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Chromosome Rod shaped structures made of DNA and proteins Carrier of genetic material Located in the nucleus Copied and passed from generation to generation
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Mendel and Meiosis
Chp 10 Pp. 252-279
Contents
• 10-2 Meiosis• 10-1 Mendel
Chromosome
Rod shaped structures made of DNA and proteinsCarrier of genetic materialLocated in the nucleusCopied and passed from generation to generation
Chromosomes
Sex chromosomes: chromosomes that determine the sex of an organismHumans X and Y Females: X XMales: X Y
Autosomes: all other types of chromosomes
Chromosomes
Homologous Chromosomes
2 copies of each autosome Same size and shapeCarry genes for the same traitEx. If 1 homologous chromosome contains gene for eye color the other homologous chromosome will too.
Homologous Chromosomes
Diploid Cell
Cell with 2 sets of chromosomesContains chromosomes for each homologous pairSomatic Cells= Body Cells: DiploidAll human cells except sex cells are diploid. One from each parent 2nHumans 2n = 46
Haploid
Cell containing one of each kind of chromosomeSperm and egg cells = Gametes1 set of chromosomesHalf the number of chromosomes of diploidnSperm + Egg = Zygoten + n = 2n
Mitosis vs. Meiosis
• Mitosis: t = two: Diploid 2n=46
• Meiosis: o = one: Haploid » n = 23
Meiosis
Gametes are produced in specialized body cellsProduces Sperm and Egg Cells2 divisions: Meiosis I and Meiosis IIMeiosis occurs in sex cells, not body cellsResults in 4 daughter cellsEach cell has half the chromosomes of the parent
Meiosis I
Interphase occurs: the cell grows and DNA replicatesMeiosis I begins Original cell produces two new cells
Prophase I
DNA Coils tightly into chromosomesspindle fibers appearEach chromosome lines up next to the homologueSynapis occurs: pairing of homologous chromosomes Tetrad: Each pair of homologous chromosomes
Crossing Over
•Crossing Over: why we do not look Crossing Over: why we do not look exactly like our parents.exactly like our parents.
Portions of the chromatid breaks off and attaches to adjacent chromatids on the
homologous chromosomePermits the exchange of genetic material
between maternal and paternal chromosomes
•Occurs during Prophase
Genetic Recombination
Crossing over produces a new mixture of genetic material
• Occurs during Prophase
Causes of Variation
Chromosomes are assorted randomlyCrossing over may occurCells do not have identical genetic info as each other or the parentGood: more chance of survival and evolutionBad: mistakes more likely
Metaphase I
Tetrads line up randomly along the mid-lineSpindle fibers attach to centromeres
Anaphase IHomologous chromosomes move to the opposite polesRandom separation or Independent Assortment results in separation of maternal and paternal chromosomes.
Telophase I
Chromosomes reach opposite ends of cellCytokinesis beginscell is haploid
Meiosis II
Occurs in each cell formed in Meiosis IInterphase does not occur again
Prophase II
Spindle fibers form and move the chromosomes to the mid-line of the dividing cell
Metaphase II
Chromosomes move to the mid-line of the dividing cell facing opposite poles of the dividing cell
Anaphase II
Chromatids separate and move to opposite poles of the cell
Telophase II
Nuclear membrane forms around the chromosomes in each of 4 new cells
Cytokinesis II
Cytoplasm divides Cell Membrane closes off
End Result:
Four new cells that contain half of the original cells number of chromosomes4 sex cells are created
Haploid = one of each kind Diploid = two of each kind
• 2n = diploid n = haploid
WHY DO WE NEED HAPLOID?
• EGG
23
SPERM
Female gamete
Male gamete
23
Fertilization restores the diploid number
2n2n
1n1n1n
2n2n
fertilizationmeiosis
Mitosis and cell growth
Gametes
formed by meiosishaploid reproductive cellshumans: meiosis occurs in the testes and ovaries
Spermatogenesis: Male
Oogenesis: FemaleOne Mature
Egg Cell
Human Karotype
Asexual Reproduction
Production of offspring from one parent Does not involve meiosisOffspring are genetically identical to parent
Sexual Reproduction
Production of offspring through meiosis and the union of sperm and eggOffspring are genetically different form parentsGenes are combined in new ways in meiosisEvolutionary advantage is that it enables species to rapidly adapt to new conditions
Mitosis vs. Meiosis
• Mitosis vs. Meiosis Animation
Nondisjunction
• Failure of homologous chromosomes to separate properly during meiosis.
• Both chromosomes of a homologous pair move to the same pole of the cell. • 1 gamete has an extra chromosome
• Or• 1 gamete is missing a chromosome
Nondisjunction Animation
• Nondisjunction Animation
10-1 Mendel
• Gregor Mendel • Austrian monk• Studied how traits are
inherited from parents to offspring
• Father of heredity• Chose garden peas
for his meticulous experiments
Garden Peas
• Reproduce sexually• W/ male & female
gametes (sex cells)• Fertilization results
in zygote • Becomes seed• Pollination male
pollen transferred to female pistil
Monohybrid Cross• Hybrid- offspring of
parents with different forms of a trait
• Tall or short• crossed true-bred
tall plants w/ true-bred short plants to get heterozygous offspring which then self-pollinated
Some Genes are Dominant
• Some Genes Are Dominant click to play
Seven Traits of Peas
Mendel’s Rules
• Alleles- different gene forms
• Rule of Dominance– Dominant –observed
trait– Recessive-
disappearing or hidden trait
Mendel’s Rules
• Law of Segregation • Every individual has 2
alleles of each gene w/ each gamete receiving 1.
• During fertilization, gametes randomly pair to produce four combinations
Phenotypes & Genotypes• Appearance=
Phenotype• Allele combination=
Genotype• Homozygous-Both
alleles alike• Heterozygous-
different alleles, one dominant & one recessive
Mendel’s Dihybrid Cross
Law of Independent Assortment
• Says that genes for different traits are inherited independently from each other.
• The alleles can recombine in four different ways.
Punnett Squares• Shorthand way to find
possible genotypes from crossing two known parents.
• Two heterozygous parents produce 1 homozygous dominant: 2 heterozygous:1 homozygous recessive1BB: 2Bb:1bb
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