Monohybrid crosses

Genotype

An organism's genetic makeup, or allele combinations.

Monohybrid cross

a cross in which only one characteristic is tracked

Alleles

Alternative forms of a gene

A(dominant--upper case

a(recessive)--lower case

dominant allele

An allele whose trait always shows up in the organism when the allele is present.

Somatic cell

any cell of a living organism other than the reproductive cells.

Gametes

sex cells

Phenotype

physical expression of a trait

ex

-red hair

-brown eyes

Three possible combinations of genotypes ?

1. homozygous dominant

2. heterozygous

3. homozygous recessive

homozygous dominant genotype

AA

heterozygous genotype

Aa

homozygous recessive genotype

aa

Autosomes

Any chromosome that is not a sex chromosome

sex chromosomes

Chromosomes that determine the sex of an individual

Male chromosomes

XY

Female chromosomes

XX

Karyotype

A display of the chromosome pairs of a cell arranged by size and shape.

Gene

A sequence of DNA bases that codes for one polypeptide

Recessive

An allele that is masked when a dominant allele is present

Loci

position of a gene on a chromosome

Multiple alleles

three or more alleles of the same gene

Codominance

situation in which both alleles of a gene contribute to the phenotype of the organism

Test cross

the crossing of an individual of unknown genotype with a homozygous recessive individual to determine the unknown genotype

sex linkage

the presence of a gene on a sex chromosome

pure breeding

Individuals that are homozygous for a trait