Chapter 10: Introduction to Genetics

2 Intro to Genetics Genetics: study of Heredity, or the passing of characteristics from parents to offspring. Traits: Inherited characteristics.

3 Fertilization: The uniting of male and female gametes. Gene: is a region of genetic information on a chromosome that “codes” for a certain trait  Gametes: The sex cells found in an individual- egg or sperm. Remember… (from last unit)

4 Father of Genetics Gregor Mendel ( ): An Austrian monk. He wanted to know how traits were passed from parent to child.

5 Mendel did many experiments with pea plants and bred them for certain traits Mendel started out with plants that he knew were only tall or short. He mated short plants with tall plants. All the offspring were tall!! What was going on??? To investigate he bred these plants over and over again and recorded his results! Mendel’s Research

6 Mendel’s Experiments TallShort Tall Tall Tall Tall Tall Short

7 In his work he named the different generations of plants: –The Parents: P1 generation –The first generation of offspring: F1 generation –The second generation of offspring: F2 generation –Ex. Mendel’s experiments P1 F1 F2

8 Mendel’s Laws 1.Law of Segregation 1.Law of Segregation: the members of each pair of alleles separate when gametes are formed. A gamete will receive one allele or the other 2.Law of Independent assortment 2.Law of Independent assortment states that when gametes are made, the genes for traits found on different chromosomes separate independently

9 AllelesAlleles : A form of a gene, one comes from the mother, one from the father. –Ex. Gene = height, the allele could be tall or short. Gene = eye color, the allele could be light or dark. We have 2 alleles for each trait (one from mom, one from dad)!  Remember  Remember: DNA twisted into chromosomes, chromosomes have genes on them, for each gene there are different forms or alleles of that trait Basic Genetics

10 Draw me in your notes and write down the info!!

11 Basic Genetics (cont’d) If there are two alleles, and only one observed trait, which allele is dominant? dominant –A dominant allele is always expressed. capital lettersWe write the dominant allele in capital letters recessive –A recessive allele; not expressed when in the presence of a dominant allele. is expressed when paired with another recessive allele. lower case lettersWe write the recessive allele in lower case letters

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13 Basic Genetics (cont’d) Phenotype: The expression of the gene itself. (what we see) Blue eyes, straight hair, brown hair are all phenotypes. Genotype: The combination of alleles for a trait. (your actual DNA) Ex. B = brown eyes b = blue eyes Genotype: Bb Phenotype : brown eyes

14 Genetics Problems So we know about genes and traits… how can we predict what our offspring will look like? Punnett Squares tell us the probability that the offspring will look a certain way!!

15 Genetics Problems Punnett Squares: a diagram used to identify possible combinations of dominant and recessive alleles in offspring Ex. - A is a dominant characteristic. - a is a recessive characteristic. - This bird has two genes for red feathers. - Its genotype is AA. - its phenotype is red - This bird has two genes for blue feathers. - Its genotype is aa. - Its phenotype is blue Mom Dad

16 Setting up your punnett square! Mom Dad Possible Offspring: 4 Red! (because A is dominant)

17 Homozygous: Two of the same allele for a trait. –Ex. AA or aa Heterozygous: Two different alleles for one trait. –Ex. Aa. AA is homozygous dominant. aa is homozygous recessive. Aa is heterozygous. More Genetics Vocab…

18 Punnett Squares (cont’d) Monohybrid cross one allele to the offspringMonohybrid cross: means “one gene”. Each parent donates one allele to the offspring

19 Punnett Squares (cont’d) Dihybrid Cross Dihybrid Cross (Two factor cross) Each parent donates two alleles to the offspring

20 Genetic Exceptions to the rules! Incomplete DominanceIncomplete Dominance One allele is not completely dominant over the other. Example: Cross red (RR) flower with a white (WW) flower. The resulting RW flower is pink.

21 Genetic Exceptions to the rules! Codominance Both alleles contribute to the phenotype Example: A red cow crossed with a white cow results red cows with white blotches.

22 Genetic Exceptions to the rules! Multiple Alleles A gene has more than one allele The result is various expressions of the gene. Example: various hair colors in mice.

23 Genetic Exceptions to the rules! Polygenic Traits Traits controlled by more than one gene –Ex. Human skin color More than 4 different genes control this trait, which is why we all look so different!

24 Genetics and the Environment Depending on the trait.. Your environment can affect your phenotype! –Ex. If you are out in the sun, your skin color may change –Ex. If you smoke, you increase your risk of lung cancer

25 Meiosis Why Meiosis?  Mitosis produces cells with exactly the same amount of chromosomes as the original cell.  If two gametes (egg and sperm) combine they must have half as many chromosomes.

26 Meiosis  Haploid: cell with one of each kind of chromosome (n)  Organisms produce gametes that are haploid…egg and sperm  Diploid: cell with two of each kind of chromosome (2n)  Body cells of animals/plants have chromosomes that occur in pairs…one from each parent  To produce haploid gametes, organisms under go meiosis

27 Meiosis  Meiosis has 2 separate divisions…Meiosis I and Meiosis II  Meiosis I begins with a Diploid cell…2n  Meiosis II finishes with 4 Haploid cells (1n)  These 4 Haploid cells are Gametes (Egg or Sperm)  With Fertilization, Sperm (23) and Egg (23).. Haploid…come together to produce a Zygote (46)..Diploid  This pattern of reproduction that involves the combining (fusion) of haploid gametes is called Sexual Reproduction  Homologous Chromosomes: Paired chromosomes, each with genes for the same traits. These exist in Diploid cells and are what determine how an individual looks.

28 Phases of Meiosis

29 Interphase 1 DNA Replication

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31 Prophase I Crossing Over can occur Each pair of homologous chromosomes come together to form a four-part structure called a Tetrad

32 Metaphase I In Meiosis, the Tetrad of homologous chromosomes lines up down the middle

33 Anaphase I Spindle fibers pull homologous chromosomes toward opposite ends of the cell

34 Telophase I At the end of Meiosis I the two new cells are still Diploid

35 Meiosis I

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37 Prophase II Meiosis II is identical to Mitosis

38 Metaphase II

39 Anaphase II

40 Telophase II Each Haploid cell has one chromosome from each homologous pair 4

41 Meiosis II

42 Mitosis vs. Meiosis Results in 2 genetically identical cells Cells are diploid Results in 4 genetically different cells Cells are haploid

43  Meiosis “shuffles” chromosomes so that the offspring are not identical to the parents  Gene combinations vary depending on how homologous chromosomes line up during Metaphase I… completely random Genetic Variation

44  Crossing Over can occur anywhere at random

45  Nondisjuction: Chromosomes fail to separate correctly  Both chromosomes from a homologous pair move to the same pole of the cell  Trisomy: zygote has an extra chromosome  Ex: Trisomy 21 Genetic Mistakes

46  Monosomy: A form of nondisjuction where zygote is missing one chromosome  In humans, most zygotes/organisms with monosomy do not survive  Ex: (non lethal) Turner Syndrome= Human females with only one X chromosome Genetic Mistakes

47 Gene Linkage Chromosomes assort independently, NOT individual genes (Mendel was lucky ~ or selective) Genes that are close together on a chromosome are less likely to separate through crossing over. –Ex. Blonde hair and blue eyes.

48 Fruit Fly Gene Map