Genomes, Genes, and Alleles

A complete set of vocabulary flashcards covering genomes, chromosomes, meiosis, and genetic inheritance principles as described in the lecture notes.

Genome

The sum total of an organism’s DNA measured in the number of base pairs contained in a haploid set of chromosomes, encompassing nuclear, mitochondrial, and chloroplast DNA.

Genomics

The study of genomes.

Nucleosomes

A structural unit of a chromosome, consisting of a length of DNA coiled around a core of histones.

Chromatid

One of the two identical parts of a duplicated chromosome.

Centromere

The primary constriction on a chromosome that joins sister chromatids and serves as the attachment point for spindle fibres.

Genes

The basic units of heredity consisting of DNA sections that code for proteins and are responsible for specific characteristics or traits.

Gene loci

The specific location of a gene on a chromosome.

Alleles

Different forms or variants of a gene, usually represented by a letter of alphabet.

Nucleotides

The building blocks of DNA, consisting of a phosphate group, a deoxyribose sugar, and a nitrogenous base (Adenine, Thymine, Cytosine, or Guanine).

Diploid number ($2n$)

The total amount of chromosomes found in an organism’s somatic cells.

Haploid number ($n$)

The number of paired chromosomes found in an organism’s somatic cells, representing the number of pairs a species has.

Kinetochore

The structure surrounding the centromere where spindle fibres attach during cell division.

Telomeres

Repeated $TTAGGG$ sequences at the ends of chromosomes that prevent them from sticking together and enable complete replication.

Linked genes

Genes that are located on the same chromosome.

Linkage groups

Groups formed by genes that are located on the same chromosome.

Karyotype

A representation of a person’s chromosomes that are isolated, stained, and rearranged by size from largest to smallest.

Homologous chromosomes

Pairs of chromosomes found in the nucleus of somatic cells.

Meiosis

A form of nuclear division occurring in specialised organs of sexually reproducing animals that results in the production of haploid gametes.

Synapsis

The process in Prophase I where homologous chromosomes lie side by side.

Bivalent

A pair of homologous chromosomes during the synapsis phase of Meiosis I.

Chiasmata

The points where homologous chromosomes become connected and where chromatids may break and re-join during crossing over.

Crossing over

The process where chromatids break and re-join at the chiasma, resulting in the swapping of DNA.

Recombinants

Chromosomes that have a new combination of alleles resulting from the process of crossing over.

Disjunction

The process during Anaphase I where spindle fibres contract and pull maternal and paternal chromosomes towards opposite ends of the cell.

Cytokinesis

The division of the cytoplasm that follows nuclear division.

Zygote

The diploid cell produced when male and female haploid sex cells fuse during fertilisation.

Phenotype

The visible or measurable expression of an organism's genetic make-up, often calculated as Phenotype = Genotype + Environmental factors.

Genotype

The combination of alleles for a particular gene that determines a specific aspect of structure or functioning.

Hemizygous

A term describing alleles that cannot be paired, specifically the $X$ and $Y$ genes in males.

Complete dominance

A relationship between alleles where the dominant allele completely masks the effect of the recessive allele in a heterozygote.

Carriers

Individuals who are heterozygotes for a trait and possess the recessive allele but do not express it phenotypically.

Co-dominance

A condition where both traits are expressed in equal measure in the phenotype of a heterozygote individual.

Incomplete dominance

A condition where both traits are expressed as an intermediate between the two parental phenotypes.

Polygenic inheritance

A pattern of inheritance where a trait is controlled by several genes, each having a small cumulative effect, leading to continuous variation.

Epigenetics

The study of how cells with identical genotypes show different phenotypes through factors that act on DNA without changing the DNA base sequence.

Methyl group ($-CH_3$)

An epigenetic tag often attached in greater quantities to genes that have been switched off.

Monohybrid cross

A genetic cross involving the alleles of just one gene and the segregation of those alleles into separate gametes.

Punnett Square

A visual representation used to calculate the probability of the outcomes of a genetic cross between parents.

Test cross

A cross performed by mating an individual with a dominant phenotype but unknown genotype with a homozygous recessive individual.

Dihybrid cross

A genetic cross that involves the study of two different genes.

Map units

A measurement of distance between genes on a chromosome, where $1$ map unit equals a $1\%$ chance of crossing over.