Genetics and Inheritance: Mendel's Laws, Traits, and Pedigree Analysis

Genetic inheritance

The process of passing genetic information, or traits, from parents to their offspring through DNA.

Blending

Offspring inherit a trait as the average of the parents' values for that trait.

Law of segregation

Alleles for each gene segregate from each other so that each gamete carries only one allele for each gene.

Law of independent assortment

Alleles for separate traits are passed independently of one another.

Law of dominance and uniformity

Some alleles are dominant while others are recessive; an organism with at least one dominant allele will display the effect of the dominant allele.

Genes

Sections on the chromosome that code for specific traits (proteins).

Locus

The position of each gene in the chromosome.

Allele

Different versions of the same gene.

Dominant traits

Only need one copy of an allele to be visible in the appearance of an individual.

Recessive traits

Only seen in the appearance of an individual when two copies of the allele are present.

Heterozygous

Individuals have two different alleles (e.g., Bb).

Homozygous

Individuals have the same alleles (e.g., BB or bb).

Carrier

A person who has or 'carries' a genetic difference in one copy of a gene but doesn't have the disease.

Complete dominance

One allele completely masks the expression of another allele.

Partial/incomplete dominance

The phenotype of the heterozygous genotype is distinct from and intermediate to the phenotypes.

Codominance

The alleles of a gene are expressed equally in an organism.

Sex-linked inheritance

The passing of traits or disorders from parents to offspring through the sex chromosomes.

Autosomal dominant

AA and Aa = affected, aa = unaffected; both males and females are affected equally.

Autosomal recessive

AA = unaffected, Aa = unaffected (carrier), aa = affected; two unaffected parents can have an affected child.

X-linked dominant

A male with the trait passes it on to all his daughters and none of his sons.

X-linked recessive

All the sons of a female with the trait are affected; more males affected than females.

Y-linked inheritance

Only males affected; trait cannot skip a generation.