AP Bio Unit 5 Heredity

Diploid

Cell with two sets of chromosomes (2n).

Haploid

Cell with one set of chromosomes (n).

Zygote

Diploid cell formed after fertilization of egg and sperm.

Homologous chromosomes

Chromosome pair with the same genes at the same loci but possibly different alleles.

Sister chromatids

Identical copies of the same chromosome joined at the centromere.

Crossing over

Exchange of DNA between homologous chromosomes during Prophase I.

Independent Assortment 

Random orientation of homologous chromosomes in Metaphase I.

Codominance

Both alleles are expressed separately (ex: black + white feathers)

Incomplete dominance

Heterozygote has a blended/intermediate phenotype (pink flowers in snapdragons)

Multiple alleles

A gene with more than two allele options (ex: IA, IB, i for blood type)

Polygenic inheritance

Trait determined by many genes, producing a continuum of phenotypes (skin color, height)

Environmental influence

Phenotype affected by environment in addition to genotype (ex: hydrangea color)

Nonnuclear inheritance

Traits inherited through mitochondrial or chloroplast DNA; passed through the mother in animals

Pleiotropy

One gene affects multiple traits (ex: dwarfism, gigantism)

Epistasis

One gene masks or affects expression of another gene (ex: mice coat color)

Sex-linked gene

Gene located on the X chromosome; males express recessive X-linked traits more often.

X-inactivation

In females, one X becomes inactive (Barr body), creating mosaic phenotypes

Gene linkage

Genes located on the same chromosome tend to be inherited together

Recombination frequency

Percent of recombinant offspring used to map genes; 1% = 1 map unit (centimorgan)

Nondisjunction

Failure of chromosomes to separate during meiosis; leads to aneuploidy (Down syndrome, Turner syndrome, etc.)

Aneuploidy

Abnormal number of chromosomes (ex: trisomy 21, XXY, XO)