Chapter 3: Mendelian Genetics Flashcards
In this approach, a scientist uses an organism that is easy to grow, and exhibits general characteristics that are applicable to other, higher forms of specimens.
Model Experimental Approach
What were the reasons for choosing pea plant as specimens of Mendel?
- Pea plant is self-fertilizing in nature, but it is easy to hybridize artificially.
- Reproduces well and grows to maturity in a single season.
These strains have traits that appear unchanged generation after generation in self-fertilizing plants.
True-breeding strain
The simplest crosses that involved only one pair of contrasting traits.
Monohybrid cross
How is monohybrid crossing done?
Made by mating two true-breeding individuals each exhibiting one of the two contrasting forms of the character under study.
It describes the original parents.
P1 or Parental generation
Describes the individuals resulting from the parental generation cross.
First filial generation (F1)
Describes the individuals resulting from self-fertilizing F1 offspring.
Second filial generation (F2)
Crosses could be made in either – pollination of dwarf plants by tall plants, or vice versa
Reciprocal crosses
Genetic characters are controlled by unit factors existing in pairs in individual organisms.
Law of Unit Factors in Pairs
True or False. In Mendelian genetics, each individual may have one of the three combinations: AA, aa, Aa where A is a dominant allele, and a is a recessive allele for the same trait. Each of the alleles comes from each parent.
True.
When two unlike unit factors responsible for a single character are present in a single individual, one factor is dominant to the other, which is said to be recessive.
Law of Dominance and Recessivity
During the formation of gametes, the paired unit factors separate, or segregate, randomly so that each gamete receives one or the other with equal likelihood.
Law of Segregation
True or False. In Mendelian genetics, if an individual contains a pair of like unit factors each of the gametes formed contain like unit factors. But if an individual contains a pair of unlike unit factors, then each of the gametes has a 50 percent chance of acquiring either one of the gametes.
True. According to the law of segregation. AA and aa individuals produce gametes having A, and a, respectively. However, an Aa individual produces gametes with an A and a in equal amounts.
The physical expression of a trait.
Phenotype
Alternative form of the gene which determines the phenotype.
Allele
The modern equivalent of unit factors.
Genes
Set of all alleles for a specific trait.
Genotype
When both alleles are present in an individual, the individual is said to be?
Homozygous or Homozygote
When the alleles are different, then the individual is said to be?
Heterozygous or Heterozygote
The genotypes and phenotypes resulting from combining gametes during fertilization can be easily visualized by constructing this diagram
Punnet square
Organism expressing the dominant phenotype but having an unknown genotype is crossed with a known homozygous recessive individual. This process is called?
Test cross
When a testcross yields offspring exhibiting the recessive trait, the parent organism expressing the dominant phenotype is?
Heterozygous for the trait
When a testcross yields all offspring exhibiting the dominant phenotype, the parent organism expressing the dominant phenotype is?
Homologous for the trait
Cross involving two pairs of contrasting traits.
Dihybrid cross (Two-factor cross)
During gamete formation, segregating pairs of unit factors assort independently of each other.
Independent assortment
True or False. according to the postulate of independent assortment, all possible combinations of gametes should be formed in equal frequency.
True
True or False. Processes of segregation and independent assortment also apply to three pairs of contrasting traits.
True
States that the probability of two or more events occurring simultaneously is equal to the product of their individual probabilities
Product law
States that the probability of obtaining any single outcome,
where that outcome can be achieved by two or more events,
is equal to the sum of the individual probabilities of all such events.
Sum law
In Mendelian genetics, the F1 progeny is achieved by?
Crossing two true-breeding individuals exhibiting the contrasting trait.
In Mendelian genetics, the F2 progeny is achieved by?
Selfing (self-pollination) of the F1 progeny
A traditional way to study inheritance where a family tree is constructed, indicating the presence or absence of the trait in question for each member of each generation.
Pedigree analysis
True or False. Pedigree analysis is usually done in humans because mating is not applicable and few offspring is available.
True
What figure represents a female in a pedigree?
Circles
What figure represents a male in a pedigree?
Square
What figure is used to indicate an individual whose sex is unknown in a pedigree?
Diamond
These parents are related by blood and are connected by a horizontal sibship line (double horizontal line)?
Consanguineous parents
Sibs are placed in birth order from what direction?
From left to right
True or False. If a specific phenotype is known to be expressed by an individual the figure that represents such individual in a pedigree is unshaded.
False.
The figure (circle, square, diamond) that represents a deceased individual receives what figure?
Diagonal line over the figure
An individual heterozygous for a recessive trait (not expressing the phenotype) receives what additional figure to its/his/her figure?
Shaded dot on the center of square/circle/diamond
True or False. Twins are indicated by diagonal lines stemming from a vertical line connected to the sibship line
True
True or False. In dizygotic twin, the diagonal lines are linked by a horizontal line and in monozygotic twin this line is absent.
False.
The individual whose phenotype first brought attention to the family is called?
Proband
Proband is indicated by?
An arrow connected to the designation p.
True or False. Autosomal recessive traits typically skip generations and appear equally in both sexes.
True
Tay-Sachs disease (TSD) results from the loss of activity of what enzyme?
hexosaminidase A (Hex-A)
This enzyme is normally found in lysosomes within cells, is needed to breakdown the ganglioside GM2, a lipid component of nerve cell membranes.
hexosaminidase A (Hex-A)
The gene that is mutated in TSD is responsible for coding what component of hexosaminidase A (Hex-A)?
Alpha sub-unit
A devastating recessive disorder involving unalterable destruction of the central nervous system and is a result of the loss of activity of a single enzyme, hexosaminidase A (Hex-A).
Tai-Sachs Disease (TSD)
Characteristics of Mendelian traits?
- Encoded by a single gene with only one allele.
- True breeding - no mixing or intermediary traits
- Does not exhibit epistasis
- There is no linkage (sex-linking is not Mendelian)
