BIO101 - Chapter 23: Patterns of Gene Inheritance

Vocabulary practice flashcards covering Mendelian genetics, inheritance laws, single-trait and two-trait crosses, autosomal disorders, and complex patterns of inheritance from Chapter 23.

Law of Segregation

Mendel's first law of inheritance stating that each individual possesses two factors for each trait, which separate randomly during gamete formation so that each gamete carries only one factor, and fertilization restores two factors to each new individual.

Law of Independent Assortment

Mendel's second law of inheritance stating that each pair of factors separates independently of other pairs during meiosis, allowing all possible combinations of factors to occur in the gametes.

Homologous Chromosomes

Pairs of chromosomes that are similar in appearance and size and contain genetic information for the same traits at identical locations, with one chromosome inherited from the mother and one from the father.

Allele

An alternative version or choice of a gene that occurs at the same specific locus on homologous chromosomes and controls the same trait.

Locus

The specific physical position or location occupied by a gene or its alleles along a chromosome.

Phenotype

The physical appearance, observable characteristics, or biochemical expression of a trait in an individual (e.g., purple flowers, freckles, or blood type).

Genotype

The actual combination of alleles present at a specific locus in an organism's cells, represented symbolically by letters (such as $FF$, $Ff$, or $ff$).

Homozygous

A condition in which an organism possesses two identical alleles for a given gene locus (either homozygous dominant, such as $PP$, or homozygous recessive, such as $pp$).

Heterozygous

A hybrid condition in which an organism carries two different alleles for a specific trait (such as $Pp$), typically resulting in the phenotypic expression of the dominant allele.

Dominant Allele

An allele that masks or hides the phenotypic expression of an alternative recessive allele when both are present in a heterozygous state.

Recessive Allele

An allele whose expression is masked in the presence of a dominant allele and which is only expressed phenotypically when an individual is homozygous for that allele.

Monohybrid Cross

A cross between two individuals that are both heterozygous for a single pair of alleles (represented as $Ff \times Ff$), typically resulting in a $3:1$ phenotypic ratio.

Punnett Square

A grid-format tool devised by British geneticist Reginald Crundall Punnett to calculate and diagram the possible combinations of parental gametes and resulting genotypes in offspring.

Product Rule of Probability

The mathematical rule stating that the probability of two or more independent events occurring simultaneously is the product (multiplication) of their individual chances of occurring separately.

Testcross

A cross between an individual displaying a dominant phenotype of unknown genotype and an individual displaying a homozygous recessive phenotype, used to reveal whether the dominant parent is homozygous or heterozygous.

Dihybrid Cross

A breeding experiment involving individuals that are heterozygous for two distinct traits (e.g., $FfSs \times FfSs$), which produces a classic $9:3:3:1$ phenotypic ratio among offspring.

Autosomes

Chromosomes that are not involved in determining the biological sex of an organism; humans have 22 pairs of autosomal chromosomes.

Pedigree Chart

A diagrammatic chart tracking the inheritance and expression of a specific trait through multiple generations of a family, utilizing circles for females and squares for males.

Carrier

A heterozygous individual who carries a recessive allele for a disorder but does not express the trait phenotypically because it is masked by a dominant allele.

Tay-Sachs Disease

An autosomal recessive disorder caused by the lack of the lysosomal enzyme hexosaminidase A (Hex A), resulting in toxic glycosphingolipid accumulation in lysosomes, progressive brain damage, and death typically by age 5.

Cystic Fibrosis (CF)

An autosomal recessive disease caused by a defect in the CFTR gene, resulting in abnormal chloride ion ($Cl^-$) channel proteins, intracellular trapping of chloride and water, and the build-up of thick, sticky mucus in the lungs and pancreas.

Phenylketonuria (PKU)

An autosomal recessive metabolic disorder caused by a deficiency in phenylalanine hydroxylase (PAH), preventing the conversion of phenylalanine to tyrosine and requiring a strict diet avoiding excess protein and aspartame.

Sickle-Cell Disease

An autosomal recessive condition caused by a single nucleotide substitution (adenine replaced by thymine) that substitutes valine for glutamic acid in the sixth codon of the $\beta$ chain of hemoglobin, distorting red blood cells into a sickle shape.

Sickle-Cell Trait

The heterozygous state of the sickle-cell gene that provides carriers with protection against malaria without manifesting full-blown symptoms of sickle-cell disease under normal conditions.

Marfan Syndrome

An autosomal dominant disorder caused by a defect in the fibrillin-1 ($FBN1$) gene, leading to defective microfibrils in elastic fibers, excess unbound TGF-$\beta$, unusually long limbs, and weakened aortic walls.

Huntington Disease

An autosomal dominant neurodegenerative disorder caused by an abnormal huntingtin protein containing more than 36 glutamines, which aggregates in brain cells, inactivates CREB binding protein (CBP), and leads to motor and cognitive decline.

Chorea

A neurological symptom named from the ancient Greek word for dance, characterized by brief, abrupt, irregular, and unpredictable involuntary movements that flow between body parts.

Incomplete Dominance

A genetic pattern where neither allele is fully dominant over the other, causing a heterozygote to express an intermediate phenotype blended between the parental forms (e.g., wavy hair or pink snapdragons).

Codominance

A pattern of inheritance in which both alleles in a heterozygote are fully and simultaneously expressed without blending or masking (e.g., roan coat color in cattle or $I^A I^B$ blood type).

Multiple Allele Inheritance

An inheritance system where more than two alternative alleles exist for a given gene locus in the population (e.g., the ABO blood type alleles $I^A$, $I^B$, and $i$), though each individual inherits only two.

Antigen

A foreign substance or surface molecule that triggers the immune system to initiate an immune response.

Antibody

A specialized immune system protein produced by B cells in response to an antigen that binds specifically to that target antigen.

Polygenic Inheritance

An inheritance pattern in which a single phenotypic trait is governed additively by two or more independent genes across multiple loci, producing continuous variation that typically follows a bell-shaped curve.