Biology Mod 5 heredity

Reproduction

The biological process of new offspring being produced from their parents

Offspring

Are the new organisms produced by parents

Asexual reproduction

Requires one parents. The offspring will have the same genetic material as the parent, ie be identical

Asexual reproduction involves a shorter gestational period and does not require a mate to be found so it requires less time and energy compared to sexual reproduction. However, as there is no genetic diversity, the survival rate is lower and organisms are more vulnerable to environmental changes.

Sexual reproduction

Requires two parents. the offspring wil have diffrent genetic material to the parent. ie be different

Fertilisation

Fertilisation is the fusion of gametes (sex cells), sperm and ova, to form offspring.

Internal fertilisation

Fusion of gametes occurs inside of the mother. This may be done on land because the female reproductive tract hydrates the gametes.
Father releases a large amount of gametes to increase chances of genetic fusion, however very few eggs are produces.
These gametes are less vulnerable to predators and the weather and are likely to survive to adulthood.
Less genetic diversity of offspring.
Occurs in birds, mammals, reptiles

External fertilisation

Fusion of gametes occurs outside of the mother in water environments. The water prevents the gametes from dehydrating.
Mother and father both release a large amount of gametes to increase chances of genetic fusion.
These gametes are extremely vulnerable to predators and the weather and are unlikely to survive to adulthood.
More genetic diversity of offspring.
Occurs in fish, amphibians.

Plants sexual reproduction: pollination

Plants sexually reproduce through pollination which is the transfer of pollen. However, because they can't move from place to place, they rely on pollination agents such as wind, water, insects, animals and humans to carry pollen which contains the male gametes.

The pollen is carried from the anther(held up by the filament) to the stigma(held by the style). A pollen tube then germinates and grows down the style to the ovary. The ovary contains ovules which produce and store ova. Fertilised ovules are seeds. These seeds are then dispersed and germinate.

Most flowering plants consist of both female and male reproductive organs and may self-pollinate(reducing genetic variation), this can be prevented in a greenhouse or by cutting off anthers. It is still sexual production and results in some diversity however not as much as pollination between two plants.

Plants asexual reproduction- vegetative propagation

Shoots or stems(runners) grow from parts of the parent plant. Eg strawberries.

Fungi: asexual budding

Budding occurs when a new individual develops from an outgrowth of a parent, splits off, and lives independently. This occurs in yeast.

Fungi: asexual spores

Sporing is when a parent plant sends out spores contianing sets of chromosomes, which grow away from the parent and develop an embryo.

Bacteria asexual: binary fission

Binary fission occurs when every organelle is copied and the organism divides in two.

Protists reproduction

Binary fission and budding, both are asexual

Fertilisation

The fusion of gametes to form offspring.

A follicle is a small sac found in the ovary that contains one immature egg. As it grows, it releases oestrogen into the bloodstream, causing the endometrium(lining of the uterus) to be thickened.

Gonadotropin-releasing Hormone(GnRH) triggers the anterior pituitary gland to produce FSH, which stimulates follicles to grow, and LH, high concentrations to which causes the egg to burst out of mature follicles to form the corpus luteum.

The ovary releases an ovum(egg) about once a month in females. Ovulation occurs on day 14 of the female reproductive cycle. The female reproductive cycle is on average 28 days. The released egg travels into the fallopian tubes via the oviduct.

The male and female copulate(have sexual intercourse). A muscular contraction(ejaculation) causes semen containing sperm cells to swim into the vagina. The sperm burrows into the ovum. The nuclei of the haploid sperm and ovum fuse forming a diploid zygote(fertilised egg).

If fertilisaiton does not occur, the endometrium disintegrates itself to the lining of the uterus.

Implantation

When a fertilised egg attaches itself to the lining of the uterus
A week after fertilisation occurs, the zygote begins to move from the fallopian tubes into the uterus and divide. It becomes a ball of 16 cells called the morula.

Once the morula reaches the uterus, the cells are rearranged and the blastocyst is formed. The blastocyst implants itself into the wall of the uterus called the endometrium.

The blastocyst contains an inner cell mass which forms the embryo. The outer cells are called trophoblast cells which begin the formation of the placenta. The placenta provides nutrients and oxygen to the embryo. The placenta is connected to the baby via the umbilical cord.

Pregnancy hormones - first trimester

The trophoblast tissue releases HCG. HCG sustains the corpus luteum, which secretes the hormones progesterone and oestrogen. Progesterone and oestrogen interact with the hypothalamus and anterior pituitary gland, decreasing the production of GnRH, FSH, and LH to stabilise the endometrium and prevent menstruation.

Progesterone also causes the uterus to enlarge, maternal parts of the placenta to grow, and breast growth. Oestrogen also helps the development of the baby's organs and the correct function of the placenta.

Relaxin is a hormone that inhibits uterus contraction to prevent premature birth. It relaxes the pelvic joints and increases blood flow to the placenta and kidneys.

Pregnancy hormones - second trimester

HCG production declines and the corpus luteum deteriorates. The placenta becomes the primary producer of oestrogen and progesterone instead. Far more oestrogen and progesterone are produced to prevent shedding of the endometrium.

Pregnancy hormones - third trimester

Increased oestrogen is released. The oestrogen induces receptors to activate on theuterus wall that can bind with the hormone oxytocin. Oxytocin causes muscular contractions of the uterus, pushing the baby towards the vaginal opening, triggering receptors. The hypothalamus stimulates the pituitary gland to secrete more oxytocin, which is carried by the bloodstream to the uterus.

The tissue of the cervic must soften and contractions must occur for birth.

Prior to birth oestrogen and progesterone levels drop significantly to destabilise the endometrium and facilitate labour.

