Biology - Reproduction: Cell division, human reproduction, chromosome abnormalities

- Cell division - Female + male reproduction - fertilization - Implantation - chromosome abnormalities

Define a polymer, a monomer, nucleotides, and a DNA sequence

Polymer: large molecule made up of repeating subunits called monomers (ex. DNA)

Monomer: small molecules that bond together to form polymers (ex. nucleotides)

nucleotides: there are 4 naturally occurring nitrogenous bases in a DNA polymer, so there are four different types of DNA nucleotides (ATCG):

• Adenine (A)

• Thymine (T)

• Cytosine (C)

• Guanine (G)

A goes with T, C goes with G.

• a DNA sequence is a chain of nucleotides, and in a DNA strand two nucleotides are connected by hydrogen bonds

• This complementary base pairing is what contains genetic information and carries the instructions for the synthesis of proteins and other biological molecules (essentially, genetic code)

what is a chromosome and chromatin?

Chromosome: each chromosome is made of DNA tightly coiled around proteins and is found in the nucleus of our cells

• typically, each human body cell has 23 pairs of chromosomes (46 total). 23 from mother, 23 from father—the last set of chromosomes are your sex chromosomes.

• females: XX Males: XY

cells are always doing one of two things, either dividing (meiosis or mitosis), or working (actively performing its functions)

when a cell is working, its DNA in the nucleus is unraveled. there is no organization besides the DNA being condensed to fit into nucleus. this bundle of unraveled DNA is called Chromatin.

what are chromatids, sister chromatids, and centromeres?

sister chromatid: two identical copies of a duplicated chromosome

chromatid: half of a duplicated chromosome (sister chromatid)

***Refer to them as chromatid if they are duplicated and connected by a centromere, when they are not connected, refer to them as chromosomes.

centromeres: area where two chromatids are joined together in the centre

what are homologous pairs/chromosomes? whats a tetrad?

homologous pair: they are a pair of chromosomes, one from mom and one from dad. they are similar in length, gene position, size, and order of genes, however the versions may be different

tetrad: consists of one homologous pair that has been duplicated/connected by centromeres (4 chromatids in total)

diploid vs haploid?

diploid: all chromosomes possible (46 in humans)

• diploid cells have two complete sets of chromosomes, most human cells are diploid, except for gametes.

• haploid: only have half the possible chromosomes (23 in humans)
  gametes (sperm and egg cells) have one set of chromosomes so that when fertilized, the zygote that is formed has a total set of 46.

describe the process of mitosis? go in depth into every step.

Mitosis: Process creates cells for growth, repair and replacement. contains 5 stages (PMAT then cytokinesis). results in two daughter cells that are identical so they can continue the role of the parent cell. daughter cells are smaller at first but grow.

cell cycle:

• G1 phase: growth phase; surface area to volume ratio increase; signal its time to split

• S phase: synthesis phase; DNA replicates/chromosomes duplicate

• G2 phase: prep. for split; necessary organelles are formed

PMAT:

• prophase: DNA condenses; nuclear membrane breaks; centrioles move to opposite poles; spindle apparatus begins to form

• metaphase: crms. line up in middle; spindle fibres attach to centromeres of each sister chromatid

• anaphase: spindle fibres shorten and break sister chromatids/centromeres; phase ends when chromosomes are in two separate groups

• telophase: chromosomes unwind into chromatin; spindle apparatus breaks down; two nuclear membranes/envelopes form around each group of chromosomes

Cytokinesis:

• means cell movement. this is the final stage and is the physical separation of the two daughter cells (cytoplasm and its contents)

• Animal cell:

  • cleavage furrow forms (divet)

  • eventually “pinching” the two membranes apart (since they have no cell wall)

• plant cell:

  • cleavage plate forms halfway between new nuclei of plant cells, however over time new cell wall material matures and hardens (plant cells have cell wall)

  • results in two individual plant cells

describe the process of meiosis? go in depth into every step.

meiosis:

• two parts (meiosis I and meiosis II)

