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Mitosis and Meiosis
Transcript of Mitosis and Meiosis
-known genes are crucial for embryonic development
-normal development requires one active copy
If not one?
abnormal development or cancer Polygenic Inheritance: a single phenotypic character is affected by two or more genes the life of a cell concerning mitosis and meiosis a type of cell division that results in two daughter cells each the same as the parent nucleus, typical of ordinary tissue growth a special type of cell division necessary for sexual reproduction in eukaryote cells.
consists of two phases: meiosis I and meiosis II Mendel
Gene Idea A number of hypotheses were suggested to explain heredity, but Gregor Mendel, a little known Central European monk, was the only one who got it more or less right. His ideas had been published in 1866 but largely went unrecognized until 1900, which was long after his death While Mendel's research was with plants, the basic underlying principles of heredity click this icon to hear the preceding term pronounced that he discovered also apply to people and other animals because the mechanisms of heredity are essentially the same for all complex life forms Mendel used peas since they are available in several varieties. He began to breed several different characteristics of these pea plants over a few generations (and many of them!) in order to observe each generations changing traits as compared to their parents and grandparents. Trait: each variant for a character (ex: purple vs white color of flower) Character: a heritable feature that varies among individuals (ex: flower color) Mendel cross-pollinated true-breeding peas varieties, which is called hybridization. The true-breeding parents are called the P-generation, and their hybrid offspring the F1 generation. This these F1 hybrids self-pollinate or cross breed with another F1 hybrid, they produce the F2 generation, which turned out to have a 3:1 phenotypic ratio of the dominant to recessive traits for all of his hundreds of trials on several different characteristics. Recessive Allele: had no noticeable effect on the organisms appearance Allele: alternate versions of a gene In the flower example, the color purple for the pea plant in dominant while white is recessive Dominant Allele: determines the organisms appearance Mendel's quantitative analysis of the F2 plants from thousands of genetic crosses allowed him to deduce two fundamental principles of heredity Law of Independent Assortment: each pair of alleles segregates independently of each other pair of alleles during gamete formation Law of Segregation: the two alleles for a heritable character segregate (separate from each other) during gamete formation and end up in different gametes Mendel used Punnett Squares to predict the allele composition of offspring from a cross between individuals of known genetic makeup Breeding an organism of unknown genotype with a recessive homozygote is called a testcross Homozygous: an organism that has a pair of identical alleles for a character Useful Vocabulary! Genotype: an organism's genetic makeup Phenotype: an organism's appearance or observable traits Heterozygous: an organism that has two different alleles for a gene Mendel derived the Law of Segregation from using F1 heterozygous parents of one particular trait (monohybrids), however the Law of Independent Assortment was identified by following two characters at the same time from F1 heterozygous parents (dihybrids) Inheritance patterns are often more complex than predicted by simple Mendelian genetics... Extensions of Mendelian genetics for a single gene Complete Dominance of either allele: heterozygous phenotype same as that of homozygous dominant Incomplete Dominance of either allele: heterozygous phenotype intermediate between the two homozygous phenotypes Codominance: both phenotypes expressed in heterozygotes Pleiotropy: one gene is able to affect multiple phenotypic characters Multiple Alleles: in the whole population, some genes have more than two alleles Development
-by Walter S. Sutton, Theodor Boveri, and others Mendelian genes are specifically located on chromosomes. Homologous chromosomes undergo segregation and independent assortment, not the alleles themselves. Thomas Hunt Morgan and Fruit Flies Extensions of Mendelian genetics for two or more genes Achievement? Figured sex-linkage Wild type Mutant Phenotype Epistasis: the phenotypic expression of one gene affects that of another Polygenic Inheritance: a single phenotype character is affected by two or more genes on a single phenotypic character (converse of pleiotropy), which indicates a gradient continuum of character variations within a population (quantitative character)
:most common phenotype observed in natural setting : phenotype caused by mutations of wild type alleles A genotype generally is not associated with a rigidly defined phenotype, but rather with a range of phenotypic possibilities due to environmental influences ( norm of reaction) Female=XX Male=XY X Chromosome 50% 50% Multifactorial: many factors, both genetic and environmental, collectively influence phenotype Pedigree: a family tree describing the traits of parents and children across generations The X-Y system
-Gender chiefly determined by sperm Others? Y Chromosome Chromosomal Determination of Sex -For some insects
