BIOL 101

general BIOLOGY with Jo Wu, Ph.D.

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Transmission Genetics

Fullerton College

(These room notes indigenous the Bio 109 online course) simple Genetics Terminology

Most of us have seen that many features of our bodies, talents and also personalities seem to it is in resemble arelative more than someone unrelated. We are going to an initial look at somebody characteristics and human diseases that space affected/caused through a singlegene on one autosomal chromosome. For the exam, you will need to know thedefinitions of an easy genetic terms, Mendel"s discoveries, how to use Punnettsquares, and be may be to fix autosomal properties problems.There are lots ofgood genes glossaries accessible (see the related web links below). However I willuse some an easy definitions while offering you an example of family members inheritance. Intend there to be a family in i beg your pardon the dad Sam and daughter Susan had actually dimples, yet the mommy Sally walk not present dimples.

separation, personal, instance Phenotype
Sam (father) DD homozygous dominant Dimples
Sally (mother) dd homozygous recessive no dimples
Susan (child) Dd heterozygous Dimples

The TRAIT (physical ormeasurable characteristic) us are focusing on in this family members is dimples. Samand Susan have actually the PHENOTYPE (visible physical makeup the this trait)of visibility of dimples, vice versa, Sally has the phenotype that no dimples.

Each person has genetic information on your chromosomes that determine whether or no they will have dimples. The dimples GENE is that section (DNA sequence) the a details chromosome that controls the expression the the Dimples trait. But there shows up to it is in two various phenotypes in ours scenario, together there room two different ALLELES (alternative develops of one gene). One allele the the Dimple gene has information (a details DNA sequence) that tells the human body to make dimples. The otherallele of the Dimple gene has actually information (a different DNA sequence) thattells the body not to make dimples. Come simplify, us will use the letter "dee"for the dimple gene through the big "D" letter because that the allele i m sorry specifiesdimples and the letter "d" for the allele which mentions no dimples.

In a nutshell, the dimples gene offers information because that the dimples trait. Allele D = dimples and allele d = no dimples.

Suppose the gene for dimples is ~ above chromosome #5. Remember the each person is diploid or has actually two sets of each type of the autosomal chromosomes (the non-sex chromosomes, types 1-22). That method each person has actually two chromosome #5, and on each chromosome #5, there sits an allele for the dimples gene. Therefore, you have a full of two alleles for this gene.

Suppose that the GENOTYPE(the genetic makeup for this trait) the Sam is "DD". That is HOMOZYGOUS (has 2 similar alleles for the gene) for the dimples gene. Sally"s genotype is "dd", therefore she is additionally considered homozygous. Susan"s genotype is "Dd",so she is considered HETEROZYGOUS (has two various alleles for aspecific gene). Back Susan has both the allele "D" to make dimples andthe allele "d" in her genotype, her phenotype is the existence of dimples.Thus the allele to make dimples is dominant (the one the is expressed evenif just copy is present) and is constantly represented with a capital letter.The tiny "d" allele is RECESSIVE as the allele will certainly not it is in expressedunless there are two duplicates present.

Remember that during the meiotic cell division process, one collection of the parental chromosomes space passed to every of the gametes. For this reason one human being egg cell will certainly contain a full of 23 chromosomes (one that each type of chromosome) and also the human sperm cell also contains 23 chromosomes. If we just focus on chromosome 5 wherein the dimples gene sits, then we watch that

Sam (who has actually DD top top his diploid chromsomes) deserve to either pass under a "D" allele to every one of his gamete cells. Sally who has actually the genotype "dd" will pass under a "d" allele to every of hergametes. In the following diagram, Sam and also Sally"s genotypes room the boxes at top. V meiosis, each create gametes (in ovals). Because ofrandom fertilization in between the gametes (there is just one opportunity in this example), the genotype the the offspring(s) is "Dd" and also the phenotype should be "Dimpled".


