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1 Genetics Overview Acton Biology. 9 Heredity Mendelian Genetics.

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Presentation on theme: "1 Genetics Overview Acton Biology. 9 Heredity Mendelian Genetics."— Presentation transcript:

1 1 Genetics Overview Acton Biology

2 9 Heredity Mendelian Genetics

3 2 Reproduction Asexual reproduction Asexual reproduction Single parent passes copies of all its genes to offspring Single parent passes copies of all its genes to offspring Offspring arise by mitosis (clone of parent) Offspring arise by mitosis (clone of parent) Sexual Reproduction Sexual Reproduction Two individuals (parents) contribute genes to offspring Two individuals (parents) contribute genes to offspring Results in greater genetic variation of offspring than asexual reproduction Results in greater genetic variation of offspring than asexual reproduction

4 3 Asexual Reproduction Binary Fission - Bacteria Binary Fission - Bacteria Budding - Yeast Budding - Yeast Vegetative Reproduction - Strawberry Vegetative Reproduction - Strawberry Spore Formation - Fungi Spore Formation - Fungi

5 4 Sexual Reproduction Combination of genetic material Combination of genetic material Results in increased genetic diversity Results in increased genetic diversity Processes: Processes: Meiosis Meiosis Fertilization Fertilization

6 5 Meiosis 2 stages of cell division: 2 stages of cell division: Meiosis I Meiosis I Meiosis II Meiosis II Results in daughter cells which has half as many chromosomes as parent cell Results in daughter cells which has half as many chromosomes as parent cell

7 6 Meiosis I Meiosis I separates homologous chromosomes, resulting in reduction from diploid to haploid cells Meiosis I separates homologous chromosomes, resulting in reduction from diploid to haploid cells Crossover occurs during Prophase I  increasing genetic diversity Crossover occurs during Prophase I  increasing genetic diversity

8 7 Meiosis II Meiosis II is similar to mitosis, except the cell undergoing division is haploid rather than diploid Meiosis II is similar to mitosis, except the cell undergoing division is haploid rather than diploid Meiosis II has produced 4 haploid gametes, each of the chromosomes has one chromatid Meiosis II has produced 4 haploid gametes, each of the chromosomes has one chromatid

9 8 Fertilization Sexual life cycle of animals Haploid gametes fuse by fertilization to form a diploid zygote. Zygote undergoes many rounds of mitosis to produce the diploid multicellular organism. Diploid germ cells undergo meiosis to produce haploid gametes.

10 10 Genetic Variation Sexual reproduction results in increased genetic variation Sexual reproduction results in increased genetic variation Specific aspects affect how genes are varied Specific aspects affect how genes are varied Alleles Alleles Crossover Crossover

11 11 Alleles For each observable trait (phenotype), organism inherits 2 alleles, one from each parent. For each observable trait (phenotype), organism inherits 2 alleles, one from each parent. Alleles make up its genotype. Alleles make up its genotype. If the 2 alleles at a locus (the region on a chromosome where a gene is found) differ, the organism is heterozygous, otherwise it is homozygous. If the 2 alleles at a locus (the region on a chromosome where a gene is found) differ, the organism is heterozygous, otherwise it is homozygous.

12 12 Crossover Crossing over occurs in Prophase I Crossing over occurs in Prophase I Nonsister chromatids of homologous chromosomes exchange portions. Nonsister chromatids of homologous chromosomes exchange portions. The recombinant chromosomes carry genes derived from different parents. The recombinant chromosomes carry genes derived from different parents.

