Timaru Girls’ High School
Level 2 Biology
External
4 Credits
Keywords for Unit: 2.5 - Demonstrate
Understanding of Genetic Variation and Change
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Allele
One of the alternative forms of a gene.
Amino acids
Any of a group of water-soluble organic compounds that possess both a
carboxyl(-COOH) and an amine (-NH2) group attached to the same carbon
atom.
Anticodon
A sequence of three nucleotides on a tRNA molecule that matches with a
specific codon on a strand of mRNA during translation.
Centromere
The part of a chromosome that attaches to the spindle during cell division.
Chromatid
A threadlike strand formed from a chromosome during the stages of cell
division.
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Chromosome
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Cloning
A threadlike structure made of DNA and (in eukaryotes) associated histone
proteins on which the genetic information of an individual is stored.
artificial production of genetically identical individuals
Co-dominance
The condition that arises when both alleles in a heterozygous organism are
dominant and fully expressed - eg. the human blood group AB.
Codon
A triplet of nucleotides within a molecule of messenger RNA that specifies
a particular amino acid during the synthesis of proteins in a cell.
Diploid
Describing a cell or organism with twice the haploid number of
chromosomes.
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DNA
Deoxyribonucleic acid. The genetic material of most living organisms. It
plays a central role in the determination of hereditary characteristics by
controlling protein synthesis in cells.
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Dominant
allele
Double Helix
The allele that is expressed when two different alleles of a gene are
present in the cells of an organism. It is denoted by a capital letter.
ladder-like molecule twisted into a helix
Eukaryotic
cells
Cells that have a distinct nucleus where the cell’s genetic information is
stored.
F1 generation
The first generation of offspring resulting from an arranged cross between
selected parents in breeding experiments.
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F2 generation
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Fertilization
The second generation of offspring in breeding experiments, obtained by
crosses between individuals of the F1 generation.
fusing of an egg and sperm
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Gametes
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Gene
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A reproductive cell that fuses with another to form a zygote - eg. eggs (ova)
and sperm (spermatozoa).
A section of DNA that codes for a particular protein and cannot be broken
by recombination.
Genetic code
The genetic information in DNA which controls the manufacture of specific
proteins by the cell. It takes the form of a series of triplets of bases in DNA.
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Genome
All the genes contained in a single (haploid) set of chromosomes.
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Genotype
The genetic composition of an organism, i.e. the combination of alleles it
possesses.
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Haploid
Describing a cell or organism with a single set of unpaired chromosomes.
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Heterozygous
Describes an organism that has two different alleles controlling a particular
feature.
Histone
Water-soluble proteins found in association with the DNA of eukaryotic
chromosomes. They serve as a scaffold around which the DNA coils.
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Homozygous
Matching pairs of chromosomes, i.e. Chromosomes that have the same
structural features. In diploid cells, one chromosome comes from the
female parent, the other from the male parent.
Describes an organism that has two of the same alleles for a trait.
Incomplete
dominance
The condition where neither allele controlling a characteristic is dominant
and the resulting phenotype is partially influenced by both alleles.
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Independent
assortment
The separation of the alleles of one gene into gametes independently of
the way in which the alleles of other genes have segregated.
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Inheritance
The transfer of genetic traits from one generation to the next.
Lethal genes
A mutant form of a gene that eventually results in the death of an organism
if expressed in the phenotype. Most of these genes are recessive, eg.
Sickle-cell anaemia.
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Homologous
Chromosomes
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Meiosis
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Mitosis
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A type of cell division that gives rise to four gametes each with half the
chromosome number of the parent cell.
A type of cell division that results in two daughter cells, each having a
nucleus containing the same number and kind of chromosomes as the
mother cell.
Monohybrid
The offspring of a cross between parents that differ in the alleles they
possess for one particular gene, one parent having two dominant alleles,
the other two recessives.
mRNA
RNA that carry’s the genetic code transcribed from DNA to the ribosomes.
Multiple alleles
Three or more alleles that produce different versions of the same protein.
Eg. The human ABO blood group system has three alleles IA, IB and i. IA
and IB are co-dominant alleles.
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Nucleotide
An organic compound consisting of a nitrogen-containing purine or
pyrimidine base linked to a sugar and a phosphate group.
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Pedigree Chart
Phenotype
a chart used to identify genotypes in families
The observable characteristics of an organism.
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Prokaryotic
cells
Cells where the genetic material is not enclosed in a cell nucleus.
Protein
synthesis
The process by which living cells assemble amino acids into proteins
based on the genetic information carried in the DNA of the chromosomes.
Punnett
Square
A grid used to calculate the expected offspring phenotype ratios resulting
from a cross between two parents of known genotypes.
Pure-breeding
A lineage where characteristics are passed on unchanged from generation
to generation.
Purines
The chemical family to which the organic nitrogenous bases adenine and
guanine belong.
Pyrimidines
The chemical family to which the organic nitrogenous bases uracil, thymine
and cytosine belong.
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Recessive
allele
An allele whose effects are masked by those of a dominant allele. It is
denoted by a lower case letter.
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rRNA
A type of RNA that is present in the ribosomes.
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SelfReplication
ability of DNA molecules to make identical copies of themselves
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Somatic cells
All cells in the body other than the reproductive cells.
Test-cross
An organism with a dominant phenotype may possess two dominant
alleles, or one dominant and one recessive. This can be determined by
crossing it with an organism showing the recessive characteristic (ie.
homozygous recessive).
Trait
feature whose appearance is determined by genes (inherited)
Transcription
The process in living cells in which the genetic information of DNA is
transferred to a molecule of mRNA as the first step in protein synthesis.
Translation
The process in living cells in which a sequence of mRNA triplets (codons)
is used to build a polypeptide chain during protein synthesis.
Triplet
A sequence of three nucleotides coding for a specific amino acid during
protein synthesis.
tRNA
RNA that is responsible for bringing specific amino acids to the site of
translation on the ribosome.
Variation
Differences between organisms created by their different genetic make-up.
It can either be discrete, where a trait is controlled by a single gene; or
continuous, where a trait is influenced by several genes.
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