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Questions and Answers
Mitosis occurs in somatic cells and results in diploid cells.
Mitosis occurs in somatic cells and results in diploid cells.
True
Meiosis produces diploid cells from haploid cells.
Meiosis produces diploid cells from haploid cells.
False
The G1 phase of the cell cycle includes preparation for cell division.
The G1 phase of the cell cycle includes preparation for cell division.
True
The S phase of the cell cycle is the resting phase before cell division.
The S phase of the cell cycle is the resting phase before cell division.
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G0 is a non-replicative optional phase in the cell cycle.
G0 is a non-replicative optional phase in the cell cycle.
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Humans have 23 chromosome pairs, consisting of 22 autosomes and sex chromosomes.
Humans have 23 chromosome pairs, consisting of 22 autosomes and sex chromosomes.
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During mitosis, DNA is copied twice, resulting in 92 chromosomes before the cell divides.
During mitosis, DNA is copied twice, resulting in 92 chromosomes before the cell divides.
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The result of meiosis is two diploid cells.
The result of meiosis is two diploid cells.
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Acentromeric chromosome fragments cannot be passed to daughter cells because they do not attach to the spindle.
Acentromeric chromosome fragments cannot be passed to daughter cells because they do not attach to the spindle.
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After separation during mitosis, each sister chromatid is called a chromosome.
After separation during mitosis, each sister chromatid is called a chromosome.
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In pea plants, the allele R is dominant over allele r.
In pea plants, the allele R is dominant over allele r.
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The genotype ratio of a cross Rr x Rr in pea plants is 2:1:1.
The genotype ratio of a cross Rr x Rr in pea plants is 2:1:1.
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Single-gene defects follow a non-Mendelian inheritance pattern.
Single-gene defects follow a non-Mendelian inheritance pattern.
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Autosomal dominant and autosomal recessive are types of inherited disease patterns.
Autosomal dominant and autosomal recessive are types of inherited disease patterns.
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Pedigree analysis is a method used to identify inherited diseases in families.
Pedigree analysis is a method used to identify inherited diseases in families.
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Meiosis includes one round of DNA synthesis followed by two rounds of division.
Meiosis includes one round of DNA synthesis followed by two rounds of division.
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In meiosis, crossing over occurs during prophase I.
In meiosis, crossing over occurs during prophase I.
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Independent assortment refers to the random segregation of sister chromatids during anaphase.
Independent assortment refers to the random segregation of sister chromatids during anaphase.
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Human sperm form continuously in the ovaries after puberty.
Human sperm form continuously in the ovaries after puberty.
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Each bivalent is composed of four chromatids.
Each bivalent is composed of four chromatids.
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Only one of the three cells produced by female meiosis becomes a functional gamete.
Only one of the three cells produced by female meiosis becomes a functional gamete.
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Human oocytes are arrested in metaphase I until fertilization occurs.
Human oocytes are arrested in metaphase I until fertilization occurs.
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The random arrangement of chromosomes during meiosis results in genetic diversity.
The random arrangement of chromosomes during meiosis results in genetic diversity.
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Recombination normally occurs during Mitosis.
Recombination normally occurs during Mitosis.
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A haploid gamete arises from a diploid precursor cell through meiosis.
A haploid gamete arises from a diploid precursor cell through meiosis.
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Each gene copy is referred to as a chromosome.
Each gene copy is referred to as a chromosome.
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The genotype refers to the physical appearance of an organism.
The genotype refers to the physical appearance of an organism.
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An individual can have different alleles of a gene, such as A and a.
An individual can have different alleles of a gene, such as A and a.
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Paternal homologs can create $2^{23}$ possible combinations in gametes.
Paternal homologs can create $2^{23}$ possible combinations in gametes.
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Phenotype is largely determined by the environment and not by genotype.
Phenotype is largely determined by the environment and not by genotype.
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Alleles can vary slightly in their DNA base sequence, contributing to genetic diversity.
