2. MORE GENE INTERACTIONS Slide 2RecombinationRecombination Slide 3Chromosome MappingChromosome Mapping Slide 4Sex LinkageSex Linkage Slide 5Cats and CodominanceCats and Codominance Slide 6Other work…Other work… Slide 7Pleiotropy and PolygenyPleiotropy and Polygeny Slide 8Epistasis - ComplementaryEpistasis - Complementary Slide 9Epistasis - SupplementaryEpistasis - Supplementary Slide 10CollaborationCollaboration

3. Even if genes are linked you still may find offspring where the linked genes have separated. This is called Recombination. It obviously increases variation. The further the two genes are from each other on the chromosome, the greater the chance that they will be separated during crossing over. RECOMBINATION Recombinants AA A BB B a a a b b b Expected gamete A B B a A b a b Lab manual page 109

4. CHROMOSOME MAPPING The further apart the genes are the more likely they will be to cross over. This allows us to be able to “map” the chromosome based on the frequency that the genes separate. Crossover value (%) = No. of recombinants No. of offspring  100 If we compare the crossover values for genes on the same chromosome we can get comparative distances, hence, map the chromosomes. See the page below for examples. Lab manual page 110-111

5. XY System  Humans, fruit flies have a pair of sex chromosomes, XY, for determination of one’s sex.  Sperm determines sex.

6. XO & ZW SYSTEM & CHROMOSOME # SYSTEMS

7. XO System Grasshopper, crickets. “O” stands for absence of chromosome. Sperm determines sex. ZW System Birds. Egg determines sex. Sex determination by chromosome # Ants, bees lack sex chromosome. Sex determined by chromosome number (autosomes). Females develop from fertilized eggs (diploid). Males develop from unfertilised eggs (haploid), fatherless.

8. SEX LINKAGE The disease is recessive. The gene X is normal, while Xc is colour blind. Y carries no information. Note: Sex-linked genotypes tend to use X something to indicate that it is carried on the X. So…XX is a normal female What other possibilities can you have? Explain why it is less common for women to be colour blind. Lab manual page 118-119 XcX = normal femaleXcXc = colour blind female XY= normal maleXcY= colour blind male Some genes are carried on the X-chromosome (called sex-linked instead of autosomal). This means that males have only one allele for that gene while females have two. A classic example is colour blindness. Have a look at this picture. DO NOT SAY WHAT YOU SEE.

9. CATS In cats one aspect of coat colour is controlled by a sex-linked gene with alleles that are codominant. These 2 females (XoXo) and (XbXb) are crossed with a male (XbY)… Draw Punnett squares to find the offspring of each cross. What is the XbXo offspring called? How do we get male Tortoiseshell? Klinefelters!

10. SOME OTHER WORK A summary comparison of different types of inheritance mechanisms: Autosomal Dominant Autosomal Recessive Sex-linked Dominant Sex-linked Recessive A way to show a number of generations of individuals and how they are affected by a specific trait is a pedigree chart. Males Females Dead Affected (but not dead – yet) Normal

11. GENE-GENE INTERACTIONS Pleiotropy :One gene (  one protein) controls many phenotypes e.g. The Hawaiian happy spider (why’s it called that?) Each leg of a pair is affected by the same gene  they are the same length. Leg pair Cheesy grin! Polygeny : Many genes control one phenotype (e.g. Human skin colour) Lab manual page 130

12. Tyrosinase Melanin a series of enzymes Thyroxine Tyrosine Protein Phenylalanine hydroxylase Phenylalanine essential amino acid Trans- aminase Hydroxyphenylpyruvic acid Errors in Metabolism 1 The faulty metabolism of phenylalanine is associated with various disorders, depending on which step in the metabolic pathway is affected: Phenylpyruvic acid Phenylketonuria This in turn causes Faulty enzyme results in buildup of Mental retardation, 'mousy’ body odor, light skin color, eczema, excessive muscular tension and activity. Faulty enzyme causes Albinism Complete lack of the pigment melanin in body tissues, including the skin and hair Faulty enzymes cause Cretinism Dwarfism, mental retardation, low levels of thyroid hormones, retarded sexual development, yellow skin color. (PKU)

13. Epistasis (supplementary) :One gene alters the outcome of the phenotype of another SubstanceProduct AProduct B E n z y m e 1 E n z y m e 2 If Enzyme 2 is bung we’ll only get product A. If Enzyme 1 is bung we’ll get nothing, no matter what Enzyme 2 is doing. What will the genotype ratio be for this cross? Try him. 9:7 Mad! Think 9:3:3:1, but group the last 3 sets. PPccppCC PpCc Parental F1 PC Pc pC pc PCPcpCpc F2 Complementary genes: Both need to be present for either to work.

14. Supplementary genes (epistasis): the second gene adds more to the first. Coat color in Labrador retrievers is controlled by two genes (B and E). At least one dominant allele for both genes is required to produce a black dog (B_E_). a.What are the genotypes of two black parental dogs that, when mated, produce black puppies, yellow puppies and brown puppies? b. What proportions of black and yellow puppies do you expect from this cross? c. This cross is an example of a what type of gene interaction? Dogs homozygous for the recessive allele b that have at least one dominant E allele (bbE_) are brown and dogs homozygous recessive for E (ee) are always yellow. Lab manual page 132/3

15. COLLABORATION This is where 2 genes interact to make a product different to that which either could make independently. The most common example is comb types in chickens. Lab manual page 129 See more chickens…