Grade 11 Bio POH - Updates

Patterns of Inheritance

Interphase:

  • G1 phase - normal growth phase, organelles start dividing

  • CHECKPOINT: is the cell functioning normally

  • S phase - chromatin duplicates

  • G2 phase - organelles finish dividing

  • CHECKPOINT: did the chromatin duplicate successfully

Mitosis:

  • Prophase - chromatin condenses into chromosomes, nuclear membrane starts disintegrating

    • Prometaphase - spindle fibers appear, start moving to poles of cell

  • Metaphase - chromosomes start lining up in the middle of cell, spindle fibers attach

  • CHECKPOINT: did the spindle fibers attach correctly to the centromeres

  • Anaphase - spindle fibers pull sister chromatids apart

  • Telophase - spindle disappears and nucleus forms around each set of daughter chromosomes. The nucleus has to be developed immediately or else the chromatids will move which creates genetic disorder

Cytokinesis: cleavage furrow forms, cell plate forms in plant cells as they don't have centrioles so a plate develops using small segments of cellulose

Types of mitosis:

  • Binary fission - when prokaryotes are tired of dividing, it goes through sexual reproduction. Two prokaryotes will create a tuba made of pili called the conjugation bridge and genetic material will pass through. Then they join together

  • Fragmentation - the whole organism is broken and the fragments grows into a new organism

  • Vegetative propagation - only a small part of the plant is broken which will grow into a whole new plant

  • Budding - budding is when there is an outgrowth and it falls of and grows into a whole new plant

What makes mitosis work:

  • Cyclins are proteins (g1 cyclin, g1/s cyclin, s cyclin, m cyclin)

    • Intermolecular signals that regulate and drive mitosis (proto oncogene)

    • They must be activated by a CDK (cyclin dependent kinase) to create a cyclin-CDK complex.

      • When this happens the CDK is activated and can modify phosphorylated target proteins

      • The CDK attaches phosphates to the target protein which acts like a switch making it more or less active

      • So when they attach, the cyclin activates the CDK but also directs the CDK to target proteins (depending on the stage of the cycle)

      • And then based on the type of cyclin and target protein, the specific stage starts

  • MPFs (m phase promoting factor)

    • Researchers found that cells in m phase had a mystery substance that could force g2 frog cells to go into m phase

    • This was just CDK attached to a M cyclin

    • During interphase, M cyclin stays low but builds up as it approaches m phase

    • As m cyclin builds up, it binds to the already present CDKs and the complex triggers m phase

    • If the cyclin lvl is too much, the cell divides out of control

    • MPF triggers it's own destruction by activating the anaphase promoting complex/cyclosome (APC/C)

      • Protein that causes m cyclins to be destroyed starting in anaphase

      • When this happens the cells gets pushed out of mitosis

      • APC/C also destroys the protein holding sis chromatids together which helps them separate in anaphase

  • They respond to cues from the environment in and out the cell

    • Growth factors: positive cues that are released from other cells. They stimulate the synthesis of cyclin

    • Density dependent inhibition: negative cues that say that if there are too many cells in the area, they will compete and it will cause a tumor

Other regulators:

  • Cell checkpoints

  • Proto oncogenes (cyclin-CDK or MPF or APC)

    • Start cell division, essential for cell development

  • Tumor suppressor genes (p53)

    • Switch of cell division

    • P53 is a gene that encodes a protein that halts the cell cycle so that DNA can be repaired for division

What happens if one of the checkpoints fails?

  • P53 commands other genes to bring cell division to a halt

  • If the damage is too serious for repair, p53 activates other genes to cause the cell to go through apoptosis

  • If repairs are made, p53 allows the cell cycle to continue

G0 phase and differentiation:

  • When cells exit mitosis or it's not necessary for them to divide, the enter g0 phase where normal cell functions continue but they don't go through m phase

    • They can stay here for years or never leave

  • Cells might stop dividing to get jobs in structure and function this is known as differentiation

    • They differentiate from stem cells

Cancer:

  • Too much cell division or too little cell death

  • If the APC gene is mutated, the cells will pile up creating a tumor

Cancerous cells do not obey checkpoints or regulators so there is no density dependent inhibition

  • Proto oncogenes require one allele (different ver of same gene) to be mutated and they are considered dominant resulting in a gain of function

  • tumor suppressor genes require one allele to be mutated and they are considered recessive resulting in a loss of function

  • Considered immortal as long as oxygenated blood is available

    • Angiogenesis - creation of new blood vessels to feed tumor

    • Telomerase - enzyme that fuels the abnormal production of cyclin

      • Telomerase is needed during development of the womb to make an organism develop faster but one it is developed, it gets turned off normally

      • Gets turned back on because of carcinogens

  • Tumors

    • Benign - encapsulated, non invasive, not deadly, can be removed

    • Malignant - invasive, grows between cells destroying issue, deadly, treated with chemo, radiation, surgery

  • Metastasis - movement of cancer cells

    • Travel through blood vessels or lymph tracts. It cannot grow in the heart, it's too hard and blood moves too quickly.

