O - Inherited Change

A2 Biology 9700 – Chapter O -‐ Inheritance Peter Ting

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Introduction: Gregory Mendel was a member of the Augustinian monastery in Brunn, Austria. His ambition was to be a teacher but repeatedly failed the necessary examinations and had to content himself with a job as substitute science teacher at the main school in Brunn. He had always been interested in the problem of heredity and this led him to carry out breeding experiments on plants. As the subject for his research he chose the garden pea, which has a number of sharply contrasting and easily recognizable characteristics: for example; long and short stem, red and white flowers, smooth and wrinkled seeds. With such clear-‐cut differences it is possible to cross or self-‐pollinate certain plants and examine the characteristics of their offspring. Starting in about 1856, Mendel carried out vast number of experiments in the garden of his monastery. The conclusions he drew forms the basis or foundations on which the study of heredity is built. This chapter introduces the concept of inheritance. It is the theory of how one trait/phenotype can be successfully passed on to the next generation. One must fully understand that between a parent and their offspring, there is remarkable similarity and yet it is no less noticeable that they also differ from each other in many respects. The science of heredity/inheritance attempts to explain both similarities and differences between parents and offspring. (a) [PA] describe, with the aid of diagrams, the behaviour of chromosomes during meiosis, and the associated behaviour of the nuclear envelope, cell membrane and centrioles (names of the main stages are expected, but not the sub-‐divisions of prophase); Key idea – In the topic of inheritance, there is this notion of variation. What is variation? Why must there be variation? Where can we see/observe variation? Variation can be explained by understanding that genes control the traits, being different in many organisms. How is it being different? Fertilization: New life begins at fertilization, when the sperm and egg combine their genetic material. Genetic material is located in the nucleus, where every gamete (reproductive cells of male and female) is unique and different. The process meiosis explains the uniqueness and the blueprint of genomic content, which is the reason why individuals are with varying shape, sizes and other observable characteristics. Meiosis involves two divisions: meiosis I and meiosis II.

• Meiosis I results in two daughter nuclei with half the number of chromosomes of the parent nucleus. This is reduction division.

• Meiosis II results in the chromosome behave as in mitosis (each of the two haploid daughter nuclei divides again)

Own notes:

Peter Ting � 11/28/12 5:57 PMComment [1]: Trait/Phenotype = observable characteristics.

Peter Ting � 11/28/12 6:01 PMComment [2]: Very often, the notion of variation can be seen as intraspecific variation or interspecific variation. Nevertheless, variation describes the observable differences in traits between 2 organisms. Peter Ting � 11/28/12 6:06 PMComment [3]: What is a gene?

Peter Ting � 11/28/12 6:28 PMComment [4]: This is a term you must be familiar with. Reduction division describes the result of the cell division which produces a daughter cell that has half of the chromosome number compared to the parental cell.


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The stages of meiosis (b) explain how meiosis and fertilisation can lead to variation; During normal cell growth, mitosis produces daughter cells identical to parent cell (2n to 2n). Meiosis results in genetic variation by shuffling of maternal and paternal chromosomes and crossing over.

Own notes:

Peter Ting � 11/29/12 12:17 AMComment [5]: 9700/41/OctNov/2010 Q9a [9] – Outline the behavior of chromosomes during meiosis. Prophase 1 1 idea of condensation of chromosomes ; 2 homologous chromosomes pair up / bivalent formed ; 3 chiasmata / described ; 4 crossing over / described ; Metaphase 1 5 homologous chromosomes / bivalents, line up on equator ; 6 independent assortment / described ; 7 ref to spindle ; 8 role of centromeres ; Anaphase 1 9 chromosomes move to poles ; 10 homologous chromosomes / bivalents, separate ; 11 pulled by microtubules ; Telophase 1 12 reduction division ; Metaphase 2 13 chromosomes line up on equator ; 14 of spindle ; Anaphase 2 15 centromeres divide ; 16 chromatids move to poles ; 17 pulled by microtubules ; 18 ref. haploid number ; Telophase 2 19 Meiosis results in total of FOUR total haploid cells.

Peter Ting � 12/10/12 1:35 PMComment [6]: Crossing over allows genetic material to be exchanged between bivalents (non-‐sister chromatid). There will be new variation of chromatids within the pair.


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No daughter cells formed during meiosis are genetically identical to either mother or father. There are reasons why that happen. During sexual reproduction, fusion of the unique haploid gametes produces truly unique offspring. The two events that take place during meiosis which help to produce genetic variation between daughter cells are:

– Crossing over, which happens between chromatids of homologous chromosomes

• in prophase I • chiasma / crossing over • between non-‐sister chromatids • homologous chromosomes / bivalents • exchange of genetic material • linkage groups broken • new combination of alleles

– Independent assortment of the homologous chromosomes

• in metaphase I • bivalents are arranged randomly on the equator

(c) explain the terms locus, allele, dominant, recessive, codominant, homozygous, heterozygous, phenotype and genotype; Glossary of terms Term Definition Genotype: the alleles of an organism. Phenotype: the observable characteristics of an organism. Allele: alternative form of a gene. Dominant allele:

an allele that has the same effect on the phenotype whether it is present in the homozygous or heterozygous state.

