biology s2 unit 1 meiosis & genetics

**homologous**

chromosomes in which one set comes from the male parent and one set comes from the female parent

diploid

cell that contains two sets of homologous chromosomes

haploid

cell that contains only a single set of genes

meiosis

process in which the number of chromosomes per cell is cut in half through the separation of homologous chromosomes in a diploid cell

tetrad

structure containing four chromatids that forms during meiosis

crossing-over

process in which homologous chromosomes exchange portions of their chromatids during meiosis

genetics

scientific study of heredity

fertilization

process in sexual reproduction in which male & female reproductive cells join to form a new cell

trait

specific characteristic of an individual

hybrid

offspring of crosses between parents w/ different traits

gene

sequence of DNA that codes for a protein & thus determines a trait; factor that is passed from parent to offspring

allele

one of a number of different forms of a gene

principle of dominance

Mendel’s 2nd conclusion, which states that some alleles are dominant & others are recessive

segregation

separation of alleles during gamete formation

gamete

sex cell

probability

likelihood that a particular event will occur

homozygous

having two identical alleles for a particular gene

heterozygous

having two different alleles for a particular gene

phenotype

physical characteristics of an organism

genotype

genetic makeup of an organism

Punnett square

diagram that can be used to predict the genotype & phenotype combinations of a genetic cross

independent assortment

one of Mendel’s principles that states that genes for different traits can segregate independently during the formation of gametes

incomplete dominance

situation in which one allele is not completely dominant over another allele

codominance

situation in which the phenotypes produced by both alleles are completely expressed

multiple alleles

a gene that has more than two alleles

polygenetic trait

trait controlled by two or more genes