inherited change- chapter 17 Flashcards
what is a genotype
- Is the genetic constitution of an organism
- Describes all the alleles that an organism has
- It determines the limits within which the characteristics of an individual may vary.
what is a phenotype
- Is the observable or biochemical characteristics of an organism.
- It is the result of the 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, that is, a sequence of nucleotide bases, that normally code for a particular polypeptide.
- This polypeptide may be an enzyme that is needed in the biochemical pathway that leads to the production of the characteristics.
- Genes exist in two, or more, different forms called alleles.
what is a locus
The position of a gene on a particular DNA molecule
what is an allele
- Is one of the different forms of a gene.
- Only one allele of a gene can occur at the locus of any one chromosome.
what are homozygous chromosomes
- when in diploid organisms the chromosomes occur in pairs
- There are two loci that each carry one allele of a gene.
what is homozygous
If the chromosomes are the same
what is heterozygus
- If the alleles are different
- Only one will show itself in the phenotype. The allele that expresses itself is said to be dominant, while the one that is not expressed is recessive.
what is homozygous dominant
A homozygous organism with two dominant alleles.
what is homozygous recessive
two recessive alleles.
what is codominance
- Occurs where instead of one allele being dominant and the other recessive, both alleles are equally dominant.
- This means that both alleles of a gene are expressed in the phenotype.
how many pairs of chromosomes do humans have
23
what is sex linkage
- Any gene that is carried on either the X or Y chromosome is said to be sex-linked.
- However, the X chromosome is much longer than the Y chromosome.
- This means that, for most of the length of the X chromosome, there is no equivalent homologous portion of the Y chromosome.
- Those characteristics that are controlled by recessive alleles on this non-homologous portion of the X chromosome will appear more frequently in the male, this is because there is no homologous portion on the Y chromosome that might have the dominant allele, in the presence of which the recessive allele does not express itself.
what is haemophilia
- Blood clots only slowly and there may be slow and persistent internal bleeding, especially in the joints.
- It is potentially lethal if not treated which has resulted in some selective removal of the gene from the population.
- condition is almost entirely confined to males
what is the main cause of haemophilia
- is a recessive allele with an altered sequence of DNA nucleotide bases that therefore codes for a faulty protein which does not function.
- This results in an individual being unable to produce a functional protein that is required in the clotting process.
- The production of this functional protein by genetically modified organisms means that it can now be given to haemophiliacs allowing to lead near-normal lives.
- The disease always comes from the mother as it’s an X linked disease.
what are autosomes
22 pairs of chromosomes (not sex chromosomes)
what is autosomal linkage
- The name given to the situation where two or more genes are carried on the same autosome
- All the link genes remain together during meiosis and so pass into gametes together.
what forms a linkage group
All the genes on a single chromosome
when does epistasis arise
when the allele of one gene affects or masks the expression of another in the phenotype
