Topic E: Mendelian Inheritance Flashcards
Why was Mendel so successful in discovering the mechanism of heredity?
- worked with true breeding lines (pure/homozygous- progeny produced always had the same phenotype as the parent)
- worked with single gene traits/simple inheritance
- worked with easily scored traits (two contrasting phenotypes)
- good model organism that was quick and easy to grow
What is a monohybrid cross?
- a cross in which a single trait or characteristic is followed
- ex. flower colour
in the F1 generation, if observing a monohybrid cross, which phenotype will be observed?
the F1 generation only ever displays one of the original parental phenotypes - the dominant phenotype is observed, and the recessive phenotype is absent
In the F2 generation, what do we see reappear?
the recessive phenotype will reappear, alongside the dominant phenotype
What is the phenotypic ratio in the F2 population, for a monohybrid cross?
3:1
3 quarters of the F2 individuals will display the dominant phenotype, 1 quarter will display the recessive phenotype
What is reciprocal parental crossing?
A cross in which the phenotypes associated with each parent has/have been switched
Ex. “male” and “female” plant are swapped, so one has one phenotype and the other one has a different phenotype, and then they are swapped to see if the outcomes are the same
All of Mendel’s reciprocal crosses produced the same outcomes with respect to phenotypic ratios
What are 3 incites provided by Mendel’s work?
- the concept of the gene, which controls genetic/phenotypic factors
- the concept of alleles. Different “forms” of the same gene.
- the concept of dominance. So when an individual possesses 2 different alleles of the same gene, one will mask the effect of the other.
How do Mendel’s monohybrid crosses support the idea of Mendel’s first law of segregation ?
Because there are two alleles of each gene, and these segregate equally from each other in the formation of gametes. (I.e. in a heterozygous individual. two alleles segregate away from each other during meiosis and do not occur in the same gamete.
How does mendel’s law of equal segregation reflect the movement of chromosomes in meiosis?
In Meiosis, two members of a homologous pair of chromosomes segregate from each other during meiosis and as a result, the alleles present on those homologs, (ex. A and a) also segregate from one another (A and A go together, a and a go together)
What is a testcross? When do we use it?
- used when we are unable to determine the genotype from the phenotype
- ex. Both genotype PP and Pp will show up purple. So how do we determine the genotype?
- by performing a testcross, essentially just breeding with a recessive phenotype.
- the tester is capable of producing only a single type of gamete, all of the tester gametes will only carry recessive alleles.
- because the tester is homozygous recessive, the phenotype of the testcross progeny will determine the genotype of the gametes of the unknown individual.
When performing a testcross, what genotype do we breed with? (what is the tester)
recessive (homozygous)
What is a dihybrid cross?
a cross in which two traits or characteristics are followed. you follow 2 phenotypes at the same time (ex. shape and colour)
What is the phenotypic ratio of the F2 generation in a dihybrid cross?
9:3:3:1
- 9/16 of the F2 generation would display both dominant phenotypes (e. R;Y)
- 3/16 would display one of the dominant phenotypes (r;Y)
- 3/16 would display one of the other dominant phenotypes (R;y)
- 1/16 would display both recessive phenotypes (r;y)
How do dihybrid crosses reveal Mendel’s second law of inheritance?
- Reveals the Law of Independent Assortment!
- alleles of different genes assort independently from one another during gamete formation.
- the inheritance of one chromosome of a homologous pair is independent of the inheritance of another chromosome of a different homologous pair
- RANDOM ASSORTMENT
F1 dihybrids produce two categories of gametes:
- Parental type gametes
- Recombinant type gametes