If the leading allele the a gene lugged on one autosome (types 1-22) reasons a details phenotype or disease, climate it is one autosomal dominant trait (disease). Examples of autosomal dominant conditions in humans encompass Huntington"s disease, achondroplasia (dwarfism), hypercholesteremia. More common autosomal recessive disease that you may have actually heard around include: cystic fibrosis, Tay-sach"s, albinism, phenylketouria. There room traits encoded by genes on the X-chromosome, which are called X-linked (dominant or recessive) traits . Hemophilia, muscular dystrophy, red-green color blindness space X-linked traits. There are additionally sometraits and also diseases encoded by gene on the Y-chromosome and are Y-linked. Which one do you know around - that half of our populace possesses? A few genes are additionally found ~ above the mitochondrial genome.

MENDEL: taken into consideration the dad of Genetics but died unrecognized for his vital discoveries

disproved the mix Theory, proved that genetic information is pass on as discrete devices (which space now recognized as gene on chromosomes) figured out principles the chromosome behavior without knowledge around cells, meiosis, genes, chromosomes used common garden peas - 280,000 plants in 8 years!!!

Why to be Mendel"s job-related so wonderful and also successful?

well-planned, organized experiments; bred plants because that 2 year to ensure the they were true-breeding; do predictions that what he should uncover good plant to use: male and also female parts are different on every flower, so self-fertilization could occur; but reproductive components are attached by flower petals therefore that small cross-fertilization with various other plants occurs to stop self-fertilization in part experiments, Mendel closely cut off the male flower parts from one plant; and then manually provide pollen from one more plant v a paintbrush used substantial numbers of tree (and avoided troubles of sampling error) - 280,000 plants in 8 years!!! kept careful detailedrecords, complied with each of the seven traits because that 4-6 generations, did reciprocal crosses and also applied probability and also statistics the 7 traits withdistinct, measurable contrasting develops that Mendel made decision (out of 34 the had access to) turns out come be gene on seven various chromosomes; therefore we can substitute "chromosome" or "gene" for his "characters" come understandhis 2 main values or regulations of inheritance

LAW the SEGREGATION: bag of "characters" separate during gamete formation

looks in ~ one gene basically describes how homologous chromosomes different in Meiosis each gamete will end up with only one allele of each gene every plant has a pair of gene for a properties (diploid) alternative forms the one properties is encoded through discrete alleles during gamete formation (meiosis), every gene (allele) segregates from each other and also passed toa various gamete every gamete has equal possibility to obtain either allele

Practice Problems

Given: In Mendel"s Peas, the height gene: T = allele for tall plants, t = allele for short plants 1) cross a homozygous tall plant v a homozygous brief plant parental genotypes: TT x tt feasible gametes: T ; t execute Punnett square

t t
T Tt (tall) Tt (tall)
T Tt (tall) Tt (tall)
Genotype probabilities that offspring = 100% Tt Phenotype probabilities that offspring = 100% tall plants

2) overcome a heterozygous high plant with a brief plant Tt x tt ----->

t t
T Tt (tall) Tt (tall)
t tt (short) tt (short)
Genotype = 50% Tt , 50% tt . Phenotype = 50% tall, 50% brief

3) cross 2 tall plants with each other cheat problem! You need to ask if this plants space heterozygous orhomozygous. Intend both space heterozygous (monohybrid cross) Tt x Tt ----->

T t
T TT (tall) Tt (tall)
t Tt (tall) tt (short)
Genotype = 25% TT, 50% Tt, 25% tt. Phenotype = 75% tall, 25% quick

4) If friend are offered a tall plant, exactly how do you recognize its genotype? It can be Tt or TT. carry out a TESTCROSS with a homozygous recessive plant and look at the offspring. to compare the offspring results of problems (1) and also (2) above. If any type of short offspring room produced, then the high parent need to beheterozygous. What if there space no short offspring the end of 500 offspring plants? Homozygous What if there room no short offspring out of 5 offspring plants? Inconclusive, because this is a very tiny sample size which might not it is in a true have fun of the theoretical probabilities.

You can test this idea that sampling error by flipping a coin. A coin has a 50% opportunity of landing as heads, and also 50% opportunity of landing together tails. Yet if friend flip only 4 times, execute you always get 2 heads and also 2 tails? but if you upper and lower reversal 400 times, do you obtain pretty close come 200 heads and 200 tails?

