Meiosis & Reproduction

Asexual Reproduction

• Identical offspring (clones)

• Mitosis

• Different kinds– Binary fission– Budding– Fragmentation– Regeneration

Sexual Reproduction

• Two parents

• Genetic variation

• Haploid gametes

• Unique offspring– Similar to parents– Similar to each other

Genetic VariationFor humans - 23 pairs of chromosomes:

• Independent Assortment – 50/50 chance that gamete gets maternal/ paternal homologous chromosome– # of possible gametes = 223

– >8 million possible gamete combinations

• Random Fertilization– (8 million)(8 million) = 64 trillion possible offspring

• Crossing over – increases genetic variation even more

Haploid vs. Diploid

HAPLOID• 1n

• One copy of each chromosome

DIPLOID• 2n

• Two copies of each chromosome

• Homologous chromosomes

Karyotyping

Human Female Karyotype

Human Male Karyotype

Life Cycles

Overview of Meiosis

• Diploid parent cell divides twice to make haploid gametes

• Homologous chromosomes

• Sister chromatids

Meiosis I

Meiosis II

Mitosis vs. Meiosis

Gamete Possibilities(due to Independent Assortment)

Crossing Over

• Increases genetic variation

• Synapsis• Tetrad• Chiasma

• Happens during Prophase I

Homologous chromosomes move toward opposite poles of a dividing cell during

A. Mitosis

B. Meiosis I

C. Meiosis II

D. Fertilization

E. Binary fission

If the DNA content of a diploid cell in the G1 phase is x, then the DNA content of the cell at metaphase I of meiosis would be

A. 0.25x

B. 0.5x

C. x

D. 2x

E. 4x

For the same cell, the DNA content at metaphase II of meiosis would be

A. 0.25x

B. 0.5x

C. x

D. 2x

E. 4x

How many different combinations of chromosomes can be packaged in gametes by an organism with a diploid number of 8 (2n = 8)?

A. 2

B. 4

C. 8

D. 16

E. 32