Meiosis occurs in germ cells to produce gametes • DNA will be copied once, but then split twice. Therefore the result is four haploid cells.
Homologous Chromosomes & Sister Chromatids • Homologous chromosomes are the same shape and size. You receive one from your Mother and one from your Father. Homologous chromatids refers to the duplicated chromosomes that remain attached by the centromere .
Comparing Mitosis & Meiosis • Meiosis has two cell divisions • During meiosis homologous chromosomes line up along the equator. • In anaphase I sister chromatids remain together. In mitosis, they separate. • Meiosis results in haploid cells, mitosis results in diploid cells.
Mature Gametes • Cells from meiosis will not be able to go through fertilization until they become mature. • The process of forming gametes is known as Gametogenesis.
The main contribution to the embryo from the sperm cell is DNA. • Sperm cell formation begins will a round cell. The cell eventually loses some cytoplasm, forms a compact head, and develops a flagellum.
The egg provides DNA, molecular building blocks, and other essential materials that the embryo needs to begin life. • Only one cell out the four produced by meiosis will produce an egg cell. • The other three cells, which are mostly just DNA are called polar bodies. They will be broken down.
Unique Gene Combinations • Sexual Reproduction is the formation of a new organism by the union of gametes. • Asexual Reproduction is the formation of offspring that are genetically identical to the parent. Only mitosis occurs.
Genetic Variation • Sexual reproduction gives rise to genetic variation within a species. This is largely due to the independent assortment of chromosomes during meiosis AND the random fertilization of gametes. • During meiosis I homologous chromosomes pair up along the equator randomly. • Fertilization and independent assortment play key roles in genetic diversity in sexually reproducing organisms.
Crossing Over • Crossing over is the genetic exchange of segments of homologous chromosomes during prophase I of meiosis. • One part of each chromatid breaks off and reattaches to the other chromosome.
Genetic Recombination • Genetic recombination refers to any mixing of parental alleles. • This will include crossing over and independent assortment.
Genetic Linkage • The further two genes are away from each other on a chromosome, the more likely they will be separated during crossing over. • Genes that are located closer together will be inherited together. The two genes will be linked together. • Genetic linkage is the tendency of two genes to be inherited together.
Sex-linked • Genes that are located on the sex chromosomes are called sex-linked genes. • Males are able to pass on an X or a Y chromosomes to their offspring, but a female can only pass on an X chromosome.