  • creates 4 daughter cells that are not genetically identical to the parent cell

  • ensures next generation is diploid

  • gives variation in a population

• makes gametes

• cell division that produces haploid eggs/sperm from diploid cells in the ovaries/testes

• DNA replication occurs only once, before meiosis I

• Meiosis is mitosis twice

Meiosis I:

• the parent cells in meiosis contain 23 homologous pairs (46 chromosomes total)

• separate homologous pairs (creating 2 cells) rather than separating sister chromatids

  • involves same 4 phases in mitosis

• differences to normal mitosis:

  • prophase one: crossing over occurs (variation)

  • metaphase one: 2 lines form (homologous pairs). the homologous pairs can be arranged in any variation, and that adds more variation to daughter cells.

  • Spindle fibres pull a part homologous pairs

• after meiosis one, cells are haploids

• 2 cells are formed

Meiosis II:

• the haploid cells produced from meiosis I still contain replicated chromatids so they need to be split a part

• is the exact same as regular mitosis

• each cell will go through PMAT again

• this time the spindle fibres pull a part the chromatids (separate sister chromatids)

• creates 4 daughter cells that are not identical to parents

Describe process of making sperm

spermatogenesis

• making gametes

• the regular meiosis we already are familiar with

steps:

• spermatogonium are the diploid germ cell within the testis, at puberty they being to undergo mitosis

  • in mitosis, two cells are formed, so for these spermatogonium daughter cells:

    • One daughter cell continues mitosis

    • one daughter cell becomes a primary spermatocyte and undergoes meiosis

• once we have the daughter cell that carries out meiosis, they are called spermatocyte.

• primary spermatocyte is when they have duplicated into sister chromatids

• primary spermatocyte divides into two cells vis meiosis I (remember, for meiosis its the separation of homologous pairs, for mitosis its chromatids)

• once we have two cells, they are known as secondary spermatocyte, and will undergo meiosis II

• the four daughter cells are referred to as spermatid

• the spermatid will stay in the epididymis where they will mature into sperm

describe structure + functions of sperm

acrosome: the head of the sperm; contains enzymes that help penetrate a ovum if it happens to find one

body: contain lots of mitochondria because its whole job is to swim, and the mitochondria helps power it

flagellum: tail; propels movement

what are the tubules?

• tubule’s function is to produce sperm, maintain sperm, and store sperm. the tubule is found in the testes, and contains spermatogonium.

• each testis has about 250m of tubule that makes upwards of 100 million sperm a day.

what are the fluids that cover the sperm? in what structure does this occur

as the sperm pass through the vas deferens, they are mixed with fluids from 3 glands, creating seminal fluid:

seminal vesicle:

• secretes mucus high in fructose (seminal sugars) which is the energy source of the sperm

prostate gland + cowpers gland:

• both secretes alkaline (basic) mucus that helps protect sperm from the acidic conditions in the urethra/vagina

• the vagina is acidic so this mucus protects the sperm when its in the vagina (this weeds out the weakest sperm and allows the strongest sperm to reach fallopian tube)

  • less mucus=weaker sperm. vice versa.

  • sperm exits through urethra

describe the hormonal control in terms of male reproduction? negative feedback or positive feedback?

• the hypothalamus releases GnRH which stimulates the anterior pituitary to release LH and FSH

• when LH reaches testes, it starts the release of testosterone

• when FSH reaches the testes, in combination with testosterone, the process of spermatogenesis occurs

• regulates by negative feedback, but this loop is very long term, and doesn’t really ”turn off” or go back and forth

• the negative feedback is to maintain the testosterone levels

describe process of making eggs

oogenesis: process b y which females produce mature egg cells in their ovaries

• oogenesis begins in fetal development

• oogonium (diploid cells) divide by mitosis to form primary oocytes

• primary oocytes are surrounded and protected by granulose cells

• a fetus has approximately 2 million primary oocytes halted in prophase I up until puberty

• when puberty states, menstrual cycle begins, then the process starts

ovarian cycle

follicular phase:

• day 1-14

• FSH levels increase which causes on follicle to mature in either ovary (its random)

• when a follicle matures, a primary oocyte finishes meiosis I and splits in two two haploid cells

  • polar body: smaller cell formed, dissolves into cytoplasm

  • secondary oocyte: has the ability to be fertilized, and continues on the journey

• on day 14, when the follicle is mature, the granulose cells release estrogen which builds up in the blood stream. the build up sends negative feedback to brain to stop release of FSH and start release of LH.