-No Y chromosome Carrier: one who carries the recessive allele and may transfer the trait to their offspring -For birds, fish, and some insects
-Sex chromosome of the egg determines sex
-chromosomes are designated with Z and W Inherited disorders can be from recessive or dominant alleles -For most bees and ants
-Sex is solely determine by the mother
-Males develop from unfertilized egg (haploid=n)
-Females develop from fertilized egg (diploid=2n) Sex Linked Genes examples of (PP)
-Huntington's disease -contain SRY gene
:gene required for the development of testes in embryo Absence of SRY gene leads to development of ovaries in embryo examples of (pp)
-Sickle-cell disease X-Linked Genes Y-Linked Genes : genes located on sex chromosomes :genes on Y chromosomes
-Fathers pass to all sons
-Rare-thus less disorders
Ex) absence of Y chromosome-> lack of sperm : genes on X chromosomes
-variety genes unrelated to sex are present
-fathers pass none to sons
-fathers pass to all daughters
-mothers pass to some daughters and sons
-more likely expressed by males
: term for indicating one allele Why? Recessive X-linked gene
-gene has to be homozygous to be expressed
-one recessive hemizygous gene can be expressed Recessive gene not expressed Recessive gene expressed X-linked Disorders Color Blindness
: hardships in distinguishing colors Duchenne Muscular Dystrophy
: weakening of muscles and loss of coordination
-rarely live past their 20s Hemophilia
: lack of one or more proteins required for blood clotting
-wide spread among loyal families of Europe during 1800s X Inactivation Barr Body:
the condensed form of inactivated X genes.
-lies along the nuclear envelope
-allow females to synthesize same amount of proteins as males despite having two X chromosomes. -Inactivation occurs in embryonic cell, randomly and independently
-results two types-cells with paternal X activated
-cells with maternal X activated
-daughter cells has same site inactivated Mechanism
-alteration in histone
-attatchment of methane groups
-XIST genes: acts on chromosome designated to be a barr body by producing RNA to be attached on the gene Examples Cats: Tortoise Shell
Humans: Mosaicism in sweat glands G0 "gap zero", non-dividing state G1 "first gap", cell grows by producing proteins and cytoplasmic organelles S "synthesis", cell copies
chromosomes G2 "second gap", cell grows by producing proteins and cytoplasmic organelles M mitosis, cytokinesis
cell division Interphase Mitosis Cytokinesis division of genetic material division of cytoplasm G1, S, G2
preparation for cell division Prophase chromatin fibers condense into distinct chromosomes
nuclear membrane disappear
nucleoli disappear Metaphase centrosomes are at opposite poles of the cell
chromosomes assemble at the metaphase plate
kinetochores of each sister chromatids are attached to kinetochore microtubules Anaphase cohesin proteins are cleaved
2 sister chromatids part, each
become a chromosome the 2 chromosomes move toward opposite ends by the motor proteins which walk on the kinetochore microtubules Telophase 2 daughter nuclei form
chromosomes are less condensed
remaining microtubules depolymerize Cytokinesis cytoplasm divides
2 daughter cells form
same number of chromosomes as parent cell Interphase cell grows
nuclear envelope encloses nucleus
chromosomes duplicate chromosomes duplicate Linked Genes : genes on the same chromosome and near each other; likely to be inherited together Morgan's flies demonstrate alleles for body color and wing size chromosomes condense
paired homologs are connected to each other
each homologous pair after crossing over has a chiasmata
nuclear envelope breakdown
microtubules from opposite poles attach to kinetochores Genetic Recombination : traits of offspring newly combined, differing from those of parents Parental Types
: Offspring with parental phenotype
:Offspring with non parental phenotype
Frequency of Recombination
=percentage of recombinant offspring Note that the phenotypes of linked genes are
more than the predicted (independent assortment) How? by crossing over
(=exchange of DNA segments)
-during prophase I
random orientation of homologous pairs
independent assortment of unlinked genes DIFFERENT! Genetic Map homologous chromosomes arrange at metaphase plate
both chromatids are attached to kinetochore microtubules 1 Map Unit=1% of recombination frequency breakdown of proteins for sister chromatid cohesion
homologs move toward opposite poles by the moving motor proteins on the kinetochore microtubule Linkage Maps Cytogenetic Maps Physical Maps -display actual location of genes
Ex) microscopic observations of stained bands -display distance of gene loci in DNA nucleotide each chromosome has 2 sister chromatids which include regions of nonsister chromatid DNA
cytokinesis forms 2 haploid daughter cells spindle apparatus forms chromosomes are positioned at the metaphase plate
due to the crossing over, the 2 chromatids of each chromosome are not identical
kinetochores of sister chromatids are attached to microtubules breakdown of proteins holding the sister chromatids together in the centrosome
chromatids move toward opposite poles as individual chromosomes nuclei form
results in 4 daughter cells each containing a haploid cell of chromosomes Comparison of Mitosis and Meiosis Why?