13 13 Terminology Homozygous: contain 2 of the same alleles for particular trait Homozygous: contain 2 of the same alleles for particular trait Heterozygous: 2 different alleles for a trait Heterozygous: 2 different alleles for a trait Phenotype: expressed traits Phenotype: expressed traits Genotype: Genetic Make-up Genotype: Genetic Make-up Testcross: determine if individual showing dominant trait is homozygous or heterozygous by crossing it with homozygous recessive individual Testcross: determine if individual showing dominant trait is homozygous or heterozygous by crossing it with homozygous recessive individual Monohybrid Cross: Cross involving study of one trait Monohybrid Cross: Cross involving study of one trait Dihybrid Cross: Cross involving study of 2 traits Dihybrid Cross: Cross involving study of 2 traits

14 19 Testcross

15 14 Inheritance Patterns Mendel used scientific approach to identify 2 laws of inheritance Mendel used scientific approach to identify 2 laws of inheritance 4 concepts that make up Mendel’s model 4 concepts that make up Mendel’s model 1) Alternative versions of genes cause variations in inherited characteristics among offspring (e.g. Alleles) 2) For each character, every organism inherits one allele from each parent 3) If the 2 alleles are different, then the dominant allele will be fully expressed in the offspring, recessive allele will have no noticeable effect on the offspring 4) The 2 alleles for each character separate during gamete production  Law of segregation

16 15 Mendel’s Law of Segregation Each plant inherits 1 allele for flower color from each parent. The 2 alleles segregate (separate) and end up in different gametes during meiosis. Random fertilization between gametes yield predictable ratios in the offspring.

17 16 Mendel’s Law of Independent Assortment States that each pair of alleles will segregate independently during gamete formation States that each pair of alleles will segregate independently during gamete formation 2 traits assort independently of each other, assuming they are on different chromosomes 2 traits assort independently of each other, assuming they are on different chromosomes

18 18 Random Fertilization When a heterozygote (Rr) forms gametes, segregation of alleles is like the toss of a coin. We can determine the probability for any genotype among the offspring of 2 heterozygotes by multiplying the individual probabilities of a gamete having a particular allele (R or r).

19 20 Laws of Probability Rule of multiplication: When calculating probability that 2 of more independent events will occur together, you multiply the probabilities Rule of multiplication: When calculating probability that 2 of more independent events will occur together, you multiply the probabilities e.g. AABbCc x AaBbCc Rule of Addition: Calculating the probability that any of two or more mutually exclusive events will occur you add together the individual probabilities. Rule of Addition: Calculating the probability that any of two or more mutually exclusive events will occur you add together the individual probabilities.

20 22 Inheritance Patterns Complete Dominance Complete Dominance Codominance Codominance Incomplete Dominance Incomplete Dominance

21 23 Complete Dominance A monohybrid cross yields a 3:1 phenotypic ratio in the F2, assuming purple flower color is dominant and white is recessive. The genotypic ratio is 1:2:1, since there are 2 types of purple- flowered plants: PP (homozygous) and Pp (heterozygous). The true-breeding P generation must have identical alleles for that gene and are homozygous. In the heterozygous F1 and F2 indivuduals, the dominant purple allele determines the phenotype.

22 24 Codominance The A, B, AB, or O phenotypes are affected by 3 different alleles. The A, B, AB, or O phenotypes are affected by 3 different alleles. IA and IB alleles produce different antigens on the surface of red blood cells, thus are dominant to the i allele which produces no antigen. IA and IB alleles produce different antigens on the surface of red blood cells, thus are dominant to the i allele which produces no antigen. IA and IB are codominant to each other because the RBCs bear both antigens. IA and IB are codominant to each other because the RBCs bear both antigens.

23 25 Incomplete Dominance When red snapdragons are crossed with white ones, the F1 hybrids have pink flowers. When red snapdragons are crossed with white ones, the F1 hybrids have pink flowers. Superscripts indicate alleles for flower color: CR for red and CW for white. Superscripts indicate alleles for flower color: CR for red and CW for white. The F2 generation produces a 1:2:1 ratio for both genotype and phenotype. The F2 generation produces a 1:2:1 ratio for both genotype and phenotype.

