Biology section 13 reproduction:

Sexual reproduction positives

produces variation that helps survive through natural selection if the environment changes. Natural selection is sped up by humans in selective breeding.

Curing genetic disorders

scientists have no way of curing disorders, even those are very serious and can shorten lives. Scientists hope that genetic engineering will be the answer, allowing them to replace faulty allele with healthy ones.

Translocations

section is attached to another chromosome

Inversions

section is flipped

Deletions

section is lost

Sexual reproduction

sensual reproduction involves a male sex cell and a female sex cell from two parents. These two special sex cells (gametes) fuse together from zygote. Gametes are formed in a special for. Of cell diffusion known as meiosis. The chromosome number of the original cell is halved, so when gametes join together, the new cell has the right number of chromosomes. The offspring that results from sexual reproduction inherit genetic information from both parents. They will have some characteristics from both parents, but are not identical to either of them. This introduces variation. The offspring or of sexual reproduction show much more variation than offspring of asexual reproduction. In plants, the gametes are the egg cells and pollen. In animals, the gametes are the egg cells (ova) and the sperm. This reproduction in risky as it relies on two sex cells, from two individuals. However, this type of reproduction takes place in living things ranging from single cell organisms to humans.

What are the different waves of reproduction

sexual reproduction and asexual reproduction.

Where are proteins synthesised

in the cytoplasm of the cells (on ribosome)

A gene

A gene is a small section of DNA on a chromosome. Each gene codes for a particular sequence of amino acids, to make a specific protein.

Genetic crosses

A genetic cross is when you consider the potential offspring that might result from two known parents. Remember that you need to look at bother the possible genotypes and possible phenotypes of the offspring.

Heterozygote

An individual with different alleles for a characteristic (for example Bb)

Asexual reproduction

Asexual reproduction only involves one per and. The cells beside by mitosis. There is no fusion of special sex cells (gametes), there is no missing of genetic information. As a result, there is no variation in the offspring (they are all identical). Asexual reproduction creates genetically identical offspring, clones. Only mitosis is involved in asexual reproduction. Asexual reproduction is common in small animals, plants, fungi and bacteria. However, some big plants can reproduce asexually. The cells of your body reproduce asexually all the time, they divide into two identical cells for growth and to reaper damaged tissue.

Where is DNA found

DNA is found in the nucleus of your cells, and controls protein synthesis.

Fertilisation

Each sex cell has a single set of chromosomes. When two sex cells join during fertilisation, a new cell is formed (has a full set of chromosomes). (egg contains 23 chromosomes, sperm contains 23 chromosomes). The combination of genes on the chromosomes of a fertilised egg is unique. Once fertilised the unique cell begins to divide by meiosis. The number of cells increases rapidly. As the embryo develops, the cells differentiate to form different tissues, organs, and organ systems.

Reproduction in plants

In plant the flowers contain organs of reproduction. The gametes are the pollen and egg cells, these are produced using meiosis. The pollen from one flower must reach the female parts of another flower: pollination. Once pollen has fused with the egg cell, seeds are formed. There is a variation as some plants are able to survive conditions better through natural selection. If a plant reproduces asexually, it uses mitosis.

DNA

Inside the nuclei of your cells, your chromosomes are made up of long molecules of a chemical known as deoxyribonucleic acid (DNA). DNA is a polymer (a long molecule made up of many repeating units). The strands of DNA are twisted to form and double helix structure. Genes are a small section of DNA. This where genetic information (information that determines your inherited characteristics) is stored. Each gene codes for a particular sequence of amino acids to make a specific protein, for example enzymes which control your cell chemistry. The genes control the portions, which control the makeup of specialised cells that form tissues. These tissues form organs and organ systems.

Mutation

Mutations are new forms of genes that result from changes in existing genes and these changes are mutation. They are often tiny changes in the sequences of bases in a strand of DNA. Mutation occur all the time, often as a result of mistakes made in copying the DNA for new cells as the reproduce. When mutations take place in coding DNA most do not alter the protein forms, or alter it slightly so it appearance and functions are not changes. A few mutations code for a change in the amino acids that results in an altered protein that folds to give a different shape. As a result, the active site of an enzyme may no longer fit the substrate, or a structural protein may lose its strength. When mutations take place in the non coding DNA, if dose not directly affect the phenotype. However, variants in the non coding DNA can affect with genes are switched on or off. By changing the genes that are expressed, changes in the non coding DNA can have a big effect in the phenotype of the organism.

Natural selection

Natural selection is the differential survival and reproduction of individuals due to differences in phenotype. It is a key mechanism of evolution, the change in heritable traits of a population over time.

