Cell Division Sexual Reproduction = egg & sperm OR Asexual Reproduction = single parent, no egg/sperm Cell Division : reproduction of cells; “cells come from cells” * Basis of all life 2 Main Roles : 1) development of fertilized egg 2) continuation of life
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Cell Division Sexual Reproduction = egg & sperm OR Asexual Reproduction = single parent, no egg/sperm Cell Division: reproduction of cells; “cells come.
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Cell Division
Sexual Reproduction = egg & sperm
OR
Asexual Reproduction = single parent, no egg/sperm
Cell Division: reproduction of cells; “cells come from cells”
* Basis of all life2 Main Roles:
1) development of fertilized egg
2) continuation of life (growth, repair)
Prokaryotes = binary fission (split in half)
OR
Eukaryotes = more complex; more genetic material
chromosome: structure which contains DNA (deoxyribonucleic acid)
chromatin: long, thin fibers of DNA & protein clumping together to form chromosomes
gene: specific region of DNA on chromosomes
somatic cell: all body cells except egg & sperm; contain chromosomes
(humans= 46)
Human egg & sperm (gametes) have 23 chromosomes
Prior to Cell Division…
* All chromosomes duplicate…result in 2 identical parts = sister
chromatids (X-shaped)
* joined at centromere
When Cells Divide
* sister chromatids separate..each goes to separate cell (daughter
cell)
* each daughter cell has complete set of chromosomes
Overview of Cell Division
* eukaryotic cells divide according to cell cycle
cell cycle: sequence of events including time a cell divides until its daughter cell divide
Phases in the Cell Cycle
1) Interphase: most of cycle here
- chromosomes duplicate
- cell grows
2) Mitotic Phase: cell division phase
Includes Mitosis & Cytokinesis
* Mitosis unique to eukaryotes* Mitosis = continuous process but separated into defined stages
Stages of Mitosis
1) Prophase
- chromatin fibers coil to form discrete chromosomes
- sister chromatids
- nuclear membrane breaks near end2) Metaphase
- sister chromatids line up along center of cell
Stages of Mitosis
3) Anaphase
- sister chromatids separate & migrate to opposite ends of cell4) Telophase
- nuclear membrane reforms around chromosomes
Cytokinesis: division of cytoplasm
- usually occurs along with telophase
- daughter cells separate
- Certain drugs can stop cell cycle by preventing DNA synthesis, or inhibiting synthesis of necessary proteins
Ex: cancer drugs target rapidly dividing cells – including hair follicles and digestive tracts
homologous chromosome: matched pair of chromosomes; same length, genes for same traits at same loci
e.g., each chromosome has gene for hair color at same loci, but the gene may be for any color of hair … impt pt = gene results in some color of hair
locus (loci = plural): specific location of a gene on a chromosome
• homologous chromosomes have matching loci &
• One chromosome of each pair inherited from mother & father
Human Example
Somatic cells = 46 chromosomes
23 pairs of homologous chromosomes
22 pairs = autosome chromosomes (F & M)
1 pair = sex chromosomes; specific to the sex (M or F)
Sex Chromosomes
Human females 1 pair (2 XX)
Human male 1 pair (1X, 1Y)
• Are human male sex chromosomes homologous?
diploid cells: cells with 2 homologous sets of chromosomes in nucleus
total # chromosomes = diploid # = 2n
human diploid # = 46 (2x23=46)
• Humans = diploid animals because most of our cells = diploid (e.g., somatic cell)
haploid cells: cells with 1 homologous set of chromosomes
haploid # = n
human haploid # = 23
• Human gametes are haploid
• Fertilized egg = zygote = ????
Why is there so much variety among species? (e.g., diversity in humans)
1) Independent orientation of chromosomes
- in Metaphase I --- way that tetrads line up is due to chance (random)
- Results in different possible combinations of chromosomes in gametes
- For humans = 8 million possible combos.!
2) Random fertilization (1 egg & 1 sperm)
What is probability that 1 of 8 million possible sperm fertilizes 1 of 8 million possible eggs????
Humans = (8 M) * (8 M) = 64 trillion possible combinations of chromosomes due to random fertilization!
3) Crossing Over
- can result in genetic recombination
genetic recombination: producing gene combinations different from those carried by original chromosomes
* During synapsis, tetrad formed – crossing over possible
1) homologous chromatids break at similar locations & chromatids join
2) h. chrom. separate at Anaphase I – crossing over
3) Meiosis II, sister chromatids separate
Mendelian Genetics
genetics = science of heredity
gene: specific region of genetic material (DNA) that provides provides the cell with a “map”
Goal: determine patterns of inheritance
Mendelian Genetics
Gregor Mendel – 1860’s monk
significant findings = offspring obtain discrete heritable factors (genes) from their parents
Mendelian Genetics
Gregor Mendel – 1860’s monk
-carefully chose organisms to study (garden pea), controlled pollinations, chose traits that were easy to observe, used statistical methods to analyze data
-significant findings = offspring obtain discrete heritable factors (genes) from their parents
Terms
self-fertilization: plant’s egg fertilized by it’s own pollen
cross-fertilization: plant’s egg fertilized by another plant’s pollen (hybridization)
P generation: parental generation
F1 generation: filial generation; hybrid offspring of the P generation
F2 generation: offspring produced by F1 generation via self-fertilization
Mendel’s Principles
1) Principle of Segregation – pairs of genes segregate during gamete formation; fertilization pairs genes again
monohybrid cross: cross of 2 individuals that differ in 1 trait
allele: alternate form of a gene found at same loci of homologous chromosomes
1) Principle of Segregation
Ex: Flower color (P = purple, p = white)
P = 1 Purple (PP) & 1 white (pp)
F1 = all Purple (Pp)
F2 = ¾ Purple (PP & Pp) ¼ white (pp)
homozygous: identical pair of alleles
heterozygous: 2 different alleles for a trait
phenotype: physical trait; appearance of organism; expressed as phenotypic ratio
genotype: genetic makeup of organism; expressed as genotypic ratio
• In the flower color example…..
What is the phenotypic ratio?
What is the genotypic ratio?
** For monohybrid cross… phenotypic ratio is always 3:1 & genotypic ratio is always 1:2:1
2) Principle of Independent Assortment
• each pair of alleles segregates independently during gamete formation
dihybrid cross: cross of 2 individuals that differ in 2 traits