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Genetics OverviewGenetics Overview

Acton BiologyActon Biology

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HeredityHeredity

Mendelian GeneticsMendelian Genetics

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ReproductionReproduction

Asexual reproductionAsexual reproduction

Single parent passes copies of all its genes to offspringSingle parent passes copies of all its genes to offspring

Offspring arise by mitosis (clone of parent)Offspring arise by mitosis (clone of parent)

Sexual ReproductionSexual Reproduction

Two individuals (parents) contribute genes to offspringTwo individuals (parents) contribute genes to offspring

Results in greater genetic variation of offspring than Results in greater genetic variation of offspring than asexual reproductionasexual reproduction

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Asexual ReproductionAsexual Reproduction

Binary Fission - BacteriaBinary Fission - Bacteria

Budding - YeastBudding - Yeast

Vegetative Reproduction - StrawberryVegetative Reproduction - Strawberry

Spore Formation - FungiSpore Formation - Fungi

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Sexual ReproductionSexual Reproduction

Combination of genetic material Combination of genetic material

Results in increased genetic diversityResults in increased genetic diversity

Processes:Processes:

MeiosisMeiosis

FertilizationFertilization

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MeiosisMeiosis 2 stages of cell division:2 stages of cell division:

Meiosis IMeiosis I Meiosis IIMeiosis II

Results in daughter cells which has half as Results in daughter cells which has half as many chromosomes as parent cellmany chromosomes as parent cell

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Meiosis IMeiosis I

Meiosis I separates homologous Meiosis I separates homologous chromosomes, resulting in reduction from chromosomes, resulting in reduction from diploid to haploid cellsdiploid to haploid cells

Crossover occurs during Prophase I Crossover occurs during Prophase I increasing genetic diversity increasing genetic diversity

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Meiosis IIMeiosis II

Meiosis II is similar to mitosis, except the Meiosis II is similar to mitosis, except the cell undergoing division is haploid rather cell undergoing division is haploid rather than diploidthan diploid

Meiosis II has produced 4 haploid gametes, Meiosis II has produced 4 haploid gametes, each of the chromosomes has one each of the chromosomes has one chromatid chromatid

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FertilizationFertilizationSexual 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.

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Genetic VariationGenetic Variation

Sexual reproduction results in increased genetic Sexual reproduction results in increased genetic variationvariation

Specific aspects affect how genes are variedSpecific aspects affect how genes are varied

AllelesAlleles

CrossoverCrossover

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AllelesAlleles For each observable trait For each observable trait

((phenotypephenotype), organism ), organism inherits 2 alleles, one from inherits 2 alleles, one from each parent. each parent.

Alleles make up its Alleles make up its genotype. genotype.

If the 2 alleles at a locus If the 2 alleles at a locus (the region on a (the region on a chromosome where a gene chromosome where a gene is found) differ, the is found) differ, the organism is heterozygous, organism is heterozygous, otherwise it is homozygous.otherwise it is homozygous.

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CrossoverCrossover Crossing over Crossing over

occurs in Prophase occurs in Prophase II

Nonsister Nonsister chromatids of chromatids of homologous homologous chromosomes chromosomes exchange portions. exchange portions.

The recombinant The recombinant chromosomes carry chromosomes carry genes derived from genes derived from different parents. different parents.

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TerminologyTerminology Homozygous: contain 2 of the same alleles for Homozygous: contain 2 of the same alleles for

particular traitparticular trait

Heterozygous: 2 different alleles for a traitHeterozygous: 2 different alleles for a trait

Phenotype: expressed traitsPhenotype: expressed traits

Genotype: Genetic Make-upGenotype: Genetic Make-up

Testcross: determine if individual showing dominant Testcross: determine if individual showing dominant trait is homozygous or heterozygous by crossing it with trait is homozygous or heterozygous by crossing it with homozygous recessive individualhomozygous recessive individual

Monohybrid Cross: Cross involving study of one traitMonohybrid Cross: Cross involving study of one trait

