Presentation on theme: "How many chromosomes do humans have?"— Presentation transcript:
1How many chromosomes do humans have? Warm-up # /23/15Draw a chromosome and label the following parts: chromosome, sister chromatid, centromereHow many chromosomes do humans have?
2Human Chromosomes Humans have 23 pairs of chromosomes (46 total) 22 pairs of autosomes1 pair of sex chromosomesKaryotype – A picture of all the chromosomes in a somatic cell arranged by size
3One chromosome in the pair came from the male parent and one came from the female parent. Homologous chromosomes – each pair has genes for the same traits
4How can 2 cells join without doubling the amount of chromosomes? Meiosis a type of cell division that results in four daughter cells each with half the number of chromosomes of the parent cell
5Meiosis: Where and Who?For humans meiosis occurs in the ovaries and testesThe process of meiosis produces egg and sperm cells gametogenesis (spermatogenesis & oogenesis)Two gametes come together by fertilization
6A cell with only one of each kind of chromosome is called haploid (n). Organisms produce gametes (sex cells) that contain one of each kind of chromosome.A cell with only one of each kind of chromosome is called haploid (n).Sex cells have one of each kind of chromosome so that when they combinethe resulting zygote is diploid
8Meiosis: Why?Mitosis divides one diploid cell to form two diploid cellsFor example: A human cell with 46 chromosomes divides to form two cells with 46 chromosomes.If each parent were to pass on a diploid cell to the offspring, that offspring would then have 4 copies of each chromosome46 chromosomes from each parent would yield a 92 chromosome offspringMeiosis allows for two divisions to divide one diploid cell into four haploid cells.
9Label the diagram Homologous chromosomes Sister chromatids Centromere
10Warm-up # /26/15How are homologous chromosomes different from sister chromatids?Sister chromatids are identicalHomologous chromosomes have the same genes, but may have different version of the geneWhat makes a cell haploid (n) or diploid (2n)?Haploid – 1 set of chromosomesDiploid – 2 complete sets of chromosomes
11Chromosomes Each chromosome can contain thousands of genes Genes can have different versions Alleles
12Meiosis Phases Meiosis I - homologous chromosomes separate Prophase IMetaphase IAnaphase ITelophase IMeiosis II - sisterchromatids separate(more similar to mitosis)Prophase IIMetaphase IIAnaphase IITelophase II
13InterphaseBefore Meiosis (just like before Mitosis) the cell must prepare for division:DNA and organelles arereplicatedDuring this phase, chromosomes are not yet visible.chromatin
19All DifferentHumans have 223 different combination for gametes!
202 1 4 2 Function Type of cells # of divisions # of daughter cells MitosisMeiosisFunctionType of cells# of divisions# of daughter cellsResults in Haploid/diploid cells?GrowthRepairReproductionCreate new cells for thepurpose of reproductionSomatic cells(body cells, anything otherthan gametes)Germ line cells(gametes/sex cells)2142HaploidDiploid
21Warm-up # /27/15Name & describe 2 events/processes that occur during meiosis that contribute to genetic variationCrossing over – recombination of allelesIndependent assortment – genes of different traits assort independently of each other
22Warm-up #10 1/28/15 Copy the diagram in your notebook. Draw the possible gametes if crossing over DOES NOT occurDraw the gametes if crossing over DOES occurWhat affect does crossing over have on the variation of gametes?
27Chromosomal Mutations Errors can also occur during Meiosis.Homologous chromosomes do not separate properly –nondisjunctionGametes with either an extra copy of a chromosome or no copyNormal ExampleNondisjunction Examples
28Identifying Chromosomal Disorders KaryotypePhotograph is taken of the paired chromosomes during metaphaseArranged according to lengthEasy to see if there are any extra or missing chromosomesThis individual has an extra Y chromosome
29Monosomy Zygote gets only one chromosome missing one chromosome Most zygotes with monosomy do not survive
30TrisomyOne copy of a chromosome from one parent and two copies from the other parent three copies
31Downs Syndrome (Trisomy 21) 3 copies of the 21st chromosomemental retardation, susceptibility to certain illness or diseases, and a shorter life span