Inherited change
Studying inheritance
Genotype – all of the alleles that an organism carries on its chromosomes.
Phenotype – observable characteristics of an organism which the result of the genotype as
well as environmental factors.
Most organisms are diploid and therefore carry two alleles for each gene that they possess
on each chromosome. Alleles can either be:
- Dominant – only a single allele is required for the characteristic to be expressed in
the phenotype. Whether the organism only has one dominant allele (heterozygous
dominant) or has two dominate alleles (homozygous dominant) the trait will be
expressed.
- Recessive – the characteristic is only expressed if there is no dominant allele
present. It therefore means that there must be two recessive alleles (homozygous
recessive) present in order for the phenotype to be expressed.
- Codominant – both alleles are expressed equally and contribute to the phenotype,
either being a blend of the two characteristic or both characteristics being seen
together.
The term pure breeding is often used and means that it is a homozygous pair of alleles.
Remember an allele is an alternative form of a gene and the locus is the specific position of
the gene on the chromosome. The two alleles (or more if there is more than two) for the
gene are both found at the same loci on the homologous pairs of chromosomes.
, Monohybrid inheritance
Monohybrid inheritance is when a phenotype or trait is controlled by a single gene. For
instance, cystic fibrosis where the individuals with doubly recessive phenotype are affected.
How to answer a monohybrid inheritance question:
Studying inheritance
Genotype – all of the alleles that an organism carries on its chromosomes.
Phenotype – observable characteristics of an organism which the result of the genotype as
well as environmental factors.
Most organisms are diploid and therefore carry two alleles for each gene that they possess
on each chromosome. Alleles can either be:
- Dominant – only a single allele is required for the characteristic to be expressed in
the phenotype. Whether the organism only has one dominant allele (heterozygous
dominant) or has two dominate alleles (homozygous dominant) the trait will be
expressed.
- Recessive – the characteristic is only expressed if there is no dominant allele
present. It therefore means that there must be two recessive alleles (homozygous
recessive) present in order for the phenotype to be expressed.
- Codominant – both alleles are expressed equally and contribute to the phenotype,
either being a blend of the two characteristic or both characteristics being seen
together.
The term pure breeding is often used and means that it is a homozygous pair of alleles.
Remember an allele is an alternative form of a gene and the locus is the specific position of
the gene on the chromosome. The two alleles (or more if there is more than two) for the
gene are both found at the same loci on the homologous pairs of chromosomes.
, Monohybrid inheritance
Monohybrid inheritance is when a phenotype or trait is controlled by a single gene. For
instance, cystic fibrosis where the individuals with doubly recessive phenotype are affected.
How to answer a monohybrid inheritance question:
