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Mendelian Genetics
and Biotechnology
OBJECTIVE: 12.01 Define key genetic terms
related to agriscience research and
biotechnology.
Terms
• DNA
•
•
Deoxyribonucleic Acid- the major nucleic acid in organisms
carries genetic information, and is responsible for the transmission of
traits.
Terms
• Gene•
segment of DNA that codes for a specific trait in an organism.
Terms
• Allele- an alternative form of a gene / trait. Ex: eye coloralleles = blue, green, hazel, brown, etc.
• Homozygous- organism with identical alleles for a given traitcan be
dominant or recessive. Ex: TT or tt
• Heterozygous- organism with different alleles for a given trait.
Ex: Tt
Terms
• Phenotype• the physical appearance of a trait
in an organism- determined but
not always indicative of the
genetic makeup of the organism.
• Ex: tall or short
• Genotype• the genetic composition of an
organism for a given trait- often
cannot be determined by looking
at an organism.
• Ex Tt or TT
Terms
• Recessive Gene / Allele- variation of a trait that can only be
expressed in the absence of a dominant allele.
• Heterozygous individuals are carriers for recessive alleles.
Terms
• Dominant Allele / Gene- variation of a trait that is expressed
over other variations of the same trait.
• Most common forms in natural populations.
• Some traits can be co dominant or exhibit incomplete
dominance.
Terms
• Chromosome•
long condensed strand of DNA forming in the nucleus of a cell prior to
cell division. Form pairs that when split, create an exact copy of DNA
in the daughter cell.
Terms
• Chromatid pairs• X-shaped structures that serve as the mechanism for the
transmission of genetic material during cell division. They are
pulled apart in the process of mitosis and meiosis.
Punnett Squares
• method utilizing the known genotypes of parent organisms
to predict the expression of a given trait or traits in offspring.
• Must know the genotype of parents and the inheritance pattern
of the trait.
Punnett Squares
• Conducting Tests
• A box should be drawn with one space for each allele expressed
by both parents. (in simple heredity, like pea height, boxes are
4x4)
• The alleles for one parent should be placed above each column
at the top, with the alleles for the other placed beside each row
on one side.
• The alleles of each parent should be distributed across and
down the box.
Punnett Square Example 1
T
T
t
T
TT
TT
Homozygous Dominant
Homozygous Dominant
Tt Heterozygous
Tt hereozygous
Genotype Ratio-2:2:0
Phenotype Ration- 4:0
Punnett Square Example 2
TG
Tg
tG
tg
Tg
TTGg
TTgg
TtGg
Ttgg
Tg
TTGg
TTgg
TtGg
Ttgg
Tg
TTGg
TTgg
TtGg
Ttgg
Tg
TTGg
TTgg
TtGg
Ttgg
Genotype Ratio- 0:4:4:4:4:0
Phenotype Ratio- 0:8:8:0
Process of Simple Heredity
• Definition- heredity is best described as the manner in which
inheritable characteristics (traits) are passed from parents
to offspring.
• Heredity is a direct outcome of the RANDOM genetic
recombination resulting
during sexual reproduction.
• ***ONLY FUNCTIONS IN SEXUAL REPRODUCTION
• ***ENSURES GENETIC DIVERSITY
• Heredity determines the genetic potential of an animal, but…
• HEREDITY & ENVIRONMENTAL INFLUENCES determine the
overall
quality of an animal.
Types of Heredity
• Simple Heredity
• One gene controls one trait- alleles are either dominant or
recessive.
• Ex: height & color in pea plants
• Complex Heredity
• Polygenic Inheritance- one trait is controlled by several genes and
possibly environmental factors- genes may even be located on
different chromosomes. This is a slow process requiring many
generations to achieve desired results.
• Ex: height in humans
• Codominance - multiple alleles for a given trait are not expressed
over one another, but in combination.
• Ex: RR (Red Flower) x WW (White Flower) = RW (Red & White Striped
Flower)
• Incomplete Dominance - similar to codominance, except
characteristics of alleles blend instead of remaining distinct.
• Ex: RR (Red Flower) x WW (White Flower) = RW (Pink Flower)
Heredity in Agriscience
• Huge factor in successful agricultural selective breeding
programs.
• Processes of heredity manipulated to create high quality
HYBRID offspring.
• Plants and animals are inbred through several generations to
isolate a specific trait or traits.
• NO MORE THAN 7 GENERATIONS TO PREVENT GENETIC DISORDERS
• The final generation of two different lines inbred for different
traits are crossed producing offspring with the beneficial traits
of both lines.
• Resulting offspring possesses hybrid vigor.
• Hybrid vigor usually lasts only one generation, as hybrid
organisms rarely express traits true to type in offspring.
• Alternative forms of the gene resurface in the new cross.