Reproduction and Inheritance

• The nucleus contains your genetic material in the form of chromosomes.
• Chromosomes are long length of DNA coiled up.
• A gene is a short section of DNA.
• Human body cells are diploid which means that they have two copies of each chromosomes, arranged in pairs. A human cell nucleus contains 46 chromosomes in total so the diploid number for humans is 46.
• All of an organism's DNA makes up the organism's genome. Each separate gene in a DNA molecule is a chemical instruction that codes for a particular protein.
• Proteins are important because they control most processes in the body. they also determine inherited characteristics (eye colour, blood type) so thus genes control out inherited characteristics.
• There are different versions of the same gene which give different versions of a characteristic like brown eyes and blue eyes. Allele is the different version of the same gene.
• A DNA molecule has two strands coiled together in the shape of a double helix. The two strands are held together by chemicals called bases which are adenine, cytosine, guanine, thymine. They are always paired A-T and C-G
• DNA controls the production of proteins in a cell. Proteins are made up of amino acids. Amino acid chains fold up to give each protein a diifrent, specific shape which means each protein can have a different function.
• It's the order of the bases in a gene that decides the order of the amino acids in a protein.
• Each amino acid is coded for by a sequence of three bases in the gene which is called a codon.
• Many regions of DNA are non-coding which means they don't code for any amino acids,
• Proteins are made in two stages (transcription and translation).
• Proteins are made in the cytoplasms (using ribosomes) but the DNA containing the code is found in the nucleus (and DNA is not allowed to leave the nucleus).
• The answer is to make a copy of the DNA called messenger RNA or mRNA. mRNA can leave the nucleus and go to the ribosomes leaving the DNA behind in the nucleus.
• Transcription - DNA stays in the nucleus then the DNA code is copied onto another molecule called messenger RNA (mRNA).
• Translation- in the cytoplasm the mRNA moves to the ribosomes. Ribosomes read the mRNA and in conjunction with molecules called transfer RNA (tRNA). they assemble the correct amino acids to make proteins.
• mRNA and tRNA are both used in protein synthesis. RNA is a very similar molecule to DNA, EXCEPT: RNA is single stranded and RNA uses the base uracil(U) instead of thymine (T).
• • In transcription, DNA unzips and one side is used as a template to make mRNA.
  • complementary bases pairing ensures this is correct (C-G, A-T)
  • RNA uses uracil instead of thymine
• • To begin the process of translation, mRNA is fed through one of the ribosomes.
  • Two tRNA molecules can fit into a ribosome at one time. Each tRNA pairs up their anticodon with a complimentary codon on the mRNA. This ensures that the correct amino acids are positioned in the correct sequence.
• • the first tRNA is then releases leaving its amino acid behind.
  • the ribosomes move along the mRNA and the process continues. More amino acids are added until a stop codon is reached. The polypeptide chain can now be folded into the final protein.
• Asexual reproduction - it involves only one parent. The offspring have identical genes to the parent so there no variation between parent and offspring.
• Mitosis is a form of cell division that produces two genetically identical cells. It has the uses of growth, repair of tissues and asexual reproduction.
• • each chromosomes makes an exact copy of itself (but remains stuck together)
  • chromosome pairs now line up on top of each other in the middle of the cell.
• • chromosomes separate and are pulled apart to either side of the cell.
  • the cell starts to split down the centre forming two identical cells.
• sexual reproduction is where genetic information from two organisms is combined to produce offspring which are genetically different to either parents.
• • in sexual reproduction, the mother and father produce gametes. Gametes are sperm cells and egg cells.
  • gametes are haploid - they have half the number of chromosomes in a normal cell.
• • at fertilisation, a male gamete fuses with a female gamete to form a zygote. The zygote ends up with a full set of chromosomes.
  • the zygote then under goes cell division by mitosis and develops into an embryo.
• • the embryo inherits features from both parents as its received a mixture of chromosomes from its mum and its dad.
  • the fertilisation of gametes is random which produces genetic variation in the offspring.
• sexual reproduction involves the the fusion of male and female gametes.
• Meiosis is used for the making of gametes and it occurs in the testes and ovaries.
• • each chromosome makes an exact copy of itself but remains stuck together.
  • chromosome pairs now pair up side by side in the middle of the cell.
• • chromosome pairs are now pulled apart to either side of the cell.
  • the cells splits for the first time forming 2 cells, chromosome pairs now line up on top of each other in each cell.
• • chromosomes in each cell now separate as they get pulled apart to either side of the cell.
  • the cell splits for the 2nd time forming 4 gametes in total.
• the stamen is the male reproductive part + the carpel is the female reproductive part.
• the stamen consists of the anther and the filament.

  • the anther contains pollen grains which produce the male gametes.
  • the filament is the stalk that supports the anther.
• the carpel consists of the ovary, style and stigma.

  • the stigma is the end bit that the pollen grains attach to.
  • the style is the rod like section that supports the stigma
  • the ovary contains the female gametes inside ovules.
• pollination is the transfer of pollen from an anther to a stigma so that the male gametes can fertilise the female gametes in sexual reproduction.
• Cross pollination is a type of sexual reproduction where pollen is transferred from the anther of one plant to the stigma of another.
• Plants that cross-pollinate rely on things like insects or the wind to help them pollinate.