Presentation is loading. Please wait.

Presentation is loading. Please wait.

Lecture 41 Prof Duncan Shaw. Genetic Variation Already know that genes have different alleles - how do these arise? Process of mutation - an alteration/change.

Similar presentations


Presentation on theme: "Lecture 41 Prof Duncan Shaw. Genetic Variation Already know that genes have different alleles - how do these arise? Process of mutation - an alteration/change."— Presentation transcript:

1 Lecture 41 Prof Duncan Shaw

2 Genetic Variation Already know that genes have different alleles - how do these arise? Process of mutation - an alteration/change in the genetic material Origin: –Internal (e.g. mistakes during replication of DNA) –External (e.g. radiation, chemicals) Most mutations have no effect or are harmful

3 Types of mutation Non-coding - not in part of gene that codes for protein - either no effect, or effect on gene expression Coding: –Synonymous - same amino acid –Missense - different amino acid –Nonsense - premature stop codon –Frameshift (deletion or insertion of bases) - change in structure of protein

4 Mutagenesis Mutagens are chemicals (or radiation, etc.) that cause heritable alterations in DNA sequence in somatic and germ cells New mutations are rare - most genetic characteristics are due to inheritance from parents Teratogens are chemicals (or radiation, etc.) that affect development of the embryo/foetus and may cause congenital abnormalities (e.g. thalidomide)

5 The human genome Its size is 3 x 10 9 bp (3000Mb) for a single copy Contains 23 pairs of chromosomes About 35,000 genes About 1 million sites in the DNA that vary between individuals (most with no effect on phenotype)

6 Meiosis and Recombination Chromosomes pair upDNA replication Chiasmata form Recombination 1st cell division 2nd cell divisionGametes Result: meiosis generates new combinations of alleles

7 How much genetic variation? About 35,000 genes in humans If each gene has only 2 allelic forms (probably an underestimate), then: –Number of possible genotypes = 3 35,000 = Far more than all the atoms in the Universe! Essentially, we are all genetically unique (except identical twins)

8 Significance of genetic variation Some alleles directly cause rare genetic diseases e.g. Cystic fibrosis, sickle-cell anemia - called simple or Mendelian genetic disease Many alleles contribute to the risk (or liability) of getting a common disease with genetic component - called complex or multifactorial disease e.g. Cancer, heart disease, asthma, schizophrenia, diabetes (polygenes)

9

10 How can you tell its a disease gene? For simple genetic disease, can track the disease gene through affected families - called linkage analysis For complex disease, can test whether certain alleles are found more frequently in patients than in healthy controls - called genetic association

11 UnlinkedLinked Parents Gametes Offspring


Download ppt "Lecture 41 Prof Duncan Shaw. Genetic Variation Already know that genes have different alleles - how do these arise? Process of mutation - an alteration/change."

Similar presentations


Ads by Google