  • Accumulation of mutations over a lifetime

    • We all have oncogenes in our genome but some ppl have stronger control mechanisms that resist mutations some have weaker

Signaling molecules:

  • Stages

    • Reception

      • signaling molecule binds to membrane receptor protein

      • Receptors and ligands are personalized to the cell

    • Transduction

      • Amplifies the signal

      • Signal transduction pathway - The chains of molecules that relay intracellular signals

      • Powered by phosphorylation

    • Response

      • Action is carried out

      • Different ligands and receptor combinations carry out different responses

Eukaryotic signaling

  • Autocrine - cells produce a hormone or chemical messenger to react to their own signals

    • Regulates cellular growth and development

    • Important in cancer, plays a key role in metastasis

    • EXAMPLE: presence of foreign antibody causes T-cells to produce a growth factor to stimulate their own production which fight the infection

  • Paracrine - cells communicate over short distances and use diffusion

    • Ligands diffuse of signal cell by exocytosis and then binds to receptors outside of a nearby cell

    • The gap between the signal cell and target cell is called the synapse

    • allows cells to locally coordinate activities with other cells

    • important during development, when they allow one group of cells to tell a neighboring group of cells what cellular identity to take on

    • EXAMPLE: neurotransmitters released from a nerve cell travel across the synapse to another cell to cause a response

  • Endocrine - long distance signaling uses the circulatory system

    • Involve hormones released from endocrine glands or cytokines

    • EXAMPLE: insulin within pancreas stimulates the uptake of glucose within cells (decreasing blood sugar levels). Glucagon is another hormone that triggers glycogen to convert into glucose and to enter your bloodstream so that your body can use it for energy

  • Cell-to-cell contact

    • Gap junctions in animals and plasmodesmata in plants

      • Water filled channels that allow intracellular mediators to diffuse between cells

      • transmits the current state of one cell to its neighbor so a group of cells can coordinate their response to a signal that only one of them may have received

      • EXAMPLE: plasmodesmata

    • Complementary proteins on the surfaces of both cells bind together

      • Interaction changes the shape of one of both proteins which transmits a signal

      • EXAMPLE: in immune cells they use cell surface markers to recognize self cells and cells infected by pathogens

  • Pheromones - chemical signals excreted into the environment to cause a response in other organisms

    • Affect the behavior of members of the same species

    • EXAMPLE: bombykol is released by female silk moths and is detected in low concentrations by males. The binding protein on males antennae binds the bombykol which triggers a wing fluttering movement to locate the mate.

  • An intracellular signaling could look like this:

    • A steroid molecules goes into the cell and binds to a protein receptor inside the cell and becomes active

    • P.R travels to the nucleus where it binds to DNA and can get transcription of a certain gene going which can encode a protein

Prokaryotic Signaling:

  • Quorum sensing

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Meiosis:

  • 3 possible types of cell cycles based on DNA content

    • Alternation of generations

      • Half and half diploid and haploid

      • Plants and most algae

    • Diploid majority:

      • In animals

    • Haploid majority:

      • Fungi and some prokaryotes

      • Spend most of their lives with haploid cells

      • Come together to make diploid cells to create variation

      • After recombining, they undergo meiosis to return to a haploid state but with different DNA composition

  • General info

    • Locus: where a gene is located

    • Alleles: different versions of the same gene (e.g. two genes both encoding for height but one gene encodes for short and another encodes for tall)

    • Genotype/genome: a complete set of genes (the entire genetic makeup)

    • Phenotype: observable traits resulting from the genotype

    • Heredity: transmission of traits from one generation to the next

      • Most DNA is for common information (e.g. blood)

      • Some DNA is for varied information (diversity amongst species)

    • Genetics: science that deals with the transmission of info in the form of DNA

    • Gene: unit of heredity info

    • Benefits of sexual reproduction: creates variation, means there exists the possibility to evolve over time in a changing environment

    • Risks: not good for endangered species it takes more time and is complicated

  • Meiosis 1: reduction division because the number of chromosomes in the parent cell will be less in the daughter cells

