Meiosis The Diploid Cell with sets of chromosomes

Meiosis

The Diploid Cell with ___ sets of chromosomes Contains chromosomes for each _____ pair _____ = Body Cells: Diploid All human cells except ______ are diploid Where does the diploid number come from? ____, where n is the number of chromosomes an individual has What is n for humans? ______ 2 n? ______

The Haploid Cell containing ___ of each kind of chromosome Examples: __________ ___ set of chromosomes _____ the number of chromosomes of diploid ___ Sperm + Egg = Zygote

Haploid = one of each kind Diploid = two of each kind + or 2 n = diploid n = haploid

Mitosis vs. Meiosis • Mitosis: t = two: Diploid 2 n=46 • Meiosis: o = one: Haploid n = 23

Meiosis _____ are produced in specialized body cells Sperm and Egg Cells __ divisions: ____________ Meiosis occurs in ____ cells, not _____ cells __ daughter cells Each cell has ____ the chromosomes of the parent

Meiosis I Interphase occurs: the cell grows and DNA replicates Meiosis I begins Original cell produces two new cells Like Mitosis

Prophase I DNA Coils tightly into chromosomes Spindle fibers appear Each chromosome lines up next to the homologue Synapis occurs: pairing of homologous chromosomes Tetrad: Each pair of homologous chromosomes

Crossing Over: why we do not look exactly like our parents. • Portions of the ______ breaks off and attaches to ________ on the _______ chromosome Permits _____________ between maternal and paternal chromosomes • Occurs during _______

Genetic Recombination Crossing over produces a new mixture of genetic material

Causes of Variation Chromosomes are assorted randomly Crossing over may occur Cells do not have identical genetic info as each other or the parent + ______________ - _______________

Metaphase I Tetrads line up randomly along the mid-line Spindle fibers attach to centromeres

Anaphase I Homologous chromosomes move to the opposite poles Random separation or Independent Assortment results in separation of maternal and paternal chromosomes.

Telophase I Chromosomes reach opposite ends of cell Cytokinesis begins Cell is now haploid

Meiosis II Occurs in each cell formed in Meiosis I Interphase does not occur again

Prophase II Spindle fibers form and move the chromosomes to the mid-line of the dividing cell

Metaphase II Chromosomes move to the midline of the dividing cell facing opposite poles of the dividing cell

Anaphase II Chromatids separate and move to opposite poles of the cell

Telophase II Nuclear membrane forms around the chromosomes in each of 4 new cells

Cytokinesis II _____ divides __________ closes off

End Result: ____ new cells that contain _____ of the original cells number of chromosomes Creates _____ = _____

What exactly is a gamete? Formed by ______________ cells In humans, meiosis occurs in the testes and ovaries

Meiosis Animation • Meiosis Animation

Why do we need haploid gametes? Female gamete Male gamete 23 23 EGG SPERM

Fertilization restores the diploid number 1 n fertilization 1 n meiosis 2 n 2 n Mitosis and cell growth 2 n

Mitosis vs. Meiosis • Mitosis vs. Meiosis Animation Notes:

Nondisjunction • • Failure of __________ to ______ properly during meiosis. _________ of a homologous pair move to the ______ of the cell. • 1 gamete has __________ Or • 1 gamete is ___________

Nondisjunction Animation • Nondisjunction Animation Notes:

Chromosome Pop Quiz! • What is a chromosome? • Where do we find them? • What do they look like? • • How many pairs of chromosomes do humans have? What determines if someone is male or female?

Trisomy: Extra Chromosomes • Trisomy 13: Patau’s Syndrome • Trisomy 21: Down’s Syndrome • XXX: Trisomy X • XYY: Jacob’s Syndrome • XXY: Klinefelter’s Syndrome

Monosomy: Missing Chromosomes • • • Most do not survive. Turner XO : develop as girls, but infertile OY: lethal