2Parents can produce many types of offspring Families will have resemblances, but no two are exactly alike
3Eukaryotic DNA is organized in chromosomes. Genes have specific places on chromosomes.Gene-carry information that go toward determining your traits. Genes control the TRAITS of the individualTrait - A physical characteristic, you inherit from your parents; this means your parents pass some of their characteristics on to you through genes. Examples of traits are height, eye color, and the ability to roll your tongue.
4Every cell has a nucleus Every nucleus has chromosomesThe number of chromosomes depends on the speciesEx. Humans have 46
5Chromosomes come in matching sets -these are called homologous pairs
6Chromosomes and Chromosome Number Human body cells have 46 chromosomesEach parent contributes 23 chromosomesHomologous chromosomes—one of two paired chromosomes, one from each parentPairs 1-22Humans have 23 pairs of homologous chromosomes pairs of autosomes1 pair of sex chromosomes
7Homologous chromosomes Same LengthSame centromere positionCarry genes that control the same inherited traits
10A somatic cell is any biological cell forming the body of an organism, somatic cells make up all the internal organs, skin, bones, blood, and connective tissue.By contrast, gametes are cells that fuse during sexual reproduction, for organisms that reproduce sexually. Sperm and egg cell.
11Fertilization n=23 egg 2n=46 zygote The fusion of a sperm and egg to form a zygoteA zygote is a fertilized eggn=23eggspermn=232n=46zygote
12A haploid cell has only one set of chromosomes N A diploid cell has two sets of chromosomes 2N.In human, the somatic cells are diploid, and the gametes are haploid.Human cheek cells have 46 chromosomes. (Diploid)Human sex cells have 23 chromosomes. (Haploid)
13Cells in your body have a complete set (all 46) - they are called DIPLOID Sex cells (sperm and eggs) only have half (23) - they are called HAPLOID
14---During Meiosis diploid cells are reduced to haploid cells In humans, a diploid cell contains a total of 46 chromosomes, while haploid cells have 23 homologous chromosome pairsAll sex cells must reduce their chromosome number as they divide. This reduction division is called meiosis and changes the chromosome number from Diploid to Haploid.---During Meiosis diploid cells are reduced to haploid cellsDiploid (2n) Haploid (n)When mitosis produces 2 identical daughter cells, both the parent and daughter cells referred to as diploid while in meiosis a diploid cell divides twice to produce 4 daughter cells that are considered haploid.
15What is the difference between Diploid and Haploid? Haploid cells contain only one set of chromosomes and diploid cells contain two sets of chromosomes.• Haploid cells are produced by meiosis, and diploid cells are produced by mitosis.• Diploid cells have the same number of chromosomes as the parent cell, and haploid cells have only a half of the number of chromosomes as the parent cell.• Diploid cells are genetically identical to the parent cell, and haploid cells are not genetically identical to the parent cell.• Haploid cells are important in sexual reproduction, and diploid cells are important in growth, asexual reproduction and genetic stability.
16The process of creating a gamete (sex cell) is called MEIOSIS It is similar to mitosis, but will produce 4 daughter cells that are each haploid.
17Why do we need meiosis?Meiosis is necessary to halve the number of chromosomes going into the sex cellsWhy halve the chromosomes in gametes?At fertilization the male and female sex cells will provide ½ of the chromosomes each – so the offspring has genes from both parents
18Mitosis vs Meiosis Mi-two-sis Mei-one-sis Produces body cells-Somatic cellsDaughter cells are diploid 2N2 Daughter cells are producedDaughter cells are genetically IDENTICAL to parentOne nuclear divisionProduces cells for growth and repairProduces sex cell-GametesDaughter cells are haploid N4 Daughter cells are producedDaughter cells have one half of the genes from the parent cell.Two nuclear divisionsProduces cells for sexual reproductionGenerates genetic diversity through crossing over
21MeiosisHas 2 stagesMeiosis 1, This is the stage where the chromosomes nuber is halvedIncludes 4 stagesProphase 1Metaphase 1Anaphase 1Telophase 1Meiosis 2
22Chromosomes replicate. Section 1Sexual Reproduction and GeneticsMeiosisMeiosis IInterphaseChromosomes replicate.Chromatin condenses.Interphase
23Each chromosome consists of two chromatids. Section 1Sexual Reproduction and GeneticsMeiosisMeiosis IProphase IPairing of homologouschromosomes occurs.Each chromosome consists of two chromatids.Prophase IThe nuclear envelope breaks down.Spindles form.
24Section 1Sexual Reproduction and GeneticsMeiosisMeiosis IProphase ICrossing over produces exchange of genetic information. Extremely IMPORTANT!!! It is during this phase that crossing over can occur.Crossing over—chromosomal segments are exchanged between a pair of homologous chromosomes.
25When homologous chromosomes hang out so close to each other they swap parts! This is called “crossing over”Crossing over increases genetic diversity
26Chromosome centromeres attach to spindle fibers. Section 1Sexual Reproduction and GeneticsMeiosisMeiosis IMetaphase IChromosome centromeres attach to spindle fibers.Metaphase IHomologous chromosomes line up at the equator.
27The Key Difference Between Mitosis and Meiosis is the Way Chromosomes Uniquely Pair and Align in MeiosisMitosisThe first (and distinguishing) division of meiosis
28Homologous chromosomes separate and move Section 1Sexual Reproduction and GeneticsMeiosisMeiosis IAnaphase IHomologous chromosomes separate and moveto opposite poles of the cell.Anaphase IContrasts mitosis – chromosomes appear as individuals instead of pairs (meiosis)
29The spindles break down. Section 1Sexual Reproduction and GeneticsMeiosisMeiosis ITelophase IThe spindles break down.Telophase IChromosomes uncoil and form two nuclei.The cell divides.Cytokinesis occurs Spontaneously with Telophase 1Results in 2 haploid daughter cells
31Figure 13.7 The stages of meiotic cell division: Meiosis I
32After Meiosis 1… Homologous chromosomes have been separated Two non-identical daughter cells have been formedThe chromosomes number has been cut in half
33Meiosis 2 is similar to Mitosis Two identical daughter cells are formed from each of the cells created in Meiosis 1Includes 4 stagesProphase 2Metaphase 2Anaphase 2Telophase 2
34A second set of phases begins Section 1Sexual Reproduction and GeneticsMeiosisMeiosis IIProphase IIA second set of phases beginsas the spindle apparatus forms and thechromosomes condense.Prophase IINucleolus/Nuclear Envelope breaks down
35A haploid number of chromosomes Section 1Sexual Reproduction and GeneticsMeiosisMeiosis IIMetaphase IIA haploid number of chromosomesline up at the equator.Metaphase II
36The sister chromatids are Section 1Sexual Reproduction and GeneticsMeiosisMeiosis IIAnaphase IIThe sister chromatids arepulled apart at the centromere by spindlefibers and move toward the opposite polesof the cell.Anaphase II
37The chromosomes reach the poles, and Section 1Sexual Reproduction and GeneticsMeiosisMeiosis IITelophase IIThe chromosomes reach the poles, andthe nuclear membrane and nuclei reform. Spindle fibers disappear.Telophase II
38Section 1Sexual Reproduction and GeneticsMeiosisMeiosis IICytokinesis results in four haploid cells, each with n number of chromosomes.Cytokinesis
39Figure 13.7 The stages of meiotic cell division: Meiosis II
40The Importance of Meiosis Section 1Sexual Reproduction and GeneticsMeiosisThe Importance of MeiosisMeiosis consists of two sets of divisionsProduces four haploid daughter cells that are not identicalResults in genetic variation