Alleles can vary slightly in their DNA base sequence, contributing to genetic diversity.
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Mitosis results in haploid cells from diploid cells.
Mitosis results in haploid cells from diploid cells.
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The G2 phase of the cell cycle is primarily involved in DNA replication.
The G2 phase of the cell cycle is primarily involved in DNA replication.
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During meiosis, genetic variation is introduced through crossing over.
During meiosis, genetic variation is introduced through crossing over.
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In somatic cells, only mitosis occurs, as meiosis is exclusive to gametes.
In somatic cells, only mitosis occurs, as meiosis is exclusive to gametes.
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The S phase lasts longer than the G1 phase in the cell cycle.
The S phase lasts longer than the G1 phase in the cell cycle.
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During mitosis, the number of chromosomes doubles before the cell divides.
During mitosis, the number of chromosomes doubles before the cell divides.
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Meiosis results in two diploid cells from one diploid cell.
Meiosis results in two diploid cells from one diploid cell.
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Sister chromatids are separated during metaphase of mitosis.
Sister chromatids are separated during metaphase of mitosis.
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Acentromeric chromosome fragments are passed to daughter cells during cell division.
Acentromeric chromosome fragments are passed to daughter cells during cell division.
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In meiosis, crossing over occurs in prophase II.
In meiosis, crossing over occurs in prophase II.
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Meiosis I involves one round of DNA synthesis followed by two rounds of division.
Meiosis I involves one round of DNA synthesis followed by two rounds of division.
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Independent assortment results in the random segregation of maternal and paternal chromosomes during meiosis.
Independent assortment results in the random segregation of maternal and paternal chromosomes during meiosis.
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The bivalent structure in meiosis consists of two homologous chromosomes each containing four chromatids.
The bivalent structure in meiosis consists of two homologous chromosomes each containing four chromatids.
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Recombination occurs during the telophase of meiosis.
Recombination occurs during the telophase of meiosis.
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Only one of the four cells produced by male meiosis becomes a functional sperm.
Only one of the four cells produced by male meiosis becomes a functional sperm.
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After puberty, human sperm are produced continuously in the ovaries.
After puberty, human sperm are produced continuously in the ovaries.
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The phenotype ratio of a cross Rr x Rr in pea plants is 3:1.
The phenotype ratio of a cross Rr x Rr in pea plants is 3:1.
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Genetic diversity in meiosis is generated by independent assortment and recombination.
Genetic diversity in meiosis is generated by independent assortment and recombination.
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Single-gene defects exhibit complex inheritance patterns.
Single-gene defects exhibit complex inheritance patterns.
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During fetal development, primary oocytes are arrested in metaphase I.
During fetal development, primary oocytes are arrested in metaphase I.
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X-linked recessive diseases are more commonly expressed in males than in females.
X-linked recessive diseases are more commonly expressed in males than in females.
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Pedigree analysis is a method used to classify X-linked dominant disorders.
Pedigree analysis is a method used to classify X-linked dominant disorders.
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The genotype ratio of a cross Rr x Rr in pea plants is 1:2:1.
The genotype ratio of a cross Rr x Rr in pea plants is 1:2:1.
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Recombination occurs during Pachytene in Meiosis I without any DNA sequences being gained or lost.
Recombination occurs during Pachytene in Meiosis I without any DNA sequences being gained or lost.
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The genotype of an organism directly refers to its physical appearance.
The genotype of an organism directly refers to its physical appearance.
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A diploid zygote is formed by the combination of haploid sperm and egg chromosomes during fertilization.
A diploid zygote is formed by the combination of haploid sperm and egg chromosomes during fertilization.
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Most cells in organisms are haploid, having only one copy of each chromosome.
Most cells in organisms are haploid, having only one copy of each chromosome.
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Polygenic traits are determined by multiple genes and typically exhibit a range of phenotypes.
Polygenic traits are determined by multiple genes and typically exhibit a range of phenotypes.