Dihybrid Cross: Cross involving study of 2 traitsDihybrid Cross: Cross involving study of 2 traits

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TestcrossTestcross

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Inheritance PatternsInheritance Patterns

Mendel used scientific approach to identify 2 laws of Mendel used scientific approach to identify 2 laws of inheritanceinheritance

4 concepts that make up Mendel’s model4 concepts that make up Mendel’s model

1)1) Alternative versions of genes cause variations in inherited Alternative versions of genes cause variations in inherited characteristics among offspring (e.g. Alleles)characteristics among offspring (e.g. Alleles)

2)2) For each character, every organism inherits one allele from each For each character, every organism inherits one allele from each parentparent

3)3) If the 2 alleles are different, then the dominant allele will be fully If the 2 alleles are different, then the dominant allele will be fully expressed in the offspring, recessive allele will have no expressed in the offspring, recessive allele will have no noticeable effect on the offspringnoticeable effect on the offspring

4)4) The 2 alleles for each character separate during gamete The 2 alleles for each character separate during gamete production production Law of segregation Law of segregation

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Mendel’s Law of Mendel’s Law of SegregationSegregation

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.

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Mendel’s Law of Independent Mendel’s Law of Independent AssortmentAssortment

States that each States that each pair of alleles will pair of alleles will segregate segregate independently independently during gamete during gamete formationformation

2 traits assort 2 traits assort independently of independently of each other, each other, assuming they are assuming they are on different on different chromosomes chromosomes

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Random FertilizationRandom 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).

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Laws of ProbabilityLaws of Probability

Rule of multiplication: When calculating probability Rule of multiplication: When calculating probability that 2 of more independent events will occur that 2 of more independent events will occur together, you multiply the probabilitiestogether, you multiply the probabilities

e.g. AABbCc x AaBbCce.g. AABbCc x AaBbCc

Rule of Addition: Calculating the probability that any Rule of Addition: Calculating the probability that any of two or more of two or more mutually exclusive eventsmutually exclusive events will occur will occur you add together the individual probabilities.you add together the individual probabilities.

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Inheritance PatternsInheritance Patterns

Complete DominanceComplete Dominance

CodominanceCodominance

Incomplete DominanceIncomplete Dominance

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Complete DominanceComplete 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.

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CodominanceCodominance The A, B, AB, or O The A, B, AB, or O

phenotypes are affected phenotypes are affected by 3 different alleles. by 3 different alleles.

IAIA and and IBIB alleles produce alleles produce different antigens on the different antigens on the surface of red blood surface of red blood cells, thus are dominant cells, thus are dominant to the to the ii allele which allele which produces no antigen. produces no antigen.

IAIA and and IBIB are are codominant to each codominant to each other because the RBCs other because the RBCs bear both antigens. bear both antigens.

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Incomplete DominanceIncomplete Dominance When red snapdragons When red snapdragons

are crossed with white are crossed with white ones, the F1 hybrids ones, the F1 hybrids have pink flowers. have pink flowers.

Superscripts indicate Superscripts indicate alleles for flower color: alleles for flower color: CR for red and CW for CR for red and CW for white. white.

The F2 generation The F2 generation produces a 1:2:1 ratio produces a 1:2:1 ratio for both for both genotypegenotype and and phenotypephenotype. .

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EpistasisEpistasis A gene at one locus may A gene at one locus may

affect phenotypic affect phenotypic expression of a gene at expression of a gene at another locus by epistasis. another locus by epistasis.

The The BB//bb gene determines gene determines the pigment color (B for the pigment color (B for black and b for brown) black and b for brown)

The epistatic The epistatic CC//cc gene gene controls whether or not any controls whether or not any pigment will be deposited pigment will be deposited in the hair. in the hair.

A homozygous recessive A homozygous recessive cccc mouse has no hair pigment mouse has no hair pigment and is albino regardless of and is albino regardless of its its BB//bb genotype. genotype.

