Test: Genetics - 2 - Class 10

Each dihybrid plant produces 4 gamete types of equal frequency. In the offspring F2 showed 4 different phenotypes : the round and yellow traits did not stay linked to each other. 

Recessive gene expression:
Recessive genes are genes that are only expressed when an individual carries two copies of the recessive allele. Let's break down the options provided and determine which conditions allow for the expression of recessive genes.
A: Homozygous condition
- In a homozygous condition, an individual carries two identical alleles for a particular gene.
- If both alleles are recessive, the recessive gene will be expressed.
- For example, if an individual has two recessive alleles for eye color (bb), they will have brown eyes because the recessive gene for brown eyes is expressed.
B: Heterozygous condition
- In a heterozygous condition, an individual carries two different alleles for a particular gene.
- If one allele is recessive and the other is dominant, the dominant gene will be expressed while the recessive gene remains hidden.
- For example, if an individual has one dominant allele and one recessive allele for eye color (Bb), the dominant gene for blue eyes will be expressed.
C: Both above conditions
- From the explanations above, we can see that recessive genes can be expressed in both homozygous and heterozygous conditions.
- Therefore, the answer is C: both above conditions.
D: None of these conditions
- This option is incorrect because recessive genes can be expressed in both homozygous and heterozygous conditions.
In conclusion, recessive genes can be expressed in both homozygous and heterozygous conditions.

Explanation:
To explain why tallness is more widespread among pea plants, we need to consider the factors that contribute to pea plant height inheritance.
1. Tallness is dominant over dwarfness:
- This means that if a pea plant inherits the tall allele from one parent, it will exhibit the tall phenotype, even if it also inherits the dwarf allele from the other parent.
- On the other hand, for a pea plant to exhibit the dwarf phenotype, it needs to inherit the dwarf allele from both parents.
- Since tallness is dominant, it is more likely for pea plants to exhibit the tall phenotype.
2. Tallness is determined by one gene having many effects:
- In some cases, a single gene can have multiple effects on an organism's phenotype.
- If tallness in pea plants is determined by a single gene that has multiple effects, it increases the likelihood of the tall phenotype being expressed.
3. Tallness is determined by many genes having multiple effects:
- In some cases, a trait like height can be influenced by multiple genes, each contributing to the overall phenotype.
- If tallness in pea plants is determined by many genes that have multiple effects, it increases the complexity of inheritance patterns and the likelihood of the tall phenotype being expressed.
Based on these factors, the most likely explanation for tallness being more widespread among pea plants is that tallness is dominant over dwarfness. This means that even if a pea plant inherits the dwarf allele from one parent, it can still exhibit the tall phenotype if it inherits the tall allele from the other parent.

Explanation:
To understand why the white color is a recessive character, we need to consider the principles of inheritance and the concept of dominant and recessive traits.
1. Principles of Inheritance:
- Inheritance is the process by which traits are passed from parents to offspring.
- Each parent contributes one copy of each gene to the offspring.
- Genes are located on chromosomes, which come in pairs.
2. Dominant and Recessive Traits:
- In a pair of genes, one allele may be dominant and the other recessive.
- Dominant alleles are expressed and mask the expression of recessive alleles.
- Recessive alleles are only expressed when both alleles in a pair are recessive.
3. Crossing Red and White Flowered Pea Plants:
- When a red-flowered pea plant (RR) is crossed with a white-flowered plant (rr), the resulting offspring are called the F1 generation.
- The red color is dominant (R), and the white color is recessive (r).
4. F1 Generation Results:
- In the F1 generation, all plants were red-flowered.
- This indicates that the presence of the dominant red allele (R) masks the expression of the recessive white allele (r).
- The plants in the F1 generation are heterozygous (Rr), meaning they have one dominant and one recessive allele.
5. Conclusion:
- The fact that all plants in the F1 generation were red confirms that the white color is a recessive character.
- This means that for a plant to have a white color, it must have two copies of the recessive allele (rr).
Therefore, the correct answer is A: Recessive character.

Explanation:
To determine the chance of their first child having curly hair, we need to understand the inheritance pattern of hair texture. Hair texture is determined by genes, and the gene for hair texture can be either straight or curly.
The man is known to be heterozygous for the trait, which means he has one copy of the straight hair gene (S) and one copy of the curly hair gene (C). The woman's hair type is not specified, so we can assume she has two copies of the straight hair gene (SS).
When two individuals with different hair textures mate, the offspring can inherit either the straight hair gene or the curly hair gene from each parent.
Here are the possible combinations of genes for their first child:
- The child can inherit the straight hair gene from both parents (SS). In this case, the child will have straight hair.
- The child can inherit the straight hair gene from the mother and the curly hair gene from the father (SC). In this case, the child will have straight hair, as the dominant straight hair gene overrides the recessive curly hair gene.
- The child can inherit the curly hair gene from both parents (CC). In this case, the child will have curly hair.
Therefore, out of the three possible combinations of genes, two result in the child having straight hair and one results in the child having curly hair.
Conclusion:
The chance that their first child will have curly hair is one in two (1/2) or 50%.