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Alleles are identical copies of a gene found on homologous chromosomes.
Alleles are identical copies of a gene found on homologous chromosomes.
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Non-disjunction during meiosis results in the loss or gain of whole chromosomes.
Non-disjunction during meiosis results in the loss or gain of whole chromosomes.
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The allele that determines a phenotype is always recessive.
The allele that determines a phenotype is always recessive.
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In somatic cells, mitosis results in haploid cells from diploid cells.
In somatic cells, mitosis results in haploid cells from diploid cells.
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The G1 phase of the cell cycle lasts approximately 10 hours and includes DNA replication.
The G1 phase of the cell cycle lasts approximately 10 hours and includes DNA replication.
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Meiosis produces four haploid gametes from one diploid precursor cell through two rounds of division.
Meiosis produces four haploid gametes from one diploid precursor cell through two rounds of division.
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Independent assortment during meiosis is the result of random segregation of sister chromatids during anaphase I.
Independent assortment during meiosis is the result of random segregation of sister chromatids during anaphase I.
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Crossing over occurs during prophase II of meiosis.
Crossing over occurs during prophase II of meiosis.
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A bivalent structure during meiosis comprises two homologous chromosomes each containing four chromatids.
A bivalent structure during meiosis comprises two homologous chromosomes each containing four chromatids.
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Recombination occurs exclusively during metaphase I of meiosis.
Recombination occurs exclusively during metaphase I of meiosis.
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Meiosis generates genetic variation primarily through a single process known as independent assortment.
Meiosis generates genetic variation primarily through a single process known as independent assortment.
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Human primary oocytes are arrested in the diplotene stage until ovulation occurs.
Human primary oocytes are arrested in the diplotene stage until ovulation occurs.
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During spermatogenesis, only one of the four cells produced by meiosis becomes a functional sperm.
During spermatogenesis, only one of the four cells produced by meiosis becomes a functional sperm.
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Independent assortment allows for $2^{23}$ different combinations of chromosomes in human gametes.
Independent assortment allows for $2^{23}$ different combinations of chromosomes in human gametes.
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The process of crossing over contributes to genetic diversity by separating maternal and paternal homologs.
The process of crossing over contributes to genetic diversity by separating maternal and paternal homologs.
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An acentromeric chromosome fragment can successfully segregate to daughter cells during cell division.
An acentromeric chromosome fragment can successfully segregate to daughter cells during cell division.
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Recombination occurs during Pachytene in Meiosis II.
Recombination occurs during Pachytene in Meiosis II.
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Haploid gametes arise through the process of mitosis.
Haploid gametes arise through the process of mitosis.
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Alleles can differ by more than just one base pair in their DNA sequence.
Alleles can differ by more than just one base pair in their DNA sequence.
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A recessive trait is always expressed phenotypically if present in the genotype.
A recessive trait is always expressed phenotypically if present in the genotype.
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During the mitotic process, genomic DNA is duplicated resulting in 46 chromosomes initially and goes to 92 before cell division occurs.
During the mitotic process, genomic DNA is duplicated resulting in 46 chromosomes initially and goes to 92 before cell division occurs.
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During fertilization, the sperm and egg contribute equally to the genetic makeup of the zygote.
During fertilization, the sperm and egg contribute equally to the genetic makeup of the zygote.
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Polymorphism in a population refers to the presence of multiple distinct phenotypes.
Polymorphism in a population refers to the presence of multiple distinct phenotypes.
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Following meiosis, the resultant cells are diploid, having retained both sets of maternal and paternal chromosomes.
Following meiosis, the resultant cells are diploid, having retained both sets of maternal and paternal chromosomes.
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Each daughter cell from mitosis retains a diploid number of chromosomes after cell division is complete.
Each daughter cell from mitosis retains a diploid number of chromosomes after cell division is complete.
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Each gene has only one allele present in diploid organisms.
Each gene has only one allele present in diploid organisms.
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The physical appearance of an organism is primarily determined by its genotype.
