Cell Division Mitosis vs Meiosis Cell division increases

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Cell Division: Mitosis vs. Meiosis • Cell division increases the number of somatic (body)

Cell Division: Mitosis vs. Meiosis • Cell division increases the number of somatic (body) cells or produces the sex cells (gametes). – Development/growth – Repair injured cells – Production of sperm or egg • Karyokinesis is division of nucleus. – Mitosis • Results in two daughter cells • Genetically identical to mother cell – Meiosis • Results in four gametes (sex cells) • Not genetically identical to mother cell • Cytokinesis is division of the cytoplasm.

Mitosis • With mitosis you get two identical cells from a parent cell •

Mitosis • With mitosis you get two identical cells from a parent cell • Precisely replicates DNA • Sends a copy of DNA to each pole of the cell • Separates into two daughter cells

Chromatin & Chromosomes • Chromatin: thin strands of DNA & protein that are present

Chromatin & Chromosomes • Chromatin: thin strands of DNA & protein that are present in nucleus when cell is not dividing. • Chromosomes: coiled, condensed chromatin (DNA) present during cell division. • Humans have 23 pairs of chromosomes. This means you have 46 chromosomes in every cell of your body except the gametes. – Diploid (2 n)= nucleus contains 2 of each type of chromosome – Haploid (1 n)= nucleus contains 1 of each chromosome

DNA: Chromatin & Chromosomes • Our body cells have 46 chromosomes • Our gametes

DNA: Chromatin & Chromosomes • Our body cells have 46 chromosomes • Our gametes contain 23 • In interphase chromosomes cannot be seen, DNA is in chromatin form • During prophase and throughout mitosis chromosomes are visible

Chromosomes • Each chromosome consist of two sister chromatids • The two chromatids possess

Chromosomes • Each chromosome consist of two sister chromatids • The two chromatids possess identical copies of the chromosomes DNA and are attached at the centromere

The Cell Cycle • The cell cycle is the life cycle of a cell.

The Cell Cycle • The cell cycle is the life cycle of a cell. • Most of the cell cycle is spent in interphase. • Three stages of interphase: 1. G 1: after a cell divides into 2, cell grows to mature size; cell doubles organelles & gathers materials needed for DNA synthesis. Many cells (muscle, nerve, bone) never leave G 1. 2. S: DNA replication occurs in this phase 3. G 2: cell makes proteins needed for cell division (like protein needed to make microtubules)

Cell Division in Prokaryotes • Bacteria have a single chromosome • Divide by binary

Cell Division in Prokaryotes • Bacteria have a single chromosome • Divide by binary fission (asexual reproduction) • Parent cell divides to produce 2 identical daughter cells

Mitosis • 4 phase of mitosis –Prophase –Metaphase –Anaphase –Telophase

Mitosis • 4 phase of mitosis –Prophase –Metaphase –Anaphase –Telophase

Prophase • Centrosomes move to opposite ends of nucleus • Nuclear envelope disappears •

Prophase • Centrosomes move to opposite ends of nucleus • Nuclear envelope disappears • Nucleolus begins to disappear • Spindle fibers appear between centrosomes • Chromosomes become visible

Metaphase • Chromosomes attach to spindle fibers at centromere • Chromosomes line up at

Metaphase • Chromosomes attach to spindle fibers at centromere • Chromosomes line up at the metaphase plate (middle of cell)

Anaphase • Centromeres divide • Sister chromatids separate to become daughter chromosomes • Daughter

Anaphase • Centromeres divide • Sister chromatids separate to become daughter chromosomes • Daughter chromosomes move to opposite poles of cell • Daughter chromosomes = 1 centromere + 1 chromatid • Cleavage furrow begins

Telophase • Spindle fibers disappear • Nuclear envelope reassembles • Chromosomes uncoil to become

Telophase • Spindle fibers disappear • Nuclear envelope reassembles • Chromosomes uncoil to become chromatin • Nucleolus reappears • Cleavage furrow deepens • Cytokinesis continues • Two diploid genetically identical daughter cells form

