topic 3 genetics

• DNA stands for deoxyribonucleic acid
• asexual reproduction advantages

  • 1 parent is needed(makes it easier to reproduce)
  • when conditions are favourable, many identical offspring can be produced.
• asexual disadvantage

  •  no variation in the population.

  This means that in changing environments, they will all be vulnerable to the same things.
• sexual reproduction advantages

  • variation in the offspring of sexual reproduction.

  .Variation means that some offspring are more likely to survive if the environment changes.

  Offspring that survive can reproduce and pass on their characteristics to the next generation.
• sexual reproduction disadvantages

  • takes longer
• meiosis

  •  meiotic cell division produces non identical genetical 4 daughter cells (the gametes).
  • used for reproduction
  • produces haploid daughter cells
  • two cell divisions
• gene is a small section of DNA that codes for a particular protein.
• DNA is a polymer made of nucleotides.

  A polymer is a long molecule made of repeating units.
• The units that make up DNA are called nucleotides.

  Each nucleotide contains a phosphate group, a sugar molecule and a base.

  
• DNA

  • base pairs are joined together by weak hydrogen bonds.
  • Has double helix shape
  • 4 different base in DNA A bonds with T and C with G
• When all the pairs join up, the nucleotides coil together to form a double helix shape.
• Genetic variation occurs when there are differences in alleles within a population. Alleles are alternative forms of a gene.
• Every organism has DNA.

  The entire set of this DNA is called the organism's genome.
• Different forms of the same gene are called alleles.
• Why do organisms that reproduce sexually have a pair of alleles for every trait?

  That's because they get half of their chromosomes from their mother's gamete, and half from their father's.
• gametes?


  sex cells - eggs in females and sperm in males.
• The gametes join together at fertilisation to give a zygote. What is a zygote?

  a fertilised egg that grows into an embryo.
• Genotype


  All of the alleles an organism has
• If they get the same allele from both their mother and father, the organism is said to be homozygous for that trait.

  If they get different alleles, the organism is said to be heterozygous for that trait.
• An organism's phenotype is all of its physical characteristics.
• Phenotype can be affected by:

  • enviroment
  • genotype
• The genotype (all the different alleles) of an organism determines which molecules are made in its body.
• Dominant allele

  •  always expressed, even if an organism just has 1 copy of that allele or if alleles are homozygous or hetrozygous
• Recessive allele expressed when:

  • if an organism has 2 copies of that allele so if an organism is homozygous recessive for the trait.
• dominant written in captial letters

  recessive written in lowercase letters
• Polydactyly is an inherited condition where a person has extra fingers or toes.

  It's caused by a dominant allele.
• Cystic fibrosis is a disorder in which a person's body produces lots of thick mucus in their airways and pancreas.

  It's caused by a recessive allele.
• Sex chromosomes determine whether the person will be male or female there is only one pair present in 23 chromosomes in body

  There are 2 types of sex chromosome: X and Y.
• If a person gets an X chromosome from both parents, they're female (XX).

  If a person gets an X chromosome from their mother and a Y chromosome from their father, they're male (XY).
• To see if you might inherit a trait use:

  • punnet squares
  • family perdigree analysis
  • ratios
  • genetic cross diagram(used for sex inheritance)
• Most characteristics are controlled by the interaction of multiple genes.
• However, a few characteristics are controlled by just one gene.
• variation


  A population can contain many different phenotypes.
• variation

  • genetic factors e.g. eye colour
  •  environmental factors( acquired characteristic) e.g. scars,tattoes
  • both factors
• The Human Genome Project was a project to map the entire human genomeShow all lines
• Human genome advantages

  •  allows scientists to study whether certain diseases are linked to certain genes.
  • also helps us to better understand and treat inherited disorders.
• Sexual reproduction leads to genetic variation

  Remember, the gametes used in sexual reproduction are formed through meiosis, a special type of cell division.

  A single organism can produce many gametes.

  The gametes produced are not the same; each has a different genetic make-up.

  When the male and female gametes fuse, their genetic information mixes.

  This mixing leads to variation in the offspring produced, so all the offspring are different.
• mutation


  sudden change in a gene or chromosome.
• Populations usually contain a lot of genetic variation.

  The different versions of the genetic code in a population are called variants.

  These variants are created by mutation.
• Most mutations don't have any effect on phenotype.