Chapter 16 Monohybrid inheritance
16.3 - Monohybrid Inheritance
1. Essential genetics vocabulary
2. Monohybrid crosses in genetic diagrams and Punnett squares
3. What a test cross is
Essential genetics vocabulary
Genetics is the study of genes and how characteristics are inherited.
To understand genetics, you first need to get to grips with some key terminology.
Term Definition
A sequence of bases on a DNA molecule that codes for a protein
Gene
(polypeptide), which results in a characteristic, e.g. a gene for eye colour
Different versions of the same gene that code for variants of a characteristic.
Allele
Represented by letters, e.g. B = brown eyes, b = blue eyes
Genotype An organism's genetic makeup - its alleles, e.g. BB, Bb, or bb
An organism's physical characteristics as determined by its genotype and
Phenotype
environment
An allele that is always expressed in the phenotype, even when only one copy
Dominant
is present in the genotype (shown with an uppercase letter)
An allele that is only expressed when it is homozygous in the genotype (two
Recessive copies are present), and is masked by a dominant allele (shown with a
lowercase letter)
Locus A locus (plural: loci) is the specific position of a gene on a chromosome
Homozygous An organism with two identical alleles for a trait is homozygous
Heterozygou
An organism with two different alleles for a trait is heterozygous
s
, Monohybrid crosses in genetic inheritance diagrams
Humans are diploid organisms and almost always have two copies of each gene. This means they
have two alleles for every characteristic. Gametes (sex cells) are haploid, which means that they
have one allele per gene.
Monohybrid (monogenic) inheritance involves the transmission of one gene from parents to their
offspring.
A monohybrid cross tracks the inheritance pattern of the alleles for a single characteristic, controlled
by one gene with two possible alleles.
Genetic diagrams
Genetic diagrams illustrate how parents can pass on alleles to their offspring. They can be used to
predict possible genotypes and phenotypes in the next generation.
The F1 generation:
This is the offspring from a cross between individuals with homozygous dominant and
homozygous recessive genotypes.
All the offspring will be heterozygous, inheriting a recessive allele from one parent and a
dominant allele from the other.
The offspring in the F1 generation will therefore all express the dominant trait in their
phenotype, as shown above.
16.3 - Monohybrid Inheritance
1. Essential genetics vocabulary
2. Monohybrid crosses in genetic diagrams and Punnett squares
3. What a test cross is
Essential genetics vocabulary
Genetics is the study of genes and how characteristics are inherited.
To understand genetics, you first need to get to grips with some key terminology.
Term Definition
A sequence of bases on a DNA molecule that codes for a protein
Gene
(polypeptide), which results in a characteristic, e.g. a gene for eye colour
Different versions of the same gene that code for variants of a characteristic.
Allele
Represented by letters, e.g. B = brown eyes, b = blue eyes
Genotype An organism's genetic makeup - its alleles, e.g. BB, Bb, or bb
An organism's physical characteristics as determined by its genotype and
Phenotype
environment
An allele that is always expressed in the phenotype, even when only one copy
Dominant
is present in the genotype (shown with an uppercase letter)
An allele that is only expressed when it is homozygous in the genotype (two
Recessive copies are present), and is masked by a dominant allele (shown with a
lowercase letter)
Locus A locus (plural: loci) is the specific position of a gene on a chromosome
Homozygous An organism with two identical alleles for a trait is homozygous
Heterozygou
An organism with two different alleles for a trait is heterozygous
s
, Monohybrid crosses in genetic inheritance diagrams
Humans are diploid organisms and almost always have two copies of each gene. This means they
have two alleles for every characteristic. Gametes (sex cells) are haploid, which means that they
have one allele per gene.
Monohybrid (monogenic) inheritance involves the transmission of one gene from parents to their
offspring.
A monohybrid cross tracks the inheritance pattern of the alleles for a single characteristic, controlled
by one gene with two possible alleles.
Genetic diagrams
Genetic diagrams illustrate how parents can pass on alleles to their offspring. They can be used to
predict possible genotypes and phenotypes in the next generation.
The F1 generation:
This is the offspring from a cross between individuals with homozygous dominant and
homozygous recessive genotypes.
All the offspring will be heterozygous, inheriting a recessive allele from one parent and a
dominant allele from the other.
The offspring in the F1 generation will therefore all express the dominant trait in their
phenotype, as shown above.
