ch 7 terms

genetic trait

any inherited characteristic of an organism

invariant trait

the SAME in all individuals of the species

variable traits

DIFFER among individuals of the same species

gene

basic unit of information affecting a genetic trait, consists of a stretch of DNA on a chromosome

allele

different versions of a given gene, ex: fur color in dogs

genotype

the genetic makeup of an individual for a given trait

phenotype

the physical expression of a given trait’s genetic makeup

dominant allele

one allele that prevents a second allele from affecting the phenotype when the two alleles are paired together

recessive allele

an allele that has no effect on the phenotype when paired with a dominant allele

homozygous

the genotype consists of two copies of the same allele, ex: BB or bb

heterozygous

the genotype consists of two different alleles, ex: Bb, the individual will show the phenotype of the dominant allele

genetic cross

a controlled mating experiment to examine how a particular trait is inherited

P generation(p for parental)

the organisms involved in the first cross

F1 generation(F for filial)

the first generation of offspring

F2 generation

the offspring resulting when the individuals of the F1 generation are crossed with each other

punnett square

a grid-like diagram used to predict the results of a genetic cross, shows all possible ways that two alleles can be brought together through fertilization

chromosome theory of inheritance

chromosomes are paired, each homologous chromosome in a pair has one allele for a gene, alleles are shuffled and recombined then separated randomly into sperm and egg cells during meiosis, during fertilization a one-in-a-million sperm fuses with a one-in-a-million egg to create a unique individual

incomplete dominance

when neither allele is able to exert its full effect, a heterozygote displays an intermediate phenotype

codominance

when the effects of the two alleles are equally visible in the phenotype of the heterozygote, ex: blood type AB in humans

complex traits

a genetic trait whose pattern of inheritance cannot be predicted by mendel’s laws of inheritance

pleiotropy

when a single gene influences a number of different traits, ex: the shape of a dog’s head and the shape of its limb bones are controlled by a single gene

polygenic traits

single traits governed by more than one gene, ex: eye color, skin color