The physical appearance of an organism is primarily determined by its genotype.
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In the process of meiosis, the bivalent structure comprises one duplicated chromosome from each set of homologous chromosomes.
In the process of meiosis, the bivalent structure comprises one duplicated chromosome from each set of homologous chromosomes.
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Acentromeric chromosomes can successfully attach to the mitotic spindle during cell division and are distributed to daughter cells.
Acentromeric chromosomes can successfully attach to the mitotic spindle during cell division and are distributed to daughter cells.
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The phenotype ratio of a monogenic disease follows a 2:1 pattern.
The phenotype ratio of a monogenic disease follows a 2:1 pattern.
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Multi-gene defects result from complex interactions between multiple alleles.
Multi-gene defects result from complex interactions between multiple alleles.
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Autosomal recessive traits are only expressed when two dominant alleles are present.
Autosomal recessive traits are only expressed when two dominant alleles are present.
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X-linked dominant conditions can affect both males and females, but X-linked recessive conditions predominantly affect males.
X-linked dominant conditions can affect both males and females, but X-linked recessive conditions predominantly affect males.
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The genotype ratio from a cross of two heterozygous pea plants is 1:2:1.
The genotype ratio from a cross of two heterozygous pea plants is 1:2:1.
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Study Notes
Cell Division
- Cell division is essential for development and the generation of new cells in adults.
- In somatic cells, division occurs through mitosis, a process that occurs as part of the cell cycle, resulting in diploid cells from diploid cells.
- Meiosis is a specialized form of cell division that produces sperm and egg cells, converting diploid cells into haploid cells.
- Humans have 23 pairs of chromosomes: 22 autosomes and one pair of sex chromosomes (XX = female, XY = male).
Cell Cycle
- The cell cycle includes a series of phases: G1, S, G2, and M.
- G1 is the period of cell growth and preparation for division, including the replication of key components like centrosomes.
- The S phase is the "synthesis" phase where DNA replication occurs.
- G2 is a short resting phase before cell division.
- Mitosis is the cell division phase, lasting approximately 2 hours.
- G0 is an optional non-replicative phase that many differentiated cells enter, like hepatocytes.
Mitosis and DNA Replication
- During mitosis, DNA is copied once, resulting in 92 chromosomes, and then the cell divides once, distributing the chromosomes evenly to create two daughter cells with 46 chromosomes each (2 x 23), maintaining the diploid state.
- The mitotic spindle plays a crucial role in segregation during cell division, ensuring each daughter cell receives a complete set of chromosomes.
- DNA replication results in two identical DNA molecules, each with one old strand and one new strand, ensuring accurate genetic transmission.
Meiosis
- Meiosis is a two-stage process that reduces the number of chromosomes from diploid to haploid.
- Meiosis I involves pairing of homologous chromosomes (bivalent/tetrad formation), recombination (exchange between maternal and paternal chromosomes), and segregation of homologous chromosomes, leading to two haploid cells.
- Meiosis II further divides the chromatids, producing four haploid cells.
Genetic Diversity in Meiosis
- Meiosis I generates genetic diversity through independent assortment and recombination.
- Independent assortment refers to the random segregation of paternal and maternal chromosomes during bivalent alignment at the metaphase plate, contributing to unique combinations of chromosomes in each daughter cell.
- Recombination occurs during Pachytene (Meiosis I) and involves physical breakage and joining of maternal and paternal chromatids, resulting in exchange of DNA sequences.
Haploid Gametes and Fertilization
- Haploid gametes (sperm and egg) are produced through meiosis from diploid precursors.
- Fertilization involves the fusion of sperm and egg chromosomes, forming a diploid zygote.
- Subsequent rounds of mitosis and differentiation lead to the development of a complete organism.
Genetic Terminology
- Most cells are diploid, containing two homologous copies of each chromosome (one maternal and one paternal).
- Each gene copy is called an allele, and different alleles can combine to produce different genotypes.
