Genetics the study of hereditary variation © 2007 Paul Billiet  ODWS
Phenotype <ul><li>Organisms have characteristic appearances </li></ul><ul><li>These appearances may vary from one individu...
Variations <ul><li>Variations between organisms may be:  </li></ul><ul><li>interspecific  – variations between different s...
Nature or nurture? <ul><li>Variations may be influenced by what is inherited from the parents (the   genotype )  </li></ul...
Studying heredity   <ul><li>The Neolithic revolution   </li></ul><ul><li>Breeding from the animals or plants </li></ul><ul...
Pea plants for genetics <ul><li>Peas have many recognisable characteristics (e.g. seed shape) </li></ul><ul><li>They are e...
Pea plants for genetics <ul><li>Peas have hermaphroditic flowers </li></ul><ul><li>Self fertilisation is possible. </li></...
Mendel’s breeding experiments <ul><li>Taking one character only as an example,  seed colour </li></ul><ul><li>Parents  ( P...
The reciprocal cross <ul><li>Mendel tried the cross the other way round  </li></ul><ul><li>Green seed female plant x yello...
Dominant and recessive traits   <ul><li>The green seed coloured trait had disappeared but it reappeared in later generatio...
Selfing <ul><li>Mendel produced a second generation of plants using the first generation.  </li></ul><ul><li>He brushed th...
Selfing First generation  ( F 1 )   Second generation  ( F 2 )   © 2007 Paul Billiet  ODWS Yellow  seed producing plants S...
Selfing © 2007 Paul Billiet  ODWS All  green  seeds Pure breeding Selfed Selfed 66% produce a mixture of  yellow  &  green...
Pure breeding <ul><li>Those plants that only produce one type are called  pure breeding  (or true breeding) </li></ul>© 20...
The particulate theory of inheritance: Genes <ul><li>Mendel concluded from this and other similar experiments, that charac...
Genes and variation <ul><li>A character is controlled by a gene that may come in different types called allelomorphs (mean...
Symbols for genes <ul><li>Dominant alleles are given  CAPITAL CASE LETTERS </li></ul><ul><li>Recessive alleles are given  ...
Monohybrid inheritance <ul><li>The behaviour of the alleles controlling different traits revealed patterns in the way they...
The Law of Segregation <ul><li>Organisms seem to possess two genes for each character (they are  diploid ). This pair of g...
Mendel and meiosis <ul><li>Mendel worked this out in 1866  </li></ul><ul><li>Though he no doubt understood fertilisation, ...
Meiosis & Mendel <ul><li>Meiosis 1: Anaphase 1 </li></ul><ul><li>Maternal and paternal chromosomes segregate (pulled separ...
The Law of Segregation revisited <ul><li>Organisms seem to possess two genes for each character (they are  diploid ). This...
Combinations of genes   <ul><li>The combination of alleles in an individual is called the  genotype </li></ul><ul><li>If t...
<ul><li>In human genetics heterozygotes who have a dominant and a recessive allele are called  carriers </li></ul><ul><li>...
Genetic diagrams © 2007 Paul Billiet  ODWS 100% Proportions Yellow Genotypes Yy Phenotypes F 1 y y Y Y Gametes yy YY Genot...
Genetic diagrams <ul><li>Where there are several possible gametes a  Punnett square  should be used </li></ul>Selfed © 200...