Recessive allele: an allele that only has an effect on the phenotype when present in the homozygous state.

Codominant alleles:

pairs of alleles that both affect the phenotype and is expressed when present in a heterozygote.

Locus:

the particular position on homologous chromosomes of a gene.

Homozygous:

having two identical alleles of a gene.

Heterozygous:

having two different alleles of a gene.

Own Notes

Peter Ting � 11/29/12 12:49 PMComment [7]: 9700/42/MayJune/2011 Q7(b) [5].

Peter Ting � 12/10/12 1:36 PMComment [8]: Due to the random alignment, there is possibility to create gametes with unique combinations of chromosomes. This means that, e.g. for 2 homologous chromosomes present, the combination of different gametes/haploids that will be produced is 4. This follow the rule 2n, where n = number of homologous chromosomes.


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Carrier:

an individual that has one copy of a recessive allele that causes a genetic disease in individuals that are homozygous for this allele.

Test cross:

testing a suspected heterozygote by crossing it with a known homozygous recessive.

(d) (i) use genetic diagrams to solve problems involving monohybrid cross -‐ single pair allele inheritance. Key Points: In each locus within the homologous chromosomes, lies a set of genes that codes a character/trait. The combination of these genes, called the genotype will control what the phenotype will be. These genes, which are two of them, occupy the locus within the homologous chromosomes. Together the genes will be expressed and one final phenotype will arise. In this form of inheritance, there are specifically TWO forms of the genes, which are now called alleles. One can have homozygous or heterozygous of those alleles, depending on what is available. The fruit fly, Drosophila melanogaster, feeds on sugars found in damaged fruits. A fly with normal features is called a wild type. It has a striped body and its wings are longer than its abdomen. There are mutant variations such as an ebony coloured body or vestigial wings. These three types of fly are shown in figure below

wild type ebony body vestigial wing There are two phenotypes in the fruit fly, body and wings. Wild type fly has striped body, allele A and longer wings, allele B. But there were other variations around, namely ebony body, allele a and vestigial wing, allele b. This is a clear example of single pair allele inheritance. For every characteristics or traits, there is a pair of alleles associated with it. No more, no less. (d) (ii) use genetic diagrams to solve problems involving monohybrid cross – multiple allele inheritance Key Points: In some cases, there are variety forms of genes for a particular trait that exists in the gene pool. You can have blue, green, and brown for eye color but you can only have two alleles. Own Notes

Peter Ting � 11/29/12 3:26 PMComment [9]: Two wild type fruit flies were crossed. Each had alleles A and B and carried alleles for ebony body and vestigial wings. Draw a genetic diagram to show the possible offspring of this cross Parental genotype: AaBb X AaBb Gametes : AB Ab aB ab (circle) Offspring genotypes: punnet square Offspring genotype : linked with genotype.

Peter Ting � 11/29/12 7:08 PMComment [10]: In a homologous chromosomes, ONLY two alleles can occupy, one for each loci.


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What causes the gene pool to have so many alleles swimming around? Variation, as it is the key to complexity in characters and traits that we see everyday around us. An example of this is the human blood groups. A single gene determines all the four blood groups A, B, AB and O. The alleles of these genes are IA, IB and IO. Alleles IA and IB are codominant and IO is recessive to both.

a) The inheritance of trypsin inhibitors in soybeans is an example of multiple allele inheritance. Compare how it is different with single pair allele inheritance? b) Give all possible genotype of a plant which only contains inhibitor A? c) Give all possible genotypes of the gametes produced by a plant that contains inhibitors B and C? d) Two soybean plants were crossed and the seeds collected and counted. The results are shown in the table.

i) Draw a genetic diagram to explain the results of this cross.

(d) (iii) use genetic diagrams to solve problems involving monohybrid cross – sex linked inheritance Key points: In humans, the chromosomes responsible to determine sex or sexual characteristics are appropriately known as the sex chromosome. Drosophila is used to illustrate how alleles on sex chromosomes are inherited in predictable Own notes

Peter Ting � 11/30/12 9:21 AMComment [11]: Do you still remember what codominant and recessive are about?

Peter Ting � 11/30/12 9:26 AMComment [12]: Peter Ting � 11/30/12 9:28 AMComment [13]: Peter Ting � 11/30/12 9:29 AMComment [14]: Peter Ting � 11/30/12 9:31 AMComment [15]:


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patterns. For example, in Drosophila the locus for eye color is located on the X chromosome. The allele for red eye color, which is normal in wild flies, is dominant to the mutant allele for white eyes.

