Intro to Genetics - 2.5 Genetic Variation and Change

Vocabulary flashcards covering key genetics concepts from the notes.

DNA

Deoxyribonucleic acid; a double helix made of two twisted strands that stores genetic information.

Gene

A section of DNA containing a specific sequence of bases that codes for a particular protein.

Chromosome

A strand of DNA tightly coiled; contains many genes.

Nucleotide

The building block of DNA strands.

Adenine

A DNA base that pairs with thymine (A pairs with T).

Thymine

A DNA base that pairs with adenine (T pairs with A).

Cytosine

A DNA base that pairs with guanine (C pairs with G).

Guanine

A DNA base that pairs with cytosine (G pairs with C).

Base pair

A pair of nucleotides on opposite DNA strands (A–T or C–G) held together by hydrogen bonds.

Hydrogen bond

Weak bonds that hold base pairs together in the DNA double helix.

Antiparallel

DNA strands run in opposite directions (5' to 3' on one strand and 3' to 5' on the other).

DNA replication

The process by which DNA is copied to produce two identical DNA molecules.

Sister chromatid

One of the two identical copies of a replicated chromosome held together at the centromere.

Chromatid

One of the two identical DNA molecules that make up a duplicated chromosome.

Centromere

The region where sister chromatids are held together and where spindle fibers attach during cell division.

Karyotype

A visual display of the chromosome content of a cell, organized by number, size and type.

Homologous chromosomes

Chromosome pairs that are similar in size, shape and gene position (one from each parent).

Allele

An alternative (variant) form of a gene.

Genotype

The genetic makeup of an individual—the specific alleles present for a gene.

Phenotype

The observable physical expression of the genotype.

Dominant allele

The allele that is expressed when present; indicated by an uppercase letter.

Recessive allele

The allele expressed only when no dominant allele is present; indicated by a lowercase letter.

Homozygous

Having two identical alleles for a gene (e.g., AA or aa).

Heterozygous

Having two different alleles for a gene (e.g., Aa).

Monohybrid cross

A genetic cross examining one gene; often yields a 3:1 phenotypic ratio under complete dominance.

Punnett square

A diagram used to predict the possible genotypes and phenotypes of offspring from parental alleles.

Test cross

Crossing an individual with an unknown genotype to a homozygous recessive to determine if the unknown is homozygous dominant or heterozygous.

Dihybrid cross

A genetic cross involving two genes; predicts offspring combinations (often 9:3:3:1 phenotype ratio under complete dominance).

Complete dominance

A form of dominance where the dominant allele completely masks the recessive allele in a heterozygote.

Incomplete dominance

Neither allele is fully dominant; heterozygotes show an intermediate phenotype (e.g., pink flowers from red and white alleles).

Co-dominance

Both alleles are fully expressed in the heterozygote; phenotypes do not blend (e.g., roan coat, tabby).

Multiple alleles

Genes with more than two possible alleles in the population (e.g., ABO blood groups).

Lethal alleles

Alleles that can cause death when present in certain genotypic combinations (e.g., AA or homozygous dominant lethal in some traits).

ABO blood group system

Blood types determined by three alleles (IA, IB, i); phenotypes A, B, AB, O; includes concepts of universal donor and recipient.

Antigen

A molecule on the surface of red blood cells that is recognized by antibodies.

Antibody

A blood plasma protein that binds to foreign antigens.

Pure-breeding (homozygous)

Individuals that are homozygous for a trait and produce offspring identical to themselves for that trait.

Phenotypic ratio

The proportional distribution of observable traits in offspring (e.g., 3:1, 9:3:3:1).

Genotypic ratio

The proportional distribution of genotypes in offspring (e.g., 1:2:1 in a monohybrid cross).

Mendel

The father of modern genetics; studied pea plants and described basic inheritance patterns.

FOIL method

A method to determine all possible gametes from a dihybrid genotype (Firsts, Outside, Inside, Lasts).

Roan

A color pattern in which co-dominant alleles produce a mixed phenotype (black and white).

Snapdragon pink (incomplete dominance)

An example where neither allele is fully dominant, resulting in a pink intermediate phenotype.

Achondroplasia

A dominant lethal allele causing dwarfism; Aa causes dwarfism and AA is usually lethal.

Drosophila curly wings

A classic example where curly-winged phenotype is caused by a dominant allele; CC is lethal, Cc is curly, cc is normal.