5.biological inheritance
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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
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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