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Cambridge Pre-U Biology - 1.6 Genes and Protein Synthesis PART 2 Sample

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This is a widescreen fully animated and editable PowerPoint presentation that covers the second half of section 1.6 of the Cambridge Pre-U Biology course.

It is 72 slides long and covers the following topics:

Genetics terminology
Inheritance
Monohybrid crosses
Codominance
Test cross
Dihybrid cross
Multiple alleles
Sex linkage
autosomal linkage
Mutations
DNA repair
Cancer

The full PowerPoint can be downloaded from mrexham.com

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Cambridge Pre-U Biology - 1.6 Genes and Protein Synthesis PART 2 Sample

  1. 1. MAKING SENSE OF Icons CC – The Pink Group Copyright©2017HenryExham Icons CC – The Pink Group Copyright©2017HenryExham
  2. 2. MAKING SENSE OFMAKING SENSE OF Gene expression Variation Inheritance 2 Mutations The genetic code and protein synthesis PART1PART2
  3. 3. Copyright © 2017 Henry Exham h) Define and use the terms allele, locus, phenotype, genotype, dominant, recessive and codominant. i) Use genetic diagrams to solve dihybrid crosses, including those involving sex linkage, autosomal linkage, epistasis, codominance and multiple alleles. j) Use and interpret the chi-squared test to test the significance of the difference between observed and expected results. 3
  4. 4. Copyright © 2017 Henry Exham • So you have already studies the structure and function of DNA, this is called molecular genetics. • But in this section you will study the transmission of DNA between whole organisms which is know as Mendelian genetics after Gregor Mendel (1822-1884) who was the monk turned scientist that pioneered this area of biology. 4
  5. 5. Copyright © 2017 Henry Exham • In order to be able to explain how genes are passed on you need to understand all the necessary vocabulary first. • When answering questions its very important to use these terms correctly and also to set out any genetic problems in a very specific way which will be explained later in this PowerPoint. 5
  6. 6. Copyright © 2017 Henry Exham 6By Emw - Own work, CC BY-SA 3.0, https://commons.wikimedia.org/w/index.php?curid=8025119 Your normal body cells contain 23 homologous pairs of chromosomes. Here is one pair. The position of each gene on a chromosome is called its locus. The genes at the same loci on each chromosome will code for the same trait but they may be different versions (alleles). The combination of alleles for a particular trait is called the person’s genotype. In this case this person has one of each allele for this gene and so they are called heterozygous, and the genotype is Aa. As ‘A’ is dominant over ‘a’ (shown by capital letter) then this allele is the one expressed in the phenotype. A a t t Cw CR The person is homozygous recessive for this particular trait and their genotype will be tt Sometimes one allele isn't dominant over the other and they can both contribute to the phenotype, these alleles are codominant.
  7. 7. Copyright © 2017 Henry Exham • You need to be able to understand and work out the following types of genetic cross: 7 One gene for one characteristic (a monohybrid cross) • Two alleles, dominant and recessive e.g. T,t • Two alleles, codominant e.g. CR, CW. • Multiple (more than two) alleles, e.g. IA, IB, IO • Sex linkage: the gene is on the X chromosome so males only have a single copy e.g XHXh x XHY- Two genes for two characteristics (a dihybrid cross) • Two genes on different chromosomes • Two linked genes on the same non-sex chromosome (“autosome”) Two genes for one characteristic (epistasis / interaction) • Epistasis: one gene masks (is “epistatic” to) another e.g. in mouse fur colour. • Interaction: phenotype is determined by the combination of dominant and recessive alleles of two genes. • We will now go through these one at a time using specific examples.
