Patterns of Inheritance

Phenotype

The physical or chemical characteristics of an organism

Genotype

The genetic information of an organism

Diploid

Two sets of chromosomes

Where does each chromosome come from in a homologous pair

One comes from the father and one from the mother

Locus

The location of a gene on a chromosome

Homozygous

Both alleles are the same

Heterozygous

Two alleles are different

Recessive alleles

Alleles that are only expressed when there are two of them

Dominant allele

Allele that is expressed over the recessive one

Monohybrid cross

Considers the inheritance of one gene at a time

True breeding organisms

Organisms that are homozygous

Not true breeding organisms

Organisms that are heterozygous

A blood group

Dominant (AA or AO)

A antigens on RBC

Anti-B antibodies

B blood group

Dominant (BB or BO)

B antigen on RBC

Anti A antibodies

AB blood group

Codominant (AB)

A and B antigens

No antibodies

O blood group

Recessive (OO)

No antigens

Anti A and Anti B antibodies

Features of organisms are used in genetic studies

Easy to grow

Have short life cycles

Produce lots of offspring

Why real genetic ratios differ from expected

Random fertilisation

Some offspring may not be counted

Environmental effects masking the phenotype

Recessive inheritance

Carrier parents can have an affected child

Two unaffected carries parents needed for an affected child

Disease can skip a generation

Dominant inheritance

Appears in every generation

An affected individual is always a carrier

Affected parent has a 50% chance of passing it on to the child

Albinism

Cause by a recessive allele that prevents melanin from being made