Biology Lab 7 Mitosis and Meiosis PDF

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Summary

Professor Jennifer Juarez-Ayala
week 7-course work
you will learn about the phases of Mitosis and Meiosis ...

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Mitosis and Meiosis ❖ Number of chromosomes differ b/w species but is constant w/in species ➢ Fruit fly-4 chromosomes ➢ Humans-46 chromosomes ➢ Some protozoans and plants-over 200 chromosomes ❖ Chromosomes constant in somatic cells ( body cells) w/in organism ➢ Gametes (sex cells: eggs and sperm) w/in an organism contain half the number of chromosomes present in the somatic cell  division ❖ Eukaryotic cell division involves nuclear division as well as cytoplasmic (cytokinesis) ➢ 2 types of eukaryotic nuclear division mechanisms ■ Mitosis ■ Meiosis ● MOST SOMATIC CELLS UNDERGO MITOSIS AND CYTOKINESIS ❖ MITOSIS ➢ What is the outcome of mitosis of a single diploid cell? ■ Two diploid daughter cells which are clones (genetically identical) ❖ MITOSIS AND CYTOKINESIS ➢ Mitosis and cytokinesis are used for growth (of a single fertilized egg into a multicellular adult organism), repair (replacement of lost cells), and asexual reproduction ❖ MEIOSIS AND CYTOKINESIS ➢ Germ cells (somatic cells), which are located in reproductive organs of males and females, go through meiosis and cytokinesis ➢ Function of meiosis and cytokinesis: g  amete production

The cell cycle ❖ Majority of time, chromosomes exist w/in nucleus as strands(long and thin) that are invisible to the light microscope ❖ INTERPHASE ➢ Both production of proteins and the replication of DNA are occurring ■ Important that DNA w/in nucleus is replicated exactly to provide full complement of DNA for the daughter cells that will result from nuclear division (mitosis and meiosis) and cytokinesis ● WHEN ARE DNA STRANDS VISIBLE? ◆ After INTERPHASE,DNA stands become coiled and become visible in light microscope --what we see as chromosomes ➢ Each chromosome is composed of 2 identical copies (S  ISTER CHROMATIDS) attached to one another by a structure called a centromere

Mitosis

❖ Involves a single nuclear division that separates sister chromatids to produce two identical daughter cells Phases in Mitosis ➢ Prophase ■ Chromosomes condense and become visible w/in the cell, often appearing as a coiled mass ➢ Metaphase ■ Chromosomes line up near center of cell and very thin hollow tubes called spindle fibers attached to the centromeres of chromosomes ● This is followed by ANAPHASE ➢ Anaphase ■ Sister chromatids are pulled apart to opposite ends (“poles”) of cell ➢ Telophase ■ Completes the nuclear division process; as the chromosomes have reached the opposite ends of the cell, they decondense and a nuclear envelope re-forms around them ➢ Cytokinesis--physical separation of one cell into two ■ Occurs during telophase either by furrowing (animal cells) or by cell plate formation (in plant cells) ■ Each one of the two genetically identical daughter cells now return to interphase, during which protein synthesis and DNA replication will occur. Ultimately, they will once again divide by mitosis and cytokinesis to form two daughter cells each

Mitosis: The Amazing process that uses Division to Multiply ❖ Mitosis is a type of cell division done by most of your body cells and important for your cells to divide ➢ Mitosis helps you grow and repair damage (ex. cuts) ❖ Mitosis is not a process that makes sperm or eggs cells ➢ This is meiosis ❖ Mitosis is done to produce body cells ➢ Makes identical cells---the goal of mitosis ■ Ex. make more identical skin cell to replace worn out or damaged skin cells ❖ Important to understand that cells are not dividing all the time ➢ If they did divide all the time, cancer can occur ❖ INTERPHASE--stage where cells are spending most of their time ➢ Growing, replicating DNA, and carrying out its daily cell functions ❖ Mitosis is a very short amount of time in respect to the whole cell cycle ❖ Mitosis is a critical process because its where cells divide and make more cells ❖ IMPORTANT: cells have an organelle called the nucleus which holds your DNA (holds your genetic information) ➢ If your going to make more cells, you need to have the same DNA in those new cells as you did in your original cells---want it to be identical

