UPCAT BIO GENETICS

Genetics

Study of heredity (passing of traits) and variation (differences among individuals)

Gene

A specific location/slot on a chromosome that codes for a heritable trait (e.g. eye color gene)

Allele

The specific version of a gene; always comes in pairs (one from mom, one from dad) (e.g. B for brown, b for blue)

Dominant Allele

Masks the expression of its partner; always expressed when present

Recessive Allele

Masked by dominant allele; only expressed when paired with another recessive allele (homozygous recessive)

Character

The broader heritable feature/category being studied (e.g. eye color)

Trait

The specific variant within a character (e.g. brown eyes)

Homozygous

Two identical alleles at a gene locus (e.g. TT or tt); basis of purebred organisms

Heterozygous

Two non-identical alleles at a gene locus (e.g. Tt); basis of hybrid organisms

Genotype

The actual alleles an organism carries in its DNA (e.g. Tt)

Phenotype

The physical trait that shows up based on the genotype (e.g. tall)

Purebred

Organism with homozygous genotype (TT or tt); breeds true

Hybrid

Organism with heterozygous genotype (Tt); result of two different alleles

Law of Dominance

If two alleles differ, the dominant allele is fully expressed; recessive has no noticeable effect

Law of Segregation

The two alleles for a trait separate during meiosis so each gamete carries only one allele

Law of Independent Assortment

Allele pairs segregate independently of each other during meiosis; traits are inherited independently

Incomplete Dominance

Two dominant alleles combine to produce a blended intermediate phenotype (e.g. red + white = pink)

Codominance

Two dominant alleles both fully expressed simultaneously; both traits visible (e.g. ABO blood type)

Sex-linked Traits

Traits coded by genes on sex chromosomes (X or Y)

Incomplete Dominance vs Codominance

Incomplete = blend of both traits; Codominance = both traits fully visible side by side

Autosomal Dominant

Only one copy of the faulty gene needed for trait to be expressed; affects both sexes equally

Autosomal Recessive

Both copies of the faulty gene needed for condition to manifest; carriers exist (heterozygous, unaffected)

X-linked Recessive

Trait carried on X chromosome; mother-to-son transmission; sons inherit affected X from carrier mother

X-linked Dominant

Trait carried on X chromosome; father-to-daughter transmission; affected father passes to all daughters

Y-linked (Holandric)

Trait carried on Y chromosome; father-to-son transmission only; all sons of affected father are affected

Karyotype

Visual display/organized photo of an organism's complete set of chromosomes arranged in pairs

Normal Human Karyotype

46 total chromosomes; 22 pairs of autosomes + 1 pair of sex chromosomes

Normal Male Karyotype

46,XY

Normal Female Karyotype

46,XX

Autosomes

The 22 non-sex chromosome pairs; code for everything except biological sex

Sex Chromosomes

23rd pair; determines biological sex; XX = female, XY = male