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

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