Inherited Change

Inheritance
1. Phenotype
  1. Expression of characteristic due to genotype
  2. Phenotype can be altered and is due to the environment
    1. Any changes to the phenotype is a modification and is not inherited by offspring
2. Genotype
  1. Genetic constitution of an organism
    1. Any change to genotype must be from mutations in the DNA
      1. Mutations are inherited by offspring
3. Gene
  1. Length of DNA that can code for a polypeptide
    1. Can also code for rRNA and tRNA
    2. Alleles are different forms of a gene
      1. Locus is the position of a gene on a DNA molecule
      2. Two dominant/recessive alleles
        Homozygous dominant/recessive
      3. One of each dominant and recessive alleles
        Heterozygous
4. Humans are diploid organisms containing 2 sets of chromosomes
  1. Two alleles for each gene
  2. Gametes contain one allele for each gene
    1. Double when fuse during fertilisation
Monohybrid Inheritance
1. Basic law of Genetics
  1. In diploid organisms, characteristics are determined by alleles that occur in pairs
    1. Only one of each pair of alleles can be present in a single gamete
2. Inheritance of a single gene
  1. 3:1 ratio
3. Pure-breeding
  1. If identical and bred together
    1. Two alleles are the same for a gene
    2. Homozygous
  2. If two pure breds are crossed then the phenotype will be which ever has the dominant allele
Dihybrid Inheritance
1. Study of how more than one characteristic is inherited
2. Two characteristics, R/r and G/g
  1. Parent 1 RrGg
    1. Set of Gametes
      1. RG
      2. Rg
      3. rG
      4. rg
  2. Parent 2 RrGg
3. 9:3:3:1 Ratio
Codominace
1. Both alleles expressed in the phenotype - both dominant
2. Multiple alleles
  1. When there are more than two alleles of the same gene
    1. Arise from mutations
      1. At different positions in the gene
  2. Blood groups are an example
    1. I^O is recessive
    2. I^A is Codominant with I^B
      1. So a heterozygous I^A would have to be I^AI^O
    3. I^A
    4. I^B
    5. I^AB
    6. I^O
3. Increases number of possible phenotypes
4. If not ratio of 3:1 or 9:3:3:1 between two heterozygous parents then the gene is codominant
Sex-linkage
1. Characteristics are said to be sex-linked when the allele that codes for it is found on a sex chromosome
  1. Sex chromosomes
    1. Male XY
    2. Female XX
    3. Y chromosome smaller than X so carries fewer genes
      1. Most of the genes carried on X chromosome (X-linked)
    4. Males often only have one allele for sex linked genes
      1. One copy means that allele is always expressed, even if recessive
        Males more likely to suffer from X-linked disorders
        E.g. haemophilia and colourblindness
        Females are likely carriers
2. Ratios change depending on parents - carriers / normal
  1. 3:1 / 2:1:1
Autosomal Linkage
1. Any two genes that occur on the same chromosome are said to be linked
  1. On the same autosome, won't be separated during meiosis
    1. Alleles will be passed on to offspring
      1. Unless crossing over splits them first
2. All chromosomes that aren't sex chromosomes are autosomes
3. The closer the two genes are on the autosome the more closely they are said to be linked
  1. Closer they are less likely to be split
  2. If two genes are autosomally link they will not give the expected phenotypic ratio
    1. Autosomal alleles inherited together, give higher proportion of offspring will have their parents genotype and phenotype
      1. Used to predict phenotypic ratio to identify the autosomal link
        Cross two parents to find offspring
        Back cross with parent and offspring to expect 1:1:1:1
        Instead get a different ratio - e.g. 8:1:1:8
        As the two 8's genotypes are so common they must be linked in the parent
        The two 8's gametes were mainly produced by parent, others still produced due to cross over
        As a result higher proportion of offspring have parents' phenotypes
Epistasis
1. Where the phenotype of one gene masks the phenotype of a second gene
  1. For example, baldness masks hair colour
  2. Also where a gene can control / effect anothers apperance
2. Results in a reduction in the number of possible phenotypes in offspring
  1. Dominant Epistasis
    1. 12:3:1
  2. Recessive Epistasis
    1. Normal 9:3:3:1
      1. Reduced from normal 4, to epistasis 3 phenotypes
    2. 9:4:3
Chi-squared
1. A math tool used to determine whether observed results match the expected theoretical results, showing they are significantly different
  1. Used for categorical data
2. To see if the results support a theory use a null hypothesis
  1. Always states there's no significant difference
    1. Tests if results are different due to chance or incorrect theory
  2. x^2 will either support or reject the null hypothosis
Pedigree Diagrams

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Chi Squared (binary/octet-stream)

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Inherited Change

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	Created by Dominic Weston over 6 years ago