Genetics - Chapter review Flashcards
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Chromosomes, genes and DNA, and the history of DNA
DNA (deoxyribonucleic acid) is a nucleic acid made up of nucleotides.
Each nucleotide is made up of three parts: sugar (deoxyribose in DNA, ribose in RNA), phosphate and a nitrogenous base (adenine, guanine, cytosine, thymine or uracil).
DNA has the shape of a double helix made up of two anti-parallel strands of nucleotides, with the outside part of the ‘ladder’ made up of a sugar– phosphate frame (alternating sugar and phosphate).
Genes are specific segments of DNA that contain the codes for the production of specific proteins that can result in the expression of particular traits.
Genes are organised into larger structures called chromosomes, which are located within the nucleus of eukaryotic cells.
The location of a gene on a specific chromosome is called its locus, whereas genes that are located on the same chromosome are said to be linked.
Chromosomes can be divided into two main types: autosomes and sex chromosomes (the X and Y chromosomes).
Unlocking the DNA code
Proteins are made up of amino acids.
The instructions for making proteins are coded for in the sequence of nitrogenous bases in DNA.
RNA is another type of nucleic acid made up of nucleotides. RNA differs from DNA in that it is single stranded, contains ribose instead of deoxyribose, and contains uracil instead of thymine. Messenger RNA (mRNA) and transfer RNA (tRNA) are two types of RNA.
Three nucleotides in DNA that code for a particular amino acid, or a start or stop instruction, are called a triplet, in mRNA a codon, and in tRNA an anti-codon.
Transcription is the process of making a complementary mRNA copy of the DNA message to make a protein. mRNA passes through the pores of the nuclear membrane into the cytoplasm to take its genetic copy of the protein instruction message to ribosomes
Translation is the process of reading the mRNA message and making the protein it codes for.
tRNA transfers the appropriate amino acid to its matching code on the mRNA, and then these amino acids are joined together by peptide bonds to make a protein.
Changing the code through mutations
DNA replication is the process by which DNA makes identical copies of itself.
Although the process of DNA replication includes checkpoints, sometimes mistakes get through, which can result in a mutation — a change in the DNA.
In an induced mutation, the cause can be identified; in a spontaneous mutation, it cannot. A factor that triggers mutations in cells is called a mutagen or mutagenic agent.
Point mutations may be due to the substitution of a nucleotide with a different nucleotide, or the addition or deletion of a nucleotide.
Exploring patterns in the genome and genetic sequences
The development of automated DNA sequencers has reduced the cost and time required to sequence DNA.
Gene sequencing identifies the order of nucleotides along a gene.
A genome is the complete complement of genetic material in a cell or organism. The study of genomes is called genomics. The genome size is often described in terms of the total number of base pairs (or bp).
The key findings from the Human Genome Project (HGP) were that the human genome has a size of around three billion base pairs (or 3000 Mb) and contains around 20 000 to 25 000 genes, and that all humans share about 99.9 per cent of their DNA.
Genome maps describe the order of genes and the spacing between them on each chromosome.
Dividing to multiple through cell division
All cells come from pre-existing cells.
Mitosis and meiosis are two types of cell division involved in cell production.
Mitosis is the type of cell division involved in growth, development and repair of tissues. It results in cells that are clones because they are genetically identical to each other and to the original cell.
Meiosis results in sex cells (or gametes) that contain half the number of chromosomes (haploid). The process of meiosis is a key source of variation due to independent assortment and crossing over of chromosomes.
Passing on genes to the next generation
The passing on of characteristics from one generation to the next is called inheritance and the study of inheritance is called genetics.
These alternative forms or expressions of a gene are called alleles.
The combination of the alleles that you have for a particular gene is called your genotype.
Your characteristics or features are examples of your phenotype.
If the allele for a dominant trait is present, it will be expressed. An allele for a dominant trait is denoted with a capital letter.
The recessive trait is hidden in the presence of the dominant trait and can be expressed only if the allele for the dominant trait is not present. An allele for a recessive trait is denoted with a lower case letter.
Individuals may be heterozygous and have different alleles at a gene (for example, Bb) or homozygous, and have the same alleles (BB or bb).
The term carrier is also used to describe someone who is heterozygous for a particular trait.