Luteal phase:

• begins when LH rises

• day 14-28

• when LH rises, this causes ovulation to occur (typically day 14 of cycle is ovulation day)

• day 14 is peak LH

• Lh causes blood vessels at the surface of the ovary to collapse and the secondary oocyte is released to the fallopian tube—this release is ovulation

• the secondary oocyte awaits fertilization in fallopian tube

when the egg is in the fallopian tube, what happens to everything else in the ovary? what happens if fertilization occurs, what happens if fertilization does not occur?

• the remainder of the follicle/granulose cells develop into the corpus luteum

• corpus luteum: secretes progesterone and estrogen. progesterone creates and maintains the endometrium lining (the endometrium lining will provide a baby with nutrients and gases from the mother)—this all happens in preparation for a baby

fertilization occurs:

• meiosis II occurs

• zygote develops into embryo and implants in uterus

• during the first trimester, placenta forms and eventually takes over the production of progesterone

• the corpus luteum regresses as the placenta takes over

fertilization does not occur:

• the corpus luteum disintegrates and estrogen/progesterone levels decrease

• progesterone decrease causes the endometrium to shed, which is known as the flow cycle (menstruation)

• shedding marks the beginning of a new cycle—everything starts again.

what is the uterine cycle?

blood vessels build up, and break down based on monthly menstruation cycle

describe fertilization to implantation

fertilization:

• when a haploid sperm cell penetrates a ovum, it has to go through two protective layers

  • the outer protective layer is the corona radiata which is a layer of jelly-like cells

  • the second layer is the zona pellucida which is a protective membrane

• it takes many sperm cells attempting to penetrate the egg in order for one to successfully make it through

  • once a sperm gets through, a depolarization occurs to prevent other sperm from entering

• cleavage begins

  • cleavage is a special type of mitosis that replicates DNA, but there is no growth. this makes it so we have cells to work with

  • cells essentially alternate between s phase and mitosis

• once cells split enough (around 16 cells have formed) it is known as a morula. that is when there are enough cells to the point they state to behave differently

• as it begins to reach the uterus, the cell fills with fluid and 2 groups of cells begin to form. this is known as a blastocyst

  • trophoblast: outer layer—becomes the chorion and placenta

  • inner cell mass: develops into 3 germ layers which then turns into embryo (clump of cells)

• once it reaches the uterus, it should be a blastocyst

• the blastocyst embeds/implants onto the endometrium

what does the trophoblast/chorion secrete

they secrete enzyme called hCG which essentially talks with corpus luteum and tells it to continue to secrete progesterone

describe the processes that take place in the outer layer of cells

after implantation happens, the trophoblast (outer layer of cells) forms into the chorion and amnion

• chorion: produces hCG which maintains corpus luteum

  • pregnancy tests identify hCG levels in the urine of a female

• amnion: layer the surrounds embryo and forms a sort of space known as the amniotic cavity which is a fluid filled sac (amniotic fluid) that insulates the embryo

• the extraembryonic coelom is a fluid filled space between the amnion and chorion

  • the yolk sac forms in that fluid filled space, and is the site of early red blood cell formation (later gets absorbed into digestive tract)

• the chorion begins to make extensions called chorionic villi which extend to endometrium

  • they form the placenta

  • placenta: where materials are exchanged between the mother and developing embryo. placenta takes over production of estrogen and progesterone

  • high levels of progesterone prevent further ovulation/another pregnancy

describe the processes that take place in the inner cells

when the blastocyst is implanted into the endometrium, gastrulation begins.

gastrulation:

• formation of different tissues

• the inner cell mass begins to change and flattens into a structure called embryonic disk

• the disk develops into three distinct layers which in turn develop into different structures:

  • ectoderm: outer/external layer; skin, hair, nervous system, neurons, teeth

  • mesoderm: middle layer; muscle (ex. cardiac muscle, skeletal muscle), bones, kidneys

  • endoderm: inner/internal layer; endocrine glands, liver, lung cells, thyroid cells, pancreatic cells.

