Genetics Chapter 3 Basic Principles of Heredity

Who discovered the Basic Principles of Heredity

Gregor Johann Mendel (1822-1884)

What was the proper experimental model that Gregor Mendel used in his study of heredity

The Garden Pea

In his experiments, Gregor Mendel used an __________ and analyzed results _________

Experimental approach; mathematically

Gregor Mendel studied models with ________

Easily differentiated characteristics (unambiguous)

Gregor Mendel articulated a hypothesis with a ________ value

Predictive

Why was Pisum sativum (garden pea) a good model organism

Fast generation time, lots of progeny, and seven easily observed unambiguous traits

Gene

An inherited factor (encoded in the DNA) that helps determine a characteristic

Allele

One of two or more alternative versions of a gene that influences traits

Locus

An “address” which is the specific place on a chromosome occupied by an allele

Genotype

Set of alleles possessed by an individual organism

Heterozygote

An individual organism possessing two different alleles at a locus

Homozygote

An individual organism possessing two of the same alleles at a locus

Phenotype/Trait

The appearance or manifestation of a characteristic; observed

What is the difference between a locus and an allele?

A locus is a place on a chromosome where genetic information is located, whereas an allele is an alternative version of a gene that encodes a specific trait.

What is the difference between a genotype and phenotype

A genotype is the set of alleles possessed by an organism, whereas the phenotype is the physical manifestation of said characteristic

Monohybrid crosses

Crosses involving a single trait crossed between 2 true breeding lineages

What do monohybrid crosses reveal

The principle of segregation and the concept of dominance

Principle of segregation

“Factors” segregate in the parent and come together in the offspring

Through one of the conclusions made by monohybrid crosses, it is noted that One character (trait) is encoded by _______

Two genetic factors

Through one of the conclusions made by monohybrid crosses, it is noted that Two genetic factors (alleles) separate (segregate) when ________

Gametes are formed

Through one of the conclusions made by monohybrid crosses, it is noted that Two alleles separate with __________ into the gametes

Equal probability

Monohybrid crosses established the concept of _______ and _______ traits and alleles

Dominant and recessive

The concept of dominance

When two different alleles are present in a genotype, only the trait encoded by one of them— the “dominant” allele, is observed in the phenotype

Mendel further tested the theory of inheritance of dominant traits using ______

Backcrosses

What is a backcross

A cross between the F₁ (Filial) generation and either parent

What is a testcross

A cross between an unknown (homozygous or heterozygous) and a known homozygous (true-breeding) recessive

Reginald Punnett (1917)

Invented the Punnett square which is a convenient way to visualize a cross and predict the outcome

3:1 phenotypic ratio in progeny

Parent genotypes: Aa x Aa

Genotypes of progeny: ¾ A_ : ¼ aa

1:1 phenotypic ratio in progeny

Parent genotypes: Aa x aa

Genotypes of progeny: ½ Aa : ½ aa

Uniform progeny (all progeny the same)

Parent genotypes: AA x AA

Genotypes of progeny: All AA

1:2:1 genotypic ratio in progeny

Parent genotype: Aa x Aa

Genotypes of progeny: ¼ AA : ½ Aa: ¼ aa

1:1 genotypic ratio in progeny

Parent genotype: Aa x AA

Genotype of progeny: ½ Aa : ½ AA

Probability

Likelihood of the occurrence of a particular event. Used in genetics to predict the outcome of a genetic cross

Multiplication rule

Used to calculate the probability of two independent events occurring together; multiply the independent probabilities together to ger the combined probability

Key indicator of the multiplication rule

“AND” (probability of event one AND event two occurring together)

Addition rule

Used to calculate the probability of any two or more mutually exclusive events occurring.

Key indicator of the addition rule

“Either/or” (Probability of either event one OR event event two)

Albinism is usually inherited as a ____ trait

Recessive

If both parents are heterozygous for albinism (Aa), what is the probability of having an albino child (aa)

Aa x Aa = ¼ Aa : ½ Aa: ¼ aa = 25% chance for albinism

Mendel’s dihybrid crosses

Examines two different traits at a time; Demonstrates the principle of independent assortment (Mendel’s Second Law)