46 terms

IGCSE Topic 19: Mutation, variation and sexual reproduction

Meiosis and the basis of variation.
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Acrosome
The bag of enzymes carried on the tip of a sperm that allows it to penetrate the coat around the egg cell.
Allele
A form of a particular gene; may affect the way in which that gene functions in the organism.
Antibiotic
A chemical drug that can kill bacteria or stop them from growing but that is safe to use in people or animals.
Antibiotic resistance
Genetic changes caused by rare mutation, that cause some bacteria to become unaffected by specific antibiotics.
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.
Chromosome mutation
Defect in a gamete caused by loss of a chromosome or keepng two copies of a chromosome. Can lead to problems like Down's syndrome.
Cystic fibrosis
A genetic condition that causes sticky mucus in the lungs and leaves sufferers very prone to infection
Daughter cell
One of the two genetically identical cells formed by mitosis, or the four non-identical cells formed after meiosis.
Deoxyribonucleic acid
The chemical name abbreviated as DNA.
Fertilise
To form a diploid zygote by fusion of haploid sperm and egg cells.
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.
Gamete
A haploid sex cell such as ovum, sperm or pollen grain.
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. Conrols the characteristics of an organism.
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.
Gi(g)antism
Growth that is significantly greater than normal often caused by over production of growth hormone
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.
Identical twins
Genetically identical individuals formed when an early embryo splits into two and both halves go on to produce a foetus.
Inbreeding
Term describing selective breeding techniques where individuals that are closely related are allowed to mate.
Internal fertilisation
When the sperm fuses with the egg inside the body.
Ionising radiation
Type of radiation such as UV, X ray or gamma rays that can cause mutations in DNA.
Karyotype
Diagram or picture that displays the chromosomes found in a cell at mitosis.
Malignant
A invasive tumour that can spread through the body is described as this.
Meiosis
Special form of cell division that generates haploid sex cells. Forms four non-identical daughter cells.
Mitosis
Normal cell division involving the production of two genetically identical daughter cells. Used for growth, repair and asexual reproduction.
Monozygotic twins
Genetically identical individuals formed when an early embryo splits into two and both halves go on to produce a foetus.
Mutagen
Something that can increase the frequency of mutations in DNA. e.g. certain chemicals or uv radiation.
Mutation
A change to the sequence of bases in DNA. Can be caused by chemicals, radiation, mistakes in copying DNA or during chromatid separation.
Replication
The process of making a copy of a DNA molecule during cell division (mitosis or meiosis).
Reproduction
Characteristic of living organisms. The ability to produce new members of the same species.
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.
Sexual reproduction
Reproduction that involves the fusion of haploid gametes from two parents. Generates variation in offspring.
Sickle cell anaemia
Inherited condition caused by a mutation in one of the genes for haemoglobin. Heterozygous individuals have some resistance to malaria.
Sperm
Mobile sex cell or gamete produced by the male of the species.
Spindle fibres
Protein fibres in the cell that pull apart sister chromatids during mitosis and meiosis.
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.
Variation
Differences between individuals resulting from a combination of genetic and environmental factors.
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.
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