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Meiosis and Mendelian Genetics Genetics
Lab 7
Scenario-discussion Scenario-discussion
Down Syndrome
Inheritance of a third chromosome (#21) when Inheritance gamete was formed gamete Chances increase with age of mother Chances
Due to abnormal egg production Due Or the older female body not having the mechanism to Or recognize an abnormal fetus and automatically abort the baby baby
Can be diagnosed through Karyotyping
Karyotype Karyotype
A method of organizing the chromosomes method of a cell in relation to their number, size, and type. and Can be used to diagnose diseases related Can to the number of chromosomes a person has (ex. Down Syndrome, Klinefelters syndrome) syndrome)
Typically, each cell of Typically, your body has 46 chromosomes..23 from each parent each So, you have what we call So, a Diploid value of 46, or Diploid referred to as 2N 2N
Karyotype -Phototograph of chromosome set
DownSyndromeKaryotype DownSyndromeKaryotype
Trisomy on chromosome 21
Notice there are three
Amazing how such a small defect can cause such pronounced physical defects
Mitosis vs Meiosis Mitosis
Mitosis
Meiosis
Produces body cells Produces (Somatic cells) (Somatic Daughter cells are Daughter diploid diploid 1 cell division There are TWO There daughter cells daughter
Produces sex cell Produces (Gametes) (Gametes) Daughter cells are Daughter haploid haploid 2 cell divisions There are FOUR There daughter cells daughter
Mitosis Mitosis
each division gives 2 identical products 1 diploid Cell 2 diploid Cells
http://tidepool.st.usm.edu/pix/mitosis.jpg
Genetics Vocab Genetics
Allele particular type of single gene (blue eyes and brown eyes are different alleles, or a+ and a) Homozygous when chromosomes from each parent has the same allele (a+/a+ or a/a) Heterozygous when chromosomes from each parent have different alleles (a+/a or a/a+) Genotype the combination of different alleles that make up an individual (a+/a, b/b+, etc.) maternal paternal
(**See appendix C for more definitions**)
Homologous chromosomes
Genetics Vocab Genetics
Dominant allele trait that will be expressed over a recessive one. Designated with a capitol letter (B) Recessive allele trait that will be covered up by a dominant one. Designated with a small letter (b) Phenotype expressed trait that results from the combination of alleles Genotype B/B B/b b/b Phenotype Black hair Black hair Brown hair Homologous chromosomes Let B be the allele for black hair Let b be the allele for brown hair
Hair color gene
B
b
Meiosis Meiosis
Cell division process in which the number of chromosomes is Cell cut in half. cut Results in the formation of gametes eggs and sperm Results Allows for sexual reproduction in eukaryotes Allows eukaryotes Meiosis is basically mitosis occurring twice But the DNA is only replicated once (interphase) Meiosis allows for shuffling of genes with Crossing over
Meiosis Meiosis
Once gametes are formed:
They combine with a gamete of another individual and They undergo fertilization fertilization Producing a zygote (2n) Producing zygote Genotype formation in new individual (1/2 from mom, 1/2 Genotype from dad) from Phenotype expression dependent upon the alleles (different Phenotype versions of same gene) inherited, whether they are dominant or recessive, and whether the offspring is homozygous or heterozygous homozygous
Meiosis allows for
Meiosis I & II Meiosis
Prophase I: Condense, chrom. homolougous chrom. pair up Metaphse I: Homologues line up at equator Anaphase I: Homologues are separated into 2 groups (some mom, some dad) Telophase I: new nuclei form Prophase II: Chrom. Condense Metaphase II: Chrom. Line up at the equator Anaphase II: Chromatides are separated Telophase II: Each daughter cell from Meiosis I will form 2 more cell for a total of 4 cells (4 sperm, 1 viable egg)
Meiosis 1 Meiosis
http://www.dac.neu.edu/biology/c.ellis/genmolbio/index.htm
Meiosis 1 Meiosis
http://www.dac.neu.edu/biology/c.ellis/genmolbio/index.htm
Meiosis 1 Meiosis
http://www.dac.neu.edu/biology/c.ellis/genmolbio/index.htm
Meiosis 1 Meiosis
http://www.dac.neu.edu/biology/c.ellis/genmolbio/index.htm
Meiosis 2 Meiosis
http://www.dac.neu.edu/biology/c.ellis/genmolbio/index.htm
Meiosis 2 Meiosis
http://www.dac.neu.edu/biology/c.ellis/genmolbio/index.htm
Meiosis 2 Meiosis
http://www.dac.neu.edu/biology/c.ellis/genmolbio/index.htm
Meiosis 2 Meiosis
http://www.dac.neu.edu/biology/c.ellis/genmolbio/index.htm
Mendelian Genetics Mendelian
Mendel's First Law - segregation of alternate factors Alternative versions of genes (called alleles) account for variations in inherited characteristics For each character, an organism inherits two alleles, one from each parent If the two alleles differ, then one, the DOMINANT, is fully expressed in the organisms appearance (phenotype); the other, the RECESSIVE, has no noticeable effect on the organisms appearance The two alleles for each character segregate during gamete production
Punnet Square Punnet
Genotype: =RR =rr =Rr Phenotype: 3/4=RR =rr
RR Rr Rr rr
Investigation 1 Modeling Meiosis Modeling
Demonstration of meiosis on the white board - the Demonstration dance of the chromosomes dance As a class, use the models to answer questions Dysjunction - failure of chromosomes to separate Dysjunction
Investigation 1 Modeling Meiosis Modeling
How is meiosis different from mitosis?
Meiosis is 2 divisions resulting in 4 haploid cells Mitosis is 1 division resulting in 2 diploid cells Each has its own purpose Both are mechanisms for cell division Meiosis II is similar to mitosis - sister chromatids separate
How are they similar?
Investigation 2 Animal and Plant Mitosis
Onpage120,step2saystodrawstagesof mitosisinFigure79,shouldbeFigure74. Onpage119,thewebsiteaddressiswrong.The correctoneishttp://biog1101
1104.bio.cornell.edu/BioG101_104/tutorials/cell_division.html
Identifystagesofmitosisinplantandanimal cells Workingingroupsof2or3andfollowingthe websiteforhelp Lookatdifferentslidesfromdifferentgroupsand trytofindthedifferentstages
Investigation 3 Investigation
Modeling Meiosis
Parents have 2 of each chromosome Parents Every gamete gets 1 of each chromosome Fertilization is a random combination of these Fertilization gametes gametes
Investigation 3 Investigation
Independent Segregation
Most alleles come in pairs - one dominant and Most one recessive recessive
Dominant - only one copy needed for characteristics Dominant (Brown eyes - B) Recessive trait is only seen if NO dominant allele Recessive is present (Blue eyes - b)
Use punnett squares to predict phenotypes Example: Coat color in sheep
Investigation 4 Punnett Squares Investigation
On page 123, should be titled Investigation 4 On Groups of two or three with the computer. Review two websites on constructing Punnett Review squares.
First website is a tutorial 2nd website is what you base your responses on (Test Crosses section, do not go beyond this) (Test Look to the course website to find these websites Look