Using Punnett squares and pedigrees
A Punnett square is a diagram that is used to predict the outcome of a genetic cross for each offspring.
A diagram that shows a family’s relationships and how characteristics are passed on from one generation to the next is a pedigree chart.
Pedigree charts can be used to observe the mode of inheritance, including autosomal dominant, autosomal recessive, X-linked dominant and X-linked recessive.
Genetic testing
Genetic tests can be used to help identify specific genetic variations within your DNA that may relate to your genetic family relationships or to your health.
As well as being used to determine gender, genetic tests can be used for the diagnosis, prediction or predisposition to particular genetic diseases or other inherited traits.
Genetic engineering and biotechnology
Genetic engineering is a type of biotechnology that involves working with DNA, the genetic material located in cells.
Genetically modified organisms have had their genetic information altered in some way. Transgenic organisms contain a genetic material (such as a gene) from a different species.
DNA fingerprinting and DNA profiling use variations in the patterns of base sequences in DNA between individuals to identify them.
CRISPR technology has been developed for genome editing.
Key terminology
alleles alternate forms of a gene for a particular characteristic
amino acid an organic compound that forms the building blocks of proteins
amniocentesis a type of prenatal screening in which a sample is collected from the amniotic fluid around a fetus
asexual reproduction reproduction that does not involve fusion of sex cells (gametes)
autosomes non-sex chromosomes
bioinformatics the science of analysing biological data through computers, particularly around genomics and molecular genetics
carrier an individual heterozygous for a characteristic who does not display the recessive trait
cell the smallest unit of life and the building blocks of living things
centromere a section of a chromosome that links sister chromatids
Chargaff’s rule a rule that states the pairing of adenine with thymine and cytosine with guanine
chorionic villus sampling (CVS) a type of prenatal screening in which tissue from the chorion is tested during pregnancy
chromatid one identical half of a replicated chromosome
chromosomes tiny thread-like structures inside the nucleus of a cell that contain the DNA that carries genetic information
clones genetically identical copies
codon sequence of three bases in mRNA that codes for a particular amino acid
complementary base pairs in DNA, specific base pairs will form between the nitrogenous bases adenine (A) and thymine (T) and between the bases cytosine (C) and guanine (G)
complete dominance a type of inheritance where traits are either dominant or recessive
cytogenetics the study of heredity at a cellular level, focusing on cellular components such as chromosomes
deoxyribonucleic acid (DNA) a substance found in all living things that contains its genetic information
deoxyribose the sugar in the nucleotides that make up DNA
diploid the possession of two copies of each chromosome in a cell
DNA ligase an enzyme that joins DNA fragments together
DNA replication process that results in DNA making a precise copy of itself
dominant a trait (phenotype) that requires only one allele to be present for its expression in a heterozygote
epigenetics the study of the effect of the environment on the expression of genes
fertilisation penetration of the ovum by a sperm
gametes reproductive or sex cells such as sperm or ova
gel electrophoresis a technique used to separate molecules based on their size through an agarose gel
gene segment of a DNA molecule with a coded set of instructions in its base sequence for a specific protein product; when expressed, may determine the characteristics of an organism
gene therapy altering genes with the intention to treat or prevent disease
genetically modified organism a organism where the genome has been altered
genetic engineering one type of biotechnology that involves working with DNA
genetic engineers scientists who use special tools to cut, join, copy and separate DNA
genetic genealogy the use of DNA along with other genealogical tests to infer relatedness between individuals
genetics study of inheritance
genome the complete set of genes present in a cell or organism
genome maps maps that describe the order and spacing of genes on each chromosome
genomics the study of genomes
genotype genetic instructions (contained in DNA) inherited from parents at a particular gene locus
haploid the possession of one copy of each chromosome in a cell
heterozygous a genotype in which the two alleles are different
holobiont a host and their associated microbiota
hologenome the sum of genetic information of a host and its microbiota
homologous chromosomes with matching centromeres, gene locations, sizes and banding patterns
homozygous a genotype in which the two alleles are identical
homozygous dominant a genotype where both alleles for the dominant trait are present
homozygous recessive a genotype where both alleles for the recessive trait are present
induced mutation a mutation of DNA in which the cause can be identified
inheritance genetic transmission of characteristics from parents to offspring
