lab 1 - probability principles used in genetics

phenotype

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

Examples: eye color, hair color, flower color

An individual’s phenotype directly related to its genotype, or genetic makeup.

Genetic information is carried in DNA. Genes are short DNA sequences.

•DNA make up chromosomes.

Humans have 2 copies of each gene…

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

alleles

Different traits arise from alternate versions of the same gene with different nucleotide sequences

recessive alleles

affects phenotype only if an individual has 2 copies

designated by a lower-case letter (a)

dominant alleles

presence hides/masks recessive alleles in phenotype

designated by upper-case letter (A)

homozygous

2 copies of same alleles

heterozygous

1 copy each of different alleles (Aa)

probability

can be applied to determine the chance of inheriting of specific alleles

chance

is the probability of something happening

coin toss

2 possible outcomes: heads or tails

Each coin toss is a mutually-exclusive event

All are independent events

Add up all the mutually exclusive events for a coin toss

1/2 [for heads] + 1/2 [for tails] = 1

addition/sum rule

this OR that simultaneously

sum the individual probabilities

Rr x Rr

2 ways to get Rr (Rr + “rR”)→ ¼ + ¼ = ½

Addition/sum rule is used…

to determine the outcome of an event with 2 mutually exclusive events from multiple pathways

multiplication/product rule

this AND that

multiple the probabilities of the individual events

Multiplication/product rule is used…

to determine the outcome of 2 independent events occurring simultaneously

monohybrid crosses

are situations of independent events

Basic rules of probability can be applied

Are an important part of Mendel’s first law (Law of Segregation)

very useful for solving genetic problems

Individual Aa produces gametes

1/2 will contain the dominant A allele

1/2 will contain the recessive a allele

When 2 heterozygotes are crossed (Aa x Aa)

AA = ¼ (Homozygous dominant)

Aa = 2/4 =½ (Heterozygous)

aa = ¼ (Homozygous recessive)

binomial expansion

Useful when determining probabilities of large group sizes which will include many possible combinations

Expectations for various combinations in group of given size (n) can be obtained

binomial formula

(a+ b)ⁿ

n is the size of the group

a is the probability of the first event

b is the probability of the alternative event

pedigrees

are family trees that show phenotype occurrence of several generations of related individuals

Probability principles can be utilized to determine the chances that offspring may having a particular condition

During lab time a pedigree will be utilized to figure out those who are homo- or heterozygotes for a certain condition