* Your assessment is very important for improving the workof artificial intelligence, which forms the content of this project
Download 1st
Koinophilia wikipedia , lookup
DNA damage theory of aging wikipedia , lookup
Mitochondrial DNA wikipedia , lookup
Genomic imprinting wikipedia , lookup
Deoxyribozyme wikipedia , lookup
Gene expression profiling wikipedia , lookup
Minimal genome wikipedia , lookup
Cancer epigenetics wikipedia , lookup
Gene expression programming wikipedia , lookup
Biology and consumer behaviour wikipedia , lookup
Cell-free fetal DNA wikipedia , lookup
Human genetic variation wikipedia , lookup
Public health genomics wikipedia , lookup
Heritability of IQ wikipedia , lookup
Epigenetics of neurodegenerative diseases wikipedia , lookup
Extrachromosomal DNA wikipedia , lookup
Epigenetics of human development wikipedia , lookup
Nutriepigenomics wikipedia , lookup
Therapeutic gene modulation wikipedia , lookup
Non-coding DNA wikipedia , lookup
No-SCAR (Scarless Cas9 Assisted Recombineering) Genome Editing wikipedia , lookup
Vectors in gene therapy wikipedia , lookup
Cre-Lox recombination wikipedia , lookup
Genome evolution wikipedia , lookup
Oncogenomics wikipedia , lookup
Population genetics wikipedia , lookup
Genome editing wikipedia , lookup
Helitron (biology) wikipedia , lookup
Genetic engineering wikipedia , lookup
Dominance (genetics) wikipedia , lookup
Site-specific recombinase technology wikipedia , lookup
Artificial gene synthesis wikipedia , lookup
Genome (book) wikipedia , lookup
Designer baby wikipedia , lookup
Frameshift mutation wikipedia , lookup
History of genetic engineering wikipedia , lookup
Quantitative trait locus wikipedia , lookup
Genetic Variation Chapter 10 and 11 in the course textbook especially pages 187-197, 227-228, 250-255 Genetic Inheritance & Variation • No 2 organisms in a sexually reproducing species are the same (except “clones” or monozygotic twins) • Genetic variation is essential for evolution and change to occur • There are 2 main processes that generate variation: – Mutation – Recombination Mutation and Recombination • Mutation is a change in the genetic information • Recombination is a different arrangement of the same genetic material • The cat sat on the mat (1) • The bat sat on the hat – mutation (2) • The cat sat on the hat – recombination of 1 and 2 The main properties of DNA • The genetic material must be able to: – – – – Store information Replicate (when cells divide) Express information (as proteins) Mutate at a low frequency (less than 1 in a million) • DNA is a molecule that is very well suited to doing all 4 of these Mutation • Can occur in any cell at any time, cause may be: – Internal (e.g. mistakes during replication of DNA) – External (e.g. radiation, chemicals) • Most mutations have no effect (neutral) • A few mutations are harmful • A very few mutations are beneficial • Only harmful and beneficial mutations are acted on by natural selection • Mutations may be non-coding (not in part of gene that codes for protein - have no effect, or affect gene expression) or coding……. Effects of coding mutations • • • • • Synonymous: the cat ate the rat Missense: the fat ate the rat Nonsense: the cat ate the Frameshift: the cax tat eth era t Synonymous has no effect on protein, nonsense makes a smaller protein, missense/frameshift make incorrect protein Mutation during DNA replication • Replication of DNA is not perfectly accurate, but there are several ways to correct the mistakes ACGTACGTAACGTG... TGCATGCATTGAACGGT DNA polymerase makes about 1 mistake per 105 bp. DNA polymerase has a “proof-reading” activity to correct its own mistakes (99%). After DNA replication there is a “mismatch repair” system to correct remaining mistakes (99.9%). This leaves an overall error rate of about 1 base in 1010. Error correction in DNA replication • Overall error rate is about 10-10 per division • About 1 mistake per cell per division in humans Mutation due to environmental factors • Mutations may be caused by chemicals or radiation • Chemicals (“mutagens”) may disrupt hydrogen bonds between bases, by modifying them or getting between them • Radiation (including ultra-violet and radioactive emissions) can damage structure of bases • These agents may be natural or man-made Mendel’s experiments • Gregor Mendel (a 19th century Czech monk) worked out the basic laws of genetic inheritance by breeding pea plants • He chose simple characteristics that are determined by single genes (monogenic) • Many characters such as height, IQ, disease susceptibility are determined by several genes (polygenic) Mendel’s first cross P1 (parental) generation: wrinkled seeds crossed with smooth seeds F1 generation: all smooth seeds. Crossed with itself………... F2 generation: smooth and wrinkled in ratio 3:1 Mendel’s genetic hypothesis AA aa A A A a Genes come in pairs. Each of the parents has 2 copies of this gene. The “A” form gives smooth seeds, the “a” form gives wrinkled. a Parents produce gametes (eggs, sperm, pollen) which have 1 copy of the gene. Aa Fertilisation produces the F1 generation, all smooth because the “A” form is dominant over “a”; “a” is recessive a Each F1 plant produces equal numbers of A and a gametes which fertilise at random to produce the F2 plants. 1/4 of them are AA (smooth), 1/2 are Aa (smooth) and 1/4 are aa (wrinkled). Cross with two genes AABB AB aabb Ab aB ab AB AB ab Ab AaBb AB Ab aB ab 4 types of gametes in equal numbers aB ab 9/16 yellow/smooth 3/16 green/smooth 3/16 yellow/wrinkled 1/16 green/wrinkled Summary of Mendel’s experiments • Genes in an organism come in pairs • Some forms (“alleles”) of a gene are dominant over other alleles which are recessive • One (at random) of each pair of genes goes into a gamete (segregation) • Gametes meet randomly and fertilise • The numbers and types of offspring in a cross are determined by the above laws • Separate genes behave independently of each other (later, exceptions to this rule were found) Genes and chromosomes • Genes can have several different forms due to mutations in DNA sequence. These forms are called alleles. Property of having different forms is called polymorphism • Normal human body cells (“somatic” cells) are diploid: 23 pairs of chromosomes: – Numbers 1-22 (autosomes) – X and Y (sex chromosomes) – XX in females, XY in males • Gametes (eggs, sperm, pollen) are haploid, i.e. they have a single copy of each chromosome Phenotype, Genotype, Alleles • The phenotype of an organism is its observable properties • The genotype is the set of alleles it has for all of its genes (5,000 in bacteria; 35,000 in humans) • New alleles are created by mutation and their effect the phenotype may be dominant or recessive Modes of inheritance • Dominant alleles affect the phenotype when present in 1 copy (heterozygous), e.g. Huntington’s disease • Recessive alleles affect the phenotype only when present in 2 copies (homozygous), e.g. cystic fibrosis • Can tell whether dominant or recessive by studying Mode of Inheritance in families Autosomal dominant inheritance Person with trait in each generation Males and females equally likely to show trait Where 1 parent is heterozygous, about 50% of offspring show trait Example: Huntington’s disease Autosomal recessive inheritance •Trait may “skip” generations •Males and females equally likely to show trait •Heterozygotes (“carriers”) do not show trait •About 25% of offspring of 2 carriers will show trait •Example: cystic fibrosis X-linked recessive inheritance Carrier (heterozygous, unaffected) mothers pass the trait to about 50% of sons Trait is never transmitted from father to son In the population, trait will be much more common in males than females. Example: muscular dystrophy