Genetics and Inheritance - Vocabulary Flashcards

Vocabulary flashcards covering key genetics terms, concepts, and historical notes from the lecture.

Genetics

The scientific study of heredity and variation in living organisms, explaining how traits are passed from parents to offspring and how differences arise within populations; considered a unifying discipline in biology.

DNA

Deoxyribonucleic acid, the primary genetic material in all known living organisms. It stores detailed biological information through its double helix structure of nucleotide sequences and is organized into chromosomes. In humans, it comprises approximately 6 billion base pairs across 46 chromosomes.

Genome

The complete and entire set of genetic instructions (DNA or RNA) contained within an organism or a cell, including all genes and non-coding sequences.

Chromosome

A thread-like structure located inside the nucleus of eukaryotic cells (and in the cytoplasm of prokaryotes) that carries genetic information in the form of genes. It is composed of DNA tightly coiled around proteins called histones, forming a DNA-protein complex known as chromatin.

Chromatin

The complex of DNA and proteins (primarily histones) that condenses to form chromosomes within the nucleus of eukaryotic cells. Its primary function is to efficiently package DNA into a smaller volume to fit into the cell, protect the DNA sequence, and allow for proper gene expression.

Gene

The fundamental unit of heredity; a specific sequence of DNA (or RNA in some viruses) that codes for a particular protein or a functional RNA molecule, thereby influencing an organism's traits.

Allele

One of two or more alternative versions of a gene that arise by mutation and are found at the same place (locus) on a chromosome. Different alleles can produce different phenotypic traits or variations of a character.

Homologous chromosomes

A pair of chromosomes (one inherited from each parent) that are similar in length, gene position, and centromere location. They carry the same genes in the same order, but may carry different alleles for those genes, and pair up during meiosis to exchange genetic material.

Diploid

A cell or organism that has two complete sets of chromosomes, one set inherited from each parent. Represented as 2N, where N is the number of unique chromosomes in a haploid set (e.g., human somatic cells are diploid with 2N = 46 chromosomes).

Haploid

A cell or organism that has a single set of unpaired chromosomes. Represented as 1N, haploid cells typically result from meiosis and are characteristic of gametes (sperm and egg cells) (e.g., human gametes are haploid with 1N = 23 chromosomes).

Mutation

A permanent, heritable change in the DNA sequence of an organism's genome. Mutations are the primary source of all genetic variation upon which natural selection acts, providing the raw material for evolution.

Point mutation

A type of gene mutation where a single nucleotide base in the DNA sequence is changed, inserted, or deleted. This localized change can significantly alter the protein produced or have no effect at all.

Insertion

A type of mutation that involves the addition of one or more nucleotide base pairs into a DNA sequence. This can alter the reading frame of genes (frameshift mutation) if not in multiples of three, leading to non-functional proteins.

Deletion

A type of mutation that involves the loss or removal of one or more nucleotide base pairs from a DNA sequence. Similar to insertions, deletions can also cause frameshift mutations, severely impacting gene function.

Aneuploidy

A chromosomal abnormality characterized by an abnormal number of chromosomes in a cell, meaning it has more or fewer chromosomes than the typical diploid (or haploid) number for that species (e.g., Trisomy 21 where there's an extra copy of chromosome 21).

Whole genome duplication

A type of polyploidy where an organism (or a cell) has acquired one or more complete extra sets of chromosomes, resulting in a multiplication of its entire genome. This can occur through errors in meiosis or mitosis.

Phenotype

The observable physical or biochemical characteristics of an organism, resulting from the interaction of its genotype with environmental influences. This includes outward appearance, development, behavior, and physiological properties.

Genotype

The genetic makeup of an organism; specifically, the set of alleles it possesses for a particular gene or genes. The genotype, along with environmental factors, determines the phenotype.

Morphological trait

An observable characteristic or feature related to the physical form, structure, or appearance of an organism (e.g., eye color, plant height, wing shape).

Physiological trait

An observable characteristic related to the functioning of an organism's bodily systems or metabolic processes (e.g., blood pressure, enzymatic activity, metabolic rate, disease resistance).

Behavioral trait

An observable characteristic or pattern of an organism's actions or reactions in response to stimuli, often genetically influenced (e.g., bird migration, mating rituals, foraging strategies).

Gene expression

The multi-step process by which the information encoded in a gene's DNA sequence is converted into a functional product, such as a protein or an RNA molecule. This process includes transcription and translation (for proteins).

Gregor Mendel

An Austrian monk and botanist widely recognized as the 'Father of Genetics'. Through his meticulous experiments with pea plants in the mid-19th century, he established the fundamental principles of heredity, including the laws of segregation and independent assortment.

Mendel’s Law of Segregation

States that during the formation of gametes, the two alleles for a heritable character (gene) segregate (separate) from each other, so that each gamete carries only one allele for each gene. This ensures genetic variation in offspring.