24 17 Epistasis A gene at one locus may affect phenotypic expression of a gene at another locus by epistasis. A gene at one locus may affect phenotypic expression of a gene at another locus by epistasis. The B/b gene determines the pigment color (B for black and b for brown) The B/b gene determines the pigment color (B for black and b for brown) The epistatic C/c gene controls whether or not any pigment will be deposited in the hair. The epistatic C/c gene controls whether or not any pigment will be deposited in the hair. A homozygous recessive cc mouse has no hair pigment and is albino regardless of its B/b genotype. A homozygous recessive cc mouse has no hair pigment and is albino regardless of its B/b genotype.

25 26 Multifactorial Traits: Melanin Human skin pigmentation is influenced by multiple genes which produce different melanin pigment molecules and shows quantitative variation. Human skin pigmentation is influenced by multiple genes which produce different melanin pigment molecules and shows quantitative variation. This polygenic inheritance also exhibits incomplete dominance. This polygenic inheritance also exhibits incomplete dominance.

26 27 Sample Questions A couple has six children, all daughters. If the woman has a seventh child, what is the probability that the seven child will be a daughter? A couple has six children, all daughters. If the woman has a seventh child, what is the probability that the seven child will be a daughter? A) 6/7 A) 6/7 B) 1/7 B) 1/7 C) 1/36 C) 1/36 D) 1/49 D) 1/49 E) 1/2 E) 1/2

27 28 Questions Which of the following is NOT true of meiosis? Which of the following is NOT true of meiosis? A) During metaphase, spindle microtubules first come into contact with chromosomes. B) The chromosome number in the newly formed cells is half that of the parent cell C) The homologous chromosomes line up along the metaphase plate, or equator of the cell D) The cytoplasm of the cell and all its organelles are divided approximately in half. E) In anaphase II, the sister chromatids travel to opposite ends of the cell.

28 29 Virtual Fly Lab http://www.mhhe.com/biosci/genbio/virtual_lab s/BL_15/BL_15.html http://www.mhhe.com/biosci/genbio/virtual_lab s/BL_15/BL_15.html

29 30 Pedigree Charts Pedigree analysis is a way to solve genetic puzzles Pedigree analysis is a way to solve genetic puzzles Useful when traits of many generation of offspring have been recorded Useful when traits of many generation of offspring have been recorded can be used to trace the passing of an allele from parents to offspring can be used to trace the passing of an allele from parents to offspring

30 31 Pedigree Symbols

31 32 Pedigree A recessive trait such as attached earlobe may skip a generation. A recessive trait such as attached earlobe may skip a generation. A dot may be placed in a symbol to represent known heterozygotes (carriers who do not exhibit the recessive phenotype). A dot may be placed in a symbol to represent known heterozygotes (carriers who do not exhibit the recessive phenotype).

32 33 Linked Genes

33 34 If the 2 genes were on different chromosomes, independent assortment should yield equal numbers of the 4 types of F2. If the 2 genes were on the same chromosome, each allele combination (B+ vg+ and b vg) should stay together and only yield parental phenotypes in the F2. The high percentage of parental phenotypes in the F2, with some nonparental (recombinant) phenotypes imply the 2 genes are physically close to each other on the same chromosome.

34 35 Genetic Recombination Recombinant phenotypes explained by crossing over of homologous chromosomes Recombinant phenotypes explained by crossing over of homologous chromosomes No new allele combinations in males  sex linked trait No new allele combinations in males  sex linked trait

35 36 Genetic Recombination

36 37 Recombinant Frequencies Recombination frequencies can be used to construct a linkage map of the chromosome Recombination frequencies can be used to construct a linkage map of the chromosome The farther apart genes are, the more likely they are to be separated during crossing over, and the higher their frequency of recombination. The farther apart genes are, the more likely they are to be separated during crossing over, and the higher their frequency of recombination.

