Question

In what practical way were people thinking about genetics before Mendel? What was the dominant theory of the time? What did it say?

What is the law of segregation? What does it tell us about the nature of the gene? How did it contrast with “blending?” What is the law of independent assortment?

Why do the laws of probability apply to genetics? What is the product rule? What is the addition rule? How do they apply to genetics?

Be able to calculate the probability of any offspring genotype given the parental genotypes. Be able to predict the phenotype for that genotype.

Know the modifications of Mendel’s laws and how to apply them. How can you account for the severity of FH by incomplete dominance?

What are monogenic diseases? Give examples? What is a pedigree? What does it tell you about disease? How can genetic screening help in families with a history of disease?

Describe the chromosomal basis of inheritance, i.e. what is the relationship among chromosomes, genes, and alleles and how do these behave during gamete formation and fertilization? What stages of meiosis underlie the law of law of segregation and law of independent assortment?

What is the role of genetics in common diseases?

What are sex-linked traits? How is their pattern of inheritance different than other traits? Give an
example.

What is the genetic material or what is the physical nature of the gene? What experiment(s) showed this?

Know the structure nucleotides and how they polymerize to form DNA or RNA. What are the base pairing rules? How is DNA replicated? What is the product?

How is RNA made. What are the different kinds of RNA and what are their roles in gene expression (transcription and translation → protein).

How does genotype determine phenotype. What is the Beadle-Tatum hypothesis?

How is mRNA processed and where does it happen?

What do we mean when we say the genetic code is redundant but not ambiguous?

Answer 1

Before Gregor Mendel, theories for a hereditary mechanism were based largely on logic and speculation, not on experimentation. In his monastery garden, Mendel carried out a large number of cross-pollination experiments between variants of the garden pea, which he obtained as pure-breeding lines. Most of the mechanisms of heredity, however, remained a mystery until the 19th century, when genetics as a systematic science began.

Understanding Dominant Traits

Before Mendel's experiments, most people believed that traits in offspring resulted from a blending of the traits of each parent. However, when Mendel cross-pollinated one variety of purebred plant with another, these crosses would yield offspring that looked like either one of the parent plants, not a blend of the two. For example, when Mendel cross-fertilized plants with wrinkled seeds to those with smooth seeds, he did not get progeny with semi-wrinkly seeds. Instead, the progeny from this cross had only smooth seeds. In general, if the progeny of crosses between purebred plants looked like only one of the parents with regard to a specific trait, Mendel called the expressed parental trait the dominant trait. From this simple observation, Mendel proposed his first principle, the principle of uniformity; this principle states that all the progeny of a cross like this (where the parents differ by only one trait) will appear identical. Exceptions to the principle of uniformity include the phenomena of penetrance, expressivity, and sex-linkage, which were discovered after Mendel's time.

Before Mendel's work, pangenesis and blending inheritance theories were the accepted theories in the biological world to explain inheritance in living organisms, but Mendel's work explained the inheritance based on scientific experiments. He is honoured with title 'Father of Genetics'.

Law of Segregation

Mendel's Law of Segregation, states that allele pairs separate or segregate during gamete formation and randomly unite at fertilization.

The Four Concepts

There are four main concepts related to this principle:

1. A gene can exist in more than one form or allele.
2. Organisms inherit two alleles for each trait.
3. When sex cells are produced (by meiosis), allele pairs separate leaving each cell with a single allele for each trait.
4. When the two alleles of a pair are different, one is dominant and the other is recessive.

Nature of the gene

The law of segregation states that the parental genes must separate randomly and equally into gametes during meiosis so there is an equal chance of the offspring inheriting either allele. No allele is favored or has an advantage over another.

Law of segregation contrast with blending inheritance

The discredited theory that inheritance of traits from two parents produces offspring with characteristics that are intermediate between those of the parents, while Segregation, states that allele pairs separate or segregate during gamete formation and randomly unite at fertilization.

Law of independent assortment

Mendel's law of independent assortment states that the alleles of two (or more) different genes get sorted into gametes independently of one another. In other words, the allele a gamete receives for one gene does not influence the allele received for another gene.This can be explained by taking the example of inheritance of height and color of flower together in pea plant. This type of cross is termed dihybrid cross

Laws of probability apply to genetics

One probability rule that's very useful in genetics is the product rule, which states that the probability of two (or more) independent events occurring together can be calculated by multiplying the individual probabilities of the events. ... We can use the product rule to predict frequencies of fertilization events.

For example, if you roll a six-sided die once, you have a 1/61/61, slash, 6 chance of getting a six. If you roll two dice at once, your chance of getting two sixes is: (probability of a six on die 1) x (probability of a six on die 2) = (1/6) \cdot (1/6) = 1/36(1/6)⋅(1/6)=1/36left parenthesis, 1, slash, 6, right parenthesis, dot, left parenthesis, 1, slash, 6, right parenthesis, equals, 1, slash, 36.

Product rule

In general, you can think of the product rule as the “and” rule: if both event X and event Y must happen in order for a certain outcome to occur, and if X and Y are independent of each other (don’t affect each other’s likelihood), then you can use the product rule to calculate the probability of the outcome by multiplying the probabilities of X and Y.

Addition Rule

In some genetics problems, you may need to calculate the probability that any one of several events will occur. In this case, you’ll need to apply another rule of probability, the sum rule. According to the sum rule, the probability that any of several mutually exclusive events will occur is equal to the sum of the events’ individual probabilities.

For example, if you roll a six-sided die, you have a 1/61/61, slash, 6 chance of getting any given number, but you can only get one number per roll. You could never get both a one and a six at the same time; these outcomes are mutually exclusive. Thus, the chances of getting either a one or a six are: (probability of getting a 1) + (probability of getting a 6) = (1/6) +(1/6) = 1/3(1/6)+(1/6)=1/3left parenthesis, 1, slash, 6, right parenthesis, plus, left parenthesis, 1, slash, 6, right parenthesis, equals, 1, slash, 3.