Mendel’s Law of Independent Assortment

States that during gamete formation, the alleles of two or more different genes assort independently of each other. This means that the inheritance of one gene's alleles does not influence the inheritance of another gene's alleles, leading to diverse combinations of traits in offspring.

Hybridization

The process of interbreeding two individuals from different species, varieties, or genetically distinct lines to produce a hybrid offspring (progeny). In genetics, it often refers to crossing organisms with different traits to study inheritance.

Progeny

The offspring resulting from a sexual or asexual reproduction event. It refers collectively to children, descendants, or the result of a genetic cross between parents.

Self fertilization

A form of sexual reproduction in plants (and some animals) where male and female gametes from the same individual combine to form offspring. This often involves pollen from a flower fertilizing the egg cells of the same flower or plant.

Cross fertilization

A form of sexual reproduction where gametes from two different individuals of the same species combine to form offspring. This ensures genetic mixing and is common in many eukaryotic organisms.

True breeding

Refers to a variety of an organism that, when self-fertilized or crossed with another true-breeding individual of the same variety, consistently produces offspring with the same phenotype generation after generation. This indicates homozygosity for the traits being observed.

Chi-squared test (\chi^2 test)

A statistical hypothesis test used to determine if there is a significant association between two categorical variables or to assess how well observed categorical data fits the expected distribution. It calculates a value (the chi-squared statistic) which, along with degrees of freedom and a p-value, helps determine if observed differences are due to chance or a genuine effect.

Dihybrid cross

A genetic cross between two individuals that are both heterozygous for two different genes (e.g., AaBb x AaBb). It is used to study the inheritance patterns of two traits simultaneously and to observe the independent assortment of alleles.

Crossing Over

An essential event during prophase I of meiosis where homologous chromosomes exchange segments of genetic material. This reciprocal exchange between non-sister chromatids creates new combinations of alleles on a chromatid, leading to genetic recombination and increased diversity in gametes.

Synaptonemal complex

A highly organized protein structure that assembles between homologous chromosomes during prophase I of meiosis. It facilitates the pairing (synapsis) of homologous chromosomes and is crucial for the process of crossing over.

Bivalent

A structure formed during prophase I of meiosis, consisting of a pair of homologous chromosomes that have undergone synapsis. Each homologous chromosome is already replicated, so a bivalent contains four chromatids (two dyads).

Chiasma

The visible X-shaped structure formed at the site where crossing over has occurred between two non-sister chromatids of homologous chromosomes during prophase I of meiosis. Chiasmata hold the homologous chromosomes together until anaphase I.

N Value

Represents the number of unique types of chromosomes in a haploid set (e.g., humans have N=23). It denotes the number of chromosome sets.

Mitosis

A type of cell division that results in two daughter cells each having the same number and kind of chromosomes as the parent nucleus. It's a process of nuclear division for growth, repair, and asexual reproduction, producing genetically identical diploid cells.

Meiosis

A specialized type of cell division that reduces the chromosome number by half (from diploid to haploid), creating four haploid cells (gametes in animals, spores in plants) that are genetically distinct from the parent cell and from each other. It involves two rounds of division: Meiosis I and Meiosis II, crucial for sexual reproduction.

Barr body

An inactivated X chromosome found in the somatic cells of female mammals. It appears as a condensed, darkly staining spot in the nucleus and is a physical manifestation of X-inactivation, serving as evidence for dosage compensation.

X-inactivation

A critical dosage compensation mechanism occurring in placental female mammals, where one of the two X chromosomes in each somatic cell is randomly and largely silenced (inactivated) during embryonic development. This ensures that females, like males, have only one functional copy of most X-linked genes.

Mary Lyon

A British geneticist who, in 1961, proposed the groundbreaking hypothesis of X-inactivation, explaining how dosage compensation for X-linked genes occurs in female mammals.

SRY

Stands for 'Sex-determining Region on the Y chromosome'. It is a gene located on the Y chromosome in mammals that acts as the primary male-determining factor. Its presence triggers the development of testes from the bipotential gonad.

SOX9

A transcription factor gene critical for male development, even in the absence of SRY in some species. In mammals, it is activated by SRY and promotes the differentiation of Sertoli cells, leading to testis formation.

FGF9

Stands for Fibroblast Growth Factor 9. It is a signaling molecule (growth factor) that plays a crucial role in testis development. SRY expression leads to the upregulation of FGF9, which helps maintain SOX9 expression and promotes the proliferation of Sertoli cells.

Bipotential gonad

An undifferentiated embryonic gonadal tissue that possesses the developmental potential to become either a testis or an ovary, depending on the presence or absence of specific genetic signals (like SRY).