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  1. 1. Genetics the study of hereditary variation © 2007 Paul Billiet ODWS
  2. 2. Phenotype <ul><li>Organisms have characteristic appearances </li></ul><ul><li>These appearances may vary from one individual to another </li></ul><ul><li>The characteristics shown by an organism is called its phenotype </li></ul><ul><li>(From the Greek phainein = to show and typos = type) </li></ul>© 2007 Paul Billiet ODWS
  3. 3. Variations <ul><li>Variations between organisms may be: </li></ul><ul><li>interspecific – variations between different species (e.g. tigers have stripes and leopards have spots) </li></ul><ul><li>intraspecific – variations within a species (e.g. blood type or height in humans) </li></ul><ul><li>It is intraspecific variations that concern us here. </li></ul>© 2007 Paul Billiet ODWS
  4. 4. Nature or nurture? <ul><li>Variations may be influenced by what is inherited from the parents (the genotype ) </li></ul><ul><li>Variations may be influenced by the environment the organism encounters as it grows and develops. </li></ul>© 2007 Paul Billiet ODWS Genotype (nature) Environment (nurture) Phenotype
  5. 5. Studying heredity <ul><li>The Neolithic revolution </li></ul><ul><li>Breeding from the animals or plants </li></ul><ul><li>Gregor Mendel </li></ul>http://history.nih.gov/exhibits/nirenberg/popup_htm/01_mendel.htm © 2007 Paul Billiet ODWS
  6. 6. Pea plants for genetics <ul><li>Peas have many recognisable characteristics (e.g. seed shape) </li></ul><ul><li>They are easy to cultivate </li></ul><ul><li>Their life cycle is reasonably short so results can be obtained quickly </li></ul><ul><li>Peas produce a large number of offspring (seeds), which makes results easier to verify </li></ul>http://www.ppdl.purdue.edu/PPDL/images/pisum-sativum.jpg © 2007 Paul Billiet ODWS
  7. 7. Pea plants for genetics <ul><li>Peas have hermaphroditic flowers </li></ul><ul><li>Self fertilisation is possible. </li></ul><ul><li>The male parts can be pulled out to emasculate the flowers, preventing self fertilisation </li></ul>jeantosti.com/fleurs4/pois.htm © 2007 Paul Billiet ODWS
  8. 8. Mendel’s breeding experiments <ul><li>Taking one character only as an example, seed colour </li></ul><ul><li>Parents ( P ) </li></ul><ul><li>First generation ( F 1 ) </li></ul>© 2007 Paul Billiet ODWS Female sex cells from a yellow -seeded plant Male sex cells in pollen from a green- seeded plant Cross fertilised ( crossed ) All seeds produced turned out yellow
  9. 9. The reciprocal cross <ul><li>Mendel tried the cross the other way round </li></ul><ul><li>Green seed female plant x yellow seed male plant </li></ul><ul><li>The same results were obtained </li></ul>© 2007 Paul Billiet ODWS
  10. 10. Dominant and recessive traits <ul><li>The green seed coloured trait had disappeared but it reappeared in later generations as though it were hidden </li></ul><ul><li>Traits that disappear and reappear (e.g. green seed colour in peas) are called recessive </li></ul><ul><li>Those that hide them are called dominant traits (e.g. yellow seed colour in peas) </li></ul>© 2007 Paul Billiet ODWS
  11. 11. Selfing <ul><li>Mendel produced a second generation of plants using the first generation. </li></ul><ul><li>He brushed the male pollen grains onto the female parts of the same flower </li></ul><ul><li>This is called self pollination and it leads to self fertilisation or selfing </li></ul>© 2007 Paul Billiet ODWS
  12. 12. Selfing First generation ( F 1 ) Second generation ( F 2 ) © 2007 Paul Billiet ODWS Yellow seed producing plants Selfed Yellow seeds 6022 Green seeds 2001 About 75% show the dominant trait About 25% show the recessive trait
  13. 13. Selfing © 2007 Paul Billiet ODWS All green seeds Pure breeding Selfed Selfed 66% produce a mixture of yellow & green seeds 33% produce yellow seeds only Pure breeding Yellow seeds 6022 Green seeds 2001 Second generation ( F 2 ) Third generation ( F 3 )
  14. 14. Pure breeding <ul><li>Those plants that only produce one type are called pure breeding (or true breeding) </li></ul>© 2007 Paul Billiet ODWS