- Genotype refers to the genetic constitution, while phenotype refers to the physical appearance or observable characteristics.
- Phenotype is primarily determined by genotype, with dominant alleles masking recessive alleles.
Human Inherited Diseases
- Genetic defects can lead to diseases, with two main categories:
- Single-gene (monogenic) defects: caused by a single disease allele, either dominant or recessive, resulting in a simple Mendelian inheritance pattern.
- Multi-gene (polygenic) defects: involve interactions of multiple genes, resulting in complex non-Mendelian inheritance patterns.
- Pedigree analysis helps identify the inheritance patterns of diseases within families, revealing autosomal dominant, autosomal recessive, X-linked dominant, and X-linked recessive modes.
Cell Division
- Cell division occurs during development and to generate new cells in adults.
- In somatic cells, division occurs by mitosis.
- Mitosis occurs as part of the cell cycle.
- Diploid cells divide to produce diploid cells.
- Meiosis is a specialized form of cell division that produces sperm and egg cells.
- Diploid cells divide to produce haploid cells.
Cell Cycle
- The cell cycle comprises four phases: G1, S, G2, and M (mitosis)
- The cell cycle can include an optional resting phase, G0
- G0 is a non-replicative phase.
- Many differentiated cells remain in G0, including for example, hepatocytes
- G1 is a period of cell growth and preparation for cell division.
- G1 includes the replication of key components such as centrosomes.
- S is the synthesis phase; DNA replication occurs.
- G2 is a short resting phase before cell division occurs.
- M is the phase where cell division occurs.
Humans
- Humans are diploid (2n), with 23 pairs of chromosomes, 22 autosomes + sex chromosomes
- Sex-determining chromosomes
- XX = female
- XY = male
Mitosis
- Mitosis describes how the genome goes from being duplicated to segregated.
- Genomic DNA is copied accurately and divided between the daughter cells.
- DNA is copied once during mitosis: 46 92 chromosomes.
- The cell divides once: 92 chromosomes / 2 cells 46 chromosomes = 2 x 23 (diploid)
Mitotic Spindle
- The centromere is essential for chromosome segregation during cell division.
- Chromosome fragments lacking a centromere (acentric) do not become attached to the spindle.
- Acentric fragments are not passed onto daughter cells.
Mitosis and DNA Replication
- The end result of DNA replication is two DNA molecules, each with one old strand and one new strand.
- Both strands of the DNA molecule have the same sequence.
- The two DNA molecules form sister chromatids.
- Sister chromatids are separated during anaphase.
- Each daughter cell gets one sister chromatid.
- After separation, each chromatid is referred to as a chromosome.
- Each daughter cell gets a full copy of the genetic information in the parent cell.
Meiosis
- Meiosis reduces diploid to haploid.
- Meiosis is preceded by one round of DNA synthesis.
- There are five stages of prophase in Meiosis I.
- Recombination: exchange between maternal and paternal chromosomes (homologs).
- Bivalent/tetrad: a four-stranded structure (two chromatids/homologous chromosomes).
- Bivalents align at the metaphase plate.
- Spindle fibers pull one complete chromosome (2 chromatids) to either pole.
- The random segregation of paternal and maternal chromosomes is independent assortment.
Division Without Replication
- Egg formation begins in fetal ovaries and arrests during prophase of meiosis I.
- Fetal ovaries contain approximately 500,000 primary oocytes arrested in the diplotene of meiosis I.
- Only one of the three (rarely four) cells produced by meiosis serves as the functional gamete, or ovum.
- Human sperm form continuously in the testes after puberty.
- Once primary spermatocytes divide, the subsequent stages of spermatogenesis, meiotic divisions in the spermatocytes and maturation of spermatids into sperm.
Mitosis Compared with Meiosis
- Mitosis results in two diploid daughter cells.
- Meiosis results in four haploid daughter cells.
Genetic Diversity
- Genetic diversity is generated during Meiosis I by two processes:
- Independent assortment
- Recombination by crossing over
- There are eight (23) different alignments that can occur for three pairs of homologs.
