AP Biology Discussion

Thursday 3/19/2015

Goals for the day

• Be able to predict patterns of inheritance and interpret pedigrees.

• Be able to use probabilities to predict the likelihood of different outcomes

• Be able to work with Sex-linked traits in genetics problems & pedigrees

Question of the day 3/19What is the probability of getting “tails” when you flip a two-sided fair coin?

Probability• Probability is the likeliness that an event will

occur.

• When talk about a probability we might think of it as a percentage or fraction.

• Let’s think about it as a fraction first:

The number of possible outcomes

The number of outcomes you want12

Probability Practice

• If I have 2 fair coins, what are the chances of getting heads on both coins when thrown simultaneously?

Probability

• If you say “AND” – multiply

• If you say “OR” - add

Probability Practice

• If I have 2 fair coins, what are the chances of getting heads on both coins when thrown simultaneously?

Probability Practice

• If I have 2 fair coins, what are the chances of getting one head and one tails?

Probability Practice• Let’s think genotypes & gametes now…• What is the probability of a heterozygote

parent giving their offspring a recessive allele?

Probability Practice• Let’s think genotypes & gametes now…• What is the probability that parents who were

both heterozygous ( )for a trait would have a homozygous dominant ( )offspring?

It will get harder…• What is the probability of a parent who has

the genotype: AaBBCcDdEeff will produce a gamete that has aBcdef?

• Just remember you can break the question into pieces! Make it managable!

Sex-linked vs Autosomal

Karyotype #1

Sex-linked vs Autosomal• Trait/gene on one

of your 22 pairs of Autosomes (non-sex chromosomes)

Possible genotypes:

Sex-linked vs Autosomal• Trait/gene linked to

sex chromosomes (X or Y)

• X-linked trait – only found on the X chromosome

Possible genotypes:Females:

Males: (HEMIzygous

Sex-linked vs Autosomal

• What kind of traits have we been dealing with?

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Pedigrees

Pedigree Conventions

STEP 1: Find parents that match each other, but don’t match their children

• From this you will be able to determine whether a trait is dominant or recessive by answering the following questions.

Can affected parents have unaffected childrenYes = ___________

How probable is it? It is impossible?

Can affected parents have unaffected childrenYes = ___________

Can unaffected parents have affected children?Yes = ___________

Can unaffected parents have affected childrenYes = ___________

Sex-linked vs. Autosomal

STEP 2: Determine whether this trait might be Autosomal

or Sex-linked.

• If it is recessive ask yourself….

• If it is dominant ask yourself…

Do only Men Have it?

Yes COULD = ___________

If it is a recessive trait, can affected mothers have unaffected sons?

Yes = ___________

Do men have the trait more often than women?

Yes COULD = ___________

If it is dominant, are the daughters of affected dads also affected?

No = ___________

Pedigrees & Probabilities Practice