BIOLOGICAL INHERITANCE

UNIT 5

Mendel (XIX century) demonstrated that hereditary characteristics are determined by independent factors which are transmitted from generation to generation.

GENETIC INHERITANCE

Chromosomes are the carriers of genetic information. Mendel independent factors are fragments of DNA that determine the characteristic of a specific trait.

GENE: Unit of DNA that transmit genetic information

ALLELE: Each variant of a gene

GENOTYPE: Set of genes that an individual has

FENOTYPE: Observable traits that an individual has

BASIC CONCEPTS

HOMOZIGOUS: both alleles are the same

HETEROZIGOUS: both alleles are different

Dominant allele prevent the alternative gene (recessive allele) from appearing

When both alleles are equally strong are called co-dominant and cause intermediate inheritance

MENDEL’S LAWS

Mendel discovered the basic principles of heredity by breeding garden peas in carefully planned experiments

Mendel chose a plant whose varieties displayed “pure” traits, which had been selected long before and which remained constant from generation to generation, making them easy to identify.

He used a self-pollinating plant. The petals enclose the stamens and the pistil completely, which means that the plant crosses with itself, so accidental crossing with different plants is avoided, and pure strains can be obtained.

Traits studied by Mendel

Principle of uniformity (1st law)

Principle of segregation (2nd law)

Principle of independent assortment (3rd law)

Yellow seed F1 Green seedThe additional experiment which Mendel carried out, to prove that alleles come in pairs and separate at the moment when gametes form, consisted of crossing F1 (yellow seeds) with the pure paternal line of green seeds (recessive homozygote). Let’s take the yellow seed to be Aa.

In this case, 50% green seeds and 50% yellow seeds are obtained.If the yellow seed had been AA, all of the seeds would have been yellow (Aa).

Test cross

Watch the video

SPECIAL CASES Multiple alleles

SPECIAL CASES Gene interaction

SPECIAL CASES Lethal genes

SPECIAL CASES Quantitative inheritance

LOCATION OF GENES

INDEPENDENT GENES

LINKED GENES

TYPES OF CHROMOSOMES

CHROMOSOMES MAPPING

EXERCISE

DETERMINING SEX

A single gene determines sex

ZZ/ZW

SEX LINKED INHERITANCE

GENE MUTATIONS

CHROMOSOMES MUTATIONS

NUMERICAL MUTATIONS