Oogenesis

The process of meiosis in the ovaries of female animals, which produces a single large, haploid egg (ovum) and smaller, non-functional polar bodies. This process involves unequal cytokinesis, concentrating most of the cytoplasm into the egg.

Spermatogenesis

The continuous process of meiosis that occurs in the testes of male animals, leading to the production of four mature, haploid sperm cells from each primary spermatocyte. This process involves equal cytokinesis and results in a large number of motile gametes.

X-linked gene

A gene located specifically on the X chromosome. The inheritance patterns of X-linked genes differ between males and females due to males having only one X chromosome (hemizygous).

XXY

A human karyotype characterized by the presence of an extra X chromosome in a male, resulting in 47 chromosomes (47, XXY). This karyotype is associated with Klinefelter syndrome, typically leading to male traits but often with reduced fertility and some feminized characteristics.

ZW sex determination

A genetic sex-determination system found in birds, some fish, and some insects and reptiles. In this system, females are the heterogametic sex (ZW) and males are homogametic (ZZ). The Z chromosome is typically larger and carries more genes.

XY sex determination

The most common genetic sex-determination system in mammals, including humans, where the presence of a Y chromosome (specifically the SRY gene) determines male development (XY individuals are male). Individuals with two X chromosomes (XX) develop as female.

Autosome

Any chromosome that is not a sex chromosome (X or Y). In humans, there are 22 pairs of autosomes, carrying genes for most of the organism's traits, independent of sex determination.

Heterozygote advantage

A phenomenon in which individuals who are heterozygous for a particular gene (carrying two different alleles) have a higher fitness or survival rate than individuals who are homozygous for either allele. A classic example is the heterozygosity for the sickle cell trait, which confers resistance to malaria.

Sickle cell anemia

A severe genetic disease caused by inheriting two copies of the abnormal hemoglobin S allele (homozygous HbS). It results in red blood cells becoming rigid, sickle-shaped, and prone to breaking, leading to anemia, pain crises, and organ damage. Heterozygotes (one HbS allele) are resistant to malaria but generally do not suffer from severe anemia.

Haploinsufficiency

A condition where having only one functional copy of a gene (due to a deletion or a non-functional allele on the other chromosome) is not sufficient to produce a normal phenotype or maintain normal biological function. This often leads to a disease state or an abnormal trait, where the normal gene is typically dominant.

Dominant mutation

A mutation that produces an observable phenotype when only one copy of the mutant allele is present, even in the presence of a normal, wild-type allele. Dominant mutations can include gain-of-function, dominant-negative, and haploinsufficiency types.

Gain of function mutation

A type of dominant mutation where the altered gene product acquires a new molecular function or activity, or its normal function becomes overactive. This often results in a phenotype that is not typically observed in the wild type.

Dominant-negative mutation

A type of dominant mutation where the mutant gene product interferes with the function of the normal protein produced by the wild-type allele. This often happens when the mutant protein forms a complex with the normal protein, rendering the entire complex non-functional.

Incomplete penetrance

A situation where not all individuals who possess a particular genotype express the expected phenotype. Even with the gene for a trait, some individuals may show the trait while others do not, despite having the same genetic predisposition.

Incomplete dominance

A form of inheritance in which the heterozygous genotype results in a phenotype that is intermediate between the phenotypes of the two homozygous genotypes. Neither allele is completely dominant over the other (e.g., a cross between red and white flowers producing pink flowers).

Codominance

A form of inheritance where both alleles for a gene are fully and simultaneously expressed in the heterozygote, resulting in a phenotype that clearly displays characteristics of both homozygous parents, without blending. An example is the AB blood type in humans, where both A and B alleles are expressed.

Wild type allele

The most common and typically functional allele of a gene found in a natural (wild) population. It is often considered the standard or reference allele against which mutant alleles are compared.

Mutant allele

A less common and often altered version of a gene (resulting from a mutation) that deviates from the wild-type allele. Mutant alleles can be dominant, recessive, or have other modes of inheritance and often lead to altered or non-functional gene products.

Genetic polymorphism

The occurrence of two or more clearly different phenotypes or genetic variations (alleles) within a population where the rarest allele is too common to be due to recurrent mutation alone. It signifies the presence of multiple common alleles for a gene in a population, contributing to genetic diversity.

Monad

In cell division, a monad refers to a single chromatid, as seen after sister chromatids have separated during anaphase of mitosis or anaphase II of meiosis. Each monad constitutes a complete chromosome as it moves to a pole.

Dyad

In cell division, a dyad refers to a replicated chromosome consisting of two identical sister chromatids joined together at the centromere. Dyads are present from prophase of mitosis until anaphase, and from prophase I of meiosis until anaphase II.

C Value

Total amount of DNA in a cell. 2c are normal diploid cells without replication. 4c are cells with replicated DNA.