Cell Division, Meiosis, Mendelian Genetics & pedigrees: Chapters 2–4

What are the three main purposes of cell division in multicellular organisms?

Repair & regeneration, growth, and reproduction.

What type of cell division occurs in somatic cells?

Mitosis.

What is the result of mitosis?

Two genetically identical daughter cells.

What is the purpose of meiosis?

To produce specialized reproductive cells (gametes) with half the number of chromosomes.

What type of cells undergo meiosis?

Sex cells (gametes).

What is the difference between diploid and haploid cells?

Diploid cells have two sets of chromosomes (2N), while haploid cells have one set (N).

What is a chromosome composed of?

DNA tightly coiled around histones.

What are sister chromatids?

Identical halves of a chromosome held together at the centromere.

What is the role of cohesin in cell division?

Cohesin holds sister chromatids together at the centromere.

How many chromosomes do human somatic cells contain?

46 chromosomes (23 pairs).

What are sex chromosomes?

Chromosomes that determine the sex of an organism (X and Y in humans).

What are autosomes?

The remaining body chromosomes that are not sex chromosomes.

What is the haploid number of chromosomes in human gametes?

23 chromosomes.

What is the significance of the Hayflick limit?

It is the maximum number of times a cell can divide before cell division stops.

What happens during the G0 phase of the cell cycle?

Cells exit the cell cycle and do not divide.

What is the longest phase of the cell cycle?

Interphase.

What are homologous chromosomes?

Chromosomes that have the same genes but may have different alleles.

What is a locus?

The position of a gene on a chromosome.

What is the difference between homozygotic and heterozygotic?

Homozygotic refers to having identical alleles, while heterozygotic refers to having different alleles.

What is the role of telomeres in cell division?

Telomeres protect the ends of chromosomes and are involved in the aging process of cells.

What is the outcome of fertilization?

The formation of a zygote with a diploid number of chromosomes (46 in humans).

What is the difference between mitosis and meiosis in terms of genetic variation?

Mitosis produces identical cells, while meiosis produces genetically unique gametes.

What is the purpose of mitosis?

To produce two identical diploid daughter somatic cells from a diploid parent cell.

What occurs during the Gap 1 (G1) phase of the cell cycle?

The cell grows to twice its original size, duplicates organelles, and increases cytoplasm volume.

What happens during the Synthesis (S) phase?

Semi-conservative replication occurs, and chromosomes duplicate.

What is the role of the Gap 2 (G2) phase?

The cell resumes growth and checks for errors in duplicated chromosomes, deciding whether to enter mitosis or undergo apoptosis.

What are the four phases of mitosis?

Prophase, Metaphase, Anaphase, and Telophase.

What characterizes prophase in mitosis?

Chromatin coils into visible chromosomes, centrioles migrate to opposite poles, and the nuclear envelope breaks down.

What occurs during metaphase in mitosis?

Chromosomes align single-file at the equator of the cell, and spindle fibers attach to sister chromatids.

What happens in anaphase of mitosis?

Sister chromatids separate and move to opposite poles of the cell.

What is the outcome of telophase in mitosis?

Two clusters of chromosomes decondense, and a new nuclear envelope forms around each cluster.

What is cytokinesis?

The process where the cytoplasm divides, resulting in two separate daughter cells.

What is the primary purpose of meiosis?

To produce four haploid gametes with genetic diversity.

What occurs during interphase I of meiosis?

Similar to mitosis interphase; chromosomes replicate, and centriole pairs replicate.

What is synapsis in meiosis?

The pairing of homologous chromosomes forming a tetrad during prophase I.

What is the significance of crossing over?

It creates genetic recombination by exchanging segments between non-sister chromatids.

What happens during metaphase I of meiosis?

Tetrads align on the metaphase plate, preparing for separation.

What is independent assortment in meiosis?

The random separation of homologous chromosomes, contributing to genetic diversity.

What is the result of meiosis I?

Two daughter cells are formed, each with a haploid set of chromosomes.

What occurs during meiosis II?

Similar to mitosis, resulting in the separation of sister chromatids and formation of four haploid cells.

How does mitosis differ from meiosis?

Mitosis produces two identical diploid cells, while meiosis produces four genetically unique haploid cells.

What is the role of centrioles during cell division?

Centrioles help organize the spindle fibers that separate chromosomes during mitosis and meiosis.

What is a cleavage furrow?

The indentation that forms in the cell membrane during cytokinesis in animal cells.

What is the significance of genetic variability in evolution?

Genetic variability allows for adaptation and survival in changing environments.

What is progeria?

A condition caused by a mutation that leads to premature aging.

What is cancer in relation to cell division?

Cancer is characterized by uncontrolled cell growth and division.

What is the outcome of meiosis in terms of chromosome number?

Meiosis produces gametes with half the number of chromosomes as the diploid parent cell.

What is interkinesis?

The period between meiosis I and meiosis II, similar to interphase but without DNA replication.

What is a tetrad?

A structure formed during meiosis I consisting of a pair of homologous chromosomes, each made of two sister chromatids.

What happens to chromosomes during telophase II?

Chromosomes uncoil, and the nuclear envelope reforms around each set of chromosomes.

Why is natural red hair considered rare?

Red hair is rare due to the specific genetic mutations associated with it, particularly in the MC1R gene.

What are the two types of melanin that determine hair color?

Eumelanin (brown/black pigment) and pheomelanin (red/yellow pigment).