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Multifactorial Traits: MelaninMultifactorial Traits: Melanin

Human skin Human skin pigmentation is pigmentation is influenced by multiple influenced by multiple genes which produce genes which produce different melanin different melanin pigment molecules pigment molecules and shows quantitative and shows quantitative variation.variation.

This polygenic This polygenic inheritance also inheritance also exhibits incomplete exhibits incomplete dominance. dominance.

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Sample QuestionsSample Questions

A couple has six children, all daughters. If the woman A couple has six children, all daughters. If the woman has a seventh child, what is the probability that the has a seventh child, what is the probability that the seven child will be a daughter?seven child will be a daughter?

A) 6/7A) 6/7

B) 1/7B) 1/7

C) 1/36C) 1/36

D) 1/49D) 1/49

E) 1/2E) 1/2

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QuestionsQuestions

Which of the following is NOT true of meiosis?Which of the following is NOT true of meiosis?

A)A) During metaphase, spindle microtubules first come into During metaphase, spindle microtubules first come into contact with chromosomes.contact with chromosomes.

B)B) The chromosome number in the newly formed cells is half The chromosome number in the newly formed cells is half that of the parent cellthat of the parent cell

C)C) The homologous chromosomes line up along the The homologous chromosomes line up along the metaphase plate, or equator of the cellmetaphase plate, or equator of the cell

D)D) The cytoplasm of the cell and all its organelles are divided The cytoplasm of the cell and all its organelles are divided approximately in half.approximately in half.

E)E) In anaphase II, the sister chromatids travel to opposite In anaphase II, the sister chromatids travel to opposite ends of the cell.ends of the cell.

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Virtual Fly LabVirtual Fly Lab

http://www.mhhe.com/biosci/genbio/virtual_labs/BL_15/BL_15.html

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Pedigree ChartsPedigree Charts

Pedigree analysis is a way to solve genetic puzzlesPedigree analysis is a way to solve genetic puzzles

Useful when traits of many generation of offspring Useful when traits of many generation of offspring have been recordedhave been recorded

can be used to trace the passing of an allele from can be used to trace the passing of an allele from parents to offspringparents to offspring

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Pedigree SymbolsPedigree Symbols

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PedigreePedigree A recessive trait A recessive trait

such as attached such as attached earlobe may skip a earlobe may skip a generation. generation.

A dot may be A dot may be placed in a symbol placed in a symbol to represent known to represent known heterozygotes heterozygotes (carriers who do (carriers who do not exhibit the not exhibit the recessive recessive phenotype). phenotype).

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Linked GenesLinked Genes

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Linked GenesLinked Genes 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.

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Genetic RecombinationGenetic Recombination Recombinant Recombinant

phenotypes phenotypes explained by explained by crossing over of crossing over of homologous homologous chromosomeschromosomes

No new allele No new allele combinations in combinations in males males sex linked sex linked traittrait

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Genetic RecombinationGenetic Recombination

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Recombinant Recombinant FrequenciesFrequencies

Recombination frequencies can be used to Recombination frequencies can be used to construct a linkage map of the chromosomeconstruct a linkage map of the chromosome

The farther apart genes are, the more likely The farther apart genes are, the more likely they are to be separated during crossing they are to be separated during crossing over, and the higher their frequency of over, and the higher their frequency of recombination.recombination.

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KaryotypeKaryotype

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What is a karyotype?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, Chromosomes are arranged and numbered by size, from largest to smallest from largest to smallest

Arrangement helps scientists quickly identify Arrangement helps scientists quickly identify chromosomal alterations that may result in a genetic chromosomal alterations that may result in a genetic disorder disorder

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Karyotype ActivityKaryotype Activity

Try it yourself!Try it yourself!

http://learn.genetics.utah.edu/content/http://learn.genetics.utah.edu/content/begin/traits/karyotype/begin/traits/karyotype/

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X-Linked InheritanceX-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.

