Meiosis

Called Somatic Cells Mitosis is 99.9% of your body’s cells. (Diploid 46 chromosoms) Copyright © 2010 Ryan P. Murphy

Gametes (Haploid) 23 Chromosomes Mitosis is 99.9% of your body’s cells. Meiosis occurs in your sex cells. Gametes (Haploid) 23 Chromosomes Copyright © 2010 Ryan P. Murphy

Only two types of cells in your body are haploid Only two types of cells in your body are haploid. Two haploids make a diploid. Sperm Eggs

Haploid or Diploid? Egg Cell Nerve Cell Skin Cell Sperm Cell Stem Cell

Fertilization: The joining of the egg and the sperm. The sperm and egg each contain ½ genetic info needed to make a diploid cell…YOU! Sex cells are also called gametes Copyright © 2010 Ryan P. Murphy

Sex Cells example/ If sex cells each had the total 46 chromosomes (2 complete sets), when they combined, there would be 92 chromosomes. If a cell with 92 combined with another cell of 92, there would be 184…this is problematic.

Reduction Division Sex cells are reduced from the diploid to ½ of the normal number (or a HAPLOID condition) In humans, 46 chromosomes must be reduced to 23 This is the number of chromosomes found only in egg and sperm cells (gametes)

Meiotic Process Reproductive cells are reduced by the process of Meiosis

Mitosis Mitosis 23 23 46 46 Egg Fertilization Sexual Reproduction: Both parents provide half of the genetic information. 46 46 Sex cell formation Meiosis Egg 23 Sperm 23 Nine months later… Fertilization Mitosis Mitosis

Homologous Pairing Homologous pairs- Chromosomes are always paired with a matching set. These are separated in Meiosis I An organism receives ½ of its chromosomes from each parent (making 1 full set)

Phases of Meiosis Meiosis is a two part process that is nearly identical to mitosis Meiosis I Prophase I – replicated pairs of chromosomes thicken and condense Metaphase I – Chromosomes line up on cell plate Anaphase I – Homologous pairs are pulled apart by spindle fibers Telophase I – Cytokinesis takes place

Meiosis II Prophase II – sister chromatids (chromosome) condense Metaphase II – sister chromatids (chromosome) center on cell plate again Anaphase II – Sister chromatids are pulled apart by spindle fibers Haploid Cells – 4 haploid cells are produced through cytokinesis

A look at both Meiosis I & II

New Chromosomal Combinations Meiosis allows for variation among organisms DNA is different on each chromosome Genetic make-up is unique to each individual Variation is good Helps organisms to more readily adapt to their surroundings and continue their survival

Reduction of genetic information Produces four different reproductive cells Copyright © 2010 Ryan P. Murphy

Reduction of genetic information Produces four different reproductive cells Copyright © 2010 Ryan P. Murphy

Reduction of genetic information Produces four different reproductive cells Copyright © 2010 Ryan P. Murphy

Reduction of genetic information Produces four different reproductive cells Copyright © 2010 Ryan P. Murphy

Reduction of genetic information Produces four different reproductive cells Copyright © 2010 Ryan P. Murphy

All Different Reduction of genetic information Produces four different reproductive cells All Different Copyright © 2010 Ryan P. Murphy

Also called Homologous Crossing Over : Genetic segments of information are swapped when the chromosomes are next to each other (random and creates millions of possibilities) Also called Homologous Recombination Copyright © 2010 Ryan P. Murphy

Which sperm will fertilize the egg? It’s usually only one. A B C D Copyright © 2010 Ryan P. Murphy

Answer. It’s completely random Answer! It’s completely random. This is what makes you completely unique. C Copyright © 2010 Ryan P. Murphy

Only one of the eggs will become a viable egg for fertilization. A B C D Copyright © 2010 Ryan P. Murphy

Only one of the eggs will become a viable egg for fertilization. A B C D Copyright © 2010 Ryan P. Murphy

Only one of the eggs will become a viable egg for fertilization. Called Polar Bodies A B C D Copyright © 2010 Ryan P. Murphy

Only one of the eggs will become a viable egg for fertilization. They shrivel and die… Called Polar Bodies A B C D Copyright © 2010 Ryan P. Murphy

Only one of the eggs will become a viable egg for fertilization. They shrivel and die… Called Polar Bodies A B C D Copyright © 2010 Ryan P. Murphy

Karyotype An ordered, visual representation of the chromosomes in a cell Chromosomes are photographed when they are highly condensed, then photos of the individual chromosomes are arranged in order of decreasing size: In humans each somatic cell has 46 chromosomes, made up of two sets, one set of chromosomes comes from each parent 5 µm Pair of homologous chromosomes Centromere Sister chromatids

Autosomes = Chromosome pairs 1-22 look alike and code for body Sex Chromosomes= The 23rd pair determines the sex of the individual (XX=female, XY=male)

Chromosome types Non-homologous chromosomes Look different Control different traits Sex chromosomes Are distinct from each other in their characteristics Are represented as X and Y Determine the sex of the individual, XX being female, XY being male (in mammals) In a diploid cell, the chromosomes occur in pairs. The 2 members of each pair are called homologous chromosomes or homologues.

Chromosomes A diploid cell has two sets of each of its chromosomes A human has 46 chromosomes (2n = 46) In a cell in which DNA synthesis has occurred all the chromosomes are duplicated and thus each consists of two identical sister chromatids Maternal set of chromosomes (n = 3) Paternal set of 2n = 6 Two sister chromatids of one replicated chromosome Two nonsister chromatids in a homologous pair Pair of homologous chromosomes (one from each set) Centromere

Chromosomal Abnormalities Nondisjunction Failure of chromosomes to separate during cell division Can cause cell death but usually does not harm the organism When nondisjunction occurs when making sperm and eggs the organisms is affected. One sperm/egg may receive an extra chromosome while another would receive one less than it should have

Nondisjunction cont. In a sperm or egg cell… Trisomy or Monosomy Monosomy – one too few chromosomes Most often causes death (XO) is an exception (Turner’s Syndrome) Trisomy: one too many chromosomes Trisomy 21 (Down’s Syndrome)

Klinefelter’s Syndrome XXY

Trisomy 18, Edward’s Syndrome

Trisomy 13 – Patau Syndrome

Chromosomal mutations Deletion – piece of the chromosome is lost Duplication – piece of DNA is copied too many times in one chromosome Inversion – segment flips within chromosome Translocation – segment breaks off and joins another chromosome

Deletion of part of the 5th Chromosome Resulting in Cri-Du-Chat Syndrome (Cat Cry Syndrome)

Duplications of Various Chromosomes: Pallister-Killian Syndrome Weak muscle tone. 30% able to walk without assistance

Inversion

Inversion Angleman’s Syndrome- developmental and intellectual retardation with frequent seizures

Translocation Sometimes it is even breaking, sometimes it is uneven. Different effects on different chromosomes

Translocation between 13 & 14 Cancer, Infertility and Down’s Syndrome are common expressions of Translocations – though most are normal.

Nondisjunction Cont. Sometimes ALL OF YOUR CHROMOSOMES can be doubled! In animals this is rare and results in death In plants, this will often produce hardier & healthier specimens Potatoes, oats, bananas, peanuts, barley, plums, wheat, apples, sugar cane, coffee & cotton are such examples