biology topic 6 - inheritance, variation and evolution

• what is DNA ?

  the chemical that all of the genetic material in a cell is made up of . DNA is a polymer made up of 2 strands forming a double helix.
• Where is DNA contained ?

  chromsomes
• What are chromosomes ?

  Really long molecules of DNA and they come in pairs
• What is a gene ?

  • small section of DNA on a chromosome and each gene codes for a particular sequence of amino acids to make a specific protein .
• What is a genome ?


  the entire genetic material of that organism
• What is the importance of the human genome ?

  Understanding it is important for science and medicine 1.It allows scientists to identify genes in the genome that are linked to different types of disease 2. understanding and treatment of inherited disorders. 3. Use in tracing human migration patterns from the past
• What is sexual reproduction?

  where genetic info from 2 organisms which is mom and dad is combined to produce offspring which are genetically different to either parent.
• What does sexual reproducion involve ?

  The fusion of male and female gametes. As there are 2 parents the offspring contains a mixture of their parents genes.
• How chromosomes does each gamete contain in a normal cell ?

  23
• Where does sexual reproduction happen in animals and plants ?

  Sperm and egg cells in animals. And pollen and egg cells in flowering plants
• What does asexual reproduction produce ?

  Genetically identical cells
• What does asexual reproduction involve ?

  Only one parent and no fusion of gametes. there is no mixing of genetical material and this lead to genetically identical (clones). Only mitosis is involved - the ordinary cell makes a new cell by dividing in two
• What is meiosis?

  a type of cell division that reduces the number of chromosomes in the parent cell by half and produces four gamete cells
• Explain the importance of meiosis

  1. Halves the number of chromosomes in gametes. 2. So when 2 gametes fuse at fertilisation the full number of chromosomes is restored.
• What happens when a cell divides to form gametes ?

  1. copies of genetic info are made 2. The cell divides twice to form 4 gametes each with a single set on chromosome.
• What do cells in reproductive organs form when divided by meiosis !

  Gametes
• Describe the process of meiosis

  DNA replicates Cells divide twice. Forming 4 cells called gametes : 1. Each with a single set of chromosomes half number of original cell. 2. All genetically different.
• What happens after fertilisation ?

  1. fertilised cell divides repeatedly by mitosis to increase number of cells . 2. ball of genetically identical cells - embryo. 3. As embryo develops cells differentiate into different types of specialised cells.
• Compare mitosis and meiosis

  1. Mitosis is a cell division that produces 2 cells whereas meiosis is a cell division that produces 4 cells . 2. mitosis maintains number of chromosomes whereas meiosis halves number of chromosomes. 3. Mitosis produces genetically identical cells whereas meiosis produces genetically different cells. 4. Mitosis happens in body cells whereas meiosis happens in reproductive organs .
• Where does meisois happen ?

  Reproductive organs
• How many pairs of chromosomes are in every human cells ?

  23 pairs
• What chromosomes do males have ?

  X and Y chromosome XY
• what chromosomes do females have ?

  2 X chromosomes XX
• What are alleles ?

  Different versions of the same gene
• What are gametes?

  sex cells of organisms and reproductive cells
• What is a dominant Allele ?

  an allele that always produces a certain phenotype in an organism . Represented by a capital letter .
• What is a recessive allele ?

  Only expressed if the individual has 2 copies and does not have the dominant allele of that gene . Represents by lower case letter
• What is heterozyguos?

  alleles that are both different for the same characteristi.
• What is homozygous?

  Both alleles are identical for the same characterisitc.
• What is genotype ?

  the combination of alleles that a person has for a particular trait.
• what is phenotype?


  physical characteristics of an organism .
• What is cystic fibrosis and what does it result in the body ?

  a genetic disorder of the cell membrane . It results in the body producing a lot of thick sticky mucus in the air passages and in the pancreas.
• What is cystic fibrosis caused by ?

  A recessive allele F carried out by 1 person in 25
• What are carriers ?

  people with Only copy of the allele won’t have the disorder
• What does the child need to have cystic fibrosis ?

  Both parents must be either carriers or have the disorder themselves
• What is the chance to have cystic fibrosis ?

  1 in 4 chance if parents are carriers
• What is polydactyl?

  a genetic disorder where a baby is born with extra fingers or toes.
• what is polydactyl caused by ?

  A dominant allele - there is a 50 chance of the child is having disorder if one parent has the D allele
• For embryos produced by IVF-

  After screening embryos with bad alleles would be destroyed
• For embryos produced in the womb - what happens during screening?

  Screening could lead to the decision to terminate the pregnancy .