Chapter 3 Flashcards
Gene
An inherited factor that determines a characteristic
Allele
One of two or more alternative forms of a gene
Locus
A specific place on a chromosome where the alleles are located
Genotype
A set of alleles that an individual organism possesses. Only the alleles of the genotype are inherited.
Homozygous
A diploid organism with a genotype consisting of 2 identical alleles
Heterozygous
A diploid organism with a genotype consisting of 2 different alleles
Phenotype
The manifestation or appearance of a characteristic/trait. Can be physical, physiological, biochemical, or behavioral.
A phenotype arises from a genotype that develops in a certain environment.
How the phenotype develops is determined by the effect of other genes and environmental factors.
Organisms do NOT transmit their phenotypes to the next generation.
Monohybrid cross
A cross between parents that only differ by a single characteristic.
Ex: homozygous plants for round seeds crossed with homozygous plants for wrinkled seeds
RRxrr
Genotypic ratio 1:2:1
Phenotypic ratio 3:1
P generation
The first generation of a cross. Parental generation.
F1 generation
Filial 1 cross. The offspring of the P generation.
Only express one of the phenotypes present in the parental generation.
F2 generation
Filial 2 generation. The offspring of the F1 generation.
Both traits from the P generation are observed.
Dominant
An allele or phenotype that is expressed in homozygotes (AA) and in heterozygotes (Aa); only the dominant allele is expressed in the heterozygous phenotype.
Traits that appeared unchanged in the F1 heterozygous offspring.
Recessive
An allele or phenotype that is expressed only when the recessive allele is homozygous. The recessive allele is not expressed in the heterozygote phenotype.
Traits that disappeared in the F1 heterozygous offspring
Principle of segregation
Mendel’s 1st law.
Each individual diploid organism possesses 2 alleles for any particular characteristic. These 2 alleles segregate when gametes are formed and 1 allele goes into each gamete in equal proportions during anaphase I.
Concept of dominance
When 2 different alleles are present in a genotype, only the trait encoded by the dominant allele is observed by the phenotype
Punnett square
A way to predict the outcomes of genetic crosses.
Each cell contains a allele from each of the corresponding gametes, generating the genotype of the fusion of those gametes.
Probability
Expresses the likelihood of the occurrence of a particular event.
# of times particular event occurs \_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_
of possible outcomes
Multiplication rule
The probability of 2 or more independent events occurring together is calculated by multiplying their independent probabilities.
The outcome of one must not influence the outcome of the other.
AND
Addition rule
The probability of any one of two or more mutually exclusive events is calculated by adding the probability of these events
The events must be mutually exclusive - one event excludes the possibility of the occurrence of the other event.
OR
Testcross
A useful tool for analyzing genetic crosses. One individual of unknown genotype is crossed with another individual with a homozygous recessive genotype for the trait in question.
Any recessive allele in the unknown genotype is expressed in the progeny (children gametes) because it will be paired with a recessive allele from the homozygous recessive parent
Incomplete dominance
The phenotype of a heterozygote that is intermediate between the phenotypes of the two homozygotes.
Ex: BB - black fur
bb - white fur
Bb - grey fur
Wild type
The phenotype or allele that is most commonly found in natural (wild) populations.
Dihybrid cross
Cross between substances that differ in 2 characteristics.
Phenotypic ration 9:3:3:1
Ex: AABBxaabb
Principle of independent assortment
Mendel’s 2nd law
Alleles at different loci separate independently of one another during anaphase I.
This is an extension of the principle of segregation.
Based o the behaviors of chromosomes in meiosis. Homologous chromosomes separate independently of all others in anaphase I so genes located on different pairs of homologs will assort independently. Genes located on the same chromosome do NOT assort independently.
