PEDIGREES

aa

aa aa aa

aa

aaAa Aa

Aa

Aa

AA or Aa

RECESSIVE PEDIGREE

MULTIPLE GENE INHERITANCE

With a fancy background

WARMUPW

hat are the odds of rolling a 6 on a die and pulling an Ace out of a standard deck of 52 cards?

W

hat are the odds of rolling a 6 on a die OR pulling an Ace out of a standard deck of 52 cards?

W

hat are the odds of rolling two die and having a total of 12?

W

hat are the odds of rolling two die and having a total of 11?

WHEN MULTIPLE GENES ARE INHERITED

T

hey are inherited independently of each other*• *with one major exception

S

o we can muse multiplication and addition rules

the same way you did on the warmups

PRACTICE

W

hat are the odds that two parents with the genotype

AaBb mate and have children that express the

dominant phenotype in both traits?

MORE PRACTICE

I

f an AaBbDd parent mates with an AAbbDd parent,

what are the odds the offspring will have the

genotype AABbdd?

SLIGHTLY HARDER PRACTICE

A

n AabbDd man and a aaBbDd woman mate. What are

the odds they have a child with the same genotype

as either one of them?

OTHER WAY TO SOLVE

D

raw a cross of all the possible sperm x all the

possible eggs

D

raw a cross for AaBb x AaBb

EXAMPLE – BLOOD TYPES

I

A, IB dominant to I

+

dominant to – (++ or +- will exhibit + blood)

I

f an individual with AB- blood mates with someone with

BO+- blood, what are the odds they have a child with A+

blood

WHAT 2 PARENTS COULD PRODUCE A CHILD WITH EVERY POSSIBLE BLOOD TYPE? SHOW THE

CROSS

EXAMPLE – EYE COLORF

or the most part, eye color is controlled

by 2 genes on separate chromosomes

I

n gene 1 brown is dominant to not brown.

If the offspring has the brown allele the

second gene is irrelevant

I

n gene 2 green is dominant to blue. This

only matters if the individual is bb in the

first gene

EYE COLOR PRACTICE

T

wo BbGg parents mate. What are the odds their

offspring have each of the possible eye colors?

*NOTE ON EYE COLOR

T

his explains the majority of eye inheritance but it is an incomplete

explanation

F

or some reason that geneticists haven’t figured out sometimes two blue

eyed parents have offspring with other color in the eyes – IT DOESN’T

MEAN YOU WERE ADOPTED OR YOUR MOM CHEATED ON YOUR

DAD

P

robably another gene affects eye color a bit – (e.g. hazel eyes, blueish

greenish eyes, how dark/light the color is etc.)

EPISTASIS

O

ften times one gene acts as a switch for whether or not another gene

can get expressed or not

S

implest example:

I

n mice, black fur color is dominant to agouti (brown)

B

UT this color gene only gets expressed if another gene (the color gene)

is active. Color (C) is dominant to no color (c)

EPISTASIS PRACTICE

I

f two BbCc mice mate, what are the odds of having a

child that is agouti?

SO WHY IS IT HARD TO TRACK MANY TRAITS LIKE HEART DISEASE OR CANCER?

M

any genes are involved, some directly, some via epistasis

S

o it’s trying to figure out a gene that affects a gene that

affects another gene that affects another gene

T

he environment has a huge effect on activating or

deactivating expression of some genes