Inherited change Flashcards
What is the genotype?
The genetic constitution of an organism.
It describes all the alleles that an organism has.
How is the genotype affected?
It may determine that a human baby could grow to be 1.8m tall, but the actual height that this individual reaches is affected by other factors, such as diet.
A lack of an element, like calcium, at a particular stage of development could mean that the individual never reaches their potential maximum height.
What is the phenotype?
The observable characteristics of an organism.
It is the result of interaction between the expression of the genotype and the environment.
The environment can alter an organism’s phenotype.
What is a gene?
A length of DNA - a sequence of nucleotide bases - that normally code for a particular polypeptide.
This polypeptide may be an enzyme that is needed in the biomechanical pathway that leads to the production of the characteristic (e.g. codes for a brown pigment in the iris).
The locus is the position of a gene on a particular DNA moleucle.
What is an allele?
Genes exist in two or more different forms called alleles.
What are homologous chromosomes?
Only one allele of a gene can occur at the locus of any one chromosome.
However, in diploid organisms, the chromsomes occur in pairs called homologous chromosomes.
There are therefore two loci that each carry one allele of a gene.
What is homozygous?
When the allele on each chromosome is the same.
If the two alleles are different, then the organism is heterozygous for the characteristic.
What is recessive and dominant?
Dominant alleles are always expressed in the phenotype.
Recessive are only present if no dominant alleles are present.
What is codominance?
When two alleles contribute to the phenotype.
In this situation, when both alleles occur together, the phenotype is either a blend of both features, or both features are represented.
What are multiple alleles?
Sometimes a gene has more than two allelic forms.
However, as there are always only two characteristics in a homologous pair, it follows that only two of the three or more alleles in existence can be present in a single organism.
Multiple alleles occur in the human ABO blood grouping system.
What is pure-breeding?
Example of Mendel’s peas:
If green pod peas are bred repeatedly with each other so they consistently give rise to green pod plants, it’s pure breeding for green pods.
The organisms are homozygous for that particular gene.
What happens when the F1 generation is bred?
The heterozygous plants are crossed with one another, the offspring, F2, are in approximate ration of 3:1 of green to yellow.
Why are actual results of genetic crosses different to predicted results?
It is chance which gametes fuse with which.
The larger the sample, the more likely the actual results are to come near to matching the theoretical ones.
It is therefore important to use large numbers of organisms in genetic crosses if representative results are to be obtained.
What is an example of codominance?
In the snapdragon plant, one allele codes for an enzyme that catalyses the formation of a red pigment in flowers.
The other allele codes for an enzyme that lacks catalytic activity and so does not produce pigment.
This produces three colours as it is codominant.
What are the different phenotypes of the snapdragon?
In homozygous red, both alleles code for the enzyme, and hence the pigment production, so produce red flowers.
Homozygous white, both alleles produce no enzyme or pigment, so produces white flowers.
Heterozygous plants produce pink flowers.
