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MeiosisMeiosis
Biology Biology
2009-20102009-2010
MeiosisMeiosis
• Def: Def: type of cell division that type of cell division that produces 4 cells with half the number produces 4 cells with half the number of chromosomes as a parent cellof chromosomes as a parent cell
• OccursOccurs in the in the sex organssex organs
• Number of chromosomes= Number of chromosomes= 46 or 23 46 or 23 pairspairs
Homologenous Homologenous ChromosomesChromosomes
• Def: Def: chromosomes that match in chromosomes that match in shape and size but not shape and size but not necessarily same DNA patternsnecessarily same DNA patterns
Homologous Chromosomes
• KaryotypingKaryotyping– Def: Def: arrangement of all 46 arrangement of all 46
chromosomeschromosomes
• Sex chromosomesSex chromosomes– The 23The 23rdrd pair pair– DeterminesDetermines the the organisms sexorganisms sex– XX= girlXX= girl– XY=boyXY=boy
Diploid vs. HaploidDiploid vs. Haploid
• DiploidDiploid– 2 homologenous sets of 2 homologenous sets of
chromosomeschromosomes– Forms the zygote Forms the zygote – 2n2n
• HaploidHaploid– 1 set of chromosomes- one from each 1 set of chromosomes- one from each
pairpair– Occurs in Occurs in fertilizationfertilization– nn
Number of ChromosomesNumber of Chromosomes
• Sex Cells each haveSex Cells each have half the half the number of chromosomes (number of chromosomes (2323))
• ZygoteZygote (fertilized egg) have (fertilized egg) have 46 46 chromosomeschromosomes
Steps of meiosisSteps of meiosis
• Differences between mitosis and meiosis:Differences between mitosis and meiosis:– Meiosis produces Meiosis produces 4 offspring cells4 offspring cells– Meiosis involves Meiosis involves exchanging of genetic exchanging of genetic
material between the Homologous material between the Homologous Chromosomes.Chromosomes.
• Sister chromosomes- exact copies of DNASister chromosomes- exact copies of DNA
• Homologenous chromosomes- DNA does Homologenous chromosomes- DNA does not have to be the samenot have to be the same
Meiosis 1Meiosis 1• Prophase 1Prophase 1
– Homologenous chromosomes stick Homologenous chromosomes stick together forming a tetradtogether forming a tetrad
– Crossing over beginsCrossing over begins
• Metaphase 1Metaphase 1– Crossing over is completeCrossing over is complete– Chromosomes line up in the centerChromosomes line up in the center
• Anaphase 1Anaphase 1– Chromosomes migrate towards the Chromosomes migrate towards the
opposite polesopposite poles
• Telophase 1Telophase 1– Each pole has a haploidEach pole has a haploid
Crossing OverCrossing Over
• DEF: DEF: Genetic materials is transferred from one chromosome to another
Crossed over
Meiosis 2Meiosis 2
• Follows the Follows the exact same steps as exact same steps as MitosisMitosis except the end results in except the end results in 4 4 cellscells instead of 2 instead of 2
Chickens have 78 chromosomes in their body cells how many
chromosomes do they have in their sex cells?
Cats have 38 chromosomes in their diploid
cells. How many do they have in their haploid cells?
Birth DefectsBirth Defects
Biology2009-2010Biology2009-2010
NumbersNumbers
• There are There are 200,000200,000 people born with people born with birth defects every yearbirth defects every year
• To break it down, there are To break it down, there are 25 25 peoplepeople born with birth defects per born with birth defects per hourhour
Causes of Birth DefectsCauses of Birth Defects
• Drugs/Alcohol/SmokingDrugs/Alcohol/Smoking
• Radiation/PollutionRadiation/Pollution
• STD’sSTD’s
• InheritanceInheritance
• MalnutritionMalnutrition
DetectionDetection
• Blood TestBlood Test
• Amniocentesis- Amniocentesis- – A sample of the amniotic fluid is taken A sample of the amniotic fluid is taken
and then the DNA is checked for and then the DNA is checked for Chromosomal defects Chromosomal defects
ChromosomesChromosomes
• Monosomy- loss of one chromoMonosomy- loss of one chromosomesome
• Trisomy- gain an extra chromosomeTrisomy- gain an extra chromosome
• Sex Chromosomes- X and YSex Chromosomes- X and Y
Down SyndromeDown Syndrome
• Occurrence-1/600 birthsOccurrence-1/600 births
• Causes- trisomy 21Causes- trisomy 21
• Chance with increased ageChance with increased age– 20’s- 1/150020’s- 1/1500– 40’s-1/4440’s-1/44
Homozygous Recessive Homozygous Recessive TraitsTraits
• Found on the Found on the X X chromosomechromosome
• Passed on from Passed on from mother’s to their mother’s to their childrenchildren
• Examples: Muscular Dystrophy and Examples: Muscular Dystrophy and color blindnesscolor blindness
MutationsMutations
• Definition- Definition- change in the DNA by change in the DNA by changing one or more geneschanging one or more genes
MutagensMutagens
• Definition- Definition- Agents that cause Agents that cause mutationsmutations
• Examples: Chemicals, x-rays, Examples: Chemicals, x-rays, radiation, geneticradiation, genetic
TwinsTwins
• Fraternal- Two fertilized eggs are Fraternal- Two fertilized eggs are implanted in the uterus at one timeimplanted in the uterus at one time
• Identical- one fertilized egg that Identical- one fertilized egg that splitssplits