Meiosis and sexual life cycles 

Offspring acquire genes from parents by inheriting chromosomes. 

genes: segments of DNA that code for the basic units of hereditary and are transmitted from one generation to the next 

gametes: reproductive cells that transmit genes from one generation to the next 

locus: the location of a gene on a chromosome 

Asexual reproduction:  a single parent is the sole parent and passes copies of all its genes to its offspring (clone)  

Sexual reproduction: two individuals contribute genes to the offspring

Fertilization and meiosis alternate in several life cycles.

life cycle: the generation to generation sequence of stages in the reproductive history of an organism 

somatic cells: (46 chromosomes) any cells in the body that are not gametes 

karyotype: picture of its complete set of chromosomes, arranged in pairs of homologous chromosomes from the largest pair, to the smallest pair 

-meiosis and fertilization are the key events in sexually reproducing life cycles 

fertilization: the combination of a sperm cell and an egg cell, one haploid gamete from the father fuses with one haploid gamete from the mother

meiosis:  the type of cell division that reduces the numbers of sets of chromosome from two to one 

Meiosis reduces the number of chromosome sets from diploid to haploid.

-the final result of meiosis is 4 daughter cells each of which has half as many chromosomes as the parent cell

Genetic variation produced in sexual life cycles contribute to evolution. 

crossing over: during prophase I the exchange of genetic material on homologous chromosomes between nonsister chromatids occur  

random fertilization: because each sperm and egg is different, as a result of independent assortment and crossing over, each combination of egg and sperm is unique

independent assortment of chromosomes: in metaphase I when the homologous chromosomes are lined up on the metaphase plates, they can pair up in any combination with any of the homologous pairs facing either pole