• each layer will give rise to specific organs and structures in the fetus

the completion of gastrulation marks the beginning of morphogenesis

morphogenesis:

• the process of cells differentiating and forming different structures ex. turning bundle of cells into a functioning heart

essentially, gastrulation puts cells in correct places, morphogenesis forms the different structures/tissues using the cells in their given layers

describe birth process. positive or negative feedback?

• parturition is birth

• positive feedback loop

• uterine contractions that stretch the cervix mark the beginning of labour

• birth is brought on by a drop in progesterone

• oxytocin is released from posterior pituitary

loop:

• baby stimulates posterior pituitary to release oxytocin

• oxytocin causes uterus to contract

• baby pushes agaisnt cervix, causing it to stretch

• stretching of cervix causes nerve impulses to be sent to brain

  • the nerve pulses cause the cycle to keep going, till something happens (birth)

lactation?

• prolactin is released from anterior pituitary and creates milk

• oxytocin is released from posterior pituitary and causes the contraction of the mammary glands (less intense then birth contractions) which allows milk to leave the glands

  • oxytocin also causes light contractions to help uterus return to pre-pregnancy size and shape

• colostrum: “early milk” that is produces for the first few days of breast feeding; lots of antibodies and proteins that help babies immune system

what is abnormal meiosis? describe the different types.

nondisjunction: failure of a pair of homologous chromosomes to separate properly during meiosis (during anaphase I or II)

• trisomy: 1 extra chromosome

  • if you had a gamete with 24 chromosomes, that would mean it has both chromosomes from one of the homologous pairs. if that gamete joins with a normal gamete of 23 chromosome from the opposite sex, a zygote containing 47 rather than 46 chromosomes would be produced

  • the zygote then has three chromosomes in place of the normal pair

• monosomy: 1 missing chromosome

  • if gamete containing 22 chromosomes joins with normal gamete of 23, the resulting zygote will have 45

  • the zygote will have only one of the chromosomes rather than the two needed to form a homologous pair (1 from mom + 1 from dad)

  • EX. turner syndrome—occurs in woman who are missing a 2nd X chromosome (XO)

    • in egg cell, both homolog X chromosomes move to same pole during meiosis I, when the egg with no X chromosomes is fertilized by a normal sperm with a X chromosome, a zygote with 45 chromosomes is produced.

    • results in sterile female

• Klinefelter syndrome: extra X chromosome

  • causes by nondisjunction in either sperm or egg

  • zygote inherits two X chromosomes and a single Y

  • males with Klinefelter are sterile

whats a prokaryote?

• Prokaryotes are organisms whose cells lack a nucleus and other organelles.

• Prokaryotes are divided into two distinct groups: the bacteria and the archaea, which scientists believe have unique evolutionary lineages.

• Most prokaryotes are small, single-celled organisms that have a relatively simple structure.

do bacterial cells undergo mitosis? why? and what does it do instead? describe it. what is exponential growth?

no, because they have a single circular chromosome and no nucleus. instead they reproduce through a form of cell division called binary fission.

binary fission (has a cell wall, remember that:

1. cell duplicates

2. cell elongates

3. septum/cell wall begins to form

4. septum forms, distinct walls form

5. cells separate

exponential growth: sequence of repeated doubling/growth

what is conjugation?

conjugation:

• involves transfer of genetic material from one cell to another by cell-to-cell contact through a bridging structure called a pilus

• creates new cells with new genetic combinations (provides a chance that some cells may be better adapted to changing conditions)

• can only take place between non-identical bacterial cells

• creates only a single genetically unique daughter, but this new cell can undergo binary fission to create a colony of cells

describe budding, vegetative reproduction, an fragmentation

budding:

• form of asexual reproduction in which a complete but miniature version of the parent grows out from the parent’s body

vegetative reproduction:

