Review of Simple Mendelian Genetics  Law of Segregation: each gene has two different alleles that are separated when gametes form  One allele goes to one gamete and the other allele to a different gamete  Law of Independent Assortment: genes for different traits are inherited independently from each other

Review of Simple Mendelian Genetics  Dominant vs. Recessive alleles for a gene  The dominant allele masks the recessive one, so you see the dominant trait (for RR or Rr)  The only way to see a recessive trait is to have two recessive alleles (rr)  Dominant allele is represented as a capital letter (R)  Recessive allele is represented as a lowercase letter (r)

Incomplete Dominance  Sometimes neither allele is fully dominant over the other  Incomplete Dominance: neither allele is dominant but combine and display a new trait that is a mixing of the two alleles

Incomplete Dominance RRR’R’ RR’ RR RR’ R’R’

Incomplete Dominance  In incomplete dominance, the two alleles are represented as  Two capital letters, one with an apostrophe to indicate the different allele that is involved  Ex. R (for the red allele) and R’ (for the white allele)  When these two alleles come together, they portray a mixing of the two phenotypes!

Codominance  Other times both alleles are fully dominant  Codominance: both alleles of a gene are dominant and the heterozygous phenotype has both traits equally expressed

Codominance x BBWW BW

Codominance Winter xgames?  In codominance the two alleles are represented as  Two capital letters: Use the first letter of one trait (B for Brown) and the first letter of the other trait (W for White)  When they come together as a heterozygote, both traits show as the phenotype

Let’s Stop and Think…  Let’s say there are two alleles for the hair color trait- red and blue  What would be the resulting phenotype of a heterozygous pair if the alleles showed codominance?  A. Red  B. Blue  C. Purple  D. Red and Blue patches  Let’s say there are two alleles for the hair color trait- red and blue  What would be the resulting phenotype of a heterozygous pair if the alleles showed codominance?  A. Red  B. Blue  C. Purple  D. Red and Blue patches

Multiple Alleles  Sometimes there are more than two alleles that govern the phenotype of a trait  Multiple Alleles: the presence of more than two alleles for a genetic trait

Multiple Alleles  Blood Type  Human blood type is governed by the presence of 3 different alleles: AA BB OO  However, each person only has 2 of these 3 alleles in their DNA

ABO Blood Type  Blood types follow both Codominant and simple Dominant inheritance  The A allele and B allele are codominant with each other  The A allele and B allele are both purely dominant over the O allele  The O allele is recessive

Which blood type are you if you have…  AA  Type A blood  BB  Type B blood  AB  Type AB blood  AO  Type A blood  BO  Type B blood  OO  Type O blood

ABO Blood Types  The blood type gene and alleles are represented differently than you have seen before  The blood type gene is I  For this I gene you can have the following alleles:  For A: I A  For B: I B  For O: i

Let’s stop and think…  What are the two allele combinations you can have for type A blood?  I A I A and I a i  What are the two allele combinations you can have for type B blood?  I B I B and I B i

Let’s Stop and Think…  What is the only allele combination you can have for type AB blood? IAIBIAIB  What is the only allele combination you can have for type O blood?  ii

Sex-Linked Traits  genes which are carried only on the sex chromosomes  ex: red green color blindness  2:25 males  1:150 females

Sex-Linked Traits  Traits are usually not seen in women because it can be masked by another dominant gene on the other X-chromosome  Female – X B X b  Male – X b Y  But it is possible for it to happen in women!

Color Blindness Test Can you see the letters and numbers in these squares?

Hemophilia

Polygenic Inheritance  Sometimes traits are carried on more than one gene, making it difficult to tell if it’s dominant or recessive  Examples: Skin color, height, body mass

Polygenic Inheritance  There’s often a wide range of phenotypes: you can be anywhere from 5’ to 7’ tall, there is no tall or short in humans!

Human Height It’s often hard to tell where a person might get their height from

Multiple Genes  In this pattern there is more than one gene responsible for a single trait  Makes it possible for many types of genotypes and phenotypes  Continuous variation

With simple patterns of inheritance like dom/rec, co-dominance and incomplete dominance you may only get a few phenotypes and each is distinct from one another. Imagine people with only these skin colors It’s very easy to distinguish each phenotype

When there are multiple genes involved with a single trait you can expect more of a continuum of variation. This is more representative of human skin color

Sorry Smurfs!