karyotype an image that orders chromosomes based on their size
kinetochore a region on a chromosome associated with cell division
linkage analysis use of markers to scan the genome and map genes on chromosomes
locus position occupied by a gene on a chromosome
maternal chromosomes chromosomes from the ovum
meiosis cell division process that results in new cells with half the number of chromosomes of the original cell
messenger RNA (mRNA) single-stranded RNA transcribed from a DNA template that then carries the genetic to a ribosome to be translated into a protein
mitosis cell division process that results in new genetically identical cells with the same number of chromosomes as the original cell
molecular genetics study of genetics at a molecular level
monohybrid ratio the 3:1 ratio of a particular characteristic for offspring produced by heterozygous parents, controlled by autosomal complete dominant inheritance
monomers molecules that are the building blocks of larger molecules known as polymers
monosomy a condition where there is only one copy of a particular chromosome instead of two
mutagen agent or factor that can induce or increase the rate of mutations
mutations changes to DNA sequence, at the gene or chromosomal level
nitrogenous base a component of nucleotides that may be one of adenine, thymine, guanine, cytosine or uracil
nucleic acids molecules composed of building blocks called nucleotides, which are linked together in a chain
nucleotides compounds (DNA building blocks) containing a sugar part (deoxyribose or ribose), a phosphate part and a nitrogen-containing base that varies
nucleus roundish structure inside a cell that contains DNA and acts as the control centre for the cell
ova female reproductive cells or eggs
paternal chromosomes chromosomes carried in the sperm
pedigree chart diagram showing the family tree and a particular inherited characteristic for family members
phenotype characteristics or traits expressed by an organism
point mutation a mutation at one particular point in the DNA sequence, such as a substitution or single base deletion or insertion
polymerase chain reaction (PCR) a process which amplifies small amounts of DNA
polymers molecules made of repeating subunits of monomers joined together in long chains
prenatal screening testing a fetus during pregnancy to detect any abnormalities
proteins molecules, such as enzymes, haemoglobin and antibodies made up of amino acids
Punnett square a diagram used to predict the outcome of a genetic cross
recessive a trait (phenotype) that will only be expressed in the absence of the allele for the dominant trait
recombinant DNA a molecule of DNA that contains fragments from more than one source
recombinant DNA technology technology that can form DNA that does not exist naturally, by combining DNA sequences that would not normally occur together
restriction enzymes enzymes that cut DNA at specific base sequences (recognition sites)
restriction fragment length polymorphisms (RFLPs) variations in the lengths of DNA fragments in individuals with different alleles of a gene
retroposons segments of DNA that can break off a chromosome and paste themselves elsewhere in the genome
ribonucleic acid (RNA) a type of nucleic acid that contains ribose sugar
ribose the sugar found in nucleotides of RNA
ribosomal RNA (rRNA) a special type of RNA that forms the structure of ribosomes
ribosome organelle found in the cells of all organisms in which translation occurs
sex chromosomes chromosomes that determine the sex of an organism
sex-linked inheritance an inherited trait coded for by genes located on sex chromosomes
sexual reproduction reproduction that involves the joining together of male and female gametes
single nucleotide polymorphisms (SNPs) genetic differences between individuals that can result from single base changes in their DNA sequences
sister chromatids identical chromatids on a replicated chromosome
somatic cells cells of the body that are not sex cells
sperm male reproductive cell
spontaneous mutation a mutation of DNA that cannot be explained or identified
symbiotic a very close relationship between two organisms of different species
telomerase an enzyme involved in maintaining and repairing a telomere
telomere a cap of DNA on the tip of a chromosome that enables DNA to be replicated safely without losing valuable information
transcription the process by which the genetic message in DNA is copied into a mRNA molecule
transfer RNA (tRNA) molecules located in the cytosol that transport specific amino acids to complementary mRNA codons in the ribosome
transgenic organism an organism with genetic information from another species in its genome
translation the process in which amino acids are joined in a ribosome to form a protein
transposition the ability of a gene to change position on the chromosome
transposons a section of chromosome that moves about the chromosome within a cell through the method of transposition
triplet a sequence of three nucleotides in DNA that can code for an amino acid
trisomy a condition where there are three copies of a particular chromosome instead of two
variation differences between cells or organisms
zygote a cell formed by the fusion of male and female reproductive cells
Stages of Mitosis
DNA labels
Heterozygous mice
