Cell Division and Reproduction

Cell Division

• Cell division is essential for growth, repair, and reproduction.

Asexual Reproduction

• Involves a single parent producing genetically identical offspring.
  • Pros: Fast reproduction don't need mate, no energy wasted
  • Cons: Lack of genetic diversity to help protect against disease, limited resources, and offspring harder to adapt to environmental changes

Sexual Reproduction

• Involves two parents contributing genetic material, producing offspring with unique combinations of genes.
  • Pros: Genetic diversity, survive in environment
  • Cons: Need mate, need proper sex organs, baby may recieve weak traits+die+

Homologous Chromosomes and Tetrads

• Homologous chromosomes: Pairs of chromosomes with similar genes, one from each parent.
• Tetrads: Paired homologous chromosomes aligned during meiosis.
• Synapsis and crossing over: Exchange of genetic material between homologous chromosomes during meiosis I, generating unique combinations of genes.

Sperm vs. Egg Production

• Sperm: Four haploid sperm cells produced from one diploid cell, through meiosis.
• Egg: One haploid egg cell and polar bodies (non-functional cells) produced from one diploid cell, through meiosis.

Karyotypes

• Karyotype: Organized photographic display of individual's chromosomes.
• Used to identify chromosomal abnormalities.

Sex Chromosomes and Gender Determination

• Sex chromosomes: Determines an individual's sex.
• XX: Female
• XY: Male

Meiosis Errors

• Nondisjunction: Failure of chromosomes to separate properly during meiosis, resulting in gametes with incorrect chromosome numbers.
• Examples of disorders:
  • Down syndrome: Trisomy 21 (extra chromosome 21).
  • Klinefelter syndrome: XXY (extra X chromosome in males).
  • Turner syndrome: XO (missing X chromosome in females).
  • Trisomy 18 (Edwards syndrome): Extra chromosome 18.
  • Trisomy 13 (Patau syndrome): Extra chromosome 13.

Mendelian Inheritance

• Punnett squares: Used to predict the probability of offspring inheriting specific traits based on parental genotypes.
• Test cross: Used to determine the genotype of an individual with a dominant phenotype, by crossing with a homozygous recessive individual.
• Incomplete dominance: Heterozygous individuals display a blended phenotype intermediate between homozygous phenotypes.
• Codominance: Heterozygous individuals express both alleles fully, resulting in a phenotype with both traits.
• Sex-linked disorders: Located on sex chromosomes (usually X).
  • Examples: Hemophilia, color blindness.

Genetic Disorders and Screening

• Genetic disorders: Caused by mutations in genes.
  • Examples: Sickle cell anemia, cystic fibrosis.
• Genetic screening: Tests to identify individuals at risk for genetic disorders.

Blood Types

• A, B, O, AB: Blood groups determined by ABO gene.
  • A: I^A allele AO
  • B: I^B allele BO
  • O: i allele
  • AB: Both I^A and I^B alleles, both expressed (codominance)
• Rh factor: Protein on red blood cells.
  • Positive (Rh+): Have the protein.
  • Negative (Rh-): Lack the protein.

Pedigrees

• Pedigree: Chart depicting family history of a specific trait.
• Reading a pedigree: Symbols represent individuals, lines depict relationships.
• Predicting genotypes: Based on phenotypes of family members.
• Modes of inheritance: How traits are passed down through generations.
  • Autosomal dominant: Affected individuals have at least one dominant allele.
  • Autosomal recessive: Affected individuals have two recessive alleles.
  • X-linked dominant: Affected females and males have at least one dominant allele on the X chromosome.
  • X-linked recessive: Affected males have one recessive allele on the X chromosome, while affected females usually have two.
  • Y-linked: Only males are affected, as they inherit the Y chromosome from their father.

Multi-trait Inheritance

• Dihybrid cross: Tracking two traits simultaneously.
• Predicted phenotypic ratio: Always 9:3:3:1 for a dihybrid cross with complete dominance.

DNA and the Code of Life

• Structure of DNA: Double helix composed of two complementary strands.
  • Pentose sugar: Deoxyribose.
  • Phosphate group: Negatively charged.
  • Nitrogenous bases: Adenine (A), Thymine (T), Cytosine (C), Guanine (G).
• Complementary base pairs: A pairs with T, C pairs with G.

