Meiosis and Sexual Reproduction
Chapter 7
7.1 Meiosis
 In some organisms __________ gametes join to form a ___________ zygote

If gametes weren’t haploid imagine how the number of chromosomes would increase of time
 Meiosis is the form of cell division that makes diploid cells haploid when forming gametes
 There are 2 divisions in Meiosis – __________ and __________
 Before Meiosis begins DNA is ____________________ so cell has homologous chromosomes
Prophase I
 Chromosomes condense
 Nuclear envelope breaks down
 Homologous chromosomes ____________________
 ____________________ occurs
 Chromatids exchange
Metaphase I
 Homologous pairs move to __________ by spindle
Anaphase I
 Homologous pairs separate and pulled towards poles
 Chromatids do not separate; still connected by ____________________
Telophase I
 Individual chromosomes gather at poles
 Most organisms now have ____________________
 2 new cells formed
 Chromosomes do not ____________________ again
Prophase II
 New spindle forms
Metaphase II
 Chromosomes line up along equator and are still attached at ____________________
Anaphase II
 Centromeres __________
 Chromatids separate; Now called ____________________
Telophase II
 ____________________forms around chromosome sets
Meiosis and Genetic Variation
 Three key ways meiosis creates new genetic variations
 ____________________
 ____________________

 ____________________
Independent Assortment
 Most organisms have more than 1 chromosome
 In humans the gamete gets 1 chromosome from the ____________________
 Which of the pair you get is chance
 This random distribution is called Independent Assortment
 Mathematically 2
23
= over ____________________combinations
Crossing Over
 Portion of 1 homologous chromosome is __________and __________ with the corresponding portion of its homologous partner
Random Fertilization
 What egg and sperm meet is also completely random
 Mathematically that means that the possible combinations of the sperm (about 8.3 million) can be multiplied by the combinations for the egg (about 8.3 million) giving ____________________possible combinations
 Meiosis generates variation in a species very quickly
 Pace of evolution is __________ due to variation
 A + B = C, a new individual not identical to its parents
Gametogenesis – Formation of Gametes
 ____________________ – sperm production occurs in testes
 Diploid cell increases in size and becomes immature germ cell
 Meiosis I = 2 immature sperm cells
 Meiosis II = 4 haploid cells

Develop __________ and become sperm
 ____________________ – egg production occurs in ovaries

Diploid cell increases and becomes germ cell

Meiosis I = after cytokinesis cytoplasm is not equally divided

Smaller one called ____________________

Meiosis II = larger cell divides again, again cytoplasm not equally divided

Forms another polar body

Polar bodies will __________

__________ (pl. = ova) is larger cell

More cytoplasm means more ____________________