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Errors and ExceptionsErrors and Exceptions

Errors in MeiosisErrors in Meiosis

Aneuploidy - Missing copy of a chromosomeAneuploidy - Missing copy of a chromosome

Polyploidy - Extra copy of a chromosomePolyploidy - Extra copy of a chromosome

Disorders due to Chromosomal AlterationsDisorders due to Chromosomal Alterations

Certain cancers are due to alterations in Certain cancers are due to alterations in chromosome configurationchromosome configuration

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NondisjunctionNondisjunction 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.

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Alterations of Chromosome Alterations of Chromosome structurestructure

Deletion – removes Deletion – removes chromosomal segmentchromosomal segment

Duplication – repeats Duplication – repeats segmentsegment

Inversion – reverses Inversion – reverses segment within segment within chromosomechromosome

Translocation – moves Translocation – moves segment from one segment from one chromosome to chromosome to another, another, nonhomologous onenonhomologous one

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Human DisordersHuman Disorders

Trisomy 21 – Down SyndromeTrisomy 21 – Down Syndrome

Extra X chromosome in a male – Kleinfelter syndromeExtra X chromosome in a male – Kleinfelter syndrome

Turner’s Syndrome – Monosomy XTurner’s Syndrome – Monosomy X

Triple X Syndrome – Trisomy XTriple X Syndrome – Trisomy X

Cri du chat – specific deletion in Chromosome 5Cri du chat – specific deletion in Chromosome 5

Chronic myelogenous leukemia (CML) – Portion of Chronic myelogenous leukemia (CML) – Portion of chromosome 22 switched places with small fragment chromosome 22 switched places with small fragment from tip of chromosome 9from tip of chromosome 9

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Sample QuestionsSample Questions

During the first meiotic division (Meiosis I)During the first meiotic division (Meiosis I)

A)A) Homologous chromosomes separateHomologous chromosomes separate

B)B) The chromosome number becomes haploidThe chromosome number becomes haploid

C)C) Crossing over between nonsister chromatids occursCrossing over between nonsister chromatids occurs

D)D) Paternal and maternal chromosomes assort randomlyPaternal and maternal chromosomes assort randomly

E)E) All of the above occurAll of the above occur

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If an individual with blood type O, whose mother has If an individual with blood type O, whose mother has blood type A, The father must have which of the blood type A, The father must have which of the following blood types?following blood types?

A)A) A, B or OA, B or O

B)B) AB or AAB or A

C)C) AB or BAB or B

D)D) AB onlyAB only

E)E) O onlyO only

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In humans, hemophilia is a sex-linked recessive trait. If In humans, hemophilia is a sex-linked recessive trait. If a man and a woman have a son who is affected with a man and a woman have a son who is affected with hemophilia, which of the following is definitely true?hemophilia, which of the following is definitely true?

A)A) The mother carries an allele for hemophiliaThe mother carries an allele for hemophilia

B)B) The father carries an allele for hemophiliaThe father carries an allele for hemophilia

C)C) The father is afflicted with hemophiliaThe father is afflicted with hemophilia

D)D) Both parents carry an allele for hemophiliaBoth parents carry an allele for hemophilia

E)E) The boy’s paternal grandfather has hemophiliaThe boy’s paternal grandfather has hemophilia

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Review of Free-Response Review of Free-Response QuestionQuestion

Genes are located on chromosomes and are the basic Genes are located on chromosomes and are the basic unit of heredity that is passed on from parent to child, unit of heredity that is passed on from parent to child, through generationsthrough generations

A)A) Explain how a chromosome mutation could occur and Explain how a chromosome mutation could occur and why mutations are detrimental to the organism in why mutations are detrimental to the organism in which they take place.which they take place.

B)B) Explain why it is that – Although there are very few Explain why it is that – Although there are very few genes located on the Y chromosome – human males genes located on the Y chromosome – human males may suffer from having just one copy of the X may suffer from having just one copy of the X chromosome, whereas females have two X’s and do chromosome, whereas females have two X’s and do not suffer as much as males.not suffer as much as males.