Presentation on theme: "Warm-up #7 1/23/15 Draw a chromosome and label the following parts: chromosome, sister chromatid, centromere How many chromosomes do humans have?"— Presentation transcript:
Warm-up #7 1/23/15 Draw a chromosome and label the following parts: chromosome, sister chromatid, centromere How many chromosomes do humans have?
Human Chromosomes Humans have 23 pairs of chromosomes (46 total) 22 pairs of autosomes 1 pair of sex chromosomes Karyotype – A picture of all the chromosomes in a somatic cell arranged by size
One 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
Meiosis a type of cell division that results in four daughter cells each with half the number of chromosomes of the parent cell How can 2 cells join without doubling the amount of chromosomes?
Meiosis: Where and Who? For humans meiosis occurs in the ovaries and testes The process of meiosis produces egg and sperm cells gametogenesis (spermatogenesis & oogenesis) Two gametes come together by fertilization
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 combine –the resulting zygote is diploid
Meiosis: Why? Mitosis divides one diploid cell to form two diploid cells –For 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 chromosome –46 chromosomes from each parent would yield a 92 chromosome offspring Meiosis allows for two divisions to divide one diploid cell into four haploid cells.
Warm-up # 8 1/26/15 How are homologous chromosomes different from sister chromatids? –Sister chromatids are identical –Homologous chromosomes have the same genes, but may have different version of the gene What makes a cell haploid (n) or diploid (2n)? –Haploid – 1 set of chromosomes –Diploid – 2 complete sets of chromosomes
Chromosomes Each chromosome can contain thousands of genes Genes can have different versions Alleles
Meiosis I - homologous chromosomes separate –Prophase I –Metaphase I –Anaphase I –Telophase I Meiosis II - sister chromatids separate (more similar to mitosis) –Prophase II –Metaphase II –Anaphase II –Telophase II Meiosis Phases
Interphase Before Meiosis (just like before Mitosis) the cell must prepare for division: –DNA and organelles are replicated During this phase, chromosomes are not yet visible. –chromatin
Law of Segregation Each gamete only gets one allele of each gene
Independent Assortment Mendel's law of independent assortment: Genes for different traits assort independently of each other Organisms inherit two alleles for each trait when gametes are produced
Variation of Traits Crossing over during Prophase I –Exchange of genetic material between homologous chromosomes
Humans have 2 23 different combination for gametes!
MitosisMeiosis Function Type of cells # of divisions # of daughter cells Results in Haploid/dipl oid cells? Growth Repair Reproduction Create new cells for the purpose of reproduction Somatic cells (body cells, anything other than gametes) Germ line cells (gametes/sex cells) Diploid Haploid
Warm-up #9 1/27/15 Name & describe 2 events/processes that occur during meiosis that contribute to genetic variation 1.Crossing over – recombination of alleles 2.Independent assortment – genes of different traits assort independently of each other
Warm-up #10 1/28/15 Copy the diagram in your notebook. (1)Draw the possible gametes if crossing over DOES NOT occur (2)Draw the gametes if crossing over DOES occur (3)What affect does crossing over have on the variation of gametes?
Without Crossing Over
With crossing over
Law of Independent assortment 2 n different combinations If we have 3 different chromosomes, how many different combinations are possible?
n=3 2 3 =8
Chromosomal Mutations Errors can also occur during Meiosis. Homologous chromosomes do not separate properly –nondisjunction Gametes with either an extra copy of a chromosome or no copy Normal Example Nondisjunction Examples
Identifying Chromosomal Disorders Karyotype Photograph is taken of the paired chromosomes during metaphase Arranged according to length Easy to see if there are any extra or missing chromosomes This individual has an extra Y chromosome
Monosomy Zygote gets only one chromosome missing one chromosome –Most zygotes with monosomy do not survive
Trisomy One copy of a chromosome from one parent and two copies from the other parent three copies
Downs Syndrome (Trisomy 21) 3 copies of the 21 st chromosome mental retardation, susceptibility to certain illness or diseases, and a shorter life span