More frequent crossover<= More location for crossover <=More Distance between genes -display distance between genes based on recombination frequencies
-approximation of chromosomes
-does not reflect the actual location of genes list of loci on specific chromosomes A moment Please! Genes on same chromosomes are said to be
when the two genes are too far
that crossing over almost certainly occurs
thus become independently assorted Genetic Mutations -may alter phenotype
;physical and chemical disturbance
-large scale mutations may cause
miscarriage or developmental disorders
-plants are more tolerable to genetic defects
than animals Alteration in Chromosome Number Cause?
:failure of homologous chromosomes to be sorted during meiosis I and II Loss of Cell Cycle Controls in Cancer Cells Conditions in Zygote Cancer cells are caused by eluding the regular regulation and divide out of control which forms tumors. Malignant tumors invade surrounding tissues and can undergo metastasis which sends cancer cells to other parts of the body. Aneuploidy
: abnormal number of particular chromosome, may be more than 1. Monosomic (for chromosome)
n+ (n-1)= 2n-1 Trisomic (for chromosome)
Down Syndrome Cause?
Trisomy in chromosome 21 Symptoms
-treatable heart defects
-developmental delay Polyploidy : general term for having more than two complete sets of chromosome
Ex) triploidy (3n), tetra ploidy(4n) Cell Cycle Regulation Signaling molecules in the cytoplasm (cyclins,Cdks) regulate the progress through the cell cycle during mitosis. The cycle has specific checkpoints where it stops and a signal is received. Triploidy
: 2n+n=3n How?
failure of normal zygote to divide after replication -common in plants
-important in evolution
-bananas (6n), strawberries (8n)
- uncommon in animals
(though seen in some fish and amphibians) Set of traits Disorders? Klinefelter Syndrome How?
Aneuploidy in sex chromosome
-abnormally small testes
-some female body characteristics
(ex) breast enlargement)
-subnormal intelligence Extra Y Triple-X Tumer's Syndrome Cause?
Trisomy X =XXX Cause?
XYY XYY Symptoms
-taller than average
-otherwise normal Symptoms
-taller than average
-possible learning disability Cause?
monosomy X=X0 Symptoms
(lack of maturity in sex organs) Others... Sex chromosome Alterations in Chromosome Structures Nonreciprocal Translocation
: A chromosome translocates segment though recieves none in return
-less common than reciprocal translocation Disorders? Chri Du Chat Chronic Myelogenous Leukemia Cause?
Deletion in chromosome 5 Symptoms
-severe intellectual disability
-abnormally small head
-unusual facial features
-cry similar to those of distressed cat (meowing)
-possible death in infancy or early childhood Cause?
between chromosome 9 and 22 (philadelphia chromosome)
during mitosis of white cell precursor Symptoms
(activation of gene leading to uncontrolled cell cycle) Biochemical tests may detect substances associated with particular disorders, and genetic testing can detect many genetic abnormalities. Karotyping shows whether the chromosomes of the fetus are normal in number and appearance. abnormally small abnormally long Genetic Imprinting : phenotype variation depending on which parent the allele is from -allele is on autosomes
-occurs during gamete formation
-zygote expresses only one imprinted gene
(other allele is silenced) How?
