Genetics Week Three
Genetics Week Three BIO310
Virginia Commonwealth University
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Popular in BIO
This 4 page Class Notes was uploaded by Jayda Abrams on Monday September 19, 2016. The Class Notes belongs to BIO310 at Virginia Commonwealth University taught by Dr. Wu in Fall 2016. Since its upload, it has received 19 views. For similar materials see Genetics in BIO at Virginia Commonwealth University.
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Date Created: 09/19/16
Genetics Week Three Notes 9/12/2016 Information from the Power Point = Blue Verbal information = Orange Chapter 2 Continued 2.5 Spermatogenesis Compared to Oogenesis The development of gametes varies between spermatogenesis and oogenesis Male gametes = spermatogenesis (produced in testes) Female gametes = oogenesis (produced in ovaries) Sperm always starts diploid. Different organisms have different chromosome numbers, haploid is half of that and the number must be even as a diploid! Primary oocyte= primary polar body. Primary spermatocyte undergoes meiosis I and produces two secondary spermatocytes then the spermatocytes undergo meiosis II and produce a total of four haploid spermatids. Genetic information is exchanged during meiosis I. Formation of ova occurs in the ovaries. The four daughter cells do not receive equal cytoplasm. Only one daughter cell receives cytoplasm and it is known as the primary polar body. The primary polar body undergoes meiosis I and II and develops into ovum One cell = One Egg and One cell = Four sperm Both the first polar body and the second polar body kill themselves. The egg is big and the sperm is small. The egg has lots of cytoplasm and the sperm has a little bit. What does this mean? Meaning: Mothers give all cytoplasm traits to their offspring. All of it comes from the egg and none of it comes from the sperm. Everything in the mitochondria comes from mom. 2.6 Meiosis and Sexual Reproduction Meiosis- Mechanisms by which diploid amount of genetic information is reduced to haploid and by which each gamete carries similar, but not identical genetic information. Sperm and egg create diversity because none of them are exactly the same. Juno Protein- Protein that blocks other sperm from joining the egg after fertilization occurs. Plant and fungi life cycles: Fungi: Haploid vegetative cells arise via meiosis – proliferate via mitotic cell division Plants: Life cycle alternates between sporophyte stage and gametophyte stage ***Know the reproduction of a flower!*** This is how seeds are made. Why do different foods have different number of seeds? Because the ovary will contain multiple ovules and each create one egg. There is lots of pollen that can drop on the eggs and this gives fruit lots of seeds. 1 ovule produces 1 seed. 2.7 Physical Nature of Mitotic and Meiotic Chromosomes Chromosomes are visible only during mitosis and meiosis. Chromatin fibers make up chromosomes coil and condense in these stages. EM of mitotic chromosomes in varying states of coiling led to postulation of the folded-fiber model Chapter 3 3.1 Mendel Mendel worked with peas and used his quantitative data to prove his theories about traits and transmission of genetic information between generations. His work was published in 1866. Mendel is the father of genetics. He worked with peas and flowers to see how genetics works. He is the father of genetics because he took the time and had the effort and patents to keep records of all of his finding and documenting simple things like which peas are smooth, round, big, small, yellow, green etc. He used many generations and identified the genetic rule. For genetics you always need more than one generation. Transmission genetics also known as Traditional Genetics or Mendel Genetics. Mendel decided to work with peas because: 1. easy to grow 2. true-breeding strains 3. controlled matings: self-fertilization or cross-fertilization 4. grow to maturity in one season 5. observable characteristics with two distinct forms Mendel used seven visible features a. each with two contrasting traits- two distinct traits like short and tall b. true-breeding strains 3.2 Monohybrid Cross Mendel the father of genetics started with translation of the genetic tree with monohybrid crossing. P 1eneration: Original parents F 1eneration: Offspring F 2eneration: Offspring of F g1neration crossed (self-fertilizing: “Selfing”) He found that everything was 3:1 and that nature has its own genetic rules. All genes that control the traits are not in sex chromosomes. What does this mean? This means it does not matter if the male or the female plant is tall, if they cross the plant will be tall period. Non sex dependent genes are called reciprocal crosses. The basic unit of heredity is a particulate unit factor also known as genes. Genes exist in pairs and genetic characteristics are controlled by this unit factors. In a pair of unit factors one is dominant and the other is recessive. Segregation- Paired unit factors segregate (separate) independently during gamete formation. These unit factors and independent and are free to come and free to go. ***Know how to do a Punnett square!*** Homozygotes with a homozygote= true breeding A test cross is a cross between dominant phenotype and homozygous recessive genotype to figure out the genotype of the individual with the dominant trait. 3.3 Mendel and the Dihybrid Cross A dihybrid cross is looking at two traits at the same time and their correlation. Example color and shape. 9:3:3:1 Ratio is used for dihybrid 3:1 Ration is used for F1 mono hybrid Product law- Used to predict frequency of two independent events occurring simultaneously. Example: F 2lant having yellow and round seeds 3/4 3/4, or 9/16. Dihybrid = two independent mono hybrid combinations. In a test cross you have two characters and the genotype is unknown. You cannot do a Punnett square because the genotype needs to be known to do a Punnett square. Yellow, round seed phenotype in F g2neration produces which genotypes: a) GGWW b) GGWw c) GgWW d) GgWw The correct answer would be none of the above. Why? Because it must be homozygous recessive. 3.4 The Trihybrid Cross Segregation and independent assortment applied to three pairs of constraining traits can be shown with a Punnett square with 64 boxes. What is the number of gametes a trihybrid parent can produce? 8. How? The formula for this is 2 and n= 3. So 2 = 8. This creates diversity because there are over 20,000 different traits. 3.5 History Chromosomes can be separated freely. In males the sex chromosomes are not homologs 3.6 Genetic Variation Independent assortment leads to extensive genetic variation Genetic variation is due to nonidentical homologous chromosomes Chromosome combination produces extensive genetic variation Are you a Genetically Modified Organism (GMO)? Yes, you are a GMO because we are modified from our parents. No one can be identical to their mom or dad.
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