  8. 8. Copyright © 2017 Henry Exham • Lets start with the easiest one, this should be revision. • A monohybrid cross is the inheritance pattern for a single gene. • Here is an example: 8 • The allele for brown is dominant and blue is recessive. • A man is heterozygous for brown eyes and he mates with a woman who is heterozygous for brown eyes, what percentage of their children will have blue eyes? Parents Genotype: Parents Phenotype: Parents gametes: F1 genotypes: F1 phenotypes: Brown Brownx Bb x Bb Father Mother 1 x BB, 2 x Bb, 1 x bb ¾ Brown ¼ Blue BB Bb Bb bb B bB bB b B b
  9. 9. Copyright © 2017 Henry Exham 9 • Good examples include the genetic diseases of cystic fibrosis and Huntington's disease. • Cystic fibrosis is a recessive condition where as Huntingdon's is caused by a dominant allele. ByOpenStaxCollege-Anatomy&Physiology,ConnexionsWebsite. http://cnx.org/content/col11496/1.6/,Jun19,2013.,CCBY3.0, https://commons.wikimedia.org/w/index.php?curid=30148626
  10. 10. Copyright © 2017 Henry Exham 10 • You should know that the first level of offspring from the parents is called the F1 generation and the second is called F2. • This example shows true-breeding (homozygous recessive) pea plants that produce either yellow or green seeds which are bred together. • The F1 generation are all yellow in phenotype but still carry the recessive green allele. • When these F1 offspring are bred together with each other the green phenotype is shown again in the F2 generation. ByCNXOpenStax-http://cnx.org/contents/GFy_h8cu@10.53:rZudN6XP@2/Introduction,CCBY4.0, https://commons.wikimedia.org/w/index.php?curid=49926348
  11. 11. Copyright © 2017 Henry Exham 11 • Geneticists use pedigree charts to show the family history of a genetic condition. • You should know how to interpret one. • Can you work out genotypes of the individuals labeled 1,2 and 3? Imagecredit“ThePunnettsquareapproachforamonohybridcross:Figure3,"byOpenStaxCollege,Biology(CCBY3.0). Alkaptonuria is a recessive genetic disorder in which two amino acids, phenylalanine and tyrosine, are not properly metabolized. Affected individuals may have darkened skin and brown urine, and may suffer joint damage and other complications.
  12. 12. Copyright © 2017 Henry Exham 12 • Where alleles show dominance it is not always possible to to tell the genotype of an organism. • For example the yellow pea seed could have either YY or Yy as its genotype. • In order to work out what it is, you would do a test cross. • This is when you cross the unknown individual with a known genotype, usually homozygous recessive. • Looking at the offspring will tell you what the genotype of the parent is. ByKatieAnn127-Ownwork,CCBY-SA4.0,https://commons.wikimedia.org/w/index.php?curid=37309605
  13. 13. Copyright © 2017 Henry Exham 13 One gene for one characteristic (a monohybrid cross) • Two alleles, dominant and recessive e.g. T,t • Two alleles, incomplete and codominant e.g. CR, CW. • Multiple (more than two) alleles, e.g. IA, IB, IO • Sex linkage: the gene is on the X chromosome so males only have a single copy e.g XHXh x XHY- Two genes for two characteristics (a dihybrid cross) • Two genes on different chromosomes • Two linked genes on the same non-sex chromosome (“autosome”) Two genes for one characteristic (epistasis / interaction) • Epistasis: one gene masks (is “epistatic” to) another e.g. in mouse fur colour. • Interaction: phenotype is determined by the combination of dominant and recessive alleles of two genes
  14. 14. Copyright © 2017 Henry Exham 14 • So as already discussed one allele can be dominant over another. But sometimes both alleles actually contribute to the phenotype neither one is fully dominant over the other. Notice carefully that in codominance both have alleles have capital letters and are shown as superscript.
  15. 15. Copyright © 2017 Henry Exham To download the whole presentation visit www.MrExham.com
  16. 16. This PowerPoint is protected under copyright. It is designed for educational use. Either personal study or to be presented to a class. It may be edited or duplicated for these purposes only. It must not be shared or distributed online in any format. Some images used are under a separate creative commons license, these are clearly marked. Copyright © 2017 Henry Exham Brought to you by MrExham.com

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