By addition of methyl group on the cytosine of nucleotides on one of the alleles
DNA methylation leads to production of enzymes that alter histones
altered histones condense the DNA locally
depending on the original function of DNA gene allele expression can be activated or inactivated Ex) Igf2 : mutant gene on mouse; expressed only when
mutant chromosome is on paternal
chromosome Chorionic Villus Sampling (CVS): when a sample of chorionic villus tissue can be taken as early as the 8th to 10th weeks of pregnancy with a suction tube is inserted through the cervix. Karotyping and biochemical and genetic tests can be performed on the fetal cells immediately, providing results within a day or so. Amniocentesis: when a sample fluid can be taken starting at the 14th to 16th week of pregnancy. Biochemical and genetic tests can be performed immediately on the amniotic fluid or later on the cultured cells. Fetal cells must be cultured for several weeks to obtain sufficient numbers for karotyping. Organelle Genes Who has extranuclear Genes?
Mitochondria, Chloroplasts, and Plastids Who has Extracellular Not Subjected to Mendelian Genetics! Karl Correns discovery-coloration of offspring plant is determined by maternal plant variegation:
coloration patterns due to mutation on plastid genes, which control pigmentation plants:
zygote receive cytoplasm of the egg, none from sperm
plastid located in cytoplasm
coloration of zygote resemble those of mother plant
zygote development allow random distribution of plastid with wild type and mutant pigmentation allele
leaf coloration depends on the ratio of wild type and mutant allele Genes in Mitochondria codes for proteins
on electron transport chain and ATP synthase defects/mutations?
-reduce ATP production
-most effect on nervous systems and muscles, where energy deprivation are crucial
-accumulated mutations during life time participate in the aging process Same Mechanism Other Common Diseases...
diabetes, heart diseases, and Alzheimer's diseases Disorders& Diseases Mitochondrial Myophathy
-weakness , intolerance of exercise, muscle deterioration Leber's Hereditary Optic Beuropathy
-produce sudden blindness
- oxidative phosphorylation in cell is affected Genes In Plastids This diagram shows an enlarged Punnett Square of two variables, pea color (yellow dominant, green recessive) and pea texture (smooth dominant, wrinkled recessive) and the predicted phenotypic ratio of the F2 generation. Although the phenotypic ratio between the two characters is 9:3:3:1, the phenotypic ratios between each individual character still remains 3:1 Background... : extranuclear genes=cytoplasmic genes Plastids:
organelles kin to chloroplasts, including chloroplasts, in photosynthetic eukaryotes Mitosis in
Cells Mitosis in
Cells These flamingos have the same genotypes, however their phenotypic ranges depend on their separate environments, which provide slightly different food sources. Flamingos are pink or orange or white depending on what they eat. Flamingos eat algae and crustaceans that contain pigments called carotenoids. For the most part, these pigments are found in the brine shrimp and blue-green algae that the birds eat. Enzymes in the liver break down the carotenoids into the pink and orange pigment molecules deposited in the feathers, bill, and legs of the flamingos. Flamingos that eat mostly algae are more deeply colored than birds that eat the small animals that feed off of algae. Comparison of Mitosis in Eukaryotic and Prokaryotic cells Chromosome Basis of Inheritance Chromosome Theory of Inheritance INTERKINESIS Period of rest that cells of some species enter during meiosis between meiosis I and meiosis II.
Many plants skip telophase I and interkinesis. Cytokinesis in Plants and Animals Diploid and Haploid Cells Diploid (indicated by 2n = 2x) cells have two homologous copies of each chromosome, usually one from the mother and one from the father. Human diploid cells have 46 chromosomes and human haploid gametes (egg and sperm) have 23 chromosomes. Human Meiosis and Fertilization Alteration of Generations in Plants