44 Questions
What was the major flaw in the preformationist theory?
It proposed that a tiny homunculus was present in the sperm or egg
Who is associated with the theory of Epigenesis?
Caspar F.Wolff & Karl Ernst von Baer
What was the significance of Jan Swammerdam and Charles Bonnet's work?
They contributed to the development of the preformationist theory
What is the main idea behind the Germplasm theory?
The theory that heredity is determined by the germplasm
Who is credited with the development of the theory of Mendelism?
Mendel
What is the main difference between the 'spermatist' and the 'ovist'?
The 'spermatist' believed that the homunculus was present in the sperm, while the 'ovist' believed it was present in the egg
What is the main idea behind Lamarckism?
The idea that acquired traits can be inherited
What was the significance of Charles Darwin's work in the context of heredity?
He developed the theory of Pangenesis
What is always used as one of the parents in a testcross?
Recessive homozygote
What is the main difference between testcross and backcross?
Use of recessive homozygote as a parent
What is the genotype of the offspring in a testcross?
Dd
What is the purpose of a testcross?
To study the principles of segregation
What is true about backcross?
It is not necessarily true that a recessive homozygote is used as a parent
What is the expected ratio of a monohybrid cross?
3:1
What is the difference between the genotype of the parents in a testcross and backcross?
Testcross has homozygous recessive and backcross has heterozygous
What is the significance of a testcross?
It helps in studying the principles of segregation
What is the name of the law of probability that relates to the operation of two monohybrid crosses?
Product Rule
What is the significance of a 9:3:3:1 ratio in experiments?
It indicates that two independent pairs of alleles are involved
What is the genotype of the other parent in a testcross?
Dd
What is the outcome of a testcross?
All offspring are heterozygous
What type of cross is represented by the genotype AABBCC X aabbcc?
Trihybrid cross
What is the main advantage of a testcross?
It helps in studying the principles of segregation
What is the genotype of the seed parent in the trihybrid ratio example?
DDGGWW
What is the phenotype of the gamete RrYy?
Round, yellow
What is the purpose of understanding the principle of dihybrid and trihybrid crosses in plant and animal breeding?
To improve the quantity and quality of agricultural and animal products
What is the ratio of the genotypic frequency to the phenotypic frequency in the dihybrid backcross?
1:1
What is the formula to calculate the probability of a binomial distribution?
P = (n!/s!t!)(psqt)
What is the probability that two babies out of four will be boys and two will be girls?
10/32
What is the probability that all four babies will be girls?
1/32
What is the probability that a given child will be normal if the parents are heterozygous for albinism?
1/2
What is the probability that all four children will be normal if the parents are heterozygous for albinism?
1/16
What is the probability that all four children will be normal except the 2nd child if the parents are heterozygous for albinism?
3/16
What is the condition for two events to be independent in probability?
The probability of one event does not affect the probability of the other event
What is the concept of studying the probability of multiple genetic events?
Probability of multiple events
What is the purpose of a testcross in genetics?
To determine the genotype of an individual organism
What is the difference between a testcross and a backcross?
A testcross uses a recessive homozygote as one of the parents, while a backcross does not
What is the purpose of the first experiment in studying the principles of segregation?
To test the principles of segregation
What is the result of crossing a heterozygote with a homozygote recessive?
Half of the offspring are heterozygous and half are homozygous recessive
What is the purpose of backcrossing in genetics?
To separate out certain characteristics in a related group of organisms
What is the advantage of using a testcross over a backcross?
A testcross always uses a recessive homozygote as one of the parents
What is the principle of segregation?
The principle that each pair of alleles separates during gamete formation
Why is a testcross useful in genetics?
Because it allows for the determination of genotypes, especially when it is unclear
What is the result of crossing two heterozygotes?
Half of the offspring are heterozygous and half are homozygous recessive
What is the main difference between a heterozygote and a homozygote?
A heterozygote has two different alleles, while a homozygote has two identical alleles
Study Notes
Historical Development of Genetics
- Preformation theory (1665): Development is simply a matter of growth of a tiny homunculus, with two opposing views - "spermatist" and "ovist".
- Epigenesis theory (1759): Development occurs through a series of complex interactions, with sex cells being homogenous bits of organic matter containing nothing resembling the body that will develop from them.
Key Figures in Genetics
- Jan Swammerdam
- Charles Bonnet
- Karl Ernst von Baer
- Charles Lamarck
- August Weismann
- Gregor Mendel
Principles of Segregation
- Useful in genetics studies for determining the genotypes of individual organisms (homozygous or heterozygous)
- Helps isolate (separate out) certain characteristics in a related group of animals or plants
First Experiment: Testing the Principle of Segregation
- F1 Generation: Cross between two individuals with different genotypes (e.g., Dd x dd)
- Backcross: F1 (progeny) is mated or crossed back to one of their parents or with an individual that has a parental genotype
Difference between Testcross and Backcross
- Testcross: A recessive homozygote is always used as one of the parents, with a specific goal of identifying the genotype of the other parent
- Backcross: Not necessarily true, with the goal of identifying the genotype of the F1 progeny### First Experiment: Testcross and Backcross
- In testcross, a recessive homozygote is always used as one of the parents.
- The testcross parent is homozygous recessive for the gene of interest.
- This is not necessarily true in a backcross.
Principles of Segregation
- The results of a testcross can be mathematically expressed as two monohybrid crosses, each expected to result in a 3:1 ratio.
- The combined result is a 9:3:3:1 ratio, which conforms to the law of probability called the "Product Rule".
Second Experiment: Dihybrid Backcross
- When a 9:3:3:1 ratio results in an experiment, geneticists may postulate that two independent pairs of alleles are involved.
- One member of each pair behaves like a dominant over its allele.
- The F1 generation is heterozygous for both genes (RrYy).
- The gametes produced are RY, Ry, rY, and ry.
- The resulting genotype and phenotype ratios are 1:1:1:1.
Trihybrid Ratios
- A cross between homozygous parents that differ in three gene pairs is a combination of three-pair crosses operating together.
- The genotype ratio is a combination of three independent monohybrid crosses.
Probability and Genetic Events
- Probability is used to calculate the likelihood of genetic events.
- The independence of genetic events is a key concept in probability calculations.
- The binomial expansion/distribution is a mathematical formula used to calculate the probability of multiple events.
- The formula is P = (n!/s!t!)(psqt), where n is the total number of events, s is the number of successes, t is the number of failures, p is the probability of success, and q is the probability of failure.
Examples of Probability Calculations
- If four babies are born at a given hospital on the same day, the probability that two will be boys and two will be girls is 10/32.
- If a heterozygous man and woman plan to have four children, the probability that any given child will be normal is 1/2, and the probability that all four will be normal is 1/16.
This quiz covers the key figures and their contributions to the development of evolutionary theory, from preformation to modern genetics.
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