❖ DNA can be organized into these condense united called chromosomes ➢ Chromosomes are made of DNA and protein ➢ Humans have 46 chromosomes ■ Found in human body cell nuclei (nucleus) ❖ If you have 46 chromosomes in a human body cell, you have to duplicate those chromosomes in i nterphase before mitosis starts ➢ Means your duplicating your DNA, since chromosomes are made of DNA and proteins ■ Have to do this b/4 mitosis starts b/c if your going to make an identical cell that has 46 chromosomes just like the original, you have to duplicate the genetic material before splitting ❖ We tend to count chromosomes by number of centromeres(PART OF CHROMOSOME WHERE SISTER CHROMATIDS ARE HELD TOGETHER) present ➢ when the 46 chromosomes duplicate, we still say there are 46 chromosomes as the sister chromatids are still attached and we’re counting by centromeres ❖ Mitosis stages of division (PMAT) ➢ 1ST STEP P  ROPHASE ■ Nucleus is still there(goes away later on) ■ Chromosomes are visible- we say “chromosomes are condensing” ● Condensing meaning thickening and visible ➢ 2ND STEP METAPHASE (Think of M as middle) ■ Chromosomes line up in the middle of the cell ■ Nucleus has been disassembled-- no longer there ➢ 3RD STEP A  NAPHASE (Think of A as away) ■ Chromosomes move away--moving to opposite sides of the cell ● Important: chromosomes are not moving by themselves, they have SPINDLES ◆ SPINDLES are fibers that help move the chromosomes to the ends ➢ FINAL STEP T  ELOPHASE (Think of T for two) ■ Chromosomes are at the complete opposite end and new nuclei are forming on each side to make two new cells ■ Nuclei start to surround chromosomes on both sides ■ End goal is two cells ● In the human body, they’re each going to have 46 chromosomes ❖ Cytokinesis is responsible for the final separation into two cells by splitting the cytoplasm ➢ Completes after the PMAT mitosis stages

Exercise 1: Onion Root Tip Mitosis ❖ Why are onions excellent specimens for viewing the process of mitosis? ➢ Chromosomes are large and few ➢ Cells are held in place by a rigid cell wall, and large numbers of neighboring cells are visible at one time ➢ There are discrete regions w/in the root where there is quite a high rate of mitosis ■ Actively dividing cells in all stages are easier to find

❖ Why do you think cells spend most of their time in interphase? ➢ Because they are growing, replicating DNA, and carrying out its daily cell function

Exercise 2: Mitosis Stimulation ❖ Interphase ➢ Happens before mitosis ➢ Cell does normal activities, like make proteins ➢ In the nucleus, there are two strongly pieces of DNA ■ Uncoiled stringy DNA is called CHROMATIN What is uncoiled stringy DNA called? Answer: Chromatin ➢ If cell has two pieces of chromatin, this means it has 2 DNA molecules ■ Each of your cells has 46 pieces of chromatin ➢ Before mitosis can occur, DNA must replicate Which of the following are true statements? Answer: DNA replicates during interphase Chromatin is made of DNA Genes are found on DNA ❖ Intro to Mitosis ➢ Mitosis is an important part of cell division, which allows you to make more cells ■ Needed for growth, development, and tissue repair ➢ Mitosis ultimately results in the formation of 2 genetically identical daughter cells ➢ Why do organisms do mitosis ■ Answer: to make more body cells, like skin cells or liver cells ➢ Mitosis divides into 4 phases ■ Prophase ■ Metaphase ■ Anaphase ■ Telophase ● This is the correct order of Mitosis ❖ Prophase ➢ Chromosomes condense and become visible ■ This means that the chromatin gets packaged up so that it is easier to move around ● Each chromosome has 2 halves ● Each half of a chromosome is called a sister chromatids ◆ Sister chromatids of a chromosome are identical ➢ In order to divide up DNA, chromosomes must move to opposite ends of cell ➢ Nucleus disintegrates during this stage of mitosis ❖ Metaphase ➢ Chromosomes line up single file down the middle of the cell ❖ Anaphase

➢ Sister chromatids split up and move toward opposite poles of the cell ❖ Telophase ➢ 2 diploid daughter cells are begin formed ➢ Each newly formed cell makes a nucleus ➢ Chromosomes then uncoil to make chromatin ❖ Cytokinesis ➢ At the same time Telophase occurs, Cytokinesis also occurs

