recombinant chromosomes

Chromosomes that have swapped alleles so the final combination differs from the original (e.g., $AB$ becomes $Ab$).

Metaphase I

The stage of meiosis where independent assortment of unlinked genes occurs.

Random Fertilization

The downstream process that mixes unique gametes together to create new phenotypic combinations in offspring.

Statistically reliable data

The result of producing large numbers of offspring, which Mendel achieved with pea plants.

Enclosed flowers

An anatomical feature of pea plants that prevents uncontrolled cross-pollination in nature.

Genotypic Ratio Definition

The proportion of different genetic combinations in the offspring of a cross.

Phenotypic Ratio Definition

The proportion of different physical appearances in the offspring of a cross.

$F_1$ Generation

The first filial generation; the immediate offspring of the parental generation.

$F_2$ Generation

The second filial generation; the offspring of the $F_1$ generation.

Allele Segregation

The process described by the Law of Segregation where alleles end up in different gametes.

$16$ boxes

The total number of squares in a Punnett square for a dihybrid cross ($YyRr \times YyRr$).

Mystery genotype

The unknown genomic state (homozygous or heterozygous) of a dominant-phenotype individual in a testcross.

$1:0$ Genotypic Ratio

The result of a testcross where the unknown individual is homozygous dominant ($PP \times pp$).

$1:1$ Genotypic Ratio

The result of a testcross where the unknown individual is heterozygous ($Pp \times pp$).

Variation accounting

A role of alleles, which provide alternative versions of genes for inherited characters.

Masking

The effect where a dominant allele produces enough protein to hide the lack of contribution from a recessive allele.