Reasons for Mendel's Success in Discovering the Principles of Inheritance:

A: He considered each character separately:

• Mendel carefully selected specific traits to study, such as seed color, flower color, and plant height.


• He conducted experiments with true-breeding plants, which means they consistently produced offspring with the same traits as the parents.


• By studying each trait separately, Mendel was able to observe clear patterns of inheritance.

B: He was lucky not to encounter linkage problem:

• At the time of Mendel's experiments, he focused on traits that were not genetically linked.


• Genetic linkage refers to the tendency of certain genes to be inherited together because they are located close to each other on the same chromosome.


• Mendel's choice of traits helped him avoid the complications of genetic linkage, allowing him to identify and understand the basic principles of inheritance.

C: The plant was pure breeding:

• Mendel worked with plants that were true-breeding, meaning they consistently produced offspring with the same traits as the parents.


• This allowed Mendel to establish a clear pattern of inheritance by observing the traits passed down from one generation to the next.


• The use of pure-breeding plants helped Mendel eliminate the influence of other factors, making it easier to identify and understand the principles of inheritance.

D: All the above:

• All of the above factors contributed to Mendel's success in discovering the principles of inheritance.


• Considering each character separately, avoiding genetic linkage problems, and working with pure-breeding plants allowed Mendel to make significant observations and formulate his laws of inheritance.

In conclusion, Mendel's success in discovering the principles of inheritance can be attributed to his systematic approach, the traits he chose to study, the absence of genetic linkage, and the use of pure-breeding plants. These factors allowed him to make accurate observations, establish patterns of inheritance, and formulate the fundamental laws of genetics.

Mendel's Success Factors
1. He observed distinct inherited traits:
- Mendel carefully selected pea plants that exhibited clear and easily distinguishable traits, such as flower color, seed shape, and plant height.
- This allowed him to track the inheritance patterns of these traits more easily and accurately.
2. He qualitatively analyzed his data:
- Mendel meticulously recorded and analyzed the observed traits in a quantitative manner.
- He counted the number of plants showing each trait and analyzed the ratios of different traits in the offspring.
- This approach enabled him to establish the laws of inheritance and make accurate predictions about the outcomes of future crosses.
3. He considered only one character at one time:
- Mendel focused on studying one trait or character at a time, such as flower color or seed shape, rather than analyzing multiple traits simultaneously.
- This allowed him to simplify the complexity of inheritance and establish clear patterns and ratios in the transmission of traits.
4. He liked pea plants:
- Mendel's interest and passion for studying pea plants played a crucial role in his success.
- Pea plants possess several advantages for genetic research, such as their short generation time, large number of offspring, and easily observable traits.
- Mendel's fondness for pea plants motivated him to conduct numerous experiments and meticulously analyze the results, leading to his groundbreaking discoveries in genetics.
Therefore, among the given options, the factor that most significantly contributed to Mendel's success was his decision to consider only one character at a time (option D).

Mendel's work was not recognized since 1900. Rediscovery of Mendel's work was done by three scientists, Karl Correns of Germany, Hugo de Vries of Netherlands, and Erich Von Tschermark of Austria. 

The genotype of an organism is the chemical composition of its DNA, which gives rise to the phenotype, or observable traits of an organism. A genotype consists of all the nucleic acids present in a DNA molecule that code for a particular trait

Diploid organisms, for example, humans, have paired homologous chromosomes in their somatic cells, and these contain two copies of each gene.

An organism in which the two copies of the gene are identical — that is, have the same allele — is called homozygous for that gene.

When an individual is having both the alleles of a contrasting character, it is said to be HETEROZYGOUS .

Explanation:
When an allele fails to express itself in the presence of another allele in the F1 generation, it is considered to be recessive. This means that the recessive allele is masked or overshadowed by the dominant allele, resulting in only the dominant allele being expressed phenotypically.
Here is a detailed explanation:
Recessive:
- When an allele fails to express itself in the presence of another allele in the F1 generation, it is called a recessive allele.
- The recessive allele is represented by a lowercase letter.
- In order for the recessive allele to be expressed phenotypically, an individual must have two copies of the recessive allele (homozygous recessive).
Codominant:
- Codominance occurs when both alleles of a gene pair in a heterozygous individual are fully expressed.
- Neither allele is dominant or recessive, and both are expressed simultaneously.
- This results in a phenotype that shows a combination of both alleles.
Complementary:
- Complementary genes refer to the interaction between two different genes that work together to produce a specific phenotype.
- They are not related to the expression of a single allele in the presence of another allele.
Epistatic:
- Epistasis refers to the interaction between genes where one gene masks or modifies the expression of another gene.
- It is different from the scenario described in the question, where a single allele fails to express itself in the presence of another allele.
Therefore, the correct answer is A: Recessive.

