Genetics and Cell Division

Cellular Reproduction & Genetics

• Chapter covers cellular reproduction and genetics

Cellular Reproduction

• Asexual reproduction involves a single parent producing genetically identical offspring
• Binary fission is the process
• Bacteria reproduce asexually in about 20 minutes
• Hydra reproduce by budding in asexual reproduction
• Sexual reproduction involves the fusion of two cells (gametes)
• This fusion forms a diploid (2n) zygote
• Offspring receive genetic information from both parents

Eukaryote Chromosome Structure

• A chromosome comprises condensed DNA and proteins, known as CHROMATIN
• DNA winds around histones to form nucleosomes, which then form thick fibers that condense
• Human cells have 23 pairs of chromosomes, totaling 46

Cell Division in Eukaryotes

• Mitosis makes identical diploid cells
• Mitosis is used for growth, repair, development, and asexual reproduction
• Meiosis occurs when gametes (n) are formed and reduces the chromosome number in half
• Meiosis makes haploid gametes
• HAPLOID (n) is one set of chromosomes
• DIPLOID (2n) is two sets of chromosomes
• n = 23 chromosomes
• 2n = 46 chromosomes

Cell Cycle

• Cell cycle has two phases: Interphase and Mitotic Phase
• During the Interphase:
  • G1 phase involves the replication of organelles
  • S phase involves DNA replicating to form sister chromatids
  • G2 phase involves the cell preparing to divide
• During the Mitotic Phase:
  • Mitosis= chromosomes divide through prophase, metaphase, anaphase, and telophase
  • Cytokinesis = cytoplasm divides
• In plant cells, cytokinesis involves the formation of a cell plate
• In animal cells, cytokinesis involves the formation of a cleavage furrow

Mitosis Phases

• Interphase involves organelles copying (G1) and chromosomes replicating (S)
• Early Prophase involves chromosomes thickening and centrioles separating to opposite poles
• Late Prophase involves the centrioles at opposite poles, while the nuclear envelope disappears
• Metaphase involves the chromosomes lining up in the middle and being pulled by spindle fibers
• Anaphase involves the chromosomes being pulled by spindle fibers to opposite poles
• Telophase involves the formation of new nuclear envelopes and the division of the cytoplasm

Cytokinesis

• Cytokinesis involves the distribution of cytoplasm
• In Animal Cells:
  • Cleavage furrow forms in the distribution of cytoplasm during cytokinesis.
• In Plant cells:
  • Cell plate forms during cytokinesis.

Meiosis

• Sexual reproduction involves the fusion of two gametes, forming a diploid (2n) zygote
• The offspring have some genetic information from both parents
• The zygote divides and grows through mitosis to form an embryo
• The embryo develops into an adult

Phases of Meiosis

• Meiosis I- homologous pairs separate
• Interphase is the first phase with G1, S, and G2 phases.
• Prophase I- Tetrads form crossing-over occurs
• Metaphase I- Homologous pairs line up
• Anaphase I- Homologous pairs separate
• Meiosis II
• Telophase I- New Nuclei form, and cytoplasm divides.
• Prophase II- Centrioles separate.
• Metaphase II- Sister chromatids line up.
• Anaphase II- Sister chromatids separate.
• Telophase II- New nuclei form, the cytoplasm divides, and four haploid gametes form, which are not identical.

Chromosomes

• Humans have 23 pairs of chromosomes.
• Chromosome pairs are called homologous chromosomes.
• One is inherited from the mother and one from the father.
• They contain genes for the same traits, such as hair and eye color
• #1-22 are autosomes
• #23 are sex chromosomes.
  • male XY
  • female XX

Important Genetic Terms

• Alleles are different forms of a gene
• Homozygous = have the same alleles for a trait, PP or pp
• Heterozygous = have different alleles for a trait, Pp
• Phenotype is the physical appearance, expressed, purple or white plant
• Genotype is what genes you have, the specific alleles, PP, Pp or pp

Mendelian Genetics

• Mendel conducted research with pea plants
• Crossed two true-breeding (homozygous) plants
• The F1 generation was all purple
• Traits are controlled by a pair of 'factors' (now alleles)
• Conclusion: purple was the dominant color

Mendel's Laws

• Law of Dominance- When he crossed two heterozygotes from the F1 generation, he got a 3:1 ratio.
  • Showed that one trait was dominant and one was recessive.
  • Dominant alleles have at least one dominant allele- Ttat least 1 capital letter- Tt or TT
  • Recessive Alleles have two recessive alleles. tt or 2 lowercase letters
• Law of Segregation:
  • Homologous pairs separate in metaphase I of meiosis.
  • Each gamete only gets one copy of each chromosome.
• Law of Independent Assortment:
  • Non-homologous chromosomes assort (line up) independently of each other at metaphase I.
  • Creates variation. 2 to the 23rd power = 8 million possibilities!!

Inheritance Patterns

• Incomplete Dominance- In snapdragons and carnations, fur color in animals.
• The phenotype of the heterozygote is intermediate to the other two phenotypes Ex. RR = red; Rr = pink; rr = white
• Multiple Alleles & Co-Dominance- There are 3 different alleles for blood type: A, B, and i. A and B are co-dominant, and i is recessive.
  • 4 different blood types: A, B, AB, and O
  • Genotypes
    • IAIA or IAi- type A
    • BIB or Bi type B
    • IAB type AB
    • ii type O

Explore monohybrid crosses, Mendel's laws, and the ABO blood group system. Understand meiosis, mitosis, and DNA replication. Learn about homologous chromosomes and cell division processes.