What is the role of the MC1R gene in hair color?

The MC1R gene encodes a protein that influences the type of melanin produced, affecting hair color.

What is the difference between wildtype and mutant MC1R alleles?

Wildtype MC1R leads to more eumelanin (brown/black hair), while mutant MC1R leads to more pheomelanin (red/yellow hair).

On which chromosome is the MC1R gene found?

Chromosome 16.

Who is known as the 'Father of Genetics'?

Gregor Johann Mendel.

What organism did Mendel use for his genetic experiments?

Pea plants (Pisum sativum).

What is a monohybrid cross?

A genetic cross between two true-breeding parents that differ by only one characteristic.

What did Mendel's experiments help to uncover?

The fundamental principles of inheritance and how traits are passed from parents to offspring.

What are the characteristics of true-breeding pea plants?

True-breeding plants consistently produce offspring with the same traits when self-pollinated.

Why did Mendel choose pea plants for his studies?

They are easy to cultivate, reproduce quickly, and have distinct traits that can be easily observed.

What is the significance of Mendel's work being recognized 35 years later?

It highlights the initial lack of understanding and acceptance of genetic principles in the scientific community.

What is the expected outcome of a monohybrid cross?

The offspring are called monohybrids and exhibit a specific trait based on the alleles inherited.

What questions did Mendel's work raise about inheritance?

Whether each parent contributes equally to offspring and if traits blend or are inherited as discrete units.

What is the primary pigment associated with red hair?

Pheomelanin.

What is the relationship between eumelanin and hair color?

More eumelanin results in darker hair colors, while less eumelanin leads to lighter colors.

What is the significance of Mendel's controlled crosses?

They allowed for the systematic study of trait inheritance by observing offspring from specific parental combinations.

What does the term 'alleles' refer to?

Different versions of a gene that can exist at a specific locus on a chromosome.

What is the expected phenotype ratio in the offspring of a monohybrid cross?

Typically a 3:1 ratio of dominant to recessive traits in the F2 generation.

What does the term 'phenotype' mean?

The observable physical or biochemical characteristics of an organism, determined by its genotype.

What is the importance of studying the inheritance of traits?

It helps in understanding genetic disorders, breeding practices, and evolutionary biology.

What type of plants did Mendel use for his experiments?

Pure-breeding pea plants that were homozygotic at the locus for particular traits.

What is the dominant phenotype for seed shape in Mendel's experiments?

Round seeds (R) are dominant over wrinkled seeds (r).

What is the phenotypic ratio observed in Mendel's F2 generation?

A 3:1 ratio favoring the dominant phenotype.

What does the Law of Segregation state?

Each individual has two alleles for each trait, which segregate during gamete formation.

What is a Punnett Square used for?

To predict the outcome of a particular cross or breeding experiment.

What is the outcome of Mendel's monohybrid crosses regarding dominant and recessive phenotypes?

Only the dominant phenotype is expressed in the F1 generation; the recessive phenotype reappears in the F2 generation.

What does the Law of Dominance state?

One allele is dominant over the other, and the phenotype reflects the dominant allele.

What is complete dominance?

A dominant allele completely masks the effect of a recessive allele.

What does the term homozygotic mean?

Having two identical alleles for a particular gene.

What does the term heterozygotic mean?

Having two different alleles for a particular gene.

What is the significance of reciprocal crosses in Mendel's experiments?

They demonstrated that the results were the same regardless of which parent contributed the dominant or recessive allele.

What is the expected genotypic ratio from a monohybrid cross?

1:2:1 ratio of genotypes.

What is the expected phenotypic ratio from a monohybrid cross?

3:1 ratio of phenotypes favoring the dominant trait.

What does the Law of Independent Assortment state?

Genes for different traits segregate independently during gamete formation.

What is the genotype of a homozygotic dominant individual?

Both alleles are dominant (e.g., PP).

What is the genotype of a homozygotic recessive individual?

Both alleles are recessive (e.g., pp).

What is the genotype of a heterozygotic individual?

One dominant and one recessive allele (e.g., Pp).

What is the phenotype of a heterozygotic individual with a dominant allele?

The dominant phenotype is expressed.

What does the term 'genetic factors' refer to?

What we now call genes, which can be present but not expressed.

What is the outcome of a cross between a smooth pea plant and a wrinkled pea plant?

The F1 generation will produce 100% smooth peas.

What happens to the recessive phenotype in the F1 generation?

It disappears and reappears in 25% of the F2 generation.

What is the expected outcome of a monohybrid cross involving 8000 plants?

A 3:1 ratio of dominant to recessive phenotypes.

What is the significance of the 3:1 ratio in Mendel's experiments?

It indicates the dominance of one allele over another in the F2 generation.

What is the relationship between dominant and recessive alleles?

Dominant alleles mask the expression of recessive alleles.

What does it mean for traits to not be blended?

Traits are discrete and do not mix; they are either dominant or recessive.

What is the principle of segregation?

The principle that gametes contain only one genetic element (allele) from each parent, and the chance of passing one allele or the other is equal.

What happens during fertilization in terms of alleles?

Single alleles from each parental gamete fuse to create a new diploid organism containing two genetic elements.

What is a phenotype?

The observable expression of a trait, where only one allele is expressed and it is never a mix.

How is a dominant trait expressed?

A dominant trait is always expressed when present alongside a recessive trait.