Multi-Gene Inheritance

Warmup What are the odds of pulling an Ace out of a deck of cards? What are the odds of pulling a spade? What are the odds of pulling the Ace of Spades?

Multiplication Rule Odds of two events both happening = odds of one x odds of another

Addition Rule Odds of one of two events happening is odds of one + odds of other E.g. odds of pulling a heart or diamond = ¼ + ¼ = 1/2

Genes on Different Chromosomes Are inherited independently, due to independent assortment during meiosis

Use Multiplication Rule to Solve Crosses of Several Genes What are the odds two AaBb parents will have an aabb child? Odds of being aa = ¼, odds of being bb=1/4, odds of being aabb =1/4*1/4 = 1/16

On Whiteboard What are odds AaBbDd dad and aaBbDD mom have a child expressing the dominant phenotype in all 3 genes?

Option 2 – If You Don’t Like Multiplication Make table with all the possible sperm x all the possible eggs AaBbDD x aaBBDd ABD AbD aBD abD ABd

On Whiteboard Draw a cross representing AaBbDd x AaBBdd What are odds of offspring showing dominant phenotype in all 3 traits? What are the odds of having a child with the identical genotype to one parent? Double check with multiplication

Additional Practice + and – represent a secondary blood protein called the Rh factor, with + coding for the protein and – not. + is dominant to -. What are the odds a man with AB+- and a woman with O- have a child with A+ blood?

BUT what about genes on the same chromosome? Called linked genes The alleles on a chromosome tend to be inherited together DRAW out the chromosomes and draw crosses based on that

Practice A/a and B/b genes are linked AABB man mates with an aabb woman. Their children are separated at birth and end up marrying each other and having children. Draw the cross showing the possible genotypes of their grandchildren

More Practice AaBbDd man and AaBbDd woman have lots and lots of children. Half of them show the dominant phenotype in all 3 genes. One quarter of them show the dominant phenotype in A and D only, while the remaining quarter the show the dominant phenotype in B only. Draw the chromosomes of the parents

More Challenging Practice A white-eyed straight winged fly is crossed with a red-eyed curly winged fly. All of the offspring are white-eyed and curly winged. These offspring are then mated with red-eyed straight-winged flies. The resulting F2 generation are half white-eyed curly-winged, one quarter red- eyed curly-winged and one quarter white- eyed straight-winged Draw the chromosomes for all 3 generations and the crosses that explain the outcome

More Complicating Factor An AaBb fly is crossed with an aabb fly. They produce the following offspring: Why? Dominant in Both Recessive in Both Dominant in A only Dominant in B only % of offspring 45 5

Crossing Over Can be used to figure out the order of genes on a chromosome The closer 2 genes are on a chromosome, the less likely crossing over occurs between them

E.g. In the case before, the recombination frequency between A and B is 10% AaCc x aacc Recombination frequency is 30% Dominant in Both Recessive in Both Dominant in A only Dominant in B only % of offspring 45 5 Dominant in Both Recessive in Both Dominant in A only Dominant in C only % of offspring 35 15

On Whiteboard The recombination frequencies between two genes are shown below for 5 genes on a single chromosome. Order the genes on the chromosome AB – 15% AC – 5% AD – 40% AE- 10% BC – 20% BD - 25% BE - 5% CD- 45% DE-30%

What Would a Recombination Frequency of 50% mean? AaBb x aabb Genes are un-linked, or on separate chromosomes Dominant in Both Recessive in Both Dominant in A only Dominant in B only % of offspring 25