1 / 17

Genetics

Genetics. Non-disjunction and Karyotypes Created by: Sandra, Abby, Jasmine, Sarah, and Thomas. Important Definitions. Genotype- refers to the alleles of an organism. Written using upper case and lower case letters. ie Tt

juliet
Download Presentation

Genetics

An Image/Link below is provided (as is) to download presentation Download Policy: Content on the Website is provided to you AS IS for your information and personal use and may not be sold / licensed / shared on other websites without getting consent from its author. Content is provided to you AS IS for your information and personal use only. Download presentation by click this link. While downloading, if for some reason you are not able to download a presentation, the publisher may have deleted the file from their server. During download, if you can't get a presentation, the file might be deleted by the publisher.

E N D

Presentation Transcript

  1. Genetics Non-disjunction and Karyotypes Created by: Sandra, Abby, Jasmine, Sarah, and Thomas

  2. Important Definitions • Genotype- refers to the alleles of an organism. Written using upper case and lower case letters. • ieTt • Phenotype-includes all characteristics of an organism. Written as a word. • ie. Tall • Dominant allele- has the same affect on the phenotype whether it is present in the homozygous or the heterozygous state. • ieTt and TT are tall

  3. Definitions continued • Recessive allele- only has an effect on the phenotype in the homozygous state. • iett is tall • Codominant alleles- a pair of alleles that both affect the phenotype when present in a heterozygote. • Locus- the particular position on homologous chromosomes of a gene • Homozygous- having two identical alleles of a gene. • iett or TT

  4. Definitions continued • Heterozygous-two different alleles of a gene. ieTt • Carrier- a heterozygous individual that has one copy of a recessive allele that causes a genetic disease in individuals that are homozygous for this allele. • Test cross- refers to testing a suspected heterozygote by crossing with a known homozygous recessive.

  5. What is Non-disjunction? • When chromosomes do not separate properly during meiosis, either in meiosis I (in anaphase I) or meiosis II (in anaphase II). • This failure to separate can lead to aneuploidy (having one extra or missing chromosome) or polyploidy (having one complete extra set of chromosomes).

  6. Non-disjunction video http://www.biostudio.com/d_%20Meiotic%20Nondisjunction%20Meiosis%20I.htm

  7. Non-disjunction in Down Syndrome • Down Syndrome is an example of a genetic disease caused by non-disjunction. • This can be seen through karyotyping when there are three chromosomes in the 21st pair.

  8. Down Syndrome • Down syndrome is a result of aneuploidy. If non-disjunction occurs in either parent, one of the 2 gametes will have 2 copies of chromosome 21. So, when the zygote is formed it will contain 3 copies of chromosome 21 and will be aneuploid. AKA: trisomy 21 • (tri=3 somy=chromosomes)

  9. Factors affecting chances of Down Syndrome • Age • Females= gametes develop before birth, so the age of the woman is the age of egg cells. The older the woman, the more damage the cells have endured. • Males= sperm is constantly produced so the age of father has less effect than age of mother. • Family history • If a relative has down syndrome, the person has an increased chance.

  10. Karyotyping • Karyotyping: process of finding the chromosomal characteristics of a cell • Chromosomes are arranged in pairs according to their size and structure starting with the largest

  11. How Karyotyping is Done • Common pre-natal testsfor diagnosis of chromosome abnormalities: • chorionic villus sampling (CVS) • CVS: can be done at 11-12 weeks. Involves taking sample of chorionic villi (finger-shaped growths found in the placenta) to get cells from tissue that originally came from the zygote. Cells will have same genetic composition as cells of unborn baby so a karyotype can be made. Can take fewer than 2 weeks.

  12. Cont. • Amniocentesis • Amniocentesis: can be done around the 16thweek of pregnancy. Take a sample of amniotic fluid (which have fetal cells) and a culture is made. Cells are photographed and chromosomes are arranged in homologous pairs. Can take up to 3 weeks.

  13. How to Determine Gender from Karyotyping • Males: 1 X and 1 Y (XY) • Females: 2 X’s (XX) • Can be distinguished on karyotype b/c Y chromosomes is smaller than an X

  14. How to Determine Non-disjunction from Karyotyping • If a chromosome is missing or if there's an extra one by looking at the number of chromosomes. • Should only be two of each chromosome. • Each 23 chromosomes should have a pair resulting in 46 chromosomes in total.

  15. Activity Goal: Arrange and pair chromosomes together to create a karyotype. Identify if your karyotype is male or female and if it has undergone nondisjunction.

  16. Works Cited http://www.southtexascollege.edu/nilsson/4_GB_Lecture_figs_f/4_GB_10_Genetics_Fig_f/13_2_NonDisjunction.GIF http://www.ncbi.nlm.nih.gov/pubmedhealth/PMH0001992/ http://www.biostudio.com/d_%20Meiotic%20Nondisjunction%20Meiosis%20I.htm http://faculty.stcc.edu/BIOL102/Lectures/lesson3/punnett.htm http://www.hematogenix.com/DirectoryofServices/Cytogenetics/tabid/70/Default.aspx http://www.angleseybonesetters.co.uk/bones_DNA.html http://www.exitmundi.nl/giggle.htm

More Related