Mitosis, Meiosis and Genetics

1. Mitosis, Meiosis and Genetics NSC 6308 Dr. Chandrasekaran Dr. Benz Dr. Wilson

2. Organization of genetic material Prokaryotes: DNA is circular, not associated with proteins Eukaryotes: DNA is linear, associated with proteins Chromatin: the “interphase” state Chromosome: condensed state seen at the start of mitosis and meiosis

4. Chromosome Structurehttp://www.micro.utexas.edu/courses/levin/bio304/genetics/chromosome.gif

5. Stages of Mitosis (http://www.marymount.k12.ny.us/marynet/06stwbwrk/06bio/amsmitosis/images/mitosis.gif)

7. Mitosis summary Daughter cells have the same number of chromosomes as parental cells Daughter cells have the same DNA content as parental cells Daughter cells have identical DNA structure as the parental cells Mitosis starts with diploid cells and produces diploid cells

8. Germ Cell Cycles and Meiosis Occurs only in organisms that use sexual reproduction Specialized cell division that only occurs in germ cells. Germ cells, through their progeny, transmit genetic information to the next generation. The product cells of meiosis are the gametes ( ex, egg, sperm).

10. During meiosis I (prophase I), there is exchange of genetic material between chromosomes: genetic recombination. Genetic recombination may allow for a competitive advantage by rearranging genetic material from generation to generation.

11. Key points about Meiosis I Germ cells start out diploid Germ cells duplicate their DNA Homologous chromosomes exchange genetic material during prophase I Meiosis I ends with the separation of the homologs and the physical division of the cells Products of meiosis I are not diploid because they do not have homologous chromosome pairs Products of meiosis I are not haploid (yet)

12. Key points about Meiosis II No DNA duplication prior to meiosis II Separation of the attached chromatids (replicated chromosomes) Four products (gametes) are genetically NOT identical to each other! Four products (gametes) are haploid—no homologous chromosome pairs

13. Meiosis to Genetics.... Meiosis produces gametes with a haploid chromosome number. During fertilization, these gametes unite to form a diploid zygote, which then develops by successive cell divisions into an organism. Thus, organisms inherit two sets of genetic information: one from each gamete (parent).

17. Genetics: Introduction Each organism displays certain traits. Traits are inherited from previous generations. The monk Gregor Mendel, through his studies of pea plants, discovered a mechanism for the inheritance of specific traits.

18. Terms and Definitions Gene: unit of information about a specific trait, passed from parent to offspring Allele: all of the different forms of the gene Gene: seed color Allele: green, yellow In diploid organisms, each gene has at least two alleles.

19. Terms and Defintions, cont. Allele combinations homozygous: when both alleles are identical heterozygous: when each allele is different Types of alleles Dominant alleles: capital letter (D) Recessive alleles: lowercase letter (d) When paired, the dominant allele will mask the effect of the recessive allele

20. Gene: seed color Alleles: green (y) and yellow (Y) Allele combinations: Genotype Phenotype YY ; homozygous dominant yellow Yy; heterozygous yellow yy; homozygous recessive green

21. For a given trait (gene), the pair of alleles in each parent separate such that the offspring only inherits one allele. Separation of alleles occurs during the meiotic divisions that produce the gametes. Tested by the monohybrid cross Mendel's Law of Segregation

22. Gene: seed color Alleles: green (y) and yellow (Y) Parental genotypes: YY (yellow) and yy (green) Offspring from this cross (F1): All were yellow. F1 were self-fertilized Offspring from this cross (F2): 75% were yellow, and 25% were green Monohybrid Cross

23. Monohybrid cross: Analysis Parental: Gametes produced by the YY parent would each contain one Y allele. Gametes produced by the yy parent would each contain one y allele. The only possible combination of alleles from these parental gametes would be Yy (genotype). All of these plants will have yellow seeds (phenotype).

24. Monohybrid cross: Analysis Self fertilization of F1: Yy x Yy. Each Yy plant (parent) will produce gametes that contain one allele: half of gametes will contain the Y allele other half of gametes will contain the y allele Combinations possible from these parental gametes can be predicted using a Punnett square (probability).

25. Punnett Square for F2 generation Circles represent gametes Phenotypic ratio predicted: 75% yellow and 25% green ( 3:1 ratio) Genotypic ratio predicted: 25% YY, 50% Yy, 25% Yy (1:2:1 ratio)

26. X-linked genes and Inheritance In humans, gender is determined by the sex chromosomes males have an X and a Y chromosome (XY) females have two X chromosomes (XX) Humans have 23 pairs of chromosomes 22 pairs: autosomal chromosomes 1 pair: sex chromosomes

27. There are genes on the X and the Y chromosome only males inherit genes on the Y chromosome both females and males inherit genes on the X chromosome

28. Analysis of X-linked genes The gene for hemophilia is recessive and is X-linked. the H allele is the non-disease; the h allele is the hemophilia allele Genotype Phenotype XHXH female; no disease XHXh female; no disease XhXh female, hemophilia XhY male, hemophilia XHY male, no disease

29. Punnett Squares and X-linked Genes