Germline Cells and Mendelian Genetics

Flashcards based on concepts from germline cells and Mendelian genetics discussed in the lecture.

Germline cells are the __ cells that are precursors for gametes.

precursor

During meiosis one, the process results in __ cells.

two

Meiosis involves __ division of chromosomes.

reduction

After meiosis two, the result is __ hyperploid cells each with 23 chromosomes.

four

An allele is an __ form of a gene or trait.

alternate

The physical expression of a genotype is called the __.

phenotype

In Mendelian genetics, the dominant traits are those that __ in a heterozygous condition.

express

Homozygous dominant means having __ identical alleles for a trait.

two

The observable traits in offspring are referred to as __ traits.

dominant

When traits blend together, it is referred to as __ inheritance.

blending

Genetic variation occurs mainly during __ one of meiosis.

prophase

Mendel conducted his experiments on __ plants to observe inheritance patterns.

pea

A test cross is used to determine the __ of an unknown genotype.

genotype

The __ square is a tool used to predict the genotype of the offspring.

Punnett

The ratio of dominant to recessive traits observed in Mendel's F2 generation is __ to one.

three

Incomplete dominance results in a phenotype that is a __ of two parent traits.

blend

The concept that each trait is controlled by a __ gene is a fundamental principle of Mendelian genetics.

single

Explain the critical function of germline cells in the context of species survival and genetic continuity.\n\n

Germline cells are specialized cells that give rise to gametes (sperm and egg cells). Their integrity and ability to pass on genetic material ensure the continuation of a species across generations, making them central to heredity.\n\n

Describe the ploidy and chromosome state of the cells immediately following Meiosis I, and what key event distinguishes this stage from mitosis.\n\n

Following Meiosis I, two haploid cells are produced, each containing replicated sister chromatids. The key distinguishing event is the segregation of homologous chromosomes, which reduces the chromosome number by half.\n\n

What is the biological significance of meiosis being a 'reduction division' in sexually reproducing organisms?\n\n

Meiosis reduces the chromosome number by half to ensure that when two gametes fuse during fertilization, the resulting zygote has the correct diploid chromosome number. This prevents a doubling of chromosomes in each successive generation.\n\n

Characterize the ploidy and genetic content of the four cells produced after Meiosis II, and explain their ultimate role.\n\n

After Meiosis II, four haploid cells are produced. Each cell is genetically unique and contains unreplicated chromosomes. These cells develop into gametes (sperm or egg), which are essential for sexual reproduction.\n\n

How do different alleles of a gene contribute to phenotypic variation within a population?\n\n

Alleles are alternate forms of a gene. Different alleles can lead to variations in the gene product or its regulation, resulting in different observable traits (phenotypes) among individuals in a population. For example, alleles for eye color result in blue, brown, or green eyes.\n\n

Distinguish between genotype and phenotype, providing an example where environmental factors might influence phenotypic expression.\n\n

Genotype refers to an organism's complete set of genes (genetic makeup), while phenotype is the observable physical or biochemical characteristics resulting from the expression of the genotype. For example, a person's genotype might predispose them to a certain height, but their actual height (phenotype) can be influenced by nutrition (an environmental factor).\n\n

Explain the principle of dominance in Mendelian genetics and its implications for predicting traits in heterozygous individuals.\n\n

The principle of dominance states that in a heterozygote, one allele (the dominant allele) will mask the expression of the other allele (the recessive allele). This means that a heterozygous individual will express the dominant phenotype, making it impossible to distinguish them phenotypically from a homozygous dominant individual.\n\n

In genetic crosses, how does knowing an individual is homozygous dominant provide more certainty about their genetic contribution to offspring compared to just knowing they express the dominant phenotype?\n\n

A homozygous dominant individual possesses two identical dominant alleles for a trait. This means they will exclusively pass on the dominant allele to all their offspring for that particular gene. In contrast, an individual expressing a dominant phenotype could be either homozygous dominant or heterozygous, and a heterozygous individual would pass on a recessive allele approximately 50% of the time.\n\n

In a monohybrid cross between two heterozygous individuals, what phenotypic ratio is expected, and how does this illustrate the concept of dominant and recessive traits?\n\n

