Meiosis Biology 2009-2010

Meiosis Def: type of cell division that produces 4 cells with half the number of chromosomes as a parent cell Occurs in the sex organs Number of chromosomes= 46 or 23 pairs

Homologenous Chromosomes Def: chromosomes that match in shape and size but not necessarily same DNA patterns Homologous Chromosomes

Karyotyping Sex chromosomes Def: arrangement of all 46 chromosomes The 23rd pair Determines the organisms sex XX= girl XY=boy

Male Karyotype

Female Karyotype

Diploid vs. Haploid Diploid Haploid 2 homologenous sets of chromosomes Forms the zygote 2n Haploid 1 set of chromosomes- one from each pair Occurs in fertilization n

Number of Chromosomes Sex Cells each have half the number of chromosomes (23) Zygote (fertilized egg) have 46 chromosomes

Steps of meiosis Differences between mitosis and meiosis: Meiosis produces 4 offspring cells Meiosis involves exchanging of genetic material between the Homologous Chromosomes. Sister chromosomes- exact copies of DNA Homologenous chromosomes- DNA does not have to be the same

Meiosis 1 Prophase 1 Metaphase 1 Anaphase 1 Telophase 1 Homologenous chromosomes stick together forming a tetrad Crossing over begins Metaphase 1 Crossing over is complete Chromosomes line up in the center Anaphase 1 Chromosomes migrate towards the opposite poles Telophase 1 Each pole has a haploid

Crossing Over DEF: Genetic materials is transferred from one chromosome to another Crossed over

Meiosis 2 Follows the exact same steps as Mitosis except the end results in 4 cells 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 Defects Biology2009-2010

Numbers There are 200,000 people born with birth defects every year To break it down, there are 25 people born with birth defects per hour

Causes of Birth Defects Drugs/Alcohol/Smoking Radiation/Pollution STD’s Inheritance Malnutrition

Detection Blood Test Amniocentesis- A sample of the amniotic fluid is taken and then the DNA is checked for Chromosomal defects

Chromosomes Monosomy- loss of one chromosome Trisomy- gain an extra chromosome Sex Chromosomes- X and Y

Down Syndrome Occurrence-1/600 births Causes- trisomy 21 Chance with increased age 20’s- 1/1500 40’s-1/44

Homozygous Recessive Traits Found on the X chromosome Passed on from mother’s to their children Examples: Muscular Dystrophy and color blindness

Mutations Definition- change in the DNA by changing one or more genes

Mutagens Definition- Agents that cause mutations Examples: Chemicals, x-rays, radiation, genetic

Twins Fraternal- Two fertilized eggs are implanted in the uterus at one time Identical- one fertilized egg that splits