- There are eight million (223) possible combinations in humans for our 23 chromosome pairs.
- Recombination occurs during Pachytene in Meiosis I.
- Physical breakage of the DNA duplex in one maternal and one paternal chromatid, and joining of the maternal and paternal ends occurs.
- DNA sequences are exchanged between chromatids; however, DNA sequences are neither gained nor lost.
- Recombination does not normally occur in mitosis; if it does occur, DNA sequences are gained or lost with negative consequences.
Haploid and Diploid
- Haploid gametes arise by meiosis from diploid precursors.
- Fertilization: sperm and egg chromosomes combine during the first mitosis, forming a diploid zygote.
- Further rounds of mitosis and differentiation form the whole organism.
Terminology
- Most cells are diploid, containing two homologous copies of each chromosome ( one maternal + one paternal)
- There are two copies of each gene, one per chromosome copy.
- Each gene copy is called an allele.
- Alleles can have slight variations in their DNA base sequence.
- An individual can have different alleles of a gene, for example: A & a.
- In populations, genes have many alleles, which is called polymorphism.
- Different alleles combine to produce different genotypes.
- AA or aa: homozygote
- Aa: heterozygote
- Genotype: genetic constitution
- Phenotype: physical appearance (healthy or disease)
- Phenotype is largely determined by genotype.
- If A determines phenotype, it is dominant.
- a is recessive.
Simple Mendelian Inheritance
- Single-gene traits.
- Recessive trait in pea plants: R = round vs. r = wrinkled (R is dominant over r).
- Cross: Rr x Rr
- Progeny genotypes: 1:2:1 (RR:Rr:rr)
- Progeny phenotypes: 3:1 (round:wrinkled)
Human Inherited Diseases
- Some diseases are caused by genetic (DNA) defects.
- Disease genotype -> disease phenotype.
- Two broad categories:
- Single-gene (monogenic) defects, single disease allele, dominant or recessive, simple Mendelian inheritance pattern.
- Multi-gene (polygenic) defects, interactions of several genes, complex (non-Mendelian) inheritance.
Pedigree Analysis
- Pedigree analysis identifies disease expression and Mendelian inheritance patterns.
- Autosomal dominant
- Autosomal recessive
- X-linked dominant
- X-linked recessive
Cell Division
- Cell division is required for development and to generate new cells in the adult.
- Mitosis is the process of cell division in somatic cells.
- Mitosis occurs as part of the cell cycle.
- Mitosis results in diploid cells dividing to produce two diploid cells.
- Meiosis is a specialized form of cell division that gives rise to sperm and egg cells.
- Meiosis results in diploid cells dividing to produce four haploid cells.
Cell Cycle
- There are four main phases in the cell cycle: G1, S, G2, and M.
- G1 is a phase when the cell grows and prepares for division.
- S is the phase where the synthesis of DNA occurs.
- G2 is a short resting phase before division begins and includes the replication of key components like centrosomes.
- M is the phase of actual cell division and is approximately two hours long.
- G0 is an optional phase where differentiated cells remain, often in a non-replicative state, such as hepatocytes.
Human Chromosomes
- Humans have 23 pairs of chromosomes (2n).
- 22 pairs are autosomes.
- The 23rd pair is sex chromosomes.
- The female sex chromosome is XX.
- The male sex chromosome is XY.
Mitosis
- Mitosis is a single sector of the cell cycle and describes how the genome transitions from its duplicated state to its segregated state.
- In mitosis, DNA is copied once: from 46 chromosomes to 92 chromosomes.
- Then the cell divides once, resulting in 46 chromosomes per cell (2 x 23 - diploid).
- The centromere is essential for segregation during cell division.
- Chromosome fragments lacking a centromere (acentric) are not passed to the daughter cells.
- The end result of DNA replication is two DNA molecules, each with one old strand and one new strand.
