58 terms

IGCSE Topic 17: Inheritance

Genetice; how different forms of genes are passed on.
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Allele
A form of a particular gene; may affect the way in which that gene functions in the organism.
Anti-sense strand
The strand of DNA in a gene that is not used to code for protein.
Base
One of the chemical units A, G, C or T that carries the genetic code in a molecule of DNA.
Base pairing rule
Refers to the way in which the bases in DNA interact to hold together the double helix. A always pairs with T; G pairs with C.
Characteristic
An observable feature of an organism
Chromatid
One half of a newly replicated chromosome. Contains one molecule of DNA.
Chromosome
A very large single molecule of DNA that carries a set of genes. DNA is wrapped around proteins called histones. After replication, consists of two chromatids held together at the centromere.
Codominant
Where a pair of different alleles of gene both contribute to the phenotype.
Colour blindness
An inherited condition in which one or more of the three type of cone cell are unable to respond to coloured light.
Complementary bases
Refers to the fact that in DNA, A (adenine) always pairs with T (thymine); G (guanine) always pairs with C (cytosine).
Complete dominance
Situation when individuals who are heterozygous for a recessive allele are identical to individuals that are homozygous for the dominant allele.
Cystic fibrosis
A genetic condition that causes sticky mucus in the lungs and leaves sufferers very prone to infection
Cytosine
One of the four bases (C) found in the DNA molecule.
Deoxyribonucleic acid
The chemical name abbreviated as DNA.
Diploid
A cell carrying two copies of every chromosome and therefore two alleles of every gene is described as this.
DNA
A larage polymer of sugar phosphate molecules carrying four possible bases that carries the genetic information in the cell.
Dominant
Type of allele which exerts its affect in an organism that carries two different alleles. The opposite to recessive.
Double helix
The structure adopted by the two strands of DNA as it zips up following the base-pairing rules.
Down's syndrome
A human genetic abnormality where an embryo develops with three copies of chromosome 21
F1 generation
The first generation of offspring from an experimental breeding experiment.
F2 generation
Offspring produced by crossing individuals from the F1 generation.
Fingerprinting
A way of analysing an individual's DNA that gives a pattern that is unique to that individual. Many uses in forensics and genetic analysis.
Fraternal twins
Non-identical individuals formed when two eggs are fertilised to form two zygotes, both of which implant and go on to produce foetuses.
Gene
A stretch of DNA that carries a specific instruction within the cell. Usually carries information on the sequence of amino acids within a specific protein. Controls the characteristics of an organism.
Genetic code
The way in which genetic information is carried in the sequence of the four chemical bases.
Genome
All the genetic material in an organism's cells.
Genotype
This describes the alleles - normally two in a diploid - present in an organism for a particular gene.
Guanine
One of the four bases (G) found in the DNA molecule.
Haemophilia
Genetic disease affecting the ability of the blood to clot
Haploid
A cell - such as a gamete - carrying only one copy of each chromosome is described as this.
Heterozygous
Carrying two different alleles of a gene.
Homologous (pair)
Term to describe the two chromosomes in a diploid cell that carry the same set of genes (though they may have different alleles).
Homozygous
Carrying two identical alleles of a gene.
Hydrogen bonds
Weak bonds that can form with hydrogen atoms in a molecule. Important in protein shape and between complementary bases in DNA.
Identical twins
Genetically identical individuals formed when an early embryo splits into two and both halves go on to produce a foetus.
Karyotype
Diagram or picture that displays the chromosomes found in a cell at mitosis.
Monozygotic twins
Genetically identical individuals formed when an early embryo splits into two and both halves go on to produce a foetus.
Nitrogenous base
Nitrogen-containing part of a nucleotide in DNA. Four are used in DNA abbreviated as A, G, C and T.
Nucleotide
One of the units that is joined together to make DNA. Consists of a sugar, a phosphate group and a nitrogenous base.
Nucleus
The membrane bound structure (organelle) within the cell where the genetic material is stored.
Ovum (ova)
Egg. Female gamete.
Pedigree
A genetic family history.
Phenotype
The physical characteristics of an organism - what it looks like.
Polynucleotide
A large polymer, such as DNA, made up of repeating nucleotide units.
Punnet square
The diagrams used to work out the offspring of a particular genetic cross.
Pure breeding
Strains of plants or breeds of animal which give rise to similar offspring when they are bred.
Recessive
Type of allele which does not exert its affect in an organism that carries another allele. The opposite to dominant.
Replication
The process of making a copy of a DNA molecule during cell division (mitosis or meiosis).
Sex cell
A haploid cell or gamete i.e. sperm or egg is also known as this.
Sex determination
The way in which inheritance of sex chromosomes controls primary sexual characteristics in an organism.
Sperm
Mobile sex cell or gamete produced by the male of the species.
Test cross
Genetic experiment using one parent with a known homozygous recessive genotype to work out the genotype of another parent with the dominant phenotype that could be homozygous or heterozygous.
Thymine
One of the four bases (T) found in the DNA molecule.
Triplet code
Describes the way in which groups of three bases code for a single amino acid in a protein.
Trisomy
Chromosomal abnormality where cells have three copies of a particular chromosome rather than two. Usually fatal (except for Down's syndrome).
Universal code
Describes the fact that the code used to convert DNA sequences into protein sequences is the same in all organisms on Earth.
Watson and Crick
The two scientists credited with the discovery of the structure of DNA in Cambridge in 1953.
Zygote
The first diploid cell formed by the fusion of gametes at fertilisation.