Meiosis and Sexual Reproduction Meiosis and Sexual Reproduction

Meiosis and Sexual Reproduction

Meiosis and Sexual Reproduction First, some vocabulary: chromosomes Structures in the nucleus of a eukaryotic cell that consist of DNA molecules that contain the genes Specific segments of DNA that control cell structure and function; the functional units of inheritance. alleles Alternate forms of a gene. homologous chromosomes are chromosomes that carry the same genes example: if a gene influencing eye color is located at a particular place on one chromosome, then the homologous chromosome has a similar gene for eye color there. gametes Haploid reproductive cells (ovum and sperm).

Picture of chromosome and gene

Homologous Chromosomes At this point, I would like you to complete the Problem-Solving Lab on page 270. diploid Cells that contain homologous chromosomes. The number of chromosomes in the cells is the diploid number and is equal to 2 n (n is the number of homologous pairs). haploid Cells that contain only one member of each homologous pair of chromosomes (haploid number = n). At fertilization, two haploid gametes fuse to form a single cell with a diploid number of chromosomes.

Chromosome #’s of common organisms Organism Fruit fly Garden pea Leopard frog Human Chimpanzee Dog Body cell (2 n) 8 14 26 46 48 78 Which # is haploid? Which # is diploid? Gamete (n) 4 7 13 23 24 39

Meiosis • the process of nuclear division where the number of the chromosomes is halved. • produces four daughter cells • all daughter cells are haploid • chromosomes are shuffled in the process, so that each daughter cell has a unique combination • used to create gametes (sperm and egg)

Meiosis diagram

What is so special about meiosis? • It gives us genetic variability!! In other words, it is what makes you different from your siblings. How does this happen? Crossing Over - chromosomes exchange sections (increases variability)

When does crossing over occur? Crossing over occurs during Prophase 1 Crossing over occurs here

Meiosis is sexual reproduction - Involves the fusion of gametes, creates unique offspring - Eggs are much larger than sperm Image of egg and sperm

Let’s see meiosis in action!!