Genetic Inheritance Patterns Quiz

Genetic Inheritance Patterns

• Genetic inheritance patterns are studied using pedigrees, which are charts showing family history over generations.
• Pedigrees illustrate how traits are passed down (e.g., disease causes).
• They predict the likelihood of offspring inheriting a trait.
• Pedigrees reveal if a trait is dominant or recessive, and if the gene is autosomal or X-linked.

Pedigree Basics

• A pedigree is a chart depicting genetic history, spanning multiple generations.
• Pedigree illustrations contain symbols for males (squares), females (circles), affected individuals (filled shapes), heterozygotes (or carriers), matings, offspring order, twins, deceased individuals, spontaneous abortions, consanguineous marriages, and unknown sex.
• Pedigree analysis reveals the pattern of trait transmission.

Interpreting Pedigrees

• To determine dominance or recessiveness, observe if the disorder appears in every generation (dominant) or skips generations (recessive).
• Recessive traits might not manifest in parents but may appear in offspring.
• Consider heterozygosity when analyzing recessive traits, as parents may carry the trait without displaying it.

Evaluating Pedigree Charts

• Pedigree analysis involves checking if the trait appears in every generation (vertical transmission) or only one (horizontal).
• Note the ratio of affected males to females.
• Observe if the disease is passed through unaffected females or through male-to-male transmission.
• Examine what percentage of children are affected (e.g., all males, none).

Common Inheritance Patterns

• Autosomal Dominant: One affected parent often transmits the trait to offspring in each generation with similar proportions between males and females affected. Vertical pattern in pedigrees and affects both sexes.
• Autosomal Recessive: Traits appear sporadically. Two heterozygous carriers (both must carry the affected gene) have a higher chance of passing the trait to an offspring. Vertical pattern, affects males and females equally.
• X-linked Recessive: Traits are more likely to appear in males, passed from mother to son.

Vocabulary

• Character: A heritable feature.
• Trait: A variant of a character.
• Monohybrid cross: A cross tracking single character inheritance in a generation.
• P generation: Parental generation.
• F1 generation: First filial generation, offspring from the P generation.
• F2 generation: Second filial generation, offspring from the F1 cross.
• Punnett square: A tool to show possible offspring genotypes resulting from a cross.
• Allele: Alternate version of a gene.
• Dominant allele: Expressed in heterozygotes.
• Recessive allele: Not expressed in heterozygotes.
• Homozygote: Pair of identical alleles.
• Homozygous dominant: Pair of dominant alleles (e.g., BB).
• Homozygous recessive: Pair of recessive alleles (e.g., bb).
• Heterozygote: Pair of different alleles (e.g., Bb).
• Genotype: Genetic makeup.
• Phenotype: Expression of traits.

Autosomal Dominant Inheritance

• A trait's expression requires only one affected allele.
• Multiple generations are typically affected.
• Males and females are equally likely to be affected.
• Male-to-male transmission is possible.
• Affected individuals often have at least one affected parent (with exceptions in rare cases).

Complicating Factors

• Non-penetrance
• New mutation
• Adult-onset conditions
• Consanguinity
• Interaction
• Sex-limited/sex influenced
• Germline mosaicism
• Anticipation
• Heterogeneity
• Pleiotropy