Biology | S-cool, the revision website

What are the key terms in genetics

By Abbas Abid Mon, 02/27/2017 - 19:04

Biology GCSE

I found this but you need to make sure that you only learn the ones that are on your specification or you will waste a lot of time and effort
Alleles
alternate forms or varieties of a gene. The alleles for a trait occupy the same locus or position on homologous chromosomes and thus govern the same trait.
Amino acid
organic molecules that are building block of proteins. There are 20 different kinds of amino acids in living things. Proteins are composed of different combinations of amino acids assembled in chain-like molecules during the process of protein synthesis.
Chromosomes
thread-like, gene-carrying bodies in the cell nucleus. They are visible only under magnification during certain stages of cell division. Humans have 46 chromosomes in each somatic cell and 23 in each sex cell.
Codon
a sequence of three nucleotide bases in RNA that codes for a specific amino acid.
Crossing-over
the exchange of genetic material between homologous chromosomes in meiosis. This result in gametes with greater genetic diversity. Specifically, a portion of a chromosome is broken and reattached on another chromosome. Also referred to as Recombination.
DNA (deoxyribonucleic acid):
a large organic molecule that stores the genetic code. DNA id composed of sugars, phosphates and bases arranged in a double helix shaped molecular structure. Segments of DNA in chromosomes correspond to specific genes.
Dominant allele
an allele that masks the presence of a recessive allele.
Double helix
the twisted ladder shapes that is characteristic of DNA molecules
Eukaryotic
multicelluar organisms (contrasted with prokaryotic or single-celled organisms)
Evolution
genetic change in a population of organisms that occurs over time.
Exon
a coding region of DNA. They are transcribed to the final mRNA molecule (contrasted with introns which are non-coding regions that are spliced out from the tRNA molecule)
Founder effect
a small population effect in which the genes of a few people (the population founders) are inherited over time by a large number of descendants.
Gametes
sex cells: sperm or unfertilized egg cells produced in the testes and ovaries of animals. Gametes are produced by meiosis. They have half the number of chromosomes found in somatic cells.
Genes
units of inheritance usually occurring at specific location, or loci, on a chromosome. A gene may be made up of hundreds of thousands of DNA bases. Genes are responsible for hereditary characteristics.
Gene flow
the transference of genes from one population to another, usually as a result of migration. The loss or addition of individuals can change the gene frequencies of both the recipient and donor populations.
Gene pool
all of the genes in all of the individuals in a breeding population.
Genetic drift
random changes in gene frequencies resulting from chance. Genetic drift occurs in small populations.
Genotype
the genetic makeup of an individual. Genotype can refer to an organism's entire genetic makeup or the alleles at a particular locus.
Heritability
the percentage of phenotypic variation attributable to genotypic variation.
Heterozygous
a genotype consisting of two different alleles of a gene for a particular trait (Tt).
Homeotic
genes involved in the regulation of development. A type of regulatory gene
Homologous chromosomes
chromosomes that are paired during meiosis. Such chromosomes are alike with regard to size and also position of the centromere. They also have the same loci coding for the same traits.
Homozygous
having the same allele at the same locus on both members of a pair of homologous chromosomes. An individual may be homozygous dominant (TT) or homozygous recessive (tt).
Macroevolution
major evolutionary changes in a population's gene pool, occurring over many generations, resulting in the development of new species.
Meiosis
cell division in specialized tissues of ovaries and testes, which results in the production of gametes. Meiosis involves two divisions and results in four daughter cells, each containing only half the original number of chromosomes—23 in the case of humans.
Microevolution
changes in gene frequencies from one generation to the next. The accumulation of micro evolutionary change can result in macroevolution.
Mitosis
the simple cell division process that occurs in somatic cells. One cell divides into two offspring cells that are identical to each other in chromosome complement
Mutation
an alteration of genetic material such that a new variation is produced. For instance, a trait that has only one allele (A) can mutate to a new form (a). This is the only mechanism to produce NEW variation. There are numerous types of mutations, including point mutations, "silent" mutations and chromosomal mutations,
Natural selection
an evolutionary mechanism that occurs when some individuals of a population are better able to adapt to their environment and subsequently, produce more offspring. Differential reproductive success between individuals is the key. Those who produce more offspring have a greater influence on the gene frequencies of the next generation.
Non-random mating
mate selection based on one or more traits that are discriminated for or against. This is a mechanism of evolution. Includes positive and negative.
Nucleotide
the basic building block of DNA and RNA. It consists of any one of four bases attached to a sugar and phosphate.
Phenotype
the observable or detectable characteristics of an individual organism: the physical expression of a genotype.
Population
a more or less distinct group of individuals within a species who tend to restrict their mate selection to members of their group. Members of a population tend to have similar genetic characteristics due to generations of interbreeding.
Proteins
any of a large number of complex organic molecules that are composed of one or more chains of amino acids. Proteins serve a wide variety of functions. Proteins may be enzymes, hormones, antibodies, structural components, or gas-transporting molecules.
Recombination
shuffling of chromosomal alleles during the process of meiosis
Recessive allele
an allele that is masked in the phenotype by the presence of a dominant allele. Recessive alleles are expressed in the phenotype when the genotype is homozygous recessive (tt).
RNA (ribonucleic acid)
a type of nucleic acid that is found in both the nucleus and the cytoplasm of cells. Unlike DNA, RNA is single stranded. Messenger RNA (mRNA) carries the genetic code from the DNA and translates it with the help of transfer RNA (tRNA) at the site of the ribosomes in the cytoplasm in order to synthesize proteins.
Speciation
the evolution of new species from older ones.
Species
a natural population of organisms that can interbreed to produce fertile offspring. Members of one species are reproductively isolated from members of all other species (i.e., they cannot mate with them to produce fertile offspring)
Zygote
fertilized egg

Tabitha Farrant Tue, 02/28/2017 - 10:27

There is an image here
http://www.s-cool.co.uk/a-level/biology/nervous-and-hormonal-control/rev...
We can put neurones into three groups on the basis of what they do:
1 sensory neurones Carries impulses from receptors to the CNS.
2 motor neurones Carries impulses from the CNS to the effector.
3 relay neurones Co-ordinate the response. Are link neurones in the CNS.
Sensory neurons have longer dendrites & shorter axons.they carry impulses from sensory organs to spinal cord/brain.
motor neurons have longer axons & shorter dendrites.they carry impulses from spinal cord/brain to the effector organs.
Receptors are cells that detect stimuli - for example, heat, pressure, light.
Sensory neurones bring impulses from receptors to the central nervous system (CNS). These are very long cells as they have to carry the impulse from the body to the place where the response is managed.
From there, the impulse may pass on to a motor neurone to be taken to a muscle or gland (the effector).
Sometimes there is an intermediate neurone (also known as a 'relay' neurone) within the CNS linking the sensory neurone with the motor neurone.

Tabitha Farrant Fri, 03/03/2017 - 14:35