Mitosis in Pla. NTS • Plant cells have no centrioles • Rigid cell wall

Mitosis in Pla. NTS • Plant cells have no centrioles • Rigid cell wall prevents cytokinesis by furrowing • Cytokinesis involves formation of a cell plate

Results of Mitosis • Two new daughter cells that are genetically identical to the

Results of Mitosis • Two new daughter cells that are genetically identical to the parent. (Chromosomes are identical)

Meiosis • Form of cell division that halves the number of chromosomes • Forms

Meiosis • Form of cell division that halves the number of chromosomes • Forms specialized reproductive cells like the gametes or spores • Requires two sets of cell division (Meiosis I & Meiosis II) • Results in 4 haploid daughter cells genetically different from parent cell • Sperm= 23 chromosomes (haploid) • Egg = 23 chromosomes (haploid) • Fertilization restores diploid number of chromsomes (46)

Meiosis: A Source of Genetic Variation • Meiosis scrambles the specific forms of each

Meiosis: A Source of Genetic Variation • Meiosis scrambles the specific forms of each gene that each sex cell (egg or sperm) receives. • This makes for a lot of genetic diversity. This trick is accomplished through independent assortment and crossing-over. • Genetic diversity is important for the evolution of populations and species.

Keys to Understanding Meiosis Chromosomes are paired. Chromosomes carry genes. The gene forms on

Keys to Understanding Meiosis Chromosomes are paired. Chromosomes carry genes. The gene forms on a pair of chromosomes may be identical. . or different. Brown eyes Tall Brown eyes Blue eyes Tall Short

One Way Meiosis Makes Lots of Different Sex Cells (Gametes) – Independent Assortment Independent

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

Another Way Meiosis Makes Lots of Different Sex Cells – Crossing-Over Crossing-over multiplies the

Another Way Meiosis Makes Lots of Different Sex Cells – Crossing-Over Crossing-over multiplies the already huge number of different gamete types produced by independent assortment.

Between Independent Assortment and Crossing-Over, No Two Gametes Are Identical.

Between Independent Assortment and Crossing-Over, No Two Gametes Are Identical.

Meiosis Following a Single Chromosome Pair Crossing over

Meiosis Following a Single Chromosome Pair Crossing over

The Key Difference Between Mitosis and Meiosis is the Way Chromosomes Uniquely Pair and

The Key Difference Between Mitosis and Meiosis is the Way Chromosomes Uniquely Pair and Align in Meiosis Mitosis The first (and distinguishing) division of meiosis

The Key Difference Between Mitosis and Meiosis is the Way Chromosomes Uniquely Pair and

The Key Difference Between Mitosis and Meiosis is the Way Chromosomes Uniquely Pair and Align in Meiosis Mitosis The first (and distinguishing) division of meiosis

Boy or Girl? The Y Chromosome “Decides” Y chromosome X chromosome

Boy or Girl? The Y Chromosome “Decides” Y chromosome X chromosome

Boy or Girl? The Y Chromosome “Decides”

Boy or Girl? The Y Chromosome “Decides”

Oogenesis – A Path of Meiosis in Humans Woman are less busy in meiosis

Oogenesis – A Path of Meiosis in Humans Woman are less busy in meiosis than men – meiosis produces only a few hundred mature eggs over a lifetime.

Spermatogenesis – Another Path of Meiosis in Humans Men are always doing meiosis, producing

Spermatogenesis – Another Path of Meiosis in Humans Men are always doing meiosis, producing roughly 250, 000 sperm per day.

“Putting It All Together” - Fertilization

“Putting It All Together” - Fertilization

What Meiosis is About Meiosis allows the creation of unique individuals through sexual reproduction.

What Meiosis is About Meiosis allows the creation of unique individuals through sexual reproduction.

Mutations A mutation is any change in the DNA sequence.

Mutations A mutation is any change in the DNA sequence.

