Biology Unit 7-Genetic Inheritance

gene

• A region of DNA that acts as instructions for the making of proteins.

• A chromosome consists a long strand of DNA containing many genes.

genotype

The pair of alleles that an organism has for its two copies of a gene.

e.g. Bb, GG, tt

phenotype

The observable characteristics of an individual result from the interaction of its genotype with the environment.

e.g. five fingers on each hand, color blindness, blood type

allele

• Alternative versions of the same gene

• Because they are the same gene, they code for the same type of protein with the same role in the cell.

• They occupy the same position (locus) on homologous chromosomes

• The majority of the DNA sequence remains the same between them; they differ from each other by up to a few base pairs.

dominant allele

• An allele that has the same effect on the phenotype whether it is paired with the same allele or a different one

• It is always expressed in the phenotype

e.g. Aa gives dominant trait A

recessive allele

• An allele that has an effect on the phenotype only when present in the homozygous state

e.g. aa gives the recessive trait

co-dominant allele

Pairs of alleles that both affect the phenotype when present in a heterozygote.

e.g. parent with curly hair and parent with straight hair can have children with varying degrees of curliness.

genome

• The complete set of genetic information in a cell or organism.

• Increased efficiency and lower cost of it sequencing has led to possible advancements in the fields of personalized medicine, ancestry testing and evolutionary biology (determining relationships between different species)

locus

A specific location on a chromosome where a gene is found.

homozygous

• Having two of the same alleles of a particular gene.

• The individual’s mom and dad passed on different versions of the gene

e.g. AA is homozygous dominant, aa is homozygous recessive.

heterozygous

Having two different alleles of a gene.

e.g. Aa is heterozygous

carrier

An individual who has a recessive allele of a gene that does not affect their phenotype.

(usually appear in mutation context)

test cross

Testing a suspected heterozygous organism by crossing it with a homozygous recessive (aa) to see if recessive trains appear in offspring.