GENES, ALLELES, AND CHROMOSOMES All living things carry their genetic information in DNA Sections of DNA with instructions for making proteins are called genes DNA coils up to form structures called chromosomes Chromosomes come in pairs, one from mom and one from dad
REVIEW: WHAT DO WE KNOW ABOUT MITOSIS? 1. It makes more cells! 2. It begins with one cell, ends with two identical cells
BIG BANG THEORY CLIP https://www.youtube.com/watch?v=hv5kpidyc3m But Why can t Sheldon actually reproduce through mitosis?
MITOSIS: Essential for growth and repair of plant, animal, and human tissue. Results in TWO daughter cells that are IDENTICAL
HOMOLOGOUS CHROMOSOMES Chromosomes that carry the same genes One from mom and one from dad Remember- genes are instructions for making proteins, and proteins determine traits
ALLELES So each of the homologous chromosomes has one copy of a gene from mom and one from dad These copies are called alleles and may be the same or different versions Green peas or yellow peas Smooth seeds or wrinkled seeds Tall plant or short plant
KARYOTYPE A photo of the chromosomes in a dividing cell that shows an individual s chromosomes arranged by size. HUMAN KARYOTYPE SHOWING 23 PAIRS OF HOMOLOGOUS CHROMOSOMES
KARYOTYPE CONT D Each of a human s 46 chromosomes has thousands of genes, so the presence of all chromosomes is essential for normal functioning Humans who are missing a chromosome don t survive past the embryo stage Humans with more than two copies of a chromosome may survive but will not develop properly (this is called trisomy).
SO WHAT S MEIOSIS???
MEIOSIS We can t use SOMATIC cells (body cells with homologous chromosomes) to reproduce sexually We need special cells called GAMETES (sperm and egg) Gametes only have ONE chromosome from each homologous pair The process of separating homologous chromosomes and making gametes is called meiosis
WHY MEIOSIS? No meiosis = no sperm or eggs. No sperm or eggs = no fertilization. No fertilization = no sexual reproduction
SPERM AND EGG CELLS ARE: Reproductive Cells Also called Gametes Haploid (n)- only have half of the normal chromosome number The normal number found in somatic cells is called diploid (2n)
PHASES OF MEIOSIS Meiosis occurs in two parts: Meiosis I - homologous chromosomes are separated, the cell splits in 2 Meiosis II - each sister chromatid is separated, both cells split in 2 for a total of 4
RESULT OF MEIOSIS: 4 HAPLOID DAUGHTER CELLS!
FERTILIZATION: Human Sperm cell Human + = Egg Cell Fertilized Egg Zygote Embryo 23 chromosomes (haploid, n) 23 chromosomes (haploid, n) 46 chromosomes (diploid, 2n)
MITOSIS Makes somatic (body) cellsskin, blood, liver Divide Once =2 Diploid Cells (2n) One division, four Phases: Prophase Metaphase Anaphase Telophase/ cytokinesis MEIOSIS Makes gametes- Sperm & Egg Divide Twice= 4 Haploid Cells (n) Two divisions, four phases each: Meiosis I Prophase I, Metaphase I, Anaphase I, Telophase I/ cytokinesis Meiosis II Prophase II, Metaphase II, Anaphase II, Telophase II/ cytokinesis
CROSSING OVER When homologous chromosomes pair up early in meiosis I, they can swap pieces (sections of DNA) This results in a new combination of alleles and increases genetic diversity
MITOSIS AND MEIOSIS SIMULATIONS http://sepuplhs.org/high/sgi/teachers/genetics_act3_si m.html
Mitosis Both makes 4 daughter Makes 2 daughter cells cells DNA replicates Makes somatic cells during interphase Makes gametes Meiosis Daughter cells are identical to parent Daughter cells are diploid (2n) one round of division One parent cell divides Prophase Metaphase Anaphase Telophase Daughter cells are different Daughter cells are haploid (n) two rounds of division individual chromosomes line up during metaphase homologous pairs line up in metaphase I
YOUTUBE VIDEO http://www.youtube.com/watch?v=zgvbahasjjm&safe=active