BIO 160 Chapter 8 Inheritance and Mendelian Genetics Lecture

Vocabulary flashcards that cover essential genetic terms, principles, and inheritance patterns discussed in the lecture notes.

Character

Any observable physical feature of an organism (e.g., flower color).

Trait

A specific form of a character (e.g., purple flowers).

True-breeding

Line whose offspring show identical traits to the parents when self- or cross-fertilized within the line.

Reciprocal cross

A pair of matings where the sexes for each phenotype are reversed to test for sex-linked effects.

P Generation

The parental individuals used at the start of a genetic cross.

F1 Generation

First filial generation; offspring produced by crossing the P generation.

F2 Generation

Second filial generation; offspring produced by self- or inter-crossing F1 individuals.

Monohybrid cross

Cross between two true-breeding lines that differ in a single trait.

Dihybrid cross

Cross between individuals differing in two traits, used to test independent assortment.

Gene

Heritable unit (DNA sequence) that determines a character.

Allele

Alternative form of a gene that produces different traits.

Genotype

The pair (or set) of alleles an individual possesses (e.g., PP, Pp, pp).

Phenotype

Observable expression of a genotype (e.g., purple vs. white).

Locus

Specific physical location of a gene on a chromosome.

Homozygous

Genotype with two identical alleles at a locus (PP or pp).

Heterozygous

Genotype with two different alleles at a locus (Pp).

Dominant allele

Allele whose phenotype is expressed with only one copy present (uppercase letter).

Recessive allele

Allele expressed only when two copies are present (lowercase letter).

Law of Segregation

Mendel’s 1st law: allele pairs separate during gamete formation so each gamete carries one allele per gene.

Punnett square

Grid that predicts offspring genotypes and phenotypes from parental gametes.

Test cross

Cross of an individual with unknown genotype to a homozygous recessive to reveal the unknown alleles.

Multiplication rule

Probability principle: chance that independent events ALL occur equals the product of their probabilities (AND).

Addition rule

Probability principle: chance that either of two mutually exclusive events occurs equals the sum of their probabilities (OR).

Law of Independent Assortment

Mendel’s 2nd law: alleles of different genes assort independently into gametes, provided the genes are on separate chromosomes or far apart.

Pedigree

Diagram showing inheritance of a trait through generations of a family.

Autosomal dominant inheritance

Pattern where every affected person has at least one affected parent; seen in every generation; sexes equally affected.

Autosomal recessive inheritance

Pattern where affected individuals often have unaffected (carrier) parents and trait may skip generations.

Hemizygous

Having only one copy of a gene (e.g., genes on the X chromosome in human males).

X-linked recessive

Trait more common in males; affected males pass allele to all daughters (carriers), never to sons.

X-linked dominant

Trait often more common in females; affected fathers pass allele to all daughters and no sons.

Y-linked inheritance

Alleles on Y chromosome passed from father to all sons, never to daughters.

Sex-influenced trait

Autosomal gene whose dominance differs between sexes (e.g., PGO example).

Sex-limited trait

Autosomal gene expressed in only one sex (e.g., beard growth, lactation).

Wild-type allele

Most common allele in natural populations; not necessarily dominant.

Mutant allele

Any allele that differs from the wild type; may be recessive or dominant.

Starch-branching enzyme mutation

Recessive SBE loss makes pea seeds low-starch and wrinkled due to osmotic water loss.

Multiple alleles

Presence of more than two allelic forms for a gene in a population (rabbit coat color C > cchd > ch > c).

Codominance

Both alleles in a heterozygote are fully and distinctly expressed (AB blood type).

Incomplete dominance

Heterozygote shows intermediate phenotype between homozygotes (pink snapdragons).

Pleiotropy

Single gene affects multiple traits (e.g., CFTR mutation in cystic fibrosis).

Epistasis

Gene interaction where one gene’s product masks or modifies expression of another (e.g., Labrador coat colors).

Polygenic (quantitative) trait

Character determined by additive effects of many genes, producing continuous variation (e.g., human height).

Cytoplasmic inheritance

Genes in mitochondria (or chloroplasts) transmitted maternally to all offspring.

Mitochondrial DNA

Circular genome in mitochondria; encodes proteins for oxidative phosphorylation and is maternally inherited.

Linkage

Genes located on the same chromosome that tend to be inherited together, violating independent assortment.

Recombination frequency

Proportion of recombinant offspring; estimates distance between linked genes.

Centimorgan (cM)

Unit of genetic distance equal to 1 % recombination frequency between two loci.

Chromosomal theory of inheritance

Sutton & Boveri proposal (1902-03) that genes reside on chromosomes, explaining Mendel’s laws.

Autosome

Any chromosome not involved in sex determination (human pairs 1-22).

Sex chromosome

Chromosome that determines biological sex (X and Y in humans).

Binary fission

Asexual cell division in bacteria producing identical clones.

Conjugation

Bacterial process where genetic material is transferred between cells through a pilus (horizontal gene transfer).

Horizontal (lateral) gene transfer

Movement of genetic material between organisms other than by descent from parent to offspring.