A 3:1 phenotypic ratio (3 dominant: 1 recessive) is expected. This illustrates that while dominant traits express themselves even in the presence of a recessive allele, recessive traits only become observable phenotypically when two copies of the recessive allele are present (homozygous recessive), as they are masked by the dominant allele in heterozygotes.\n\n

Contrast incomplete dominance with complete dominance, specifically regarding the phenotypic outcome in heterozygous individuals and the implications for 'blending inheritance'.\n\n

In complete dominance, the heterozygote expresses the dominant phenotype. In incomplete dominance, the heterozygote exhibits an intermediate phenotype that is a 'blend' of the two parental traits (e.g., red and white flowers produce pink). This disproves the historical idea of 'blending inheritance' where traits were thought to permanently merge, as alleles remain distinct and can segregate in subsequent generations.\n\n

Identify and explain the two primary mechanisms during Meiosis I that generate significant genetic variation among gametes.\n\n

The two primary mechanisms are: 1. Crossing Over (Prophase I): Exchange of genetic material between homologous chromosomes, creating new combinations of alleles on chromatids. 2. Independent Assortment (Metaphase I): Random alignment of homologous chromosome pairs at the metaphase plate, leading to different combinations of maternal and paternal chromosomes in the daughter cells.\n\n

Critically evaluate why Pisum sativum (garden pea) was an exceptionally suitable model organism for Mendel's foundational studies in genetics.\n\n

Pea plants were suitable due to: 1. Distinct, easily observable traits: (e.g., flower color, seed shape) with clear dominant/recessive patterns. 2. Controlled crosses: They can self-pollinate or be cross-pollinated manually. 3. Short generation time and numerous offspring: Allowed for quick observation of multiple generations and statistical analysis. 4. True-breeding varieties: Available to establish baseline parental lines.\n\n

Explain the methodology and purpose of a test cross. What specific information does it aim to reveal?\n\n

A test cross involves mating an individual with an unknown genotype (showing a dominant phenotype) with a homozygous recessive individual. Its purpose is to determine the unknown genotype. If any offspring express the recessive phenotype, the unknown parent must be heterozygous; if all offspring express the dominant phenotype, the unknown parent is likely homozygous dominant.\n\n

Construct a Punnett Square to illustrate a dihybrid cross between two individuals heterozygous for two unlinked traits (e.g., AaBb x AaBb). What are the expected phenotypic ratios?\n\n

A Punnett square for AaBb x AaBb would show a phenotypic ratio of 9:3:3:1 for the four possible phenotypes (Dominant/Dominant : Dominant/Recessive : Recessive/Dominant : Recessive/Recessive). It visually represents all possible combinations of gametes and their resulting offspring genotypes and phenotypes, based on Mendelian probabilities.\n\n

How does Mendel's Law of Segregation fundamentally explain the consistent 3:1 phenotypic ratio observed in the F2 generation of a monohybrid cross?\n\n

The Law of Segregation states that during gamete formation, the two alleles for a heritable character separate (segregate) from each other such that each gamete receives only one allele. In an F1 heterozygous cross (Aa x Aa), half the gametes carry A and half carry a. Random fertilization then leads to genotypes AA:Aa:aa in a 1:2:1 ratio, resulting in a 3:1 dominant:recessive phenotypic ratio.\n\n

Given a plant species where flower color shows incomplete dominance (Red is RR, White is WW, Pink is RW). If two pink-flowered plants are crossed, predict the genotypic and phenotypic ratios of their offspring.\n\n

If two pink-flowered plants (RW x RW) are crossed:\n- Genotypic Ratio: 1 RR : 2 RW : 1 WW\n- Phenotypic Ratio: 1 Red : 2 Pink : 1 White\nThis demonstrates that incomplete dominance results in a distinct phenotypic expression for heterozygotes.\n\n

While Mendel's work focused on traits controlled by a single gene, discuss how modern genetics acknowledges more complex inheritance patterns such as polygenic inheritance and pleiotropy.\n\n

Modern genetics reveals that many traits are more complex:\n- Polygenic inheritance: Multiple genes contribute to a single phenotype (e.g., human height, skin color), resulting in continuous variation.\n- Pleiotropy: A single gene affects multiple distinct phenotypic traits (e.g., the gene for sickle cell anemia affects red blood cell shape, anemia, and resistance to malaria). These patterns show that the one-gene-one-trait model is often a simplification.\n\n