reproduction

asexual reproduction

cell cycle

  • growth and DNA replication
  • mitosis

growth and DNA replication

  • increases its amount of subcellular organelles such as mitochondria
  • duplicates its DNA so there are now 2 x 46

Mitosis

  • the chromosomes line up at the centre of the cell
  • spindle fibres pull the x shapes apart to opposite ends of the cell
    -membranes form around each of the sets of chromosomes forming two new nuclei
  • the cytoplasm and cell membrane divide forming two new cells

produces identical duploid cells

sexual reproduction

meiosis

  • the cell duplicates its genetic information forming two armed chromosomes
  • the chromosomes line up in pairs in the centre of the cell and then get pulled apart, resulting in cells with only one double copy of each chromosome ( father or mothers)
  • in the second division the x shaped chromosomes line up in the centre of the cell and then get pulled apart forming four gametes

gametes

  • a gamete is a sexual cell from either the father or the mother (sperm or egg cell)
  • each gamete contains 23 chromosomes
  • gametes are genetically different from each other because the chromosomes are shuffled during meiosis resulting in a random mixture of fathers and mothers chromosomes

fusion

  • the sperm cell containing 23 chromosomes and the egg cell containing 23 chromosomes fuse together to form a cell with 23 pairs of chromosomes
  • the offspring inherits features from both parents

sexual reproduction is where genetic material from two organisms are combined to form offspring that are genetically different to either parent

evaluation

pros

cons

evaluation

pros

cons

only requires one parent which eliminates time and effort spent finding a mate

faster than sexual reproduction

many identical offspring can be produced

no natural selection

no variation which leaves the species at risk

chromosomes from both parents results in natural variation

  • variation increases the chances of a species surviving because it leads to positive adaptations
  • can use selective breeding to speed up natural selection and create plants and animals with desirable characteristics


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DNA

DNA structure

  • DNA is composed of bases, sugars and phosphates
  • one of each forms a nucleotide
  • the sugar and the phosphate form the backbone of the double helix structure
  • the bases form the connections between the two strands
  • the bases pair:
  • A+T , C+G

protein synthesis

  • each three bases of the gene code for a specific amino acid
  • the mRNA or template molecule copies the DNA from the nucleus and transports it to the ribosomes
  • the carrier molecule or tRNA carries the corresponding amino acids to the template and these are bonded with peptide bonds forming a protein

  • DNA - a chemical that all the genetic material in a cell is made up of, found in a double helix structure within the nucleus of a cell


  • chromosomes - really long strands of DNA, 23 pairs in a regular cell


  • Gene - a small section of DNA on a chromosome. each gene codes for a specific sequence of amino acids which make a specific protein for a specific purpose


  • genome - the entire set of genetic material within an organism

mutations

  • mutations are changes in the DNA sequence, this alters the protein formed
  • most mutations do not have serious effects on the proteins
  • however some do

inheritance

each individual created by sexual reproduction receives two alleles (a version of a gene), one from either person this can be represented in a punnet cross diagram . - if the organism has two dominant alleles then the dominant allele will show in the phenotype, - if the organism has one dominant and one recessive allele then the dominant allele will show in the phenotype - only if the organism has two recessive alleles then the recessive allele will show in the phenotype

homozygous - two alleles for a specific gene are the same in a person
heterozygous - two alleles for a specific gene are different in a person

  • genotype - alleles present in an organism
  • phenotype - characteristics expressed in an organism

inherited disorders

cystic fibrosis is caused by a recessive allele

  • results in a lot of sticky mucus in the air passages and pancreas

polydactyly is caused by a dominant allele - genetic disorder where babies are born with extra fingers or toes

embryonic screening

pros

  • helps people to stop suffering
  • saves the government and individuals a lot of money

cons

  • implies that people with genetic disorders are undesirable
  • could give rise to designer babies
  • expensive

sex determination

  • the 23rd pair of chromosomes are you 'sex' chromosomes which determine your sex
  • females have XX
  • males have XY
  • one is inherited from the mother and one from the father resulting in it being a 50/50 chance