mitosis and meiosis
cells divide? Growth Development Repair Asexual reproduction Formation of gametes
How does a cell know when to divide?
the cell cycle A repeating process of cell growth and division during the life of an organism.
Amoeba sisters
Can you control it? http://nobelprize.org/educational_games/med icine/2001/cellcycle.html
Somatic cell division Amoeba sisters
Purpose of mitosis: produce new cells genetically identical to the original parent cell and allow organisms to grow, repair damage and reproduce asexually
song
prophase Chromosomes become visible Nuclear envelope dissolves Spindle forms
Formation of the spindle
centromere
metaphase Spindle fibers connect to centromeres. Chromosomes line up along the equatorial plane.
Centromeres divide Chromatids are separated (chromosomes) chromosomes are pulled toward opposite poles anaphase
telophase Nuclear membrane reforms at each pole Chromosomes uncoil Spindle dissolves Cytokinesis begins
cytokinesis Cytoplasm divides daughter cells are formed
Review Mitosis stages animation
the genetic blueprint of an organism
homologous chromosomes (similar in size, shape and genetic content) Allele A Allele a Gene locus
Karyotype human karyotype* *shows the homologous chromosomes arranged by size
gamete formation
Mitosis and meiosis are part of an organism s life cycle.
gamete formation
It s all about passing on genetic information. Gender determination
Meiosis is similar to mitosis cell cycle, same phases of division Meiosis is different than mitosis 2 cell divisions, reduces chromosome number in cells by half, produces gametes Sperm Ovum
alternation of generations
MEIOSIS I: Separates the Homologues
MEIOSIS II: Separates sister chromatids (mitosis)
meiosis
sexual reproduction asexual reproduction through budding
here s a question Does a chromatid contain the same information as a chromosome? chromosome rearrangement during meiosis can lead to changes in genetic information --- which provides diversity!
centromere replicated unreplicated Sister chromatids
homologous chromosomes (similar in size, shape and genetic content) Allele A Allele a Gene locus
independent assortment Homologous pairs line up and are separated independently from one another.
crossing over sister chromatids
depending on how many chromosomes an organism has Bat face morphology variety increases For humans 2 23 different combinations (8,388,608)
revisit the question Does a chromatid contain the same information as a chromosome? chromosome rearrangement during meiosis can lead to changes in genetic information --- which can also lead to problems
Mutations A mutation is a change in the genetic material of a cell that can be passed on from the cell to its daughter cells during the process of cell division. Spontaneous mutations can also occur during zygote development. polyploidy
Some mutations involve only a single base pair in a DNA molecule. These mutations are called point mutations. Other mutations involve rearrangements in big regions of chromosomes. These are called chromosomal mutations. Other mutations involve changes in chromosomal number. And still Other mutations are caused by mutagenic agents like chemicals and radiation.
meiotic errors. when good chromosomes go rogue Aneuploidy: one or more chromosomes are lacking or present in excess Aneuploidy can nearly always be detected by growth anomalies if it is not lethal from the outset. Single additional chromosomes, so-called trisomy, cause the smallest damages and are the most common
Nondisjunction is the cause of aneuploidy. An error is made in unequal division of the homologous pairs during Metaphase I OR the sister chromatids fail to separate during Metaphase II.
about two thirds are missing the paternal X chromosome monosomy X (Turner s syndrome) one of the most common chromosomal abnormalities. More than 95% of adult women with Turner syndrome exhibit short stature and infertility. In the US: Frequency is approximately 1 in 2000 live-born female infants. As many as 15% of spontaneous abortions have a 45 X karyotype.
trisomy 21 (Down s syndrome)
Trisomy 13 (Patau syndrome) It is rare for fetuses with this condition to go to term, so it occurs in only 1 in 6000 live births. It is rare for babies to survive for very long if liveborn because of the multitude of anomalies that are usually present. This baby with trisomy 13 has cyclopia (single eye) with a proboscis (the projecting tissue just above the eye). full trisomy 13 at age 7 years (survival beyond the first year is uncommon). He is deaf and legally blind.
Chromosomal mutations
translocation a chromosome may break and be rejoined incorrectly to another chromosome Translocation has been pinpointed as the cause of chronic myeloid leukemia, a type of cancer.
duplication and deletions inversions Occasional mutations will flip a stretch of DNA within a chromosome
Without repair, DNA damage can cause mutations
Mutations can also be caused by a mutagenic agent
Electromagnetic radiation (x-rays and gamma rays) Photons of radiation cause damage directly OR indirectly by producing free radicals from water which damage DNA
(ultra-violet light (UV)) causes formation of pyrimidine dimers (TT and CC) resulting in point mutations. DNA sequence must have adjacent pyrimidines in order for dimers to form.
Dimers form (usually between TT or CC)
Given enough time and low exposure, cells can repair the damaged DNA. Too much damage cannot always be repaired.
Protect yourself.
Sunscreens can damage skin, researchers find Two-photon fluorescence intensity images of cells deep in the epidermis showing reactive oxygen species activity following sunscreen application to the skin surface. Reactive oxygen species can react with cellular components, leading to skin damage and increasing the visible signs of aging. Credit: K. Hanson, UC Riverside
Chemical mutagens Mutation is caused by foreign molecules binding to a cell s DNA, causing it to be misread. Examples or chemical mutagens are benzopyrene (found in cigarette smoke), vinyl chloride (found in the plastics industry), aflatoxin (found in certain molds) and hetrocyclic amines (found in over-cooked food). that modify nitrogenous bases base analogues intercalating agents inserting DNA
intercalating agents a chemical that can insert itself into the DNA chain causes deletion or addition of bases during DNA replication. Can result in frame-shift mutations
modify nitrogen bases remove nitrogenous bases chemically change nitrogenous bases by covalent additions the modification of a base results in a heritable mutation
chemicals that are structurally similar to normal bases and can be incorporated into DNA base analogues
Protection against mutagens antioxidants are an important group of anticarcinogenic com pounds that may help remove ROS or potentially harmful chemicals. These may be found naturally in fruits and vegetables.
Examples of antioxidants are vitamins A, C and E, and various other compounds such as β-carotene - the red-orange colored compounds found in vegetables like carrots and tomatoes. Flavonoids, such as EGCG in green tea, have also been shown to be effective antioxidants and may have anti-cancer properties. Epidemiological studies indicate that a diet rich in fruits and vegetables is associated with lower incidence of some cancers and longer life expectancy, however, the effectiveness of antioxidant supplements in cancer prevention in general is still the subject of some debate
Top 10 antioxidant foods
Top 10 antioxidant herbs