Biology Term 2

Heredity

Passing genetic information from parents to offspring

Study of heredity = genetics

Gregor Mendel

Discovered patterns of inheritance

Traits

Characteristics of an organism

Influenced by genes (DNA) and environment

Inheritance

Transmission of genetic traits from parents to offspring

Traits are determined by genes

Genes

Sections of DNA that code for proteins

Most human genes have two alleles

Alleles

Different versions of a gene

One inherited from each parent

Can be dominant or recessive

Dominant allele

Expressed even when pair with a different allele

Uppercase letter

Recessive allele

Only expressed when two recessive alleles are present

Lowercase letter

Homozygous

Two identical alleles

Eg: BB, bb

Heterozygous

Two different alleles

Eg: Bb

Locus

Position of a gene on a chromosome

Genotype

Combination of alleles an organism has

Phenotype

Observable characteristics

Purpose of punnet squares

Used to predict possible offspring genotypes and phenotypes

Complete dominance

One allele completely masks the other

Eg: red = dominant, white = recessive

Incomplete dominance

Neither allele dominates

Traits blend each other

Eg: Red x White = pink

Codominance

Both alleles are fully expressed

Eg: red and whites together

Pedigree charts

Diagram showing inheritance of traits through generations

Used to track genetic conditions

What does a square represent

Unaffected male

Shaded square

Affected male

Half shaded or dot in middle of square

Male carrier

Circle

Unaffected female

Shaded circle

Affected female

Half shaded or dot in circle

Female carrier

What’s an important rule when reading a pedigree chart

Siblings are listed left to right in order of birth

Autosomal dominant (A)

Cannot skip generations

Males and females equally affected

Autosomal recessive (a)

Can skip generations

Males and females equally affected

X-linked dominant (Xᴬ)

Cannot skip generations

Females more likely affected

X-linked recessive (Xᵃ)

Can skip generations

Males more likely affected