LAW of elevation ASSORTMENT: gene for one trait go not influence gene of another trait

watch at 2 differentgenes (on different or non-homologous chromosomes) random line-up that maternal and also paternal chromosomes in ~ Metaphase ns equator; genes situated on NON-homologous chromosomes assort right into gametes separately of each various other Predicts 9:3:3:1 phenotypic ratio with a dihybrid overcome (Dihybrids are heterozygous for two genes) The following lecture "Two-gene Inheritance" go into more detail about this concept.

What is remarkable is the Mendeldid no know about genes, chromosomes or meiosis... Once he carry out hisexperiments and also figured out his vital contributions to the field of genetics.Mendel"s 2nd Law of live independence Assortment is really easy to follow,if friend recall how the chromosomes moved throughout Meiotic Division. Throughout metaphaseI, chromosomes lined up randomly at the equator, which ultimately resultsin a mixture of paternal and also maternal chromosomes in each gamete.

Suppose there is a gene A on chromosome 3 and also another gene B on chromosome 7. One parental is heterozygous because that both genes; or has the genotype "AaBb". Just how are these two genes passed ~ above the gametes and also then come the following generation? instead of illustration the alleleson chromosomes (as in the previous hyperlink), us will usage a faster way andjust compose the letters of the alleles.

Again, sometimes the A allele will certainly be passed right into a gamete cell together with the B allele. Sometimes, the A allele and also b allele are passed into a gamete. There room two much more possible combinations. The math formula for all the possible combinations would certainly be 2(^n) or 2 come the nth power, with n = variety of genes. I don"t know just how to create superscript in HTML.Two gene here, so there is a complete of four possible combos. There are several different ways to figure out the various combinations of alleles. Remember that each gamete should always have one allele of each gene.

Here is the FOIL technique you may have actually learned from math course too. You write out the alleles because that gene A ~ above the left and alleles because that gene B on the right. My drawing of the FOIL technique looks choose a face.


F: take the FIRST allele of eachgene (left eyebrow) to make one feasible gamete. O: take the OUTER alleles (big smile) to do one feasible gamete. I: take it the INNER alleles (nose curve) to make one possible gamete. L: take it the LAST allele of every gene (right eyebrow) to make one feasible gamete.

Another method is the BRANCHING method, which is especially valuable when considering even an ext genes. In this case, I have written the alleles from gene A be separate vertically (see left column). From allele "A", the is feasible to have actually either (branching arrows) "B" or "b" allele pass (big horizontal arrow) to the gamete mix (letters in oval). The feasible gamete combine are precisely the exact same ones you gained with the foil method.

currently that us know just how to obtain the gametes from a dihybrid parental (heterozygous because that two different genes), let"s try to cross 2 dihybrid parental together. We will have to use a huge Punnett square, prefer this one:
Mom gamete 1 Mom gamete 2 Mom gamete 3 Mom gamete 4
Dad gamete 1 Offspring Offspring Offspring Offspring
Dad gamete 2 Offspring Offspring Offspring Offspring
Dad gamete 3 Offspring Offspring Offspring Offspring
Dad gamete 4 Offspring Offspring Offspring Offspring

As there room four possible gametesfrom every parent, random fertilization to produce a full of 16 different possiblecombinations because that each offspring. Let"s finish our difficulty example.

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The Punnett Square for the cross AaBb x AaBb
need to look like this:

There are four different phenotypes. The phenotypic proportion is 9:3:3:1 for a classic or Mendelian dihybrid cross (if the 2 genes are similar to the factors that Mendel operated on). Note that it is very easy to recognize which phenotype course has all recessive alleles for both genes. How?

Suppose the dihybrid problem was that two spotted, long-eared dog parental had

18 spotted, long-eared puppies, 6 spotted, short-eared puppies, 6 solid, long-eared puppies, and also 2 solid, short-eared puppies.

Can you tell which room the dominant and also recessive traits?


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