  15. 15. The particulate theory of inheritance: Genes <ul><li>Mendel concluded from this and other similar experiments, that characters are controlled by factors (later called genes ) </li></ul><ul><li>These genes like separate particles, passed on from generation to generation </li></ul><ul><li>They are not changed or diluted to give intermediates </li></ul><ul><li>The gene is the unit of hereditary information </li></ul>© 2007 Paul Billiet ODWS
  16. 16. Genes and variation <ul><li>A character is controlled by a gene that may come in different types called allelomorphs (meaning “other forms”) or alleles </li></ul><ul><li>These different alleles produce the different traits in a character </li></ul><ul><li>In the above example </li></ul><ul><li>Pea seed colour is controlled by the seed colour gene </li></ul><ul><li>There are two alleles of this gene ( dialleleic ), the yellow allele and the green allele. </li></ul><ul><li>The yellow allele is dominant and the green allele is recessive. </li></ul><ul><li>About 30% of human genes are thought to be diallelelic </li></ul>© 2007 Paul Billiet ODWS
  17. 17. Symbols for genes <ul><li>Dominant alleles are given CAPITAL CASE LETTERS </li></ul><ul><li>Recessive alleles are given small case letters </li></ul><ul><li>Use letters that look different when written as small case and capital case (e.g. avoid C, O, P, S, U ) </li></ul>© 2007 Paul Billiet ODWS
  18. 18. Monohybrid inheritance <ul><li>The behaviour of the alleles controlling different traits revealed patterns in the way they are inherited </li></ul><ul><li>These patters always seemed to be the same so they are considered as a scientific law </li></ul><ul><li>If we only consider the inheritance of one character (e.g. seed colour) and ignore all the others (such as flower colour, seed shape etc) this is called monohybrid inheritance </li></ul>© 2007 Paul Billiet ODWS
  19. 19. The Law of Segregation <ul><li>Organisms seem to possess two genes for each character (they are diploid ). This pair of genes segregate (separate) when gametes are made (they are haploid) </li></ul><ul><li>Pairs of genes are reformed when the gametes fuse and they recombine in definite proportions (e.g. 75% to 25%) </li></ul>© 2007 Paul Billiet ODWS
  20. 20. Mendel and meiosis <ul><li>Mendel worked this out in 1866 </li></ul><ul><li>Though he no doubt understood fertilisation, meiosis was not observed until 30 years later </li></ul>© 2007 Paul Billiet ODWS
  21. 21. Meiosis & Mendel <ul><li>Meiosis 1: Anaphase 1 </li></ul><ul><li>Maternal and paternal chromosomes segregate (pulled separate on the spindle) </li></ul><ul><li>They move to opposite poles </li></ul>© 2007 Paul Billiet ODWS
  22. 22. The Law of Segregation revisited <ul><li>Organisms seem to possess two genes for each character (they are diploid ). This pair of genes segregate (separate) when gametes are made (they are haploid) </li></ul><ul><li>= meiosis </li></ul><ul><li>Pairs of genes are reformed when the gametes fuse and they recombine in definite proportions (e.g. 75% to 25%) </li></ul><ul><li>= fertilisation </li></ul>© 2007 Paul Billiet ODWS
  23. 23. Combinations of genes <ul><li>The combination of alleles in an individual is called the genotype </li></ul><ul><li>If the two alleles are the same it is homozygous </li></ul><ul><li>If the two alleles are different it is heterozygous </li></ul>© 2007 Paul Billiet ODWS
  24. 24. <ul><li>In human genetics heterozygotes who have a dominant and a recessive allele are called carriers </li></ul><ul><li>They are carrying a recessive allele without expressing it </li></ul><ul><li>Many genetic diseases are caused by recessive alleles </li></ul>© 2007 Paul Billiet ODWS Pure breeding Green Homozygous yy Yellow Heterozygous Yy Pure breeding Yellow Homozygous YY Phenotypes Genotypes
  25. 25. Genetic diagrams © 2007 Paul Billiet ODWS 100% Proportions Yellow Genotypes Yy Phenotypes F 1 y y Y Y Gametes yy YY Genotypes Green seed X Yellow seed Phenotypes P
  26. 26. Genetic diagrams <ul><li>Where there are several possible gametes a Punnett square should be used </li></ul>Selfed © 2007 Paul Billiet ODWS y Y Gametes 100% Proportions Yellow Genotypes Yy Phenotypes F 1 25% 75% Proportions: Green Yellow Phenotypes: yy Yy y Yy YY Y y Y Genotypes: F 2
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