MORE GENE INTERACTIONS

1. MORE GENE INTERACTIONS Slide 2 Recombination Slide 3 Chromosome Mapping Slide 4 Sex Linkage Slide 5 Cats and Codominance Slide 6 Other work… Slide 7 Pleiotropy and Polygeny Slide 8 Epistasis - Complementary Slide 9 Epistasis - Supplementary Slide 10 Collaboration

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

3. No. of recombinants Crossover value (%) =  100 No. of offspring 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. 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

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

5. XO & ZW SYSTEM & CHROMOSOME # SYSTEMS

6. 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.

7. SEX LINKAGE Note: Sex-linked genotypes tend to use Xsomething to indicate that it is carried on the X. 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. The disease is recessive. The gene X is normal, while Xc is colour blind. Y carries no information. So… XX is a normal female What other possibilities can you have? Explain why it is less common for women to be colour blind. XcX = normal female XcXc = colour blind female XY = normal male XcY = colour blind male Lab manual page 118-119

8. 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!

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

10. GENE-GENE INTERACTIONS Cheesy grin! 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 Polygeny: Many genes control one phenotype (e.g. Human skin colour) Lab manual page 130

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

12. PC Pc pC pc F2 Parental PPcc ppCC PC Pc PpCc F1 pC pc Epistasis (supplementary): One gene alters the outcome of the phenotype of another Substance Product A Product B Enzyme 1 Enzyme 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. Complementary genes: Both need to be present for either to work. 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.

13. 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_). 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. • 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? Lab manual page 132/3

14. 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. See more chickens… Lab manual page 129