Unit 2 Genetics: DNA, Genes, Inheritance, and Pedigrees

Vocabulary flashcards covering genetics concepts from DNA structure to inheritance patterns, crosses, and pedigrees.

DNA

A large molecule with a long sequence of nucleotides (A, C, T, G) that encodes the genetic code read along the strand to make proteins.

Gene

A section of DNA that codes for a specific protein or RNA and helps determine a trait.

Chromosome

A structure that carries DNA; humans have 23 pairs and many genes per chromosome.

Karyotype

An organized image of the chromosome complement (22 pairs of homologous chromosomes plus the sex chromosomes).

Homologous pair

Two chromosomes of a pair that are the same size and shape and carry the same genes, though not necessarily identical.

Allele

Different versions of the same gene; alleles can be dominant or recessive.

Homozygous

Having two identical alleles for a gene (e.g., two dominant or two recessive).

Heterozygous

Having two different alleles for a gene (one dominant, one recessive).

Dominant allele

An allele that determines the phenotype when present in the genotype.

Recessive allele

An allele whose phenotype is shown only when two copies are present or when no dominant allele masks it.

Genotype

The actual allele combination an individual has for a gene (e.g., FF, Ff, ff).

Phenotype

The observable trait or physical appearance resulting from the genotype.

Punnett square

A grid used to predict offspring genotypes and phenotypes from parental gametes.

Monohybrid cross

A cross focusing on one gene; typically yields a genotype ratio 1:2:1 and a phenotype ratio 3:1 when parents are heterozygous.

Dihybrid cross

A cross involving two genes; typically yields a 9:3:3:1 phenotypic ratio when both parents are heterozygous for both traits.

Independent assortment

Random distribution of chromosome pairs into gametes during meiosis, creating multiple combinations.

Pedigree

A family tree diagram using squares (males) and circles (females) to track inheritance of traits; filled means affected.

Autosomal

A trait encoded on non-sex (autosome) chromosomes.

X-linked

A trait carried on the X chromosome; inheritance patterns differ between males and females.

Y-linked

A trait carried on the Y chromosome; passed from father to son; no female carriers.

Carrier

Someone who is heterozygous for a recessive trait and does not show the trait but can pass it to offspring.

Complete dominance

One copy of the dominant allele is enough to show the dominant phenotype; recessive trait requires two copies.

Incomplete dominance

Heterozygotes show an intermediate phenotype between the two homozygotes (e.g., sickle cell example).

Codominance

Both alleles are expressed independently in the phenotype (e.g., blood type AB shows both A and B antigens).

Polygenic trait

A trait controlled by many genes, leading to a wide range of phenotypes (e.g., height, skin color).

Sex-influenced trait

Trait affected by hormones; not strictly on a sex chromosome but expression differs by sex.

ABO blood group

System with IA, IB, and i alleles; A and B are codominant, O is recessive; phenotypes A, B, AB, and O.

Blood type AB

AB phenotype with genotype IAIB; both A and B antigens are expressed.

Color blindness

X-linked recessive trait affecting color vision; more common in males due to single X chromosome.

Swyer syndrome

XY individual with mutations causing female development, due to loss of a Y-linked gene responsible for male development.

Huntington’s disease

Autosomal dominant disorder; one copy of the dominant allele is enough to express the disease.

Cystic fibrosis

Autosomal recessive disorder; two defective copies needed; carriers exist; symptoms include thick mucus buildup.

Sickle cell anemia

Example of incomplete dominance (HbA and HbS alleles); heterozygotes have an intermediate phenotype and some malaria resistance.

Meiosis

Cell division that produces haploid gametes through two rounds of division (I and II) and random assortment.

Mitosis

Cell division that produces two genetically identical somatic cells.