Probability Principles Used in Genetics (LAB 1)

Phenotype

Observable properties of an individual resulting from BOTH genetic & environmental factors

Genotype

Genetic makeup

Dna make up

Chromosomes

How many copies of each gene in humans

2 (because it is produced by fusion of 2 gametes, with 1 copy of each gene)

Gametes are

Haploid (1 copy of each chromosome)

Somatic cells are

Diploid (2 copies of each chromosome)

Alleles

Same gene with DIFFERENT nucleotide sequences

Probability in related to alleles

Can be applied to determine the chance of inheriting specific alleles

Chance

Probability of something happening

Mutually-exclusive event

Event that cannot happen at the same time

Example of mutually-exclusive event

Heads or tails in coin toss; neither are more likely to occur

Independent event

One event has no impact on results of the current event

Example of independent event

In coin tosses, previous/future coin tosses have no impact on results of current one (random)

TWO WAYS probability of an event can occur

• Addition/sum rule

• Multiplication/product rule

Addition/sum rule

“This or that SIMULTANEOUSLY); you need to sum the individual probabilities

Example of addition/sum rule

Probability of having a dominant trait, so:

• Rr + rR + RR = ¼ + ¼ + ¼ = ¾

• Probability of heterozygote + probability of homozygote

If you were to roll a six-sided die, what is probability of getting a 3 OR 4?

1/6 + 1/6 = 1/3

Multiplication/Product Rule

“this AND that simultaneously”; MULTIPLY the probabilities of the individual events

Example of multiplication/product rule

Tossing 2 coins, calculate probability that both will come up heads

• ½ x ½ = ¼

• Can also be one coin tossed and then tossed AGAIN

How to determine probability of multiple events when the order is not specific

First determine individual probabilities, then the total probability

How to determine probability of multiple events with the order is specific

Only need to calculate probability of the specified condition!

Monohybrid crosses are situations of

Independent events

Mendels first law

Law of Segregation

Law of Segregation

Every individual organism contains two alleles for each trait, and these segregate so that each sperm or egg cell only receives one allele

Autosomal recessive allele

Only shows up if organism inherits two copies of it

Binomal expansion is used to

Determine probabilities of large group sizes which will include many possible combinations

Binomal expansion formula

(a+b)ⁿ

• n = size of the group

• a = probability of first event

• b = probability of alternative event

• a+b=1

Use for factorials

When the probability of only a certain combination in a given-sized group is required

Pedigrees

Family trees that show phenotype occurrence of several generations of related individuals

Use of probability in gene combinations

Can be used if two genes are independently assorting, so use individual probabilities