Mendels law of inheritence

Laid the foundation for undertsanding heredity in plants and animals. This allowed people to do selective breeding and artificial pollination.

Chromosomal theory of inheritance

By Sutton and Boven proposed that chromosomes exist in pairs, inherited from each parent. This allowed a better understanding of selective breeding.

DNA Sequencing

DNA sequencing was invented. This allowed the
identification of alleles responsible for traits and helped
the development of recombinant DNA technology.

Recombinant DNA technologies

Enabled the creation of genetically modified organisms (GMOs) that enhanced crop and livestock characteristics. For example, plants may be more herbicide-resistant, have more vibrant flowers, or be more tasty.

CRISPR-Cas9 technology

discovered by Charpentier and Doudna. Genetic manipulation (and the creation of GMOs) became cheap, fast, and accurate.

Chromosomes

All body cells have 23 pairs of chromosomes. The two chromosomes in each pair are called homologous chromosomes.

22 pairs of chromosomes are autosomes and 23rd pair are sex chromosomes(gametes). They determine biological sex(XX is female XY is male). Sperm cells can carry either an X or Y chromosome(and 22 others). Ova can carry only an X chromosome(plus 22 others.)

Diploid

Two complete pairs of chromosomes

Haploid

Containing one complete pair of chromsomes

Mitosis

The cloning of a parent cell to produce two identical daughter cells, used for growth and repair.

Interphase(before mitosis):
During the G1 phase, the cell increases in size. There is one chromatid in a chromsome.
During the S phase, the DNA is replicated. There are two chromatids in a chromosome.
During the G2 phase, the cell grows more and organelles and proteins develop in preparation of cell division.

1. Prophase: Chromosomes condense (rather than being long and stringy) and become visible (as they become thicker by coiling up). Spindle fibres emerge from the centrosomes and the nuclear membrane breaks down. Centrosomes move toward opposite poles.

2. Metaphase: The chromosomes line up at the metaphase plate. Each sister chromatid is attached to a spindle fibre originating from opposite poles.

3. Anaphase: Centromeres split in two, each having one chromatid. Each chromatid is now a chromosome. The chromosomes are pulled toward opposite poles.

4. Telophase: The chromosomes arrive at opposite poles. The nuclear envelope surrounds each set of chromosomes. The mitotic spindle breaks down. Chromosomes decondense.

Cytokinesis(occurs after mitosis): The daughter cells separate.

Meiosis

A form of cell division that creates gametes and only occurs in the reproductive organs of organisms that reproduce sexually.

Meiosis is almost the same as mitosis. The steps occur twice, so there's prophase I and II, metaphase I and II, etc.

Genetic variation from meiosis

1. In prophase I, chromosomes pair up with their homologous
   partners. Crossing over occurs between the pairs, exchanging
   genetic material and forming recombinant chromatids. The
   exchange of genetic material occurs between non-sister
   chromatids at points called chiasmata.

2. In metaphase I, the orientation of homologous chromosomes towards the opposing poles is random. Thus, genes and alleles of one trait are inherited independently of genes and alleles of other traits. This is known as independent assortment.

3. When the chromatids split during anaphase II, the set of chromosomes in each cell is random. This is called random segregation, since the chromosomes ae randomly distributed into gametes.

DNA

DNA, which stands from deoxyribonucleic acid, is double-stranded(consists of two strands). It will always have a backup copy of all genetic information so our body can repair the damage to the DNA. These strands are arranged in a ladder-like structure called a double helix.

Nucleotide structure

DNA is made of millions of tiny subunits knows as nucleotides. Each nucleotide consists of a phosphate group, pentose sugar, and nitrogenous base. The pentose sugars and phosphate groups make up the sugar-phosphate backbone.

There are four types of bases. Adenosine and thymine bond together with two hydrogen bonds. Cytosine and guanine bond together with three hydrogen bonds.

Each strand of DNA is antiparallel, because they are parrallel but in opposite directions. One strand goes from 3' to 5'. The other strand goes from 5' to 3'.

DNA replication

1. Helicase unzips the DNA at the replication fork by breaking the hydrogen bonds between the bases. Each separated strand serves as a template for making a new strand of DNA. Therefore, replication is semi-conservative, because one half of the original strand is always saved, reducing the chance of errors.

2. RNA Primase makes a short complementary segment of DNA nucleotides on the template strand, known as a primer.

3. Free floating nucleotides attach to the bases using complementary pairing rules. DNA polymerase III joins the nucleotides together by complementary pairing rules. DNA polymerase III joins the nucleotides together by catalysing condensation reactions between adjacent sugars and phosphates.

DNA polymerase III can only add nucleotides in a 5' to 3' direction, thus, it travels from the 5' to 3' end of the leading strand, which follows helicase as it unwinds. The other strand goes from 3' to 5' and is referred to as the lagging strand. Thus, on that strand, Okazaki fragments are created.

4. DNA ligase forms covalent bonds, linking together Okazaki fragments by sealing their sugar-phosphate backbones.

5. DNA polymerase I proofreads the DNA and removes the RNA primers, replacing them with DNA.

Mitosis effect on continuity of species

Mitosis replicates parent cells to maintain optimal functioning of an organism. Mitosis is needed for an organism to grow an ideal size and shape. Mitosis is important for repair because it can regenerate damaged cells. All of this allows an organism to survive and reproduce.

Meiosis effect on continuity of species

Enhance the genetic variation of a species due to random segregation, independent assortment and crossing over. It introduces new traits due to mutation, which may be passed on and result in the evolution of a species. This increases the tolerance of the species to various selection pressures, decreasing the likelihood of extinction. In addition, meiosis is necessary to produce gametes that fuse during reproduction, increasing the likelihood of producing offspring.