Meiosis Why do you share some but not all characters of each parent? 2/21/2019 Meiosis Why do you share some but not all characters of each parent? What are the rules of this sharing game? G. Podgorski, Biology 1010

Asexual reproduction is reproduction that requires only one parent. • Most single-celled organisms, like bacteria and protozoans, reproduce this way.

Cell division is a type of asexual reproduction. • Your body cells reproduce this way. • In asexual reproduction, the DNA and internal structures are copied. • Then the parent cell divides, forming two cells that are exact copies of the original.

Meiosis 2/21/2019 What Meiosis is About Meiosis allows the creation of unique individuals through sexual reproduction. G. Podgorski, Biology 1010

Keys to Understanding Meiosis 2/21/2019 Keys to Understanding Meiosis Chromosomes are paired. Chromosomes carry genes. The gene forms on a pair of chromosomes may be identical .. Brown eyes Tall Brown eyes Blue eyes Tall Short or different. G. Podgorski, Biology 1010

MEIOSIS: A type of cell division that results in daughter cells with half as many chromosomes as the parent cells

• Meiosis is the process of cell division in which gametes -sex cells (eggs and sperm) are formed

n = number of chromosomes from each parent Meiosis 2/21/2019 n = number of chromosomes from each parent Gametes are haploid diploid(n) Body cells are diploid 2(n) – cells with two of each kind of chromosome G. Podgorski, Biology 1010

Chromosomes Humans: 46 (23 pairs) Mosquito: 6 (3 pairs) Toad: 22 (11 pairs) Potato: 48 (24 pairs) Dog: 78 (39 pairs)

Homologous chromosomes are paired chromosomes with genes for the same traits arranged in the same order

Bellringer Thu, 12/04 What are gametes? What is a gene? Name the 2 processes that meiosis does to scramble genes and create variety in the gametes. USE YOUR NOTES FROM YESTERDAY!!! REMINDERS: HW #14 due Fri, Progress Reports, LAB FEE anytime, Notebook check tomorrow!!!

Stages of Meiosis: Meiosis I Stages of Meiosis: PMAT I and II Meiosis I: reduces chromosome number

Stages of Meiosis: Meiosis II 2/21/2019 Meiosis II: separates chromatids G. Podgorski, Biology 1010

Prophase I: homologous pairs (and copies) synapse or pair up Prophase I: chromatin condenses, homologous pairs (with copies) align Metaphase I: homologous pairs (and copies) align at metaphase plate Meiosis 2/21/2019 Meiosis I Prophase I: homologous pairs (and copies) synapse or pair up Metaphase I: chromosomes align at the middle at the equator of the cell G. Podgorski, Biology 1010

Meiosis I continued Anaphase I: homologous chromosomes (each with two chromatids) move to opposite ends Telophase I:two nuclei form, original cell divides

Meiosis II: PMAT part II No INTERPHASE or DNA copied between I and II Prophase II: chromosomes condense again and start to move toward the equator Metaphase II chromosomes line up in the middle

Meiosis II continued Anaphase II: chromatids separate to opposite poles Telophase II: two nuclei form - and cells divide Cytokinesis as in mitosis!

Results after meiosis… In males -Four sperm cells are formed All sex cells are haploid (n) - half as many chromosomes as parent cell (2n)

In females meiosis results in one large egg cell and 3 polar bodies 2/21/2019 In females meiosis results in one large egg cell and 3 polar bodies Women are less busy in meiosis than men – meiosis produces only a few hundred mature eggs over a lifetime. G. Podgorski, Biology 1010

In males meiosis results in 4 sex cells 2/21/2019 In males meiosis results in 4 sex cells Men are busy – meiosis produces roughly 250,000,000 sperm per day. G. Podgorski, Biology 1010

Meiosis 2/21/2019 The Key Difference Between Mitosis and Meiosis is the Way Chromosomes Uniquely Pair and Align in Meiosis The first (and distinguishing) division of meiosis Mitosis G. Podgorski, Biology 1010

Crossing-over -exchange of genetic material between homologous pairs Meiosis 2/21/2019 Crossing-Over Crossing-over -exchange of genetic material between homologous pairs G. Podgorski, Biology 1010

Chromosomes 1 to 22 are autosomes Chromosome #23 sex chromosome Meiosis Chromosomes 1 to 22 are autosomes Chromosome #23 sex chromosome 2/21/2019 G. Podgorski, Biology 1010

Boy or Girl? The Y Chromosome “Decides” Meiosis 2/21/2019 Boy or Girl? The Y Chromosome “Decides” X chromosome Y chromosome G. Podgorski, Biology 1010

Meiosis 2/21/2019 G. Podgorski, Biology 1010

Boy or Girl? The Y Chromosome “Decides” Meiosis 2/21/2019 Boy or Girl? The Y Chromosome “Decides” G. Podgorski, Biology 1010

“Putting It All Together” - Fertilization Meiosis 2/21/2019 “Putting It All Together” - Fertilization G. Podgorski, Biology 1010

Meiosis 2/21/2019 One Way Meiosis Makes Lots of Different Sex Cells (Gametes) – Independent Assortment Independent assortment produces 2n distinct gametes, where n = the number of unique chromosomes. In humans, n = 23 and 223 ≈ 8,000,0000. That’s a lot of diversity by this mechanism alone. G. Podgorski, Biology 1010

A fertilized egg, called a zygote, has a diploid set of chromosomes. • For each homologous pair, one chromosome comes from the mother, and one from the father. • After fertilization, the zygote rapidly divides by mitosis and becomes an embryo.