Inherited change Flashcards
What is a Genotype
the genetic constitution of an organism and it describes all the alleles that an organism has
- the genotype determines the limits within which the characteristics of an individual may vary
What is a Phenotype
the 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 organisms phenotype
What is a gene?
a length of DNA that normally code for a particular polypeptide
- the polypeptide may be an enzyme that is needed in the biochemical pathway that leads to the production of the characteristic
- genes exist in two or more forms called alleles
- the position of a gene on a particular DNA molecule is known as the LOCUS
What is an allele?
one of the different forms of a gene
- only one allele of a gene can occur at the locus of any one chromosomes
homologous chromosomes
chromosome pairs one from each parent that are similar in length, gene position and centromere location
define homozygous
having two identical alleles of a particular gene
define hetrozygous
having two different alleles of a particular gene
Dominant and Recessive allele
The allele of the hetrozygote that expresses itself in the phenotype is said to be dominant whereas while the one that is not expressed is said to recessive
homozygous dominant
a homozygous organism with two dominant alleles
homozygous recessive
a homozygous organism with two recessive alleles
codominant
in some cases, two alleles both contribute to the phenotype
multiple alleles
sometimes a gene has more than two allelic forms
- they occur in the human ABO blood grouping system
What is a zygote?
The cell formed by the union of a sperm and an egg and the zygote develops into the embryo
What is an autosome?
A chromosome not considered as a sex chromosome
What is a sex chromosome?
A chromosome that involves the determination of the sex as well the development of sexual characteristics in an organism
What is monohybrid inheritance
the inheritance of a single gene
what is dihybrid inheritance
a cross between two different genes that differ in two observed traits
An example of dihybrid inheritance
one of Gregor Mendel investigated the inheritance of two characters of a pea plant at the same time. These were:
- seed shape: where round shape is dominated to wrinkled shape
- seed colour: where yellow-coloured seeds are dominant to green-coloured ones
When does co dominance occur?
when instead of one allele being dominant and the other recessive, both alleles are equally dominant. This means both alleles of a gene are expressed in the phenotype
What are multiple alleles and give an example
A gene that may have more than two alleles so it has multiple. An example of this is the inheritance of human ABO blood groups
- There are 3 alleles associated with the gene ! (immunoglobulin gene) which lead to the presence of different antigens on the cell surface membrane of red blood cells:
- allele I^A which leads to the production of antigen A
- allele I^B which leads to the production of antigen B
- allele I^O which doesn’t lead to the production of either antigen
> alleles I^A and I^B are codominant, wheread allele I^O is recessive
Sex inheritance in humans
In humans the sex chromosomes are X and Y this means:
- as females have two X chromosomes, all the gametes are the same in that they contain a single X chromosome
- males have one X chromosome and one Y chromosome, they produce two different types of gamete– half have an X chromosome and half have a Y chromosome
what is haemophilia?
- blood clots slowly and there may be slow and persistent internal bleeding
- the condition is mostly confined to males because haemophillic females usually died with the onset of mestruation of puberty
- haemophilia is a recessive allele with an altered sequence of DNA nucleotide bases that codes for a faulty protein that doesn’t function for blood clotting
inheriting haemophilia from mother
- as males only maintain their Y chromosome from their father ,it follows that their X chromosome from their mother
- As the defective allele that does not code for the clotting protein is linked to the X chromosome, males always inherit the disease
- if the mother doesn’t suffer from the disease, she may be heterozygous for the character (X^HX^h)
- as males pass the Y chromosome on to their sons, they can’t pass haemophilia to them, however they can pass the allele to their daughters via the X chromosome, who would then become carriers
Autosomal Linkage
The name given to the situation where two or more genes are carried on the same autosomal linkage
What are autosomes
the remaining 22 chromosomes other than sex chromosomes
Mendel’s Law of Independent Assortment
Assuming there is no crossing over, all the linked genes remain together during meiosis and so pass into gametes and hence the offspring. They do not segregate in accordance with Mendel’s Law of Assortment
When does Epistasis arise?
When the allele of one gene affects or masks the expression of another in the phenotype
Other forms of Epistasis
where genes act in a sequence by determining the enzymes in a biochemical pathway
