lec 22/23 Flashcards
(26 cards)
What is the physical appearance of an organism called?
Phenotype
Phenotype refers to the observable characteristics resulting from the genotype.
What term describes the genetic makeup of an organism?
Genotype
The genotype includes all the genes and alleles present in an organism.
What are different forms of a gene called?
Alleles
Alleles can be dominant or recessive.
What is a homozygous individual?
An individual with two identical alleles for a trait (e.g., ss)
Homozygous individuals are ‘true-breeding’.
What is a heterozygous individual?
An individual with two different alleles for a trait (e.g., Ss)
Heterozygous individuals exhibit variation in traits.
Define ‘character’ in genetics.
Observable physical feature (e.g., seed shape)
Characters are traits that can be measured or observed.
What does ‘trait’ refer to?
Form of a character (e.g., round or wrinkled)
Traits are specific variations of characters.
What is Mendel’s First Law?
Law of segregation: the two copies of a gene separate during meiosis
Each gamete receives only one copy of each gene.
What is a monohybrid cross?
A genetic cross involving one trait
It allows for the observation of inheritance patterns of a single character.
What phenotypic ratio is expected from a monohybrid cross?
3:1 ratio
This ratio indicates the ratio of dominant to recessive phenotypes.
What genotypic ratio is expected from a monohybrid cross?
1:2:1 ratio
This ratio reflects the combinations of alleles in the offspring.
True or False: Different genotypes can give the same phenotype.
True
This is known as phenotypic variability.
What is a test cross?
Crossing F1 individuals (with unknown genotype) with homozygous recessive individuals (rr)
The outcome reveals the genotype of the unknown parent.
What is Mendel’s Second Law?
Independent assortment: alleles of different genes assort independently of one another
This law applies to dihybrid crosses.
What is the phenotypic ratio of a dihybrid cross?
9:3:3:1 ratio
This ratio results from two traits being considered simultaneously.
Define linked genes.
Genes that do not assort independently and are located on the same chromosome
Linked genes can affect inheritance patterns.
What is hemizygous?
A single copy of a gene, typically in males regarding X-linked genes
Males have one X and one Y chromosome.
What is X inactivation?
The process where one X chromosome is silenced in XX individuals
This ensures dosage compensation between sexes.
What is complete dominance?
A single gene where one allele masks the effect of another
This results in a dominant phenotype being expressed.
What is incomplete dominance?
A situation where a heterozygote has an intermediate phenotype
Example: red and white flowers producing pink offspring.
What is codominance?
Two alleles produce distinct phenotypes that are both expressed in the heterozygote
Example: AB blood type in humans.
Define pleiotropy.
One allele has multiple phenotypic effects
Example: a single gene affecting multiple traits.
What is epistasis?
Phenotypic expression of one gene is influenced by another gene
Example: Labrador retriever coat color where ‘E’ gene affects ‘B’ gene expression.
What are polygenic traits?
Traits influenced by multiple genes interacting cumulatively
These traits often show a continuous distribution.