 

In F2 -3 tall : 1 dwarf This is the law of segregation. 1 Homozygous tall 1 Homozygous dwarf 2 Heterozygous tall.

All red flowered plants; according to Mendel's law of dominance. 

Almost everyone has around a 50% chance of having a boy and a 50% chance of having a girl. What we can say is that dad's sperm determines whether a baby will be a boy or a girl. About half of his sperm will make a boy and half a girl. The sex of the baby depends on which sperm gets to the egg first.

To determine the proportion of dwarf progeny, let's analyze the cross between a heterozygous tall plant (Tt) and a homozygous dwarf plant (tt).
Genotype of tall plant: Tt
Genotype of dwarf plant: tt
When these two plants are crossed, the possible genotypes of the progeny are as follows:
1. Tt (tall)
2. Tt (tall)
3. tt (dwarf)
4. tt (dwarf)
From these genotypes, we can see that 2 out of 4 possible genotypes (50%) will result in dwarf progeny.
Therefore, the proportion of dwarf progeny is 50% (option A).

Explanation:
When a true breeding tall plant is crossed with a true breeding short plant, the F1 generation will have all tall plants. This is because the allele for tallness is dominant over the allele for shortness.
When the F1 generation is self-pollinated, the offspring in the F2 generation will show a segregation of alleles. This means that some plants will have the tall allele and some will have the short allele.
The ratio of true breeding tall plants to true breeding short plants in the F2 generation can be determined using the Punnett square. In this case, the genotype of the F1 generation would be Tt (where T represents the allele for tallness and t represents the allele for shortness).
Using the Punnett square, we can determine that the possible genotypes in the F2 generation are:
- TT (tall)
- Tt (tall)
- Tt (tall)
- tt (short)
The ratio of true breeding tall plants to true breeding short plants in the F2 generation is therefore 3:1.
Answer: B. 1 : 1

According to the law of dominance, a trait is represented by two contrasting factors of a gene in a heterozygous individual; the allele/factor that can express itself in a heterozygous individual is called as a dominant trait. The other factor whose effect is masked by the presence of dominant factor is called recessive factor. Since blue eye colour is recessive to brown eye colour, the genotype of blue eyed woman will be “bb”. Since brown eyed man had blue eyed mother (bb); he must have inherited one copy of “b” allele from the mother and thus is heterozygous brown eyed (Bb). A cross between blue eyed woman (bb) and heterozygous brown eyed man (Bb) will produce blue eyed and brown eyed children in 1:1: ratio. A cross between two pure breeding organisms obtains uniform F₁ generation; here father is not pure breeding. Recessive individuals never outnumber the dominant one. 

The human sex chromosomes are a typical pair of allosomes. These chromosomes determine the sex of an individual when reproducing. Allosomes are also referred to as sex chromosomes or idiosomes

A mutation is a change that occurs in our DNA sequence, either due to mistakes when the DNA is copied or as the result of environmental factors such as UV light and cigarette smoke.

De Vries Mutation Theory:
The De Vries mutation theory, proposed by Dutch botanist Hugo de Vries in the late 19th century, revolutionized the understanding of genetic inheritance. De Vries conducted extensive research on plant hybrids and discovered the concept of mutation, which challenged the prevailing theory of blending inheritance.
Plant Popularized by De Vries Mutation Theory:
The plant that was made popular by the De Vries mutation theory is Oenothera lamarkiana. This plant species, also known as Lamarck's evening primrose, played a significant role in De Vries' studies on mutations. He observed sudden and heritable changes in the traits of Oenothera lamarkiana, which led him to propose the concept of mutation as a mechanism for genetic variation.
Other Options:
While Oenothera lamarkiana is the correct answer, it's helpful to know about the other options as well:
- Triticum vulgare: This refers to common wheat, which is not directly associated with De Vries' mutation theory.
- Pisum sativum: This refers to garden pea, which is famous for Gregor Mendel's experiments on inheritance, not specifically related to De Vries' research.
- Primula vulgaris: This refers to the common primrose, which is not directly linked to De Vries' mutation theory.
Conclusion:
Oenothera lamarkiana is the plant species that gained prominence through the De Vries mutation theory. De Vries' research on this plant demonstrated the occurrence of sudden and heritable changes, leading to the concept of mutation as a mechanism for genetic variation.

The Barr body, also sometimes called the sex chromatin, is the inactive X chromosome in female somatic cells. Human females have two X chromosomes, while males have one X and one Y. In all of the female somatic cells, which don’t take part in sexual reproduction, one of the X chromosomes is active.

In 1952, Hershey & Chase were the ones to conclusively prove that DNA is the genetic material. They worked with bacteriophages – viruses that infect bacteria. A bacteriophage attaches and delivers its genetic material into a bacterial cell, where it generates more virus particles.

The proof for the fact that protein synthesis occurs through enzymes was given by George Beadle and Edward Tatum. They proposed the one gene one enzyme theory. According to this theory, one gene accounts for producing one protein. The scientists won the Nobel Prize for this concept in 1958.