Ch.14 Mendel Flashcards
Explain how Mendel’s particulate mechanism differed from the blending theory of inheritance
Particulate Theory: trait units are passed to children and stay separate.
Blending Theory: traits passed to children blend; blended traits cannot separate
Define the following terms: true breeding, hybridization, monohybrid cross, P generation, F1 generation, F2
True-Breeding: plants that produce offspring of the same
variety when they self-pollinate.
P Generation: true-breeding parents
F1 Generation: hybrid offspring of the P generation
F2 Generation: When F1 individuals self-pollinate or cross-pollinate with another F1 individual
List and explain the four components of Mendel’s hypothesis that led him to deduce the law of segregation.
- alternative versions of genes account for variations in inherited characters.
- For each character an organism inherits two alleles one from each parent
- If the two alleles at the locus differ then won the dominant allele the times organisms appearance and the other recessive has no noticeable effect on appearance
- Law of segregation the two alleles for a heritable character separate during gamete formation and end up in different gametes
Distinguish between the following pairs of terms: dominant and recessive; heterozygous and homozygous; genotype and phenotype.
An organism with two identical alleles of homozygous different alleles are heterozygous
Genotype equals genetic makeup phenotype equals physical appearance
explain how a test cross can be used to determine if an individual with the dominant phenotype is homozygous or heterozygous
to determine the genotype we can carry out a test cross breeding the mystery individual with a homozygous recessive individual
State Mendel’s of law of independent assortment and describe how this law can be explained by the behavior of chromosomes during meiosis
Law of independent assortment each pair of alleles segregate independently of each other pair of alleles during gamete formation
Use the rule of multiplication to calculate the probability that a particular F2 individual will be homozygous recessive or dominant.
Rule of multiplication probability that independent events will occur simultaneously is the product of their individual probabilities
Ex: Pp x Pp - what is the probability it will be homozygous recessive (pp)?
egg - F1 (Pp) will get p allele = ½
sperm - F1 (Pp) will get p allele = ½
½ x ½ = ¼ chance of (pp)
Given a Mendelian cross, use the rule of addition to calculate the probability that a particular F2 individual will be heterozygous.
two ways to become heterozygous
1/2 dom. x 1/2 rec. = 1/4 dom.-rec. or
1/2 rec. x 1/2 dom. = 1/4 rec.-dom.
The combined probability is the two added together
Use the laws of probability to predict from a trihybrid cross between two individuals that are heterozygous for all three, traits the expected proportion of the offspring that would be a homozygous recessive for two specific traits and heterozygous for the third
For example: AaBbCc x AaBbCc
Complete gametes: (1/8 ABC + 1/8 AbC + 1/8 aBC + 1/8 ABc. + 1/8 Abc +
1/8 aBc + 1/8 abC + 1/8 abc)2
Cases
A: 1/8 abc x 1/8 abC + 1/8 abC x 1/8 abc + 1/8 aBc x 1/8 abc + 1/8 abc x 1/8 aBc + 1/8 Abc x 1/8 abc + 1/8 abc x 1/8 Abc = 3/32
Explain why it was important that Mendel used large sample sizes in his studies.
Mendel used large sample size to get a better idea of the chances of the pea plant offspring having various traits. In other words, he hoped to understand all possible variation in pea plant offspring.
Give an example of incomplete dominance and explain why it does not support the blending theory of inheritance
Incomplete dominance can happen in flowers such as snap dragons where a red flower plant and a white flower plant have an offspring that is neither red nor white but is a mix so in this case it would be pink. It does not support the blending theory as it does not get its colour from the dominant plant in this case but from both
Explain how phenotypic expression of the heterozygote differs with complete dominance, incomplete dominance, and codominance.
In complete dominance, one allele is fully expressed in the heterozygote and the other is masked. Tay-Sachs disease occurs when an effected individual is missing critical enzymes that metabolize certain lipids, resulting in a degeneration of the nervous system. Only individuals carrying two copies of the disease allele will have the disease, hence at the organismal level, Tay-Sachs disease is recessive (the normal allele exhibits complete dominance). However, a heterozygote that exhibits a phentotype that is the intermediate between the two homozygotes exhibits incomplete dominance. The enzyme activity level for heterozygotes for the Tay-Sachs alleles is midway between the enzyme activity level for the homozygous conditions, therefore at the biochemical level, the normal allele and the Tay-Sachs allele are codominant.
Explain why Tay-Sachs is considered recessive at the organismal level and co-dominant at the molecular level.
Children with two Tay-Sachs alleles (homozygotes) have the disease.
Both heterozygotes with one working allele and homozygotes with two working alleles are healthy and normal at the organismal level.
The activity level of the lipid-metabolizing enzyme is reduced in heterozygotes. At the biochemical level, the alleles show incomplete dominance.
Heterozygous individuals produce equal numbers of normal and dysfunctional enzyme molecules. At the molecular level, the Tay-Sachs and functional alleles are codominant.
Explain why genetic dominance does not mean that the dominant allele subdues a recessive allele. Illustrate your explanation with the example of round versus wrinkled pea seed shape.
Dominant alleles do not subdue or suppress recessive alleles in any way because the two do not physically interact.
Dominance and recessiveness refer to the mechanisms by which genotype is translated into phenotype.
In the case of round vs. wrinkled seeds…
Round seeds (homozygous dominant and heterozygous) make enough of a certain enzyme that allows them to convert accumulating sugars and water into starches. This gives the peas more volume, smoothness, and roundness.
Wrinkled seeds (homozygous recessive), on the other hand, lack the ability to make that enzyme- so, no starch is formed, and the seeds wrinkle when they dry
Explain why dominant alleles are not necessarily more common in a population. Illustrate your explanation with an example.
It depends on the trait. If the dominant genotype is selected for more often than the recessive genotype, then the dominant allele will become more common in the gene pool. If the recessive genotype is selected for more often than the dominant genotype, the recessive allele will become more common than the dominant allele in the gene pool. For example, in humans, having five digits on hands and feet is recessive, and six digits is dominant. Most people have five digits because the recessive allele for numbers of digits is much more common in the human gene pool than the dominant allele.