    • Prophase 1

      • chromosomes come close in pairs of homologous chromosomes. When they come close this is called synapsis which creates a tetrad of chromosomes (2n = 4, 8 sister chromatids)

      • The pairs crossing over, exchanging genetic information aka recombination. The point where they cross over is known as the chiasma(ta)

      • The only exception to this is in XY chromosomes, they only join at the tips

      • Nuclear membrane dissolves

    • Metaphse 1:

      • The pairs of chromosomes line up in the middle of the cell side by side and the spindle fibers attach to the centromeres of the pairs of sister chromatids

    • Anaphse 1

      • The pairs separate so opposite poles

    • Telophase 1

      • nuclear membrane forms and cytokenises happens, making 2 different daughter cells

    • Result: 2 non identical daughter cells with 23 chromosomes

  • Meiosis 2: mitosis

    • Result: 4 non identical daughter cells with 23 chromosomes

Gametogenesis:

  • How is genetic variety possible?

    • crossing over/recombination

    • independent assortment: metaphase and anaphase

    • Random fertilization

  • Oogenesis: making of one egg cell

    • At the end of mitosis, you have 2 oogoni(a)um

    • After they go through recombination, they become primary oocyte

    • In cytokinesis 1, the division is not equal and one of the daughter cells is much more bigger than the other

    • The bigger daughter cell is a secondary oocyte and the smaller daughter is a polar body

    • The secondary oocyte creates 2 daughter cells, one will be bigger known as an egg and the other is just a polar body

    • The polar body from before creates 2 polar bodies

    • In the end, there's only one egg cell made

  • Spermatogenesis: making of sperm cells

    • At the end of mitosis, you have 2 spermatogoni(a)um

    • After they go through recombination, they become primary spermatocyte

    • The resulting haploid daughter cells are called secondary spermatocyte

    • After they go through meiosis 2, the resulting daughter cells are spermatids and all of them develop into sperm

Nondisjunction

  • Abnormal chromosome number

    • Aneuploidy - a cell can have one or a couple of chromosomes missing

    • polyploidy - extra complete sets of chromosomes

    • Monosomy - fertilization involves a gamete that is missing a chromosome (45)

    • Polysomy - fertilization involves a gamete that has one extra chromosome (47)

      • Trisomy - fertilized egg has triplicate chromosomes (2n+1) e.g. Trisomy 21 is down syndrome so the 21st pair of a karyotype has one extra chromosome

    • In meiosis 2/mitosis, the resulting cells will have n+1, n-1, n and n if there are 2 other cells

    • In meiosis 1, the resulting cells will have n+1 and n-1

    • Karyotype notation - #of chromosomes, sex, which pair the problem is (in down syndrome it's (47,XX,+21))

  • Abnormal chromosome structure

    • Deletion: segments exchanged involve a bigger segment being exchanged for a smaller segment, therefore nucleotides are lost and genetic information is also lost. Lethal if essential genes are missing

      • Cri-du-chat syndrome is loss or genetic misplacement from the 5th chromosome. The crying sounds like a cat crying

    • Duplication: two or more copies of the same DNA is produced

      • Pallister killian syndrome is where the 12th chromosome is duplicated. developmental delay, intellectual disability, recurrent infections, seizures

    • Inversion: a segment breaks off and reattaches within the same chromosome, but in reverse orientation

      • Hunter syndrome. Clouding of the front part of the eye, respiratory infections, Enlarged tonsils and distinct facial features

    • Translocation: a piece of one chromosome breaks off and attaches to another chromosome

      • Translocation Down syndrome three # 21 chromosomes, just like there are in trisomy 21, but one of the 21 chromosomes is attached to another chromosome, instead of being separate

Syndromes

  • Cri-du-chat

    • Karyotype: 46XX or 46XY

    • 5th chromosome deletion

    • Cry which sounds like that of a cat in distress because the larynx is improperly developed

    • Small cranium, small jaw, moon-shaped face

    • Deletion of half the short arm of chromosome number 5

  • Patau syndrome

    • Karyotype: 47XX or 47XY

    • 13th chromosome trisomy

    • Abnormal cerebral functions, death in early infancy, pronounced clefts of the lip and plate, broad nose, polydactyly, small cranium, dysfunctional eyes, heart defects, neurological challenges

  • Edwards syndrome

    • Karyotype: 47XX or 47XY

    • 18th chromosome trisomy

    • Severe neurological challenges, elongated skull, narrow pelvis, rocker bottom feet, malformed heart, grasping of the two central fingers by thumb and index

  • Down syndrome

    • Karyotype: 47XX or 47XY

    • 21st chromosome trisomy

    • Short stature, broad hands, stubby fingers and toes, a wide rounded face, a large tongue (hard to talk), neurological challenges

