Chapter 7Lesson 2

“Production of Reproductive Cells”

I. Chromosome Numbers and CharacteristicsA. Chromosomes

1. Different amounts in every organism

a. Human b. Fruit Fly

c. Dog

23 pairs

4 pairs

39 pairs

2. Same #’s are always passed on.

B. Diploid

1. Having 2 of each chromosome

2. 2n (n = # of paired chromosomes)

so… 2n or 2(23) = 46 chromosomes

3. Homologue – 1 chromosome

a. How many homologues?

b. Combinations of different

homologues determine specific

traits.

2

II. MeiosisWhere do animal and plant cells get their

homologues from?

A. Haploid Sex Cells1. Def – cells that contain ½ of a parents genetic information.

a. Haploid cells = sperm/egg represented by “n”

2. Sexual Reproduction – 2 haploid cells fuse together to form a diploid cell. (zygote)

forms mature multicellular organism

Male and female reproduction zygote (single fertilized egg)

parents

n n

2n (zygote)

½ female info ½ male info

B. Def of Meiosis – the process by which haploid cells are produced.

or the formation of sperm and egg

only occurs in reproductive tissues

provides the right # of chromosomes

1. 2 parts

a. Meiosis I and Meiosis II

III. Meiosis I (In males) (pg. 184-185)A. Interphase I

-chromosomes are duplicated

B. Prophase I

-nuclear membrane dissolves

-centrioles move apart

-spindle forms

-tetrads form (group of 4)

C. Metaphase I

-tetrads line up at the equator

-centrioles are found at the poles

D. Anaphase I

-centromeres do not break

-sister chromatids stay connected

-separation of the homologous pair

E. Telophase I

-cell begins to pinch

-2 cells formed

IV. Meiosis II*Similar to mitosisA. Interphase – no DNA replication; briefB. Metaphase II – chromosomes move to the

equatorC. Anaphase II – centromeres split and sister

chromatids move to the poles.D. Telophase II – cell pinches; 4 haploid cells

are produced -cells now contain “n”

4 sperm cells

V. Meiosis in Females (pg. 187)*Similar process but a couple different twists*

1. Go through meiosis when in the womb (approx. 12 weeks)2. 1 cell survives per cycle

A. Meiosis I1. Cell divides; unequal sizes

a. Large cell continues to meiosis IIb. Small cell usually dies

B. Meiosis II2. Cell divides; unequal sizes

a. Large cell can become fertilized (n)b. Small cell usually dies

1 egg cell

VI. Why Meiosis?A. Produce haploid cells

B. Continues life cycle

C. Genetic Variation…

1. mitosis replica cells

2. meiosis variation of cells

a. Allows change

b. Better chance of survival (natural selection)

c. Genetic Recombination – reshuffling of chromosomes and genetic information.