MONOHYBRID
INHERITANCE
Monohybrid Inheritance

Inheritance of one characteristic controlled by one
gene, which can have two or more different alleles
at the same locus on a homologous pair.
Monohybrid Inheritance


Inheritance of one characteristic controlled by one
gene, which can have two or more different alleles
at the same locus on a homologous pair.
Individuals always inherit two alleles for each
characteristic (one from mum and one from dad).
Monohybrid Inheritance



Inheritance of one characteristic controlled by one
gene, which can have two or more different alleles
at the same locus on a homologous pair.
Individuals always inherit two alleles for each
characteristic (one from mum and one from dad).
The genetic information on the alleles is the
genotype.
Monohybrid Inheritance




Inheritance of one characteristic controlled by one
gene, which can have two or more different alleles
at the same locus on a homologous pair.
Individuals always inherit two alleles for each
characteristic (one from mum and one from dad).
The genetic information on the alleles is the
genotype.
The expression of this genetic information in the
individual is the phenotype.
Complete Dominance

Occurs when the info on one allele, the dominant
allele, is always expressed in the phenotype when
that allele is present in the genotype.
Complete Dominance


Occurs when the info on one allele, the dominant
allele, is always expressed in the phenotype when
that allele is present in the genotype.
The presence of a dominant allele masks the
presence of the recessive allele.
Complete Dominance



Occurs when the info on one allele, the dominant
allele, is always expressed in the phenotype when
that allele is present in the genotype.
The presence of a dominant allele masks the
presence of the recessive allele.
A recessive allele is expressed in the phenotype
only when both alleles in the genotype are
recessive.
Complete Dominance





Occurs when the info on one allele, the dominant
allele, is always expressed in the phenotype when
that allele is present in the genotype.
The presence of a dominant allele masks the
presence of the recessive allele.
A recessive allele is expressed in the phenotype
only when both alleles in the genotype are
recessive.
EG – Phenotype = dimples. Genotype = DD/Dd
Phenotype = smooth cheeks. Genotype = dd
Complete Dominance

When both alleles in the genotype are the same
(DD/dd) the individual is homozygous for that trait
and is said to be a pure breeder.
Complete Dominance


When both alleles in the genotype are the same
(DD/dd) the individual is homozygous for that trait
and is said to be a pure breeder.
When both alleles are different (Dd), the individual
is heterozygous for the trait (and isn’t a pure
breeder because it can pass either type of allele
on)
Punnetts







Cross an individual homozygous for dimpled cheeks
with an individual who has smooth cheeks
What are the genotypes of the offspring?
What are the phenotypes of the offspring?
F1 generation means the ones inside the square
Cross the offspring together
What is the ratio of dimpled to smooth?
What generation is this?
Punnetts

The expected ratio of phenotypes is the statistical
probability (likelihood) of the event occurring.
Punnetts


The expected ratio of phenotypes is the statistical
probability (likelihood) of the event occurring.
It is determined by chance
Punnetts



The expected ratio of phenotypes is the statistical
probability (likelihood) of the event occurring.
It is determined by chance
Two heterozygotes crossed need not have four
offspring and even if they do, they do not have to
produce the 3:1 ratio of phenotypes.
Punnetts




The expected ratio of phenotypes is the statistical
probability (likelihood) of the event occurring.
It is determined by chance
Two heterozygotes crossed need not have four
offspring and even if they do, they do not have to
produce the 3:1 ratio of phenotypes.
It could be possible that all four have the recessive
trait for example.
Punnetts





The expected ratio of phenotypes is the statistical
probability (likelihood) of the event occurring.
It is determined by chance
Two heterozygotes crossed need not have four
offspring and even if they do, they do not have to
produce the 3:1 ratio of phenotypes.
It could be possible that all four have the recessive
trait for example.
The dominant trait does not have to be the most
common.