Chapter 8

 Asexual reproduction – new organisms/cells are genetically identical to parent cells/organisms  Sexual reproduction – offspring have a combination of genes from both parents.

 Budding - plants  Vegetative propagation -plants  Binary fission -bacteria  One cell dividing to become two –mitosis  Hermaphroditic organisms are NOT asexual!!!

 To make more cells they must divide  Mitosis – one cell divides to make two genetically identical cells for asexual reproduction and growth and repair.  Meiosis – One cell divides twice to create 4 cells that are not genetically identical. These cells are eggs or sperm (gametes)

 Interphase – cell does normal job, grows, and duplicates genetic material to prep for division, 90% of cell cycle  G1, S, G2  Mitosis – division of genetic material  Cytokinesis- division of cytoplasm, usually occurs after mitosis

 Interphase  G1- first gap, growth, normal function, makes proteins etc  S phase- synthesis, cell copies DNA to prepare for division  G2- second gap, growth and final preparation for division

 DNA in a non-dividing cell is disorganized  Called chromatin  When a cell prepares to divide the chromatin (DNA and proteins called histones) coil into chromosomes  Each chromosome is made of two identical halves called sister chromatids  Sister chromatids are connected by a centromere

 In animal cells a cleavage furrow develops. The cell pinches from the outside  In plant cells a cell plate forms. A new cell wall develops from the inside and works out to the borders

 Must be attached to a surface  Will stop dividing when they touch each other- density dependent inhibition  Secretion of proteins called growth factors  Three key checkpoints in the cell cycle  G1  G2  M-

 Do not respond normally to checkpoints in the cell cycle  Excessive cell division, wasting of cellular resources, form masses called tumors  Benign- stays in original location  Malignant- spreads from original location- metastasis

 Occurs in somatic or non-sex cells  Creates two genetically identical cells from one cell  The cells created are diploid (2n)– having a full set of chromosomes.  Used for repair and growth

 Diploid cells in ovaries and testes divide by meiosis to create haploid gametes.  Gametes are egg and sperm.  Haploid cells have a half set of chromosomes  Haploid gametes combine to form a diploid zygote  Diploid zygotes divide by mitosis to form Multicellular organisms

 Humans have 22 pairs of autosomes – non- sex chromosomes and one pair of sex chromosomes  Females have two X chromosomes  Males have an X and a Y chromosome

 Two divisions  Meiosis I; meiosis II  Major differences  Prophase I- homologous chromosomes pair into a tetrad. Sometimes the homologous pairs exchange small pieces – crossing over  Synapsis – the exchange of pieces

 1. Crossing over – creates chromosomes that are mosaics of both maternal and paternal genes.  Is a random event and doesn’t happen for every meiotic cycle  Occurs in prophase I  Called genetic recombination

2. Law Of Segregation  Each haploid cell inherits only one chromosome from each parent. Homologous chromosomes carry genes for the same trait but not necessarily the same gene – Law of Segregation.  The physical process that underlies this law occurs in Anaphase I

 3. Law of Independent assortment  Each homologous chromosome pair lines up side by side and separates randomly in metaphase I.  Creates many different random combinations of chromosomes in each egg or sperm  Different possibilities = 2 to the n power, where n= the haploid number

 4. Random fertilization increases genetic variability in a species  Why is variation needed?  Organisms with very similar genomes have no raw material for natural selection should the environment abruptly change

 Are carried on chromosomes  Each trait in your body is determined by at least two genes on two different homologous chromosomes – one from dad, and one from mom

 Crossing over  Separation in anaphase I and/or anaphase II  Nonreciprocal crossovers- exchange of pieces of DNA of different sizes  Inversion- pieces of chromosomes are reattached incorrectly  Non homologous crossovers  Failure to separate – nondisjunction

 Chromosomes missing parts due to non reciprocal cross overs have deletions  Chromosomes with too much info have duplications.  Fragments reattached in the wrong sequence are inversions  Translocations occur when non-homologous chromosomes cross-over

 Cri du chat- deletion on # 5, “cry of the cat” in babies  Down Syndrome can be caused when #21 attaches to another chromosomes  Chronic myelogenous Leukemia (CML)- non homologous cross over activates a cancer gene. Call it the “Philadelphia chromosome”

 Can occur in anaphase I or anaphase II  Results in organisms with the wrong number of chromosomes for their species – aneuploid individuals  Most situations with missing or extra chromosomes lead to spontaneous miscarriage

 Trisomy  Trisomy #21 – Down’s Syndrome  Trisomy- # 18- Edward’s Syndrome  Trisomy #13- Patau’s Syndrome

 Individual with only one X- Turner Syndrome, female, sterile, can have other physical traits  XO  Individual with two X chromosomes and one Y, - Klinefelter’s Syndrome male, sterile, some female characteristics, taller than normal  XXY

 Amniocentesis – performed at weeks, a needle is inserts into the uterus to extract amniotic fluid which contains fetal cells. Cells are cultured for a few weeks  Chorionic villi sampling- placental tissue is removed and cultured within 24 hours, can be performed at the 8 th week  Both carry a small risk of miscarriage

 Fetal cells or blood and tissue samples are cultured and are used to make pictures of chromosomes called karyotypes  White blood cells are useful for karyotyping