Genetic terms

Picture a gene as a position on a chromosome. An allele is the particular form of information in that position on an individual chromosome. The alleles presented in an individual, known as the genotype, work at the level of the DNA molecules to control the proteins made. These proteins result in characteristics, that are expressed as the phenotype of the organism. Some alleles are expressed in the phenotype even when they are only present on one of the chromosomes. The phenotype coded for by these alleles is dominant, so the alleles expressed if they are present. Use a capital letter they represent the alleles for dominate phenotypes. Some alleles control the development of characteristics, if they are present in both chromosomes. These phenotypes are recessive. Use a lowercase letter to represent recessive alleles.

Making proteins

Protein synthesis is in the cell is controlled by the DNA in the nucleus. Genes in the DNA produce a template for the protein. The template reflects the sequence of bases in the DNA, but is it small enough to leave the nucleus membrane. The template levees the nucleus and binds to the surface of a ribbon. The cytoplasm contains carrier molecules, each attached to the specific amino acid. The carrier's molecules attach themselves to the template in the order given to them by the DNA. The amino acids join together to form a specific protein. Carrier molecules bring specific amino acids to add to the growing protein chain in the correct order until the template is completed. The protein detaches from the carrier molecule and the carrier molecule detach from the temple and returns cytoplasm to pick up more amino acids. Once the protein chain is complete the molecule folds up to form a unique shape that will enable it to carry out its functions. Any change in the order of the bases in the DNA structure will alter the template that is made. This could lead to a driftnet sequence of amino acids joining together and so results in a change in the pristine synthesised by a gene.

More about DNA

The key to the structure and functioning of the DNA molecules if the way these bases join up. In complementary strands of DNA, a C is always linked to a G on the opposite strains. T is always linked to A. this holds the structure of the DNA double helix together.

Genotype

This describes the alleles present or generic makeup of an individual regarding a particular characteristic (for example Bb or bb)

Polyploidy

an entire extra chromosome or set of chromosomes

Homozygote

an individual with two identical alleles for a characteristic (for example BB or bb)

Concerns about embryo screening

could lead to a miss carriage. Not always accurate. Leads to decision of whether or not to terminate a pregnancy. Expensive.

Meiosis

female gametes are egg cells/ ova: made in the ovary's. Male gametes are sperm: made in the testes. Gametes are formed my meiosis, through this the chromosome number is reduced by half. In body cells, there are two sets of each chromosome, one inherited by the mother and the other by the father. When a cell divides for gametes, the genetic information if copied (four sets of each chromosome, instead of two). Each chromosome forms a pair of chromatids. The cells then divide twice to form four gametes, with a single set of each chromosomes. Each gamete that is produced is different. Gametes contain random mixtures of the original chromenos.

Nucleotide units

grouped into threes, each group of three bases codes for a particular amino acid. (each gene is made up of thousands of these). The orders of the bases control the order in which the amino acids are assembled to produce a particular portion for use in your body cells. Each gene codes for a particular combination of amino acids, which make a specific protein. A change or mutation in a single group can be enough to change or disrupt the whole protein structure and the way it works.

Why does the genome matter?

helps us to understand inherited disorders. More lightly to predict any risks for an individual, so they can help reduce the risk. Helps us understand human evolution and history.

Variation

in asexual reproduction, the offspring are produced as a result of mitosis from the parent cells. They contain exactly the same chromosomes and the same genes as their parent. There is no variation on their genetic material. In sexual reproduction, the gametes are produced by meiosis in the sex organs of the parents. This introduces variation as each gamete is different. Then, when the gametes fuse, there is chromosome form each parent, adding more variation. The combination if genes in the new pair of chromosomes will contain different forms of the same genes (alleles) form each parent. This varies characteristics in offspring.

Asexual reproduction positives

inly needs one parent, time and energy efficient, faster.

Carrying out screening

one cells have been controlled from an embryo or fetes, ether before implantation or by techniques such as amniocentesis and chorionic villus sampling, they need to be screened. DNA is isolated from the embryo cells and tested for specific disorders. If the screening show that the fetes is affected, the parents have a choice. They may desire to keep the baby, knowing that will have a genetic disorder when it is born. On the other hand, they may decide to have an abortion or not proceed with implantation. Then parents try again for a healthy baby. They may choose to have pre implantation embryo screening using IVF to avoid having another affected pregnancy.

Sex determinations

one feature of your phenotype in inherited not by a single gene or multiple genes but by a single part of chromosomes. Humans have 23 pairs of chrome sons. In the majority of cases each chromosome, in the pair are similar shapes. Each chromosome has genes carrying information about the different characteristics of your body. One pair of chromosomes are different, these are sex chromosomes and they determine the sex of the offspring. In female the sex chromosomes are the same (xx). In male, the sex cells are different (xy). The Y chromosomes is very small and carried few genes over then those related to sexual characteristics. When cells undergo meiosis to form gametes, one sex chromosome goes into each game. This means that human egg cells contain an x chromosome. Half of the sperm also contain x and other contain the y.