• takes place in many plants

• ex. strawberry plants can spread across a garden by extending thin creeping stems—a new strawberry plant develops at the end of each stem

  • once the new plant has taken root, the stem disintegrates, separating the new plant form its parent

fragmentation:

• creation of new plants from a fragment (portion) of a parent plant

• ex. for potatoes, entire new plants are grown from a fragment of a parent plant

• gardeners rely on fragmentation to prpagate new garden plants from cuttings

describe parthenogenesis

form of asexual reproduction in which an unfertilized egg develops into an adult

ex. in honeybees, the queen bee lays both fertilized and unfertilized eggs. the fertilized eggs develop into female worker beets, while the unfertilized eggs develop into male drones

describe spores

A spore is a cell that certain fungi, plants (moss, ferns), and bacteria produce. Certain bacteria make spores as a way to defend themselves. Spores have thick walls. They can resist high temperatures, humidity, and other environmental conditions.

• structure that contains genetic material and cytoplasm surrounded by a protective sheath or wall

• the wall protects the contents until conditions are favourable, at which point the sport wall opens and the organism begins to develop

• since spores tend to be very small, they are readily dispersed in water and by the wind

• spores may be haploid or diploid, and not all spores are the product of asexual reproduction

• some organisms produce spores by meiosis, resulting in an alteration of generations

what is the alternation of generations

the life cycle of plants consists of two generations: a haploid generation, and a diploid generation (gametophyte generation and sporophyte generation)

• ex. imagine if humans gave birth to sperm and eggs, which then grew up and had lives of their own before mating to create a new diploid baby.

the term “alternation of generations” refers to diploid and haploid generations, which is only found in plants.

some animal life cycles alternate between asexually-reproducing and sexually reproducing phases. ex. jellyfish

description:

• the diploid generation of a plant is called the sporophyte (spore-making body)

  • through the process of meiosis, the sporophyte produces one or more haploid spores

• these spores develop without fertilization

• each haploid spore grows into a plant body called the gametophyte (gamete-making body)

• gametophyte produce male and female gametes, which fuse at fertilization and develop into another sporophyte.

• the cycle then repeats

describe the alternation of generations in mosses and conifers

mosses:

• the leafy green mat that is a characteristic of mosses is the gametophyte (haploid)

• at certain times of the year, a stalk grows up from this mat

  • the stalk is the sporophyte, and spores are cast from its cap

  • spores fall on the ground and develop into the leafy mat gametophyte

• special structures within the gametophyte produce sperm and eggs

• the sperm swim to the eggs and fertilize them

• each fertilized egg then develops into a new stalk

note: since sperm must swim to the eggs, mosses can only grow in environments that are moist for at least part of the year

conifers:

• the tree itself is the diploid sporophyte

• the haploid gametophytes are microscopic structures within the male and female cones that are produced by the tree

• the single-celled female gametophyte develops from a spore that is produced by a specialized structure at the top of each scale of the female cone (the larger woody cone)

  • the female gametophyte stays inside the spore-producing structure

• the male gametophyte is produced by a structure that is found on the male cone (the smaller cone)

  • the male gametophyte is released in the pollen that is cast by male cones

  • the pollen is dispersed by the wind and if the pollen reaches a female cone then sperm from the gametophyte will grow and fertilize the egg within the female gametophyte

  • the fertilized zygote forms a seed that is attached to the scale of the female cone

advantages and disadvantages of reproductive strategies

sexual reproduction advantages:

• offers a population a way to adapt to a changing environment

  • ex. some offspring may have a greater ability to resist parasites or toxins in the environment or to take advantage of new food sources

• competition among siblings may be reduced if they are genetically diverse

• pairing of homologous chromosomes and crossing over offer opportunities to replace or repair damaged chromosomes

asexual reproduction advantages:

• quicker than sexual reproduction

• does not require presence of second parent organism

• requires less energy

• many forms ex. vegetative and budding help maximize chances that individual offspring will survive

  • in these forms of asexual reproduction, the daughter organism does not fully separate from the parent until it is capable of independent survival