37 38 Karyotype

38 39 What is a karyotype? Organized profile of a person's chromosomes Organized profile of a person's chromosomes Chromosomes are arranged and numbered by size, from largest to smallest Chromosomes are arranged and numbered by size, from largest to smallest Arrangement helps scientists quickly identify chromosomal alterations that may result in a genetic disorder Arrangement helps scientists quickly identify chromosomal alterations that may result in a genetic disorder

39 40 Karyotype Activity Try it yourself! http://learn.genetics.utah.edu/content/begin/tr aits/karyotype/ http://learn.genetics.utah.edu/content/begin/tr aits/karyotype/

40 41 X-Linked Inheritance X-linked inheritance. A father with the disorder will transmit the mutant allele to all daughters but to no sons. If the mother is a dominant homozygote, the daughters will have the normal phenotype but will be carriers of the mutation.

41 42 Errors and Exceptions Errors in Meiosis Errors in Meiosis Aneuploidy - Missing copy of a chromosome Aneuploidy - Missing copy of a chromosome Polyploidy - Extra copy of a chromosome Polyploidy - Extra copy of a chromosome Disorders due to Chromosomal Alterations Disorders due to Chromosomal Alterations Certain cancers are due to alterations in chromosome configuration Certain cancers are due to alterations in chromosome configuration

42 43 Nondisjunction Nondisjunction can produce gametes with an extra or missing chromosome, or aneuploidy. Homologous chromosomes may fail to separate during meiosis I. Sister chromatids may fail to separate during meiosis II.

43 44 Alterations of Chromosome structure Deletion – removes chromosomal segment Deletion – removes chromosomal segment Duplication – repeats segment Duplication – repeats segment Inversion – reverses segment within chromosome Inversion – reverses segment within chromosome Translocation – moves segment from one chromosome to another, nonhomologous one Translocation – moves segment from one chromosome to another, nonhomologous one

44 45 Human Disorders Trisomy 21 – Down Syndrome Trisomy 21 – Down Syndrome Extra X chromosome in a male – Kleinfelter syndrome Extra X chromosome in a male – Kleinfelter syndrome Turner’s Syndrome – Monosomy X Turner’s Syndrome – Monosomy X Triple X Syndrome – Trisomy X Triple X Syndrome – Trisomy X Cri du chat – specific deletion in Chromosome 5 Cri du chat – specific deletion in Chromosome 5 Chronic myelogenous leukemia (CML) – Portion of chromosome 22 switched places with small fragment from tip of chromosome 9 Chronic myelogenous leukemia (CML) – Portion of chromosome 22 switched places with small fragment from tip of chromosome 9

45 46 Sample Questions During the first meiotic division (Meiosis I) During the first meiotic division (Meiosis I) A) Homologous chromosomes separate B) The chromosome number becomes haploid C) Crossing over between nonsister chromatids occurs D) Paternal and maternal chromosomes assort randomly E) All of the above occur

46 47 If an individual with blood type O, whose mother has blood type A, The father must have which of the following blood types? If an individual with blood type O, whose mother has blood type A, The father must have which of the following blood types? A) A, B or O B) AB or A C) AB or B D) AB only E) O only

47 48 In humans, hemophilia is a sex-linked recessive trait. If a man and a woman have a son who is affected with hemophilia, which of the following is definitely true? In humans, hemophilia is a sex-linked recessive trait. If a man and a woman have a son who is affected with hemophilia, which of the following is definitely true? A) The mother carries an allele for hemophilia B) The father carries an allele for hemophilia C) The father is afflicted with hemophilia D) Both parents carry an allele for hemophilia E) The boy’s paternal grandfather has hemophilia

48 49 Review of Free-Response Question Genes are located on chromosomes and are the basic unit of heredity that is passed on from parent to child, through generations Genes are located on chromosomes and are the basic unit of heredity that is passed on from parent to child, through generations A) Explain how a chromosome mutation could occur and why mutations are detrimental to the organism in which they take place. B) Explain why it is that – Although there are very few genes located on the Y chromosome – human males may suffer from having just one copy of the X chromosome, whereas females have two X’s and do not suffer as much as males.


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