How inheritance works

the chromosomes you inherit carry your generic information in the form of genes. Many of these genes have different forms, or alleles. Each allele code for a different protein. The combination of alleles you inherit will determine your characteristics. We can make biological models that help us predict the outcome of any generic cross.

Phenotype

the describes the physical appearance of an individual regarding a particular characteristic (for example black fur or brown fur in a mouse)

the human genome

the genome if the entire genetic material of the organism. This include all of the chromosomes and the genetic material. Mitochondria contain their own DNA, this is always inherited from your mother because it comes from mitochondria in the egg.

Reproduction in fungi

the most common form of production in fungi is asexual. Many fungi are made up of a mass of thin threads called hyphae. In asexual reproduction, the fungal spores are produced by mitosis: they are genetically identical to their parent. When fungi reproduce sexually, two hyphae's join and their nucleus's fuse (new hypha has 46 chromosomes). This undergoes meiosis to make haploid spores, each with only one set of chromosomes (different to original). Some spores may produce fungi better adapted to some conditions.

Genetic diagrams such as Punnett squares shows you

the predicted ratios of the different phenotypes. They do not tell you the actual offspring because Every time gametes meet they are carrying a unique and random mixture of genes. You only see the expected ratios of phenotypes if you carry out lots of genetic crosses. This is why plants and animals are bread fast and produced lots of offspring are widely used to study genetic.

Reproduction in malaria parasites

there reproduce differently in driftnet stages of their life style. Malaria parasites reproduce asexually in human liver and blood cells. When a mosquito drinks human blood the temp difference triggers sexual reduction.

Long strands of DNA

these are made up of alternating sugar and phosphate sections. These make up the backbone of the molecule. Attracted to each sugar if one of four different compounds called bases.

The bases

these are represented by the letters A, C, G, and T. The combination of a sugar, a phosphate and the base if called nucleotide. The DNA polymer is made up of repeating nucleotide units.

Cystic fibrosis

this is a genetic disorder that affects many organs of the body. This is a disorder of the cell membrane that prevents the movement of certain substances from one side to the other. Mucus made by cells beckons think and sticky. Organs like lungs can be clogged, preventing them from working properly. The pancreas cannot make and secret enzymes, as the tubes witch enzyme s are released in to the small intestine are blocked. The reproductive system is also affected (infertile). Treatments: physiotherapy, antibiotics. Enzymes are used to replace the ones in the pancreas cannot produce and to thin the mucus. There is not really a cure. This is cause but a recessive allele so it must be inherited from both operating.

Screening embryos amniocentesis

this is carried out about 15 to 16 weeks of pregnancy. It involves taking some of the fluid from about the developing fetes. This fluid contains feral cells, which can then be used for genetic screening.

Screening embryos chorionic villus

this is done at the earlier stage of pregnancy (10 to 12 weeks), take a small sample of tissue from the developing placenta.

Polydactyly

this is the name for when babies are born with extra twos or fingers. This is most commonly cause but a dominant allele. It can be inherited from one parents who has the condition. If you have this and are heterozygous, you have 50% change of passing on the disorder to any child you will have. This is because half of your gametes will contain the faulty dominant allele. Of you are homozygous your children will definitely have the condition. Some dominant genetic disorders have a much wider spread effect on the way the body works than polydactyly

Screening embryos

to screen an embryo or foetus, you first need to harvest some cells from the developing individual. There are two methods.

Gene expressions

when a gene codes for a protein that is synthesised in the cell, the gene is said to be expressed. Most DNA if not actually code for proteins. (scientists don't know what the non coding part of the DNA dose). Parts of the DNA are involved in switching genes on and off. Each gene can control the synthesis of lots of different proteins. This may depend on how much of a gene is switched on or off, or how many are. Scientists thinks variations in the non coding areas of our DNA may affect how out genes are expressed.

Using genetic diagrams

you can model genetic crosses using a genetic diagram such as a Punnett square to predict the outcome of the different generic crosses. A genetic diagram gives us: the alleles for a characteristic carried by the parents, the possible gametes that can be formed from these, how these may combine to form the characteristic in their offspring. The possible genotypes of the offspring allow you to work out the possible phenotypes too. Inheriting diffrent alleles can result in the development of quite different phenotypes. Genetic diagrams such as Punnet squares help to explain what is happening and predict what the possible offspring might be like.