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Human Traits – DISCRETE DEFINED OUTCOMES (one or the other) Controlled by a SINGLE GENE Dominant or recessive

Human Traits – DISCRETE (one or the other) Tongue Roll ROLL = DOMINANT NON ROLL = recessive

Human Traits – DISCRETE (one or the other) Eye Pigment **NOT COLOUR SPECIFIC** PIGMENT = DOMINANT (green, brown, black) NO PIGMENT= recessive (blue, grey)

Human Traits – DISCRETE (one or the other) Ear lobe attachment FREE = DOMINANT ATTACHED= recessive

Human Traits – DISCRETE (one or the other) Mid-digital hair HAIR = DOMINANT NO HAIR= recessive

IS Height DiScrete??

Polygenic Traits Occurs when more than one gene controls the expression of the trait The expression of one gene may depend on the expression of another ie. interaction between many genes EXAMPLES in HUMANS Height, skin colour, eye colour, intelligence

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ALL OF THIS INCREASES VARIATION ALONG THE CONTINUUM Polygenic traits Are NON – DISCRETE (expressed along a continuum) Genes can have multiple alleles, be co-dominant, incompletely dominant and/or affected by environment ALL OF THIS INCREASES VARIATION ALONG THE CONTINUUM

Epistatic Genes Some genes mask the expression of other genes, similar to dominant and recessive alleles (dominant masks effect of recessive) The gene that masks the effect of another gene is an epistatic gene Sometimes they create a new phenotype Does NOT produce the “normal” phenotypic ratios

Epistatic Genes Coat colour in dogs provides an example of epistatic genes. As shown in the Punnett square, the allele B produces black coat-colour, while the recessive allele b produces brown coat-colour. However, a second gene also affects coat-colour. The allele W of this second gene prevents the formation of pigment, thereby preventing colour. The recessive allele w does not prevent colour. The genotype wwBb would be black, but the genotype WwBb would appear white. The W allele masks the effect of the B colour gene. In humans, the gene responsible for albinism is epistatic. This gene interferes with the expression of genes that determine pigment formation in the skin, hair, and eyes

Environment and Phenotype Certain environmental factors can control the expression of certain traits Every CELL in the body has identical DNA, but the EXPRESSION of that DNA differs depending on environmental conditions!!

Environment and Phenotype Examples Himalayan Rabbits and Siamese Cats Pigment is expressed ONLY in cells BELOW a certain temperature GARY

Environment and Phenotype Examples Freckles Sunshine causes freckle phenotype to develop

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Sex – Linked Traits Genes located on sex xsomes are called sex-linked On X or Y xsome Ex. Gene for hairy ears – on Y xsome!! Many are located on the X xsome Male – XY Female – XX X – linked show up MORE in MALES – why??

Sex linked Traits Dominant = R Recessive = r Notation FEMALE MALE XR XR XR Xr MALE XRY XrY

Inheritance Males can only pass on Y-linked traits to their SONS Females can be carriers of a recessive allele – MALES CANNOT

Example

Barr Bodies Every FEMALE body cell has only ONE functioning X xsome The INACTIVE X xsome is condensed into a BARR BODY (totally random) Why do you think this happens? HINT – think about AMOUNT of DNA in males vs females

Example – Calico or Tortoiseshell Cats Alleles for Black and Orange fur Visible effects can be seen in HETEROZYGOUS females

Inheritance Patterns – important in pedigree analysis Autosomal Dominant Disease or disorder is carried on the DOMINANT ALLELE (only need ONE dominant allele to exhibit) Autosomal Recessive Disease or disorder is carried on the RECESSIVE ALLELE (must be homozygous recessive to exhibit) Sex-linked Dominant or recessive** NOTATION X X and X Y

HELPFUL HINTS READ QUESTIONS CAREFULLY!!! WRITE DOWN YOUR VARIABLES!!! Type of inheritance guides notation ONLY use XX, XY notation when SEX LINKED!!!! Don’t just assume because it says a man and woman have a child that it is sex linked INHERITANCE: Dominant/recessive Multiple Alleles (blood types, hierarchy) Codominance and Incomplete dominance Polygenic traits Epistatic genes Sex-linked 3 types of inheritance PATTERNS (show up in PEDIGREE) AUTOSOMAL (dominant and recessive) SEX-LINKED READ QUESTIONS CAREFULLY!!! WRITE DOWN YOUR VARIABLES!!! PRACTICE PRACTICE PRACTICE!!!

YAY – we’re done!!! (types of inheritance…)