Ch.7: Meiosis and Sexual Reproduction Biology Fall 2012 E.Baker

Cell Division/Cell Reproduction 2 Main Types of Cell Reproduction I. Asexual-requires only one parent; results in clones (organism is genetically identical to parent) 1.Binary fission- cell divides into 2 cells 2.Budding-individual occurs as an outbranch of another 3. Fragmentation (regeneration)-development of a new organism from its parts Each cell is identical to the other. II. Sexual-requires two parents involving the union of 2 gametes; allows for genetic variation.

Meiosis-cell division to reduce the number of chromosomes to form the gametes; occurs only in testis and ovaries. Gametogenesis-process responsible for producing gametes Spermatogenesis-formation of sperm in testes Oogenesis-formation of egg in ovaries Fertilization-union of egg (n) and sperm (n) to form a zygote (2n) Zygote repeatedly divides by mitosis to form complete organism.

Diploid cells have homologous chromosomes, haploid cells do not. Gonads-organs in which meiosis occurs. Female gonads are the ovaries. Male gonads are the testes.

Nondisjunction-failure of a chromosome pair to separate properly and the resulting gametes will have either too many of too few chromosomes. Monosomy-having 1 less the normal number of chromosomes (denoted by 2n-1). Trisomy-a gamete with one extra chromosome combines with a normal gamete (2n+1) A zygote with more than 47 chromosomes usually does not survive to form an embryo.

Autosomal trisomy-children with an extra 21 chromosome (Down Syndrome) Autosomal trisomy-children with an extra 21 chromosome (Down Syndrome). Features such as almond shaped eyes, short limbs, thick tongues, etc. Heterosomal Trisomy and Monosomy Klinefelter syndrome-males w/ an extra X chromosome. Features such as sterility, and some may show some degree of mental retardation. Metafemale-Females with an extra X chromosome (XXX). Develop normally, maybe sterile Turner’s syndrome-egg fertilized by sperm with no sex chromosome, designated as XO. Features such as sterility, short, thickened or webbed neck, etc.

Prenatal Testing Amniocentesis- a small amount of amniotic fluid is removed from the sac surrounding the fetus; performed during 14 or 15 week of pregnancy. Chorionic Villi Sampling-a sample of the chorionic villi (fingerlike extensions of the placenta are removed; can be done earlier in pregnancy.