- The two DNA molecules form sister chromatids.
Meiosis
- Meiosis is a two-stage process that reduces diploid cells to haploid cells.
- Meiosis is preceded by one round of DNA synthesis.
- Prophase 1 of meiosis has 5 stages.
- During prophase 1, maternal and paternal chromosomes (homologs) exchange segments, a process known as genetic recombination.
- Recombination occurs during the pachytene stage of meiosis.
- The bivalent (tetrad) is a 4-stranded structure composed of two homologous chromosomes and their associated chromatids.
- The bivalent aligns at the metaphase plate.
- Spindle fibers pull one complete chromosome (2 chromatids) to either pole.
- During meiosis 1, the random segregation of maternal and paternal chromosomes results in independent assortment.
- Meiosis 2 results in two divisions without replication.
- Meiosis 1 results in 4 haploid cells.
- In humans, egg formation begins in the fetal ovaries and becomes arrested during prophase 1 of meiosis 1.
- Fetal ovaries contain around 500,000 primary oocytes arrested in the diplotene stage of meiosis 1.
- Only one of the three cells produced by meiosis serves as the functional gamete (ovum).
- Human sperm formation occurs continuously in the testes after puberty.
- Once sperm cells divide to produce primary spermatocytes, the subsequent stages of spermatogenesis involve meiotic divisions in the spermatocytes and maturation of spermatids into sperm.
Comparison of Mitosis and Meiosis
- Mitosis replicates chromosomes once and divides the cell once, resulting in two identical diploid cells.
- Meiosis replicates chromosomes once and divides the cells twice, resulting in four haploid cells.
Mechanisms of Variation
- Meiosis I generates genetic diversity through two processes: independent assortment and recombination by crossing over.
- Two homologous chromosomes can align in two different ways (maternal-paternal or paternal-maternal).
- With 23 chromosome pairs in humans, there are 8.4 million (223) possible combinations from independent assortment.
Haploid and Diploid
- Haploid (n) cells have one copy of each chromosome.
- Diploid (2n) cells have two copies of each chromosome.
- Haploid gametes arise by meiosis from diploid precursors.
- During fertilization, sperm and egg chromosomes combine, forming a diploid zygote.
- Further mitosis and differentiation occur to form the whole organism.
Genetic Terminology
- Most cells are diploid with two homologous copies of each chromosome (one maternal and one paternal).
- Each copy of a gene is called an allele.
- Alleles can vary in their DNA base sequence.
- Individuals can have different alleles of a gene.
- Alleles exist in populations in many variations, known as polymorphism.
- Different alleles combine to form genotypes.
- Homozygotes have two identical alleles (AA or aa).
- Heterozygotes have two different alleles (Aa).
- Genotype is the genetic constitution of an individual.
- Phenotype is the physical appearance of an individual.
- Phenotype is determined largely by genotype.
- A dominant allele determines the phenotype even when paired with a recessive allele.
Mendelian Inheritance
- In Mendelian inheritance, a single gene determines a single trait.
- For example, the gene for round (R) or wrinkled (r) peas has two alleles: R is dominant, and r is recessive.
- A cross between two heterozygotes (Rr x Rr) produces a genotype ratio of 1:2:1 (RR:Rr:rr) and a phenotype ratio of 3:1 (round:wrinkled).
Human Inherited Diseases
- Some diseases are caused by genetic defects, and the disease genotype can lead to a disease phenotype.
- Diseases can be categorized as single-gene defects or multi-gene defects.
- Single-gene defects are caused by a single disease allele, which can be dominant or recessive.
- Multi-gene defects involve interactions of multiple genes and have complex inheritance patterns.
- Pedigree analysis is used to identify genes and their inheritance patterns in families.
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Test your knowledge on cell division processes including mitosis and meiosis, as well as the stages of the cell cycle. This quiz covers essential concepts such as chromosome counts and the phases of cell growth and replication. Perfect for students looking to solidify their understanding of biology fundamentals.