Mutations

• Point mutations: Changes in a single DNA nucleotide.
  • Substitution: One base is replaced by another.
  • Insertion: One or more bases are added.
  • Deletion: One or more bases are removed.
• Spontaneous mutations: Occur naturally due to errors in DNA replication.
• Induced mutations: Caused by environmental factors like radiation or chemicals.
• Example: Lactose intolerance caused by a mutation in the lactase gene.

Cell Division

• Used for growth, repair, and reproduction
• Occurs in two main stages: mitosis (for growth and repair) and meiosis (for sexual reproduction)

Asexual Reproduction

• Pros: Efficient, allows for rapid population growth, requires only one parent
• Cons: Limited genetic variation, offspring are genetically identical to the parent

Sexual Reproduction

• Pros: Creates genetic variation, offspring are unique, increases adaptability to environmental changes
• Cons: Requires two parents, can be less efficient, involves complex processes

Meiosis

• Homologous chromosomes: Paired chromosomes, one from each parent
• Tetrads: Formed when homologous chromosomes pair up during Meiosis I
• Synapsis and crossing over: The exchange of genetic material between homologous chromosomes, resulting in genetic variation
• Sperm production: Occurs in the testes through meiosis, producing four haploid sperm cells
• Egg production: Occurs in the ovaries through meiosis, producing one haploid egg cell and three polar bodies
• Karyotypes: Ordered visual representation of an individual's chromosomes
• Sex chromosomes: Determine an individual's biological sex (XX = female, XY = male)
• Meiosis errors: Can lead to genetic disorders, examples include:
  • Down syndrome (trisomy 21)
  • Klinefelter syndrome (XXY)
  • Turner syndrome (XO)
  • Cri-du-chat syndrome (chromosome 5 deletion)
  • Edwards syndrome (trisomy 18)

Mendelian Inheritance

• Punnett squares: Used to predict the possible genotypes and phenotypes of offspring in a cross
• Test cross: Used to determine the genotype of an individual with a dominant phenotype by crossing it with a homozygous recessive individual
• Incomplete dominance: Neither allele is fully dominant, resulting in an intermediate phenotype
• Codominance: Both alleles are expressed equally in the phenotype
• Sex-linked disorders: Disorders caused by genes located on the X chromosome, more common in males because they have only one X chromosome
• Genetic disorders and screening: Various methods are used to identify carriers of genetic disorders or diagnose genetic disorders in individuals

Blood Types

• Blood types are determined by the presence or absence of specific antigens on the surface of red blood cells
• Four main blood types: A, B, AB, O
• Rh factor: An additional antigen on red blood cells, either present (positive) or absent (negative)

Pedigrees

• Creation: A visual representation of a family's genetic history, showing phenotypes of individuals
• Modes of inheritance:
  • Autosomal dominant: Affected individuals have at least one dominant allele
  • Autosomal recessive: Affected individuals have two recessive alleles
  • X-linked dominant: Affected females have one dominant allele, affected males have one dominant allele on their X chromosome
  • X-linked recessive: Affected females have two recessive alleles, affected males have one recessive allele on their X chromosome
  • Y-linked: Affects only males, passed from father to son

DNA & Code of Life

• Structure of DNA: A double helix composed of nucleotides, each having three components:
  • Pentose sugar (deoxyribose)
  • Phosphate group
  • Nitrogenous base (adenine (A), thymine (T), cytosine (C), guanine (G))
• Complementary base pairs: Adenine (A) pairs with thymine (T), cytosine (C) pairs with guanine (G)
• DNA model: Two antiparallel strands held together by hydrogen bonds between complementary base pairs
• Scientists and their findings:
  • Watson and Crick: Discovered the double helix structure of DNA
  • Rosalind Franklin: Used X-ray diffraction to capture images of DNA structure

Mutations

• Point mutations: Changes involving one or a few nucleotides
  • Substitution: One base is replaced by another
  • Insertion: One or more bases are added
  • Deletion: One or more bases are removed
• Spontaneous mutations: Occur naturally due to errors during DNA replication
• Induced mutations: Caused by environmental factors, such as radiation or chemicals
• Example of mutation: Lactose intolerance is caused by a mutation in the gene for the lactase enzyme, resulting in the inability to digest lactose

Explore the essential processes of cell division, including asexual and sexual reproduction. Understand the roles of homologous chromosomes, tetrads, and genetic variation in these processes. This quiz will help you grasp the significance of these biological concepts for growth, repair, and reproduction.