SL Bio Genetics 3.1 - 3.3

Genes

Units of heredity that contain the instructions for building proteins.

DNA

Deoxyribonucleic acid, the molecule that carries the genetic information in all living organisms.

Protein

A large biomolecule made up of amino acids that performs various functions in the body.

Point mutation or substitution

A type of genetic mutation where a single nucleotide base is replaced with another.

Missense mutation

A type of point mutation where the change in the DNA sequence results in a different amino acid being incorporated into the protein.

Silent mutation

A type of point mutation where the change in the DNA sequence does not result in a change in the amino acid sequence of the protein.

Nonsense mutation

A type of point mutation where the change in the DNA sequence results in the premature termination of protein synthesis.

Intron

A non-coding region of DNA that is transcribed but not translated into protein.

Exon

A coding region of DNA that is transcribed and translated into protein.

Codon

A sequence of three nucleotides in DNA or RNA that codes for a specific amino acid.

Base pair

A pair of complementary nucleotides (adenine-thymine or cytosine-guanine) that are held together by hydrogen bonds.

Germ line cell mutations

Mutations that occur in the cells that give rise to eggs or sperm and can be passed on to offspring.

Frame shift

A type of mutation where the addition or deletion of nucleotides shifts the reading frame of the genetic code, resulting in a completely different amino acid sequence.

Amino acids

The building blocks of proteins, coded for by specific sequences of nucleotides in DNA or RNA.

Pentose sugar

A five-carbon sugar molecule that is a component of nucleotides.

Phosphate group

A chemical group consisting of phosphorus and oxygen atoms that is a component of nucleotides.

Nitrogenous base

A molecule that contains nitrogen and forms the "rungs" of the DNA double helix, including adenine, thymine, cytosine, and guanine.

Purines

Nitrogenous bases that have a double-ring structure, including adenine and guanine.

Pyrimidines

Nitrogenous bases that have a single-ring structure, including cytosine, thymine, and uracil.

Complementary base pairing

The specific pairing of nitrogenous bases in DNA and RNA, where adenine pairs with thymine (in DNA) or uracil (in RNA), and cytosine pairs with guanine.

Replication

The process of copying DNA to produce an identical copy.

Transcription

The process of synthesizing RNA from a DNA template.

DNA template

The DNA strand that is used as a guide to synthesize a complementary RNA strand.

Messenger RNA (mRNA)

The type of RNA that carries the genetic instructions from DNA to the ribosome for protein synthesis.

Transfer RNA (tRNA)

The type of RNA that carries amino acids to the ribosome during protein synthesis.

Ribosomal RNA (rRNA)

The type of RNA that forms part of the ribosome and is involved in protein synthesis.

Loop

A region of RNA where the sequence folds back on itself, forming a hairpin-like structure.

DNA

Definition:A double helix made of two antiparallel strands of nucleotides that carries hereditary information and instructions for protein production.

Nucleotide

Definition:The building blocks of DNA, consisting of a sugar, a phosphate group, and a nitrogenous base.

Complementary base pairs

Definition:The pairing of nucleotides in DNA, where adenine (A) pairs with thymine (T) and guanine (G) pairs with cytosine (C).

RNA

Definition:A nucleic acid that is involved in protein synthesis and is produced from DNA.

Base sequence

Definition:The order of nucleotides in a DNA strand, which encodes genetic information.

Genetic code

Definition:The set of rules that determines how the nucleotide sequence of DNA is translated into the amino acid sequence of a protein.

Gene mutation

Definition:A change in the nucleotide sequence of a gene, which can result in a change in the amino acid sequence of the protein produced.

Antiparallel

Definition:Referring to the arrangement of the two strands of DNA, where one strand runs in the opposite direction of the other.

Double helix

Definition:The twisted ladder-like structure of DNA, formed by the two strands of nucleotides.

Codon

Definition:A sequence of three nucleotides in mRNA that corresponds to a specific amino acid or a stop signal during protein synthesis.

Amino acid

Definition:The building blocks of proteins, encoded by codons in the genetic code.

Mutation

Definition:A permanent change in the nucleotide sequence of DNA, which can result in a change in the phenotype of an organism.

Point mutation

Definition:A mutation that involves the substitution of a single nucleotide in the DNA sequence.

Insertion

Definition:A mutation that involves the addition of one or more nucleotides to the DNA sequence.

Deletion

Definition:A mutation that involves the loss of one or more nucleotides from the DNA sequence.

Silent mutation

Definition:A mutation that does not result in a change in the amino acid sequence of the protein produced.

Missense mutation

Definition:A mutation that results in a change in the amino acid sequence of the protein produced.

Nonsense mutation

Definition:A mutation that results in the formation of a premature stop codon, leading to a truncated protein.

Frame shift

Definition:A mutation that results in a shift in the reading frame of the genetic code, leading to a change in the amino acid sequence of the protein produced.

Gene

A heritable factor that consists of a length of DNA and influences a specific characteristic.

Allele

Alternate forms of a gene that code for the variations of a trait.

