Inherited change Flashcards
1
Q
What is inheritance?
A
- the fact that children resemble both their parents to a greater or lesser degree and yet are identical to neither has long been recognised
- however, it took the re-discovery, at the beginning of the last contrary, of the work of a scientist and monk, called Gregory Mendel, to establish the basic laws by which characteristics are inherited
- characteristics are inherited from one generation to the next and how this can produce genetic variety within a population
- let us begin by looking at some of the terms and conventions that are used in studying inheritance
2
Q
What are genotypes?
A
- genotype is the genetic constitution of an organism
- it describes all he alleges that an organism has
- the genotype determines the limits within which the characteristics of an individual may vary
- it may determine that the 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 for the growth of bone at a particular stage of development could mean that the individual never reaches his/her potential maximum height
3
Q
What are phenotypes?
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
4
Q
What are genes?
A
- a gene is a length of DNA that is a sequence of nucleotide bass, that normally code for a particular polypeptide
- a gene does this by coding for a particular polypeptide
- this polypeptide may be an enzyme that is needed in the biochemical pathway that leads to the production of the characteristic for example, a gene could code for a brown pigment in the iris of the eye
- genes exist in two, or more different forms called alleges
- the position of a gene on a particular DNA molecule is known as the locus
5
Q
What are alleges?
A
- an allege is one of the different forms of a gene
- in pea plants, for example, there is a gene for the colour of the seed pod
- this gene has two different forms or alleles, an allele for a green seed pod and another allele for a yellow pod
6
Q
What are homologous chromosomes?
A
- only one allele of a gene can occur at the locust of any one chromosome
- however, in diploid organisms the chromosomes occur in pairs called homologous chromosomes
- there are therefore two loci that each carry one allege of gene
- if the allele on each of the chromosome is the dame for example, both alleges for green pods are present then the organism is said to be homozygous for the character
- if the two alleles are different for example, one chromosome has an allele for green pods and the other chromosome has an allele for yellow pods then the organism is said to be heterozygous for the characteristic
7
Q
What happens when two alleles are present in the phenotype?
A
- in most cases where two different alleges are present in the genotype (heterozygous state) only one of them shows itself in the phenotype
- for instance in our example where the alleges for green pods and yellow pods are present in the genotype, the phenotype is always green pods
- the allege of the heterozygote that expresses itself in the phenotype is said to be dominant, while the one that is not expressed is said to be recessive
- a homozygous organism with two dominant alleges called homozygous dominant, whereas one with two recessive alleges is called homozygous recessive
- the effect of a recessive allege is apparent in the phenotype of a diploid organism only when it occurs in the presence of another identical allege, that is, when it is in the homozygous state
8
Q
What happens when two alleles both contribute to the phenotype
A
- in some cases, two alleges both contribute to the phenotype, in which case they are referred to as codominant
- in this situation when both alleges occur together, the phenotype is either a blend of both features for example, shorten cattle with roan coat colour resulting from an allege for red hairs and an allege for white hairs or both features are represented for example the presence of both A and B antigens in blood group AB
9
Q
What happens when a gene has more than two allelic forms?
A
- in this case the organism is said to have multiple alleges for the character
- however as there are always only two chromosomes in a homologous pair, it follow that only two of the three or more alleges in existence can be present in a single organism
- multiple alleges occur in the human ABO blood grouping system
10
Q
What is diploid?
A
cells in the nucleus that contain two sets of each chromosomes
11
Q
What is haploid?
A
refers to all cells that contain a single copy of each chromosome
12
Q
What is homozyous?
A
all alleles of a particular gene are identical
13
Q
What is heterozygous?
A
alleles of a particular gene are different
14
Q
What is dominant?
A
an allele that is always expressed in the phenotype of an organism
15
Q
What is recesive?
A
the effect of an allele is only presented in a diploid organism in the presence of another identical allele