 • The chromosome number has been reduced by the END of MEIOSIS I

• The chromosome number has been reduced by the END of MEIOSIS I • Each daughter cell now has only 23 chromosomes (haploid)

Mutations in Reproductive Cells • Only in gametes could be passed on to offspring

Mutations in Reproductive Cells • Only in gametes could be passed on to offspring

Mutations in Body Cells • Somatic (normal/non-sex cells) • cannot be passed on to

Mutations in Body Cells • Somatic (normal/non-sex cells) • cannot be passed on to offspring

Types of Mutations • Gene mutationschanges to a specific gene. (DNA base pairs) •

Types of Mutations • Gene mutationschanges to a specific gene. (DNA base pairs) • Chromosomal mutations- changes to a portion of the chromosome • Can effect many genes

Different Types of Gene Mutations • Point mutation-a change in a single base pair

Different Types of Gene Mutations • Point mutation-a change in a single base pair in the DNA. THE DOG BIT THE CAT THE DOG BIT THE CAR THE DOG BAT THE CAR THE DIG BAT THE CAR

Point Mutation

Point Mutation

Frameshift Mutation • a single base pair is added or deleted, causing a shift

Frameshift Mutation • a single base pair is added or deleted, causing a shift in how the strand will be read. THE DOG BIT THE CAT THE DOB ITT HEC AT

Chromosome Mutations • Deletion-part of a chromosome is left out.

Chromosome Mutations • Deletion-part of a chromosome is left out.

There is a small section of chromosome #5 that has been deleted

There is a small section of chromosome #5 that has been deleted

 • Insertion-part of a chromatid breaks off & attaches to its sister chromatid.

• Insertion-part of a chromatid breaks off & attaches to its sister chromatid.

 • Inversion-part of a chromosome breaks off & reinserts backwards.

• Inversion-part of a chromosome breaks off & reinserts backwards.

 • Translocation-part of one chromosome breaks off & is added to a different

• Translocation-part of one chromosome breaks off & is added to a different chromosome.

Karyotype • A photographic inventory of an individual’s chromosomes • Chromosomes are arranged in

Karyotype • A photographic inventory of an individual’s chromosomes • Chromosomes are arranged in pairs starting with the longest • Used to detect abnormalities in chromosome #

 • Nondisjunction- have an abnormal number of chromosomes – Caused by errors in

• Nondisjunction- have an abnormal number of chromosomes – Caused by errors in Mitosis or Meiosis • Most die before birth • Results in either monosomy or trisomy

Down’s Syndrome Traits • Down’s Syndrome is an example of nondisjunction • Results from

Down’s Syndrome Traits • Down’s Syndrome is an example of nondisjunction • Results from trisomy of the 21 st pair of chromsomes (3 chromosomes) • Mental retardation, short stature, heart defects, most are sterile, and other problems

Down’s Syndrome There is an extra chromosome on the 21 st pair

Down’s Syndrome There is an extra chromosome on the 21 st pair

Abnormal Sex Chromosome Numbers • Klinefelter syndrome : extra X sex chromosome (XXY) –

Abnormal Sex Chromosome Numbers • Klinefelter syndrome : extra X sex chromosome (XXY) – male sex organs but sterile(testes small) – Breast enlargement with other female characteristics • Turner syndrome: missing X sex chromosome (XO) – Short stature, web of skin extending between neck & shoulders – Sterile with immature sex organs – Poor development of breast and secondary sex characteristics

Turner’s Syndrome Traits • Turner’s Syndrome occurs only in females • Results from monosomy

Turner’s Syndrome Traits • Turner’s Syndrome occurs only in females • Results from monosomy X • People with syndrome are sterile • Secondary sex characteristics don’t develop

What causes mutations? • spontaneous mistakes • environment – any agent that can cause

What causes mutations? • spontaneous mistakes • environment – any agent that can cause a change in DNA is called a mutagen. (x-rays, UV light, asbestos)

DNA Repair • enzymes in our cells remove the incorrect nucleotides & replace them

DNA Repair • enzymes in our cells remove the incorrect nucleotides & replace them with the right ones. – this works well, but is not perfect