Mutation

A change in the nucleotide sequence of a section of DNA coding for a specific trait.

Chromosome

Discrete structures in which DNA is packaged and organized.

Locus

The position of a gene on a particular chromosome.

DNA

The genetic blueprint that codes for the characteristics/traits of an organism.

mRNA

The transcript of DNA that carries the genetic information for protein synthesis.

Amino acids

The building blocks of proteins.

Frameshift mutation

A type of mutation that results in the insertion or deletion of nucleotides, causing a shift in the reading frame of the genetic code.

Point mutation

A type of mutation that involves the substitution of one nucleotide for another.

Substitution

A type of mutation that involves the replacement of one nucleotide with another.

Insertion

A type of mutation that involves the addition of one or more nucleotides.

Deletion

A type of mutation that involves the removal of one or more nucleotides.

Premature stop signal

A mutation that results in the formation of a stop codon before the normal termination point, leading to the premature termination of protein synthesis.

No stop signal

A mutation that does not result in the formation of a stop codon, leading to the elongation of the protein.

Missense mutation

A type of mutation that results in the change of one amino acid in the protein sequence.

Nonsense mutation

A type of mutation that results in the formation of a premature stop codon, leading to the truncation of the protein.

Silent mutation

A type of mutation that does not result in any change in the amino acid sequence of the protein.

Somatic mutation

A mutation that occurs in the body cells and affects only the organism in their lifetime.

Germ line mutation

A mutation that occurs in the reproductive cells and can be passed down to the next generation.

Genome

The totality of genetic information of a cell, organism, or organelle, including all genes and non-coding DNA sequences.

Human Genome Project

A 13-year international cooperative venture to sequence the human genome, which showed that humans share the majority of their sequence with short nucleotide polymorphisms contributing to diversity.

Genotype

The combination of genes an organism has, which can be homozygous (two of the same gene) or heterozygous (two different genes).

Phenotype

The physical appearance or characteristics of an organism, determined by its genotype.

Dominant Trait

A trait that is expressed if it is present, masking the recessive trait.

Recessive Trait

A trait that is only expressed if an organism possesses two recessive alleles.

Homozygous Dominant

Genotype with two dominant alleles (e.g., XX).

Homozygous Recessive

Genotype with two recessive alleles (e.g., xx).

Heterozygous

Genotype with one dominant and one recessive allele (e.g., Xx).

Chromosome

A linear DNA molecule associated with histone proteins, carrying genes in a linear sequence.

Homologous Chromosomes

Chromosome pairs that carry the same sequence of genes but not necessarily the same alleles of those genes.

Centromere

The constriction point of a chromosome that divides it into a shorter p arm and a longer q arm.

GenBank

An online databank used to identify the locus of a human gene and its polypeptide product.

Meiosis

The process of separating homologous chromosomes in gametes to prevent doubling of chromosome numbers in each generation.

Diploid

Nuclei with pairs of homologous chromosomes are diploid (symbolised by 2n). These nuclei possess two gene copies (alleles) for each trait.

Haploid

Nuclei with only one set of chromosomes are haploid (symbolised by n). These nuclei possess a single gene copy (allele) for each trait.

Autosome

The remaining chromosomes (pairs 1-22) in the organism are called autosomes. They do not determine sex.

Heterosome

Biological sex is determined by the "sex" chromosomes (23rd pair), also referred to as heterosomes.

Karyogram

A karyogram shows the chromosomes of an organism in homologous pairs of decreasing length, with sex chromosomes shown last.

Karyotyping

The process of determining the number and types of chromosomes in a eukaryotic cell by staining and photographing the chromosomes to generate a visual profile known as a karyogram.

Aneuploidies

Chromosomal abnormalities such as Down syndrome, where the individual has three copies of chromosome 21 (trisomy 21).

Cairns' Technique

A technique pioneered by John Cairns to visualize uncoiled chromosomes using autoradiography. It involves growing cells in a solution containing radioactive thymidine and using radioactively-sensitive solutions to visualize the chromosomal DNA.

Chromosome Number

The characteristic feature of members of a particular species, indicating the number of chromosomes they possess.

Meiosis

The process by which diploid nuclei divide to produce four haploid nuclei, allowing for the formation of gametes and genetic variation through crossing over and random orientation.

Meiosis

The process of cell division that results in the formation of four haploid cells.

Mitosis

The process of cell division that results in the formation of two identical daughter cells.

Interphase

The phase of the cell cycle where DNA is replicated.

Sister chromatids

Two identical copies of a chromosome that are held together by a centromere.

Homologous chromosomes

Chromosomes that have the same genes at the same loci, but may have different alleles.

Bivalent/tetrad

A pair of homologous chromosomes that are held together during meiosis.

Crossing over

The exchange of genetic material between non-sister chromatids of homologous chromosomes.

Random assortment

The random orientation of homologous chromosomes during metaphase I of meiosis.

Gametes

Haploid cells (sperm and egg) that fuse during fertilization to form a diploid zygote.

Genetic variation

Differences in genetic makeup between individuals.