Mendelian Genetics Flashcards
What is the complete complement of an organism’s DNA?
Genome
How is cellular DNA organized?
In chromosomes
What have specific places on chromosomes (loci)?
Genes
What is the genetic composition of an organism?
Genotype
What is the physical expression of an organism’s traits?
Phenotype
What are variations of a gene?
Alleles - Represented with letters for different types of alleles (PP, Pp, pp)
What is a pair of identical alleles for a character (PP, pp)?
Homozygous
What is two different alleles for a gene (Pp)?
Heterozygous
What is a heritable feature?
A character
What is a variant for a character?
A trait
What are all offspring of the same variety called?
Purebred
What is the crossing of two different true-bred organisms called?
Hybrid
What are the different generations of a cross called?
-P generation (parents)
-F1 generation (1st filial generation)
-F2 generation (2nd filial generation)
What type of genotype is it when both recessive alleles are present (rr)?
Recessive
What type of genotype is it when at least one dominant allele is present (R-)?
Dominant
Who was Gregor Mendel?
Austrian monk from the 1800’s who suggested that when crossed, organisms had heritable traits
What did Gregor Mendel do?
He examined pea plants over many generations
What did Mendel discover? What were these things called?
-Three laws of inheritance.
-They are called:
- Law of Dominance
- Law of Segregation
- Law of Independent Assortment
What happened in Mendel’s Pea Plant Experiments?
- Mendel examined plants of varying heights (tall or short 🡪 T = tall, t = short)
- In the experiment he crossed two parent (P) plants (short x tall) and got ALL tall plants in the F1 generation
- He crossed the F1 plants and found that ¾ were tall in the F2 generation
What is a monohybrid cross?
The examination of one trait (height)
What did the results of these experiments mean?
- Mendel went on to examine other traits on pea plants (round x wrinkled, yellow x green) and got similar results
- Ratio of ~3:1 in F2 generation
- He concluded that there must be a dominant trait that is always expressed when present, and a recessive trait that is expressed only when the dominant trait is not present
Explain Mendel’s Law of Dominance
- In a cross of parents that are pure for contrasting traits, only one form of the trait will appear in the F1 generation
- The dominant trait will be expressed (phenotype), while the recessive trait will be hidden
- Factor that remained hidden in F1 generation but is present in the F2 generation is the “recessive factor”
Explain Mendel’s Law of Segregation (3 points)
- Alleles (one from each parent) result in variations in inherited characteristics
- For each character, an organism inherits two alleles (1/parent)
- The alleles for each character segregate during meiosis
- Alleles for a trait are recombined at fertilization → genotype of offspring
Explain Mendel’s Law of Independent Assortment
Alleles for different traits are distributed to sex cells (and offspring) independent of one another
How do you predict patterns of inheritance?
- Punnett Squares: Tool for diagramming possible genotypes of offspring
- Laws of Probability: When you flip a coin, what is the likelihood that you will get heads? Tails? Basic genetics problems can be solved using the foundational laws of probability
How do you determine if an organism is homozygous dominant or heterozygous?
- When the above information is not given, a test cross must be done to confirm
- Always performed between the unknown genotype and a homozygous recessive genotype
- Cross the individual with the dominant trait with an individual that exhibits the recessive trait
-Results reveal the genotype: All offspring display the dominant phenotype, then the the individual in question is homozygous dominant. Offspring display both dominant and recessive phenotypes, then individual is heterozygous
What are test crosses?
- When the genotype of an organism is not known, one can cross this organism with another that is homozygous recessive for the traits in question
- This is called a test cross
