chap 14 inheritance

• inheritance refers to the transmission of traits from one generation to another
• why does observed ratio of traits often differ from the expected ratio of traits ?

  as sample size is small making the data inaccurate
• gene is a sequence of DNA nucleotides that controls the formation of a single polypeptide, it is also a unit of inheritance
• if 2 plants reproduce, 1 with Tt homozygous and 1 with tt heterozygous: what is the ratio of genotypes of the offspring ?

  Tt : tt

  1 : 1
• what are alleles ?

  they are different forms of the same gene, occupying the same relative position on a pair of homologous chromosomes
• combination of alleles for a particular gene is called the genotype
• expressed trait or outward appearance is called the phenotype
• homozygous refers to having 2 identical alleles of a particular gene (eg. DD or dd)
• homozygous dominant has 2 dominant alleles for the gene (eg. DD)
• homozygous recessive has 2 recessive alleles for the gene (eg. dd)
• heterozygous refers to having 2 different alleles of a particular gene (eg. Dd)
• codominance is where both alleles express themselves in the heterozygote, which has the phenotype intermediate between that of its pure- bred parents
• what sex chromosomes does males have ?

  xy
• what sex chromosomes do females have ?

  xx
• variation is the differences in traits between individuals of the same species
• in variation, there are discontinuous and continuous variation
• is eyelids a discontinuous or continuous variation ?

  discontinuous
• is skin colour or tone a discontinuous or continuous variation ?


  continuous
• discontinuous involves a few clear- cut phenotypes white continuous variation involves a range of phenotypes
• discontinuous variation is controlled by 1 or a few genes white continuous variation is controlled by many genes
• discontinuous variation genes do not show additive effect while continuous variation genes show additive effect
• discontinuous variation are relatively unaffected by environmental conditions while continuous variation are greatly affected by environmental conditions
• what are some sources of genetic variation ?

  meiosis, random fertilisation, mutation, mutagen
• mutation is a change in the sequence of a gene or in the chromosome number
• can mutations be inherited ?

  yes
• what are some examples of genetic mutations ?

  albinism and sickle cell anaemia
• what is an example of chromosome mutation ?

  down syndrome
• albinism is a recessive gene mutation, who are homozygous for the albinism allele
• sickle cell anaemia is a gene mutation where it results in a change in the structure of the gene
• what is the difference in the haemoglobin in sickled rbc and normal rbc ?

  HbS is almost the same as normal haemoglobin A (HbA) except in one amino acid, changing the 3D shape of the haemoglobin molecule
• what is the effect of sickle cell anaemia ?

  • sickle shaped cells lose their ability to transport oxygen
  • they are fragile and sticky and can get stuck in narrow blood vessels
  • this slows or blocks the flow of oxygen to parts of the body, possibly killing the person
• down syndrome occurs when a zygote has an extra copy of chromosome 21 due to a mutation (usually in the female) where zygote receives 3 copies of chromosome 21
• natural selection refers to a process in which organisms with desirable genes and characteristics are 'selected' or 'favoured' to survive and pass on their genes to their offspring
• due to the change in environment, those that survive will reproduce and pass down their favourable genes to their offspring