Inheritance
Humans are diploid organisms so we have two alleles for each gene whereas gametes
contain only one allele for each gene
Genetic diagrams can be used to predict the genotypes and phenotypes of the offspring
produced if two parents crossed/bred
Monohybrid inheritance is the inheritance of a characteristic controlled by a single gene.
Monohybrid crosses show the likelihood of the different alleles of that gene being inherited
by offspring of certain parents
Codominant alleles:
Occasionally, alleles show codominance where both alleles are expressed in the phenotype,
neither one is recessive e.g. sickle-cell anaemia allele in humans. Therefore, people who are
heterozygous have an in-between phenotype called the sickle-cell trait- they have some
normal haemoglobin and some sickle haemoglobin.
, Multiple alleles are where there are more than two alleles, of which only two may be
present at the loci of an individual’s homologous chromosome Some characteristics are sex-
linked:
- The genetic information for biological sex is carried on two sex chromosomes.
Females have XX and males have XY
- A characteristic is said to be sex-linked when the allele that codes for it is located on
a sex chromosome
Humans are diploid organisms so we have two alleles for each gene whereas gametes
contain only one allele for each gene
Genetic diagrams can be used to predict the genotypes and phenotypes of the offspring
produced if two parents crossed/bred
Monohybrid inheritance is the inheritance of a characteristic controlled by a single gene.
Monohybrid crosses show the likelihood of the different alleles of that gene being inherited
by offspring of certain parents
Codominant alleles:
Occasionally, alleles show codominance where both alleles are expressed in the phenotype,
neither one is recessive e.g. sickle-cell anaemia allele in humans. Therefore, people who are
heterozygous have an in-between phenotype called the sickle-cell trait- they have some
normal haemoglobin and some sickle haemoglobin.
, Multiple alleles are where there are more than two alleles, of which only two may be
present at the loci of an individual’s homologous chromosome Some characteristics are sex-
linked:
- The genetic information for biological sex is carried on two sex chromosomes.
Females have XX and males have XY
- A characteristic is said to be sex-linked when the allele that codes for it is located on
a sex chromosome