As females have two chromosomes X (with a locus for eye color), they might be homozygous or heterozygous for either allele. Males, who carry only one X chromosome, are always hemizygous. They carry only the one X chromosome inherited from their mother, and it determines their eye color.

In the left hand example, homozygous red eyed females (RR) mate with hemizygous white eyed males (w-‐). In the offspring, all the daughters are red eyed heterozygotes (Rw) and all sons are red eyed hemizygotes (R-‐). In the right hand, homozygous white eyed females (ww) mate with hemizygous red eyed males (R-‐). In the offspring, all the daughters are red eyed heterozygotes (Rw) and all sons are white eyed hemizygotes (w-‐).

Sex linkage – If an allele for a gene is only on the X chromosome, then females will have two copies while men will only have one. In addition to their role in determining sex, this chromosome has genes for many characters; these are called sex-‐linked genes. Fathers can pass their sex-‐linked alleles to their daughters but not their sons. Mothers can pass their sex-‐linked alleles to both sons and daughters. Own notes

Peter Ting � 11/30/12 10:02 AMComment [16]: Do you know that sex chromosomes may not necessarily be homologous? Look at X and Y, they do not have the same length, in fact they are quite significantly different in terms of length. Q – In your opinion, would the sex chromosomes pair up during meiosis? Food for thought: The human Y chromosome has lost 1,393 of its 1,438 original genes over the course of its existence. Peter Ting � 11/30/12 10:03 AMComment [17]: You have heard of heterozygous and homozygous. Hemizygous describes an individual who has only one member of a chromosome pair or chromosome segment rather than the usual two.


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E.g. Red – green color blindness X chromosome has a locus for colour vision with two alleles:

– XN = Normal colour vision – Xn = Red-‐green colour blindness

Y chromosome does not have a colour vision locus. If a male receives the Xn allele he will have impaired colour vision, whereas a female with XNXn will not. Parental Phenotypes Carrier Female x Normal Male Genotypes XNXn XNY

Gametes XN Xn XN Y Circle all Offspring 1 Genotypes Female gamete XN Xn Males gamete XN XNXN XnXn

Y XNY XnY X-‐chromosome inactivation Key points: Human females inherit two copies of every gene on the X chromosome, whereas males inherit only one. But for the hundreds of other genes on the X, are males at a disadvantage in the amount of gene product their cells produce? The answer is no, because females have only a single active X chromosome in each cell. During interphase, chromosomes are too tenuous to be stained and seen by light microscopy. However, a dense, stainable structure, called a Barr body (after its discoverer) is seen in the interphase nuclei of female mammals. The Barr body is one of the X chromosomes. Its compact appearance reflects its inactivity. So, the cells of females have only one functioning copy of each X-‐linked gene — the same as males. X-‐chromosome inactivation (XCI) occurs early in embryonic development. In a given cell, which of a female's X chromosomes becomes inactivated and converted into a Barr body is a matter of chance. After inactivation has occurred, all the descendants of that cell will have the same chromosome inactivated. Thus X-‐chromosome inactivation creates clones with differing effective gene content. Own notes

Peter Ting � 11/30/12 11:24 PMComment [18]: The pseudoautosomal regions get their name because any genes located within them (so far only 9 have been found) are inherited just like any autosomal genes. Males have two copies of these genes: one in the pseudoautosomal region of their Y, the other in the corresponding portion of their X chromosome. So males can inherit an allele originally present on the X chromosome of their father and females can inherit an allele originally present on the Y chromosome of their father. Crossing over occurs in two regions of pairing, called the pseudoautosomal regions.


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E.g. – Tortoiseshell fur coat in female cats In cats, the fur pigmentation gene is X-‐linked, and depending on which copy of the X chromosome each cell chooses to leave active, either an orange or black coat color results. X inactivation only occurs in cells with 2 X chromosomes, which explains why almost all tortoiseshell cats are female.

i) What is the genotype of a tortoiseshell cat? ii) Explain why there is no male tortoiseshell cat?

(d) use genetic diagrams to solve problems involving monohybrid cross – codominance inheritance Key points: Have you wondered what determines your blood group? At the beginning of the 20th century an Austrian scientist, Karl Landsteiner, noted that the serum from other individuals agglutinated the RBCs of some individuals. He made a note of the patterns of agglutination and showed that blood could be divided into groups. This marked the discovery of the first blood group system, ABO, and earned Landsteiner a Nobel Prize..

Own notes

Peter Ting � 11/30/12 11:41 PMComment [19]: Ans : Peter Ting � 11/30/12 11:41 PMComment [20]: Ans :

Peter Ting � 12/1/12 4:19 PMComment [21]: What is the characteristics of an offspring showing co-‐dominance? Use the example of ABO blood group to describe your answer


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(d) use genetic diagrams to solve problems involving monohybrid cross – multiple gene inheritance Key points: The garden peas studied by Gregor Mendel involved pairs of alleles with only three possible genotypes and two phenotypes per trait. For example, the gