A Level Biology - Patterns of Inheritance Flashcards

Vocabulary flashcards covering key terms in genetics, variation, and inheritance, designed to aid in exam preparation.

Gene

A segment of DNA that contains the instructions for making a specific polypeptide or protein. Genes determine the inherited characteristics or traits of an organism.

Allele

Different versions of a gene that exist at the same locus on a chromosome. Alleles are responsible for the variation in inherited characteristics.

Locus

The specific location or position of a gene on a chromosome. The locus is a fixed point along the chromosome where a particular gene is always found.

Genotype

The combination of alleles an individual possesses for a particular gene. The genotype determines the genetic makeup of an individual, which can influence their phenotype.

Phenotype

The observable characteristics or traits of an organism, which are determined by the interaction of its genotype and the environment. The phenotype includes physical appearance, behavior, and other measurable traits.

Homozygous

Having two identical alleles for a particular gene. Homozygous individuals produce gametes with only one type of allele for that gene.

Heterozygous

Having two different alleles for a particular gene. Heterozygous individuals can produce gametes with different types of alleles for that gene.

Dominant Allele

An allele that is always expressed in the phenotype, whether the individual is homozygous or heterozygous for that allele. Dominant alleles mask the presence of recessive alleles.

Recessive Allele

An allele that is only expressed in the phenotype when the individual is homozygous for that allele. Recessive alleles are masked by the presence of dominant alleles.

Codominance

A situation in which both alleles of a gene are equally expressed in the phenotype of a heterozygous individual. In codominance, neither allele is dominant over the other, and both traits are visible.

F1 Generation

The first generation of offspring resulting from a cross between two true-breeding (homozygous) parents. In a typical Mendelian cross, the F1 generation is heterozygous for the trait being studied.

F2 Generation

The second generation of offspring resulting from a cross between two individuals from the F1 generation. The F2 generation typically shows a segregation of traits, with both dominant and recessive phenotypes appearing.

Test Cross

A cross between an individual with an unknown genotype and a homozygous recessive individual. Test crosses are used to determine whether the individual with the dominant phenotype is homozygous dominant or heterozygous.

Linked Genes

Genes that are located on the same chromosome and tend to be inherited together. Linked genes do not assort independently during meiosis unless crossing over occurs between them.

Sex-linked Genes

Genes that are located on a sex chromosome (X or Y) and exhibit a unique pattern of inheritance. Sex-linked traits are more commonly expressed in one sex than the other.

Autosomal Linkage

Genes that are located on autosomes (non-sex chromosomes) and are inherited together. Autosomal linkage occurs when genes are close together on the same autosome.

Phenotypic Variation

The range of differences in phenotype that exist among individuals in a population. Phenotypic variation can be caused by genetic factors, environmental factors, or a combination of both.

Crossing Over

The exchange of genetic material between non-sister chromatids of homologous chromosomes during prophase I of meiosis. Crossing over results in new combinations of alleles and increases genetic variation.

Independent Assortment

The random separation of homologous chromosomes during anaphase I of meiosis. Independent assortment results in different combinations of alleles in daughter cells and increases genetic variation.

Random Fusion of Gametes

The random union of male and female gametes during fertilization. Random fusion of gametes increases genetic variation in offspring.

Monohybrid Inheritance

The pattern of inheritance of a single gene. Monohybrid inheritance involves the transmission of alleles from parents to offspring for one particular trait.

Epistasis

The interaction of two or more genes to control a single phenotype. In epistasis, one gene can mask or modify the expression of another gene.

Chi-squared Test

A statistical test used to determine whether observed data fit an expected pattern or distribution. The chi-squared test is commonly used to analyze genetic crosses and determine if the results are statistically significant.

Continuous Variation

A type of variation in which traits can take on a range of values. Continuous variation is often influenced by multiple genes and environmental factors.

Variation

The differences that exist between individuals of the same species. Variation can be either continuous or discontinuous.

Discontinuous Variation

A type of variation in which traits fall into distinct categories. Discontinuous variation is typically controlled by one or a few genes.

Selection Pressures

Factors in the environment that affect the survival and reproduction of organisms. Selection pressures can drive natural selection and lead to evolutionary change.

Stabilising Selection

A type of natural selection in which the average phenotype is favored and extreme phenotypes are selected against. Stabilizing selection reduces variation in a population.

Directional Selection

A type of natural selection in which one extreme phenotype is favored over other phenotypes. Directional selection leads to a shift in the allele frequencies in a population.

Genetic Drift

A random change in allele frequencies in a population due to chance events. Genetic drift is more pronounced in small populations.

Genetic Bottleneck

A sharp reduction in the size of a population due to a catastrophic event or other environmental factor. Genetic bottlenecks can lead to a loss of genetic diversity.

Founder Effect

The loss of genetic variation that occurs when a new population is established by a very small number of individuals from a larger population. The founder effect can lead to a different allele frequency distribution in the new population.

Hardy-Weinberg Principle

A principle stating that allele frequencies in a population will remain constant from one generation to the next in the absence of disturbing factors. The Hardy-Weinberg principle provides a null hypothesis for testing whether evolution is occurring in a population.

Genetic Isolation

The prevention of gene flow between two populations. Genetic isolation can lead to the divergence of populations and the formation of new species.

Speciation

The process by which new species arise from existing species. Speciation can occur through allopatric or sympatric mechanisms.

Allopatric Speciation

A mode of speciation in which new species arise due to geographic isolation. Allopatric speciation occurs when populations are separated by physical barriers and evolve independently.

Sympatric Speciation

A mode of speciation in which new species arise without geographic isolation. Sympatric speciation can occur through mechanisms such as disruptive selection or polyploidy.

Artificial Selection

The selective breeding of plants and animals by humans to enhance desirable traits. Artificial selection can lead to rapid evolutionary change in domesticated species.