    • Prone to respiratory infections, leukemia, and heart defects

  • Jacobs

    • Karyotype: 47XYY (extra Y)

    • Nondisjunction of the Y chromosome during meiosis

    • ONLY IN MEN

    • Tall, develop heavy acne, neurological challenges

  • Klinefelter

    • Karyotype: 47XXY or 47XXXY (1 or 2 extra X)

    • Tall stature, small testicles, developed breasts, sterility

    • ONLY IN MEN

  • Turner Syndrome

    • Karyotype: 45XXX or 45X

    • X carrying sperm fertilized an ovum that lacks an X

    • Or when sperm lacking an X or Y fertilizes an X egg

    • ONLY GIRLS

    • Short, chunky build, webbed neck, no menstruation, no breast development, sterile

  • Triple X

    • Karyotype: 47XXX

    • ONLY GIRLS

    • Underdeveloped genitalia and limited fertility

    • Neuromotor delays

Mendelian Genetics - Laws of inheritance

  • Mnedel’s Law of Dominance

    • Only one of the two alleles from one of the parents is present and expresses itself in the offspring

  • Mendel’s Law of Independent Assortment

    • Inheritance of one pair of alleles is independent of inheritance of another pair of alleles

    • the alleles of two (or more) different genes get sorted into gametes independently of one another

  • Mendel’s Law of Segregation

    • An individual possesses two alleles - one from each parent

    • during meiosis,allele pairs segregate and re-unite randomly during fertilization

After Mendel Genetics or Non-mendelian traits

  • COMPLETE DOMINANCE

    • Mendelian genetics, only one out of the two alleles are expressed

  • INCOMPLETE DOMINANCE (or blending inheritance)

    • The genetic info is blended together (red+white = pink)

    • Neither phenotype is completely dominating

  • CODOMINANCE

    • Both alleles are expressed (speckled cows)

  • POLYGENIC INHERITANCE

    • Multiple alleles code for a phenotype (height, skin tone)

    • Happens because of quantitative characters

    • Skin color depends on how many copies of the same genes for making melanin you inherited from your parents

  • EPISTASIS

    • One gene depends on another gene to be expressed

    • Several genes interact to create the phenotypes of hair (texture, thickness, color)

    • Phenotypic expression is reduced which is why there is a 9:3:4 ratio opposed to the normal 9:3:3:1 ratio

Multiple Alleles

  • Multiple versions of the same allele

  • Blood cells have proteins on their surface that are called antigens which trigger an immune response if foreign to the body (A, B, AB, or O)

    • If type B blood was donated to a person who had type A blood, it can lead to shock or clumping which is fatal because the white blood cells begin killing the new blood cells

    • Type O is a universal donor because it has NO antigens

    • Type AB is a universal receiver because it has BOTH antigens

  • If the blood type has a +, the blood cell has a protein called the RH factor

  • If the blood type has a -, the blood cell does not have an RH factor

  • BLOOD TYPE IS INHERITED!!!

Epigenetics:

  • Field of research showing how environmental influences have an impact on genes

  • Nature vs Nurture are both 50-50

  • Epigenome

    • Collection of chemical marks on DNA that determine gene expression

    • The experiences of children can change the epigenome which explains why identical twins can develop differently

  • Experiences affect how information is released by genes even though inherited genes provide the information

Twin Study

  • Compare monozygotic (identical - fertilized egg splits into two) and dizygotic (fraternal - two separate eggs are fertilized by two separate sperm) to estimate how genetics are influenced by the environment

  • IT share 100% of genes but FT only share 50% so researches can compare them

  • Twin studies rely on two main assumptions:

    • Equal environments: Identical and fraternal twins experience equally similar environments

    • Little or no assortative mating: People don't tend to choose partners similar to themselves

  • Twin studies have shown genetic influences on many traits like schizophrenia, personality, cognitive skills, etc. They estimate heritability as well as shared and unshared environmental influences.

  • Advances in molecular genetics have largely supported findings from twin studies, validating them as an exploratory tool.

  • Twin studies remain valuable even with DNA-based research

  • Twin studies are still important for studying complex traits where specific genes are hard to identify

    • Explore potential genetic bases of traits

    • Estimate trait expression in people with certain genes (using identical twins)

    • Provide age-matched samples for genetic mapping (using fraternal twins)

  • They can help examine gene-environment interactions by comparing heritability estimates across different environments.

  • Twin studies complement molecular genetics and social science in understanding how genes and environment combine to influence human traits and behaviors.