Inheritance, Variation and Evolution

• What are the two types of reproduction?

  Sexual reproduction where two gametes from different parents join together, and asexual which involves only one parent.
• What type of cell division produces cells for asexual repro?

  Mitosis produces cells for asexual reproduction, so the offspring are all genetically identical (clones) as all the DNA comes from one parent.
• What type of cell division produces cells for sexual repro?

  Meiosis produces gametes for sexual reproduction.
• How are gametes different to normal cells?

  Gametes produced in meiosis are not genetically identical. Also they have half the DNA of a normal cell, so when they join (fuse) the new cell has the full amount.
• What are the gametes called in animals?

  Sperm cells are male gametes and egg cells are female gametes.
• What are the gametes called in flowering plants?

  Pollen are male gametes and egg cells are female gametes.
• What happens during meiosis to make gametes?

  • The DNA is replicated (copied)
  • Then the cell divides twice to give four gamete cells. Each gamete is slightly different genetically to the other gametes.
• Why is it important that gametes are genetically varied?

  As each gamete is slightly different to the others, it mean offspring of sexual reproduction are genetically varied too. This gives species a better survival chance.
• Why do gametes have half the DNA of a body cell?

  So that when the male and female gametes join during fertilisation the new cell formed will have the normal chromosome number.
• What is DNA?

  DNA is a chemical polymer made up of two strands joined together and coiled into a double helix shape.
• What is a chromosome?

  A chromosome is a molecule of DNA that has been coiled up tightly to make a much shorter and fatter molecule.
• What is a gene?

  A gene is a short section of DNA in a chromosome that codes for a single protein. The code of the DNA in the gene is for a particular sequence of amino acids.
• What is a genome?

  A genome is all of the DNA of an organism.

  For example, the human genome is all of the DNA that every human would have.
• Why is the human genome important?

  Scientists have studied the human genome and now know what protein every single gene codes for.

  This will help scientists studying inherited disorders in future.
• How can the human genome help with human history?

  Scientists have used the genome to map where humans migrated from and to in the past.
• What is an allele?

  A different version of a gene. Different alleles occur because mutations happen. Mutations change the DNA code, and alter the amino acid sequence of a protein.
• What does "expressed" mean in genetics?

  Expressed means that a characteristic is visible in an individual because the DNA code has been read and the resulting protein made.
• What is a dominant allele?

  An allele that is always expressed in the phenotype. It is represented by a capital letter, eg B
• What is a recessive allele?

  An allele that only shows in the phenotype when there is no dominant allele in the genotype. It is represented by a lower case letter, eg b
• What does heterozygous mean?

  The genotype when an organism has two alleles that are different, eg Bb
• What does homozygous mean?

  The genotype when an organism has two alleles that are the same as each other.

  Eg, BB is homozygous dominant, and bb is homozygous recessive.
• What is an inherited disorder?

  Any disorder that can be passed on from one or both parents.
• What is polydactyly?

  This disorder gives a sufferer extra fingers and/or toes. It is caused by a dominant allele.
• What is cystic fibrosis?

  This disorder affects the cell membranes of sufferers and causes thick mucus to be produced which affects many parts of the body. It is caused by a recessive allele.
• What is embryo screening?

  Testing the DNA of an embryo to find out if it will be a sufferer of a particular disorder. Parents can choose whether to continue with the pregnancy.
• Why do some people think embryo screening is good?

  It reduces the number of children born with inherited disorders. This reduces suffering and distress, and also reduces the cost for the NHS as fewer treatments are needed
• Why do some people think embryo screening is bad?

  It results in otherwise healthy embryos being destroyed. Some people disagree with this as every embryo is a potential life.
• How many chromosomes does a normal human cell have?

  Every human body cell has 46 chromosomes, arranged as 23 pairs. One of each pair came from each parent during fertilisation.
• What are the sex chromosomes?

  Pair 23 are the sex chromosomes.
• What are the sex chromosomes in a female?

  XX
• What are the Sex Chromosomes for Men:

  
  

  They have one X and one Y, so we say males have XY.
• What are the chances of an embryo being male or female?

  Every embryo a 50% chance of being male or female.
• What is variation?

  Any differences in appearance between individuals of the same species in a population.
• What causes variation?

  Variation in a population is caused by the different genes they have inherited, or the environment they developed in, or a combination of genes and environment.
• How does variation arise?

  Variation in DNA is caused by mutations altering the DNA code. Most mutations don't have any effect on phenotype, but a few do.
• How often do mutations occur?

  Mutations are always occurring, but most are not noticed as they don't affect the phenotype of the individual.
• How does natural selection work?

  If a mutation causes a new allele, and the new phenotype gives a survival advantage in the environment, the allele will be passed on more often to the offspring.
• What is evolution?

  A change in the inherited characteristics of a population over time through a process of natural selection, which may result in the formation of a new species.
• What does the theory of evolution suggest?

  That all living species have evolved from simple life forms that existed over three billion years ago.
• How do new species form?

  If two populations of the same species evolve differently they will no longer be able to interbreed and produce fertile offspring. We say they are different species.