Cell Division, Genomes and Chromosomes

Cell Division

• Cells divide for reproduction in single-celled organisms and for growth and repair in multicellular organisms.
• Prokaryotes divide through binary fission, and their DNA is located in the cytoplasm.

Prokaryotic Cytokinesis

• FtsZ protein is important for prokaryotic cytokinesis.
• Plants and animals divide via binary fission.

Genomes & Chromosomes

• A genome is the entire set of genetic material in an organism.
• A chromosome is a thread-like structure of nucleic acids and protein that carries genetic information in the form of genes.

Somatic vs. Reproductive Cells

• Somatic cells are any biological cells forming the body of a multicellular organism other than gametes, germ cells, gametocytes or undifferentiated stem cells
• Reproductive cells (Gametes) are cells used during sexual reproduction to produce a new individual organism

Haploid & Diploid

• Haploid refers to having a single set of unpaired chromosomes, notated as n.
• Diploid refers to having two complete sets of chromosomes, one from each parent, notated as 2n.

Mitosis vs. Meiosis

• Mitosis results in two identical daughter cells, while meiosis results in four genetically different daughter cells.

Chromosome Structure

• A duplicated chromosome consists of two identical sister chromatids.
• A karyotype is the number and appearance of chromosomes in the nucleus of a eukaryotic cell.

Chromosome Pairs

• Heterologous chromosomes are non-matching, while homologous chromosomes are matching pairs with genes for the same traits.

Cell Cycle Overview

• The cell cycle includes interphase and mitotic phase.
• A cell spends most of its time in interphase, and DNA is duplicated during the S phase of interphase.

G0 Phase

• G0 is a resting phase where cells spend the majority of their time, not actively dividing.

Interphase

• Interphase consists of G1, S, and G2 phases.

Cell Cycle Control

• The cell cycle is controlled by internal and external signals.

Cell Cycle Regulators

• Positive regulators promote cell cycle progression; examples include cyclins and cyclin-dependent kinases (Cdks).
• Negative regulators inhibit cell cycle progression; examples include tumor suppressor proteins like p53 and Rb.

Checkpoints

• Checkpoints ensure that the cell cycle proceeds correctly.
• A mutation in a checkpoint gene can lead to uncontrolled cell division.

MPF

• Maturation-Promoting Factor (MPF) is crucial for cell cycle regulation.
• MPF triggers the transition from G2 to mitosis.

Loss of Cell Cycle Control

• One major consequence of losing cell cycle control is cancer.

Proto-oncogene vs. Oncogene

• Proto-oncogenes are normal genes that help cells grow
• Oncogenes are mutated genes that cause cells to grow and divide uncontrollably.

Tumor Suppressor Genes

• A tumor suppressor gene normally inhibits cell division when working correctly.

Tumors

• A tumor is a mass of abnormal cells.
• Tumors can be benign (non-cancerous) or malignant (cancerous). Malignant tumors are really bad
• Metastasize means to spread to other sites in the body by the process of metastasis. Metastasis is a very bad process

Cell Cycle Arrest

• If a cell can't pass G1, it may enter G0 or undergo apoptosis; if it can't pass S or G2, the cell cycle halts for repair or undergoes apoptosis.

Checkpoint Functions

• Checkpoints monitor DNA integrity, chromosome segregation, and other critical processes.

BRCA1 & BRCA2

• BRCA1 and BRCA2 are examples of tumor suppressor genes; everyone has them.
• A mutation in BRCA1 or BRCA2 increases the risk of certain cancers.

Autosomes

• Autosomes: Humans have 22 pairs, inherited equally from both parents.

Sex Chromosomes

• Sex Chromosomes: Females have XX, males have XY; the male determines the baby's gender.

Karyotype

• Karyotype: Visual representation of an organism's chromosomes.

Asexual Reproduction

• Advantages of asexual reproduction include rapid population growth, while disadvantages are a lack of genetic diversity.

Genes & Alleles

• Gene: Unit of heredity.
• Allele: Variation of a gene.
• Individuals inherit two alleles, one from each parent, for each gene.

Chromosome Alignment

• Homologous chromosomes do not line up in mitosis.
• The alignment of homologous chromosomes is important in meiosis to create genetic diversity.

