Transmission Genetics

Gregor Mendel

The father of modern genetics who discovered the basic principles of genetic transmission.

True-breeding

A genetic type where the organism consistently passes down its traits to offspring, homozygous phenotypes.

Blending Theory of Heredity

The discredited theory that progeny traits are a mixture of parental characteristics.

Dominance

A relationship between alleles in which one allele masks the expression of another.

what did mendel discover within the blending theory experiment

traits must be derived from discrete factors that come from parents and combine in offspring

particulate inheritance

each trait is determined by two “particles of heredity”, or alleles

Mendel's First Law of Equal Segregation

States that alleles segregate independently during gamete formation.

Test Cross

A method to determine the genotype of an individual with the dominant phenotype by crossing it with a homozygous recessive.

Independent assortment

The principle that alleles for different traits segregate independently of one another during gamete formation.

Forked-line (branch tree) diagram

another diagram to help identify the different probabilities

possible because of independent assortment

9:3:3:1 ratio

The phenotypic ratio of offspring observed in dihybrid crosses.

Probability Theory in Genetics

A set of principles for predicting the outcomes of genetic crosses.

What phase of meiosis accounts for different alleles segregating from each other (disregard crossing over)

Meiosis I: homologous chromosomes pair and separate

independent assortment is due to?

metaphase I as different arrangements are possible to obtain

Product rule

The rule that the joint probability of independent events is the product of their individual probabilities.

Sum rule

Calculates the probability of mutually exclusive events by summing individual probabilities.

Conditional Probability

the product and sum rules are used BEFORE a cross in order to predict the likelihood of certain outcomes

Binomial Probability

predicting the likelihood of a series of events with the use of binomial expresion

Autosomal inheritance

The transmission of genes located on autosomes, which are non-sex chromosomes.

Autosomal Dominant Inheritance

A pattern of inheritance where only one copy of the dominant allele causes the trait.

Characteristics of Autosomal Dominant Inheritance

1. Males and females have equal frequency of trait

2. Each individual who has the trait has at least ONE parent with the trait

3. Either sex can give the trait to the child

4. if neither parent has the trait, then the individual cannot have the trait

Characteristics of RARE Autosomal Dominant Inheritance

1. those with the trait are likely heterozygous and in crosses where one parent has the trait and the other does not, half of the offspring will have the trait

2. if both parents have it, they may produce children who do not have it (because they are heterozygous)

Autosomal Recessive Inheritance

A pattern in which two copies of a recessive allele must be present for the trait to be expressed.

Features of Autosomal Recessive Inheritance

1. males and females have equal trait frequency

2. individuals who have the trait are often born to parents who do not have it (parents are heterozygous)

3. if both parents have the trait, all children will have it (100%)

4. the trait is not usually seen in each generation, rather it is seen among siblings

5. if only one parent has the trait, a child can only have the trait if the other parent is heterozygous

X-linked recessive inheritance

A pattern where males are more frequently affected due to having only one X chromosome.

Characteristics of X-linked recessive

1. unaffected females with affected sons/fathers

2. more affected males than females because females can mask the trait easier

Characteristics of X-linked dominant

1. affected males with 100% daughters affected because only daughters will get the x^A

Y- linked characterisitcs

1. affected male has 100% male offspring with the trait because this is exclusively males

Organellar inheritance

The inheritance of traits through genes found in organelles, typically passed from mother to offspring.

Chi-Square Analysis

A statistical method used to test the fit between observed and expected genetic outcomes.

value lower than table chi square?

fail to reject; accurate data

value greater than table chi square?

reject; not very accurate data

Mendel's Law of Independent Assortment

States that the segregation of alleles for one trait is independent of the segregation of alleles for another trait.

Dihybrid Cross

A genetic cross involving two traits that Mendel used to study independent assortment.

Segregation of Alleles

The separation of alleles during gamete formation as described in Mendel's inheritance laws.

Homozygous

An organism that has two identical alleles for a specific trait.

Heterozygous

An organism that has two different alleles for a specific trait.

Mitochondrial inheritance

A type of inheritance where genes in mitochondrial DNA are passed from mothers to offspring.