Meiosis ❖ Meiosis and Cytokinesis produce G  ametes (sex cells) ❖ Meiosis occurs only in germ cells located in ovaries and testes ➢ Leads to the production of eggs or sperm ❖ Meiosis reduces the chromosome content of the daughter cells to exactly one half of that parent cell ➢ Diploid to Haploid ❖ alignment s and movements of chromosomes in meiosis separate Homologous Chromosomes, so that each resultant cell receives one copy from each pair of homologous chromosomes ❖ Meiosis similar to mitosis, with a few important changes ➢ 1st. Meiosis involves two sets of divisions ■ 1st division (meiosis1) ● homologous chromosomes lie next to each other during Metaphase 1, and are pulled to opposite poles during Anaphase 1 ■ 2nd division (meiosis 2) ● Similar to mitosis, w/ chromosomes arranged along the equator during metaphase 2, and sister chromatids pulled to opposite poles during Anaphase 2 ❖ 1st set of division serves to separate homologous chromosomes, 2nd set of division separates sister chromatids, resulting in 4 genetically different daughter cells each containing half of genetic information contained in the parent cell ❖ During Meiosis 1, two events occur ➢ Crossing over ➢ homologous chromosomes (genetic recombination)

Meiosis ❖ Process that contributes to genetic variety ❖ Doesn’t make body cells ❖ Meiosis makes sperm and egg cell ➢ Known as gametes ❖ Human sperm cells and egg cells have 23 chromosomes ➢ If a sperm cell has 23 chromosomes and egg cell has 23 chromosomes, when they come together it makes 46 chromosomes----allows newly formed fertilized egg to develop into a human ❖ What happens before meiosis can start? ➢ Interphase (also happens in mitosis)

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When the cell is growing, replicating its DNA, and carries out cell processes ➢ Starting cells has 46 chromosomes, and you have to duplicate those chromosomes in interphase before meiosis starts ■ You are duplicating your DNA Tricky part ➢ Because we tend to count chromosomes by the number of centromeres present, when the 46 chromosomes duplicate, we still say there are 46 chromosomes because the sister chromatids are still attached and we're counting by centromeres ■ In duplication, we go from 46 chromatids to 92 In meiosis, you still use prophase, metaphase, anaphase, & telophase, B  ut because meiosis is actually a reduction, you're going from 46 chromosomes to 23 ➢ You are dividing twice in meiosis ■ You do PMAT twice!! Meiosis 1 stages ➢ Prophase 1 ■ Where chromosomes are going to condense and thicken ■ Are going to line up w/ their homologous pairs ● Homologous- c hromosome are approximately the same size and contain the same types of genes in the same location ■ During this phase, crossover occurs ● When the chromosomes are lined up in homologous pairs, they have a way that they can transfer their genetic information and exchange it b/w each other ■ Crossover makes for R  ecombinant Chromosomes ➢ Metaphase 1 ■ Chromosomes are going to be in the middle of the cell ● Chromosomes are going to be in pairs in the middle of the cell ➢ Anaphase 1 ■ Chromosomes are going to be pulled away by the spindle fibers ➢ Telophase 1 ■ You have two newly formed nuclei and it becomes obvious that you will end meiosis 1 with two new cells ➢ Cytokinesis ■ Spilts the cytoplasm Meiosis 2 stages ➢ Prophase 2 ■ Not going to have homologous pairs or the process of cross-over ■ Chromosomes and the spindles start to form like in prophase 1, but not as eventful ➢ Metaphase 2 ■ Chromosomes going to line up in the middle, this time they are in a single file line

■ Not in pairs ➢ Anaphase 2 ■ This time the chromatids are getting pulled away by spindle fibers ➢ Telophase 2 ■ Nuclei reforms and the 2 cells are each going to divide so you can see that 4 cells are going to be formed ➢ Cytokinesis ■ Cytoplasm is being split ❖ Meiosis in males produce sperm cemm and in females, produces egg cells ❖ Because of independent assortment and crossing over, you're going to have variety ➢ Ex: in a male, 4 sperm cells that are produced each time, they are all different from each other. Also different from starting cell because the starting cell has 46 chromosomes and the ending cells only have 23 ■ Not identical to the original or each other--- leads to variety ● Reason why siblings with same parents can look different ❖ Nondisjunction ➢ When a cell can receive too many or too few chromosomes in the separation ■ Contributes to genetic disorders

Exercise 3: Karyotype of Human Chromosomes ❖ Chromosomes are visualized in a laboratory preparation called a karyotype. ➢ Each chromosome has a distinct size, length, centromere location, and banding (staining) patterns

Exercise 4: Meiosis ❖ Video presentation information ❖ in mitosis, the homologous pairs do not pair up but rather, all 46 chromosomes independently line up at the metaphase plate (equator of cell) and then are pulled apart ➢ In meiosis I, the homologous pairs are joining to form tetrads (tetra = 4) before lining up at the equator to be separated...