Meiosis Necessity

• Meiosis is needed for sexual reproduction to maintain the correct chromosome number in offspring.

Chromosome Numbers

• Human diploid number (2n) is 46.
• Human haploid number (n) is 23.

Meiosis Process

• Meiosis starts with a diploid cell.
• Meiosis concludes with four haploid cells after two rounds of nuclear division.

Meiosis Location

• Meiosis occurs in germline cells in reproductive organs to produce gametes.

DNA Replication in Meiosis

• DNA replication occurs once before meiosis I.

Goals of Meiosis

• Meiosis I separates homologous chromosomes.
• Meiosis II separates sister chromatids.
• There is typically a brief interphase-like period (interkinesis) but no DNA replication between meiosis I and II.

Chromosome Pairing & Separation

• Homologous chromosomes pair up and separate during meiosis I.
• Sister chromatids separate during meiosis II.

Crossing Over

• Crossing over exchanges genetic material between homologous chromosomes.
• Crossing over increases genetic variation and occurs during prophase I.

Meiosis I Knowledge

• Knowledge of the events in each step of meiosis I is needed, especially regarding homologous pairs.

Meiosis II Knowledge

• Knowledge of the events in each step of meiosis II is needed, especially regarding sister chromatids.

Genetic Diversity

• Two major factors increasing genetic diversity are crossing over and independent assortment.

Non-disjunction

• Non-disjunction is the failure of chromosomes to separate properly during meiosis.
• Down Syndrome is an example of non-disjunction involving chromosome 21.
• Other disorders are caused by non-disjunction.

Genetics - Gregor Mendel

• Gregor Mendel used the pea plant as his model organism.
• Mendel's traits included easily observed characteristics: seed color and plant height made it a good model organism.

Genetics - Vocabulary

• Important genetic terms include: genotype, phenotype, homozygous, heterozygous, dominant, and recessive.
• "Bred true/true breeding" corresponds to homozygous.

Genetics - Generations

• P stands for parental generation.
• F1 stands for the first filial generation.
• F2 stands for the second filial generation.

Genetics - Homozygous Cross

• Crossing homozygous parents (one dominant, one recessive) guarantees a heterozygous genotype for the F1 offspring.

Genetics - Phenotype

• The F1 offspring will display the dominant phenotype.

Genetics - Punnett Square

• The Punnett square predicts allele distribution in offspring.

Genetics - Testcross

• A testcross determines the genotype of an individual with a dominant phenotype by crossing with a homozygous recessive individual.

Genetics - Monohybrid Cross

• A monohybrid cross involves one character.
• A monohybrid cross differs from a single-character cross.

Monohybrid Cross Ratio

• A monohybrid cross results in a 3:1 phenotypic ratio.

Punnett Square

• Ability to perform a Punnett square is required.

Probability of Sex

• The probability of having a boy or a girl is approximately 50%.
• A Punnett square can illustrate these probabilities.

Complex Punnett Squares

• A 16-square Punnett square will not be required.
• F.O.I.L. is needed for meiotic allele combinations.

Multi-trait Probability

• Ability to calculate multi-trait probabilities is needed.

Sex-linked Traits

• Sex-linked traits are usually on the X chromosome.

Calico Cats

• Calico cats exemplify X-chromosome inactivation.

Hemophilia

• Consider the probability of hemophilia inheritance in a family with a carrier mother and a normal father.

Simple Dominance

• Simple dominance exists, in addition to other inheritance patterns.

Multiple Alleles

• The human gene for blood type exemplifies multiple allele systems.

Codominance

• The human gene for blood type exemplifies codominance.
• Punnett squares determine blood type possibilities.

Blood Type

• The “positive” or “negative” part of blood type is about the presence or absence of the Rh factor.

Blood Transfusions

• Blood types must match for transfusions to prevent reactions.
• Blood Type can only receive certain blood types

Universal Blood Types

• Type AB is the universal recipient.
• Type O is the universal donor.

Pleiotropy

• Pleiotropy is when one gene influences multiple traits. Two genetic disorders are examples of pleiotropy

Epistasis

• Epistasis influences coat color in lab dogs.

Environmental Influence

• The environment influences phenotype.

Continuous Variation

• Continuous variation is due to multiple genes and environmental factors.