1 / 35

Refresh of Mendelian Genetics

Refresh of Mendelian Genetics. Who was Gregor Mendel?. He was monk living in a monastery in Czechoslovakia in mid-1800’s. He was in charge of the monastic vege garden. He did breeding expt on peas. He cultivated ~29,000 peas plants!! …..his data was meticulously recorded.

jaimie
Download Presentation

Refresh of Mendelian Genetics

An Image/Link below is provided (as is) to download presentation Download Policy: Content on the Website is provided to you AS IS for your information and personal use and may not be sold / licensed / shared on other websites without getting consent from its author. Content is provided to you AS IS for your information and personal use only. Download presentation by click this link. While downloading, if for some reason you are not able to download a presentation, the publisher may have deleted the file from their server. During download, if you can't get a presentation, the file might be deleted by the publisher.

E N D

Presentation Transcript

  1. Refresh of Mendelian Genetics

  2. Who was Gregor Mendel? • He was monk living in a monastery in Czechoslovakia in mid-1800’s. • He was in charge of the monastic vege garden. • He did breeding expt on peas. • He cultivated ~29,000 peas plants!! …..his data was meticulously recorded. • The amount of data is what makes his findings so reliable.

  3. Thanks to Mendel…. We know about words like…. • Homozygous dominant and recessive • Heterozygous • Genes • Alleles • Genotype • Phenotype • Mendel’s laws…. YOU WOULD HAVE LEARNT THESE TERMS LAST YEAR To see what you can remember.... Match and paste...

  4. Review • Chromosome structure • Gene – unit of inheritance – segment of DNA • Alleles • 2 versions of a gene (alleles) • Dominant, recessive • Alleles separated in the formation of gametes • Each gamete carries one allele for each pair • At fertilisation there is random uniting of gametes

  5. Monohybrid crosses • You learnt about these in Y11 science…. • They are genetic crosses of just one trait. • Punnet squares have 4 squares.

  6. Test Cross • An individual that displays a dominant trait can either be homozygous dominant or heterozygous • Eg. Straight thumb (H) is dominant to hitchhikers thumb (h) How do we tell if a straight thumbed individual is homozygous dominant or heterozygous?

  7. DO NOW • Tongue rolling (T) is dominant to non-tongue rolling (t). A tongue roller and non-tongue roller had children and produced tongue rollers and non-tongue rollers as children. • What were the genotypes of the parents? • Draw a punnet square to show possible off spring combinations.

  8. Incomplete Dominance • Sometimes alleles are not completely dominant over another allele. • Example: A red snapdragon flower crossed with a white flower could create a pink offspring. • F1 are all heterozygous. • Self-crossed F2 yields a ratio of: 1 : 2 : 1 Red: Pink: White

  9. Codominance • The heterozygous genotype shows both traits. • Example: BB = Black spotted cat bb = orange spotted cat Bb = Black and orange spotted cat Ratio 1 : 2 : 1 Black : Black+Orange : Orange • BLOOD GROUPS ALSO SHOW CODOMINANCE

  10. Lethal Alleles • Alleles which cause death when occurring as one of the homozygous genotypes • These cause death at embryo stage and so the ratio is 1:2 • Example: Achondroplastic dwarfism… 1 : 2 : 1 AA : Aa : aa Died:Dwarf:Normal

  11. Types of Explanations • Dwarfism is a result of autosomal dominantmutation in the fibroblastgrowth factorreceptor gene 3 (FGFR3), which causes an abnormality of cartilage formation. In normal circumstances, FGFR3 has a negative regulatory effect on bone growth. In achondroplasia, the mutated form of the receptor is constitutively active and this leads to severely shortened bones.

  12. Multiple Alleles • More than one allele can be positioned at a gene loci (address) • Example: Blood groups in people….. The protein's structure is controlled by three alleles; i, IA and IB. The first allele is, i, the recessive of the three, and IA and IB are both co-dominant when paired together

  13. Explanation • A and B are co-dominant and both are dominant to O….so O is recessive. • I is the allele that makes the antigen. • The antibody causes foreign antigens to clump together.

  14. Multiple alleles • Wool Fibre Diameter – B2A gene • A finest wool • B • C thickest wool • Another wool fibre gene KRT 1.2 • Wool protein • Many alleles

  15. Dihybrid Cross • A cross between two organisms where the inheritance patterns of TWO GENES are studied • There are a greater number of gamete types produced when two genes are considered • The genes are carried by separate chromosomes and are sorted independently of each other (WE WILL COVER THIS POINT SOON!)

  16. Dihybrid Crosses • Answer questions • Dihybrid Easy • More difficult dihybrid • Problems in

  17. Back of books 1-10 • Definitions

  18. Sex Linkage • Genes located on one sex chromosome but not on the other are called sex-linked genes. • The traits that show this kind of inheritance are almost always carried on the X chromosome • Examples: red-green colour blindness, haemophilia,

  19. Thought to be Y linked!!

  20. Sex-Linked Genes • For males, any sex linked gene on the X chromosome will show up because the Y has no matching gene to mask the effect • In females (having two X’s) the effect usually is masked – however they are ‘carriers’ (we will make sense of this statement!!)

  21. Example • A woman with normal vision whose father was colour- blind marries a man who is colour blind. Give the possible phenotype and genotype of such a cross. C = normal c = colour blind

  22. Homework • Research the genetics of tortoisehell cats and hand to me tomorrow on a separate piece of paper

  23. Mendels Laws • Mendel’s law of segregation – ‘of the two genes controlling each characteristic, only one is present in each gamete’. • Mendel’s law of Independent Assortment – ‘the segregation of one pair of alleles does not affect the segregation of another pair’

  24. Mendels Laws • The Law of Segregation states that the members of each pair of alleles separate when gametes are formed. A gamete will receive one allele or the other.

  25. Law of Segregation • the pair of alleles of each parent separate and only one allele passes from each parent on to an offspring • which allele in a parent's pair of alleles is inherited is a matter of chance  • segregation of alleles occurs during the process of gamete formation (meiosis) • randomly unite at fertilization

  26. Law or Independent Assorment • The Law of Independent Assortment: As chromosome pairs line up, each chromosome pair is sorted independently. Which chromosome of each pairs ends up in which cell is random = produces different combinations of parents chromosomes in gametes. • The Law of Segregation states that the members of each pair of alleles separate when gametes are formed. A gamete will receive one allele or the other.

  27. Law of Independent Assortment • During meiosis the homologous chromosomes line up at the equator of the spindle in pairs during Metaphase 1. • How they line up provides the basis for Independent Assortment.

  28. Independent assortment • http://www.sumanasinc.com/webcontent/animations/content/independentassortment.html

  29. 2 chromosome pairs alignment

  30. Exam question(2008) • During the process of meiosis, independent assortment and crossing over (recombination) can occur. This results in genetic variation in the offspring of sexually reproducing individuals • Describe what happens during independent assortment • Explain how crossing over (recombination) can contribute to the genetic variation that results from sexual reproduction. You may wish to draw a diagram. • Genetic variation can be a results from mutation. Explain the results of mutation sin somatic and gametic cells

More Related