Pack 12 - Inheritance

Genotype:
1. Genetic makeup of an organism, all alleles an organism has.
2. Phenotype:
  1. Observable or biochemical characteristics
What is a gene
1. A sequence of nucleotide bases coding for a polypeptide or functional RNA
2. An allele is a different version of the same gene
  1. Each gene of diploid cells should have 2 alleles, unless sex chromosones
The locus is the position of a gene on a chromosome
Types of chromosomes:
1. Homozygous
  1. Alleles on each chromosome are the same
2. Heterozygous
  1. 2 alleles on the chromosome are different
Types of alleles:
1. Dominant
  1. When present in genotype it's always expressed in phenotype
2. Recessive
  1. Only expressed when homozygous recessive
Codominance
1. This is when two alleles both contribute to the phenotype
Monohybrid Inheritance
1. This is the inheritance of a single gene
Pedigree Diagrams
1. Diagrams show ancestral relationships and transmission of genetic traits
2. Exam hint:
  1. If asked whether an allele is dominant or recessive, look for two parents that do not have the characteristic but have children that do have it
    1. Shows it is recessive
Dihybrid Inheritance
1. Two different characters, determine by different genes located on two different chromosomes are inherited
Mendel's Laws
1. Law of segregation:
  1. Characteristics of an organism are controlled by genes that occur in pairs, only one of each pair can be carried in a gamete
2. Law of independent assortment
  1. Each member of a pair of alleles may combine randomly with either of another pair
3. In terms of meiosis:
  1. Homologous chromosomes pair up in prophase 1
  2. In metaphase 1:
    1. Homologous chromosomes line up on equator in pairs
    2. Random segregation of c'somes either side of equator leads to different combinations and so different alleles in gametes
  3. Homologous chromosomes separated in Anaphase 1
Autosomal linkage
1. An autosome is a chromosome that is not a sex chromosome
2. Any two genes occuring on the same chromosome are said to be linked
  1. Autosomal linkage is when two or more genes are carried on the same autosome
Sickle cell anaemia
1. Due to single base substitution.
  1. Results in one amino acid being altered in the 146 long Beta polypeptide chain
Multiple alleles
1. Some genes have more than two alleles
  1. Only two of these alleles can be present in an individual at one time
  2. e.g. human blood groups
Epistasis
1. This is where an allele of one gene affects or masks the expression of another in the phenotype
2. Example: Coat colour in mice
  1. Gene A controls melanin distribution in hair
    1. Dominant = black bands
    2. Recessive when homozygous = uniformly black
  2. Gene B determines the expression of gene A:
    1. Dominant allele = production of melanin
    2. Recessive = when homozygous no melanin produced.
Sex inheritance in humans
1. Humans have 22 pairs of autosomes and a pair of sex chromosomes
2. Females have two X's
  1. Males have one X one Y
    1. Produce gametes with X and Y
  2. Produce gametes of only X
3. Sex Linkage
  1. All genes carried on the sex chromosomes are transmitted along with those during sex
  2. Because Y is smaller than X, there is no equivalent part of X to half of Y
    1. This means that in males, recessive alleles on non-homologous part of X will be expressed
      1. This is because there is no equivalent dominant allele
  3. Expressed as: X^N X^a and X^N Y
Haemophilia
1. This is the failure of the blood to clot and is potentially fatal if not treated.
2. One cause is the recessive allele of a gene that codes for a protein needed in the clotting process
Stats Tests
1. The chi-squared test
  1. Used to test whether deviations between observed and expected numbers are significant or not
  2. Null Hypothesis:
    1. No statistically significant difference between observed and expected frequency, any difference is due to chance
  3. Cut off point where p=0.05 is whether you accept or reject null hypothesis
    1. If X^2>critical value or equal too, reject null hypothesis
      1. The probability that the differences occured by chance is less than or equal to 0.05
    2. If X^2<critical value, accept null hypothesis
      1. No significant difference, probability that difference is due to chance is greater and 0.05
  4. Then, calculate degrees of freedom (number of categories minus one)

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Pack 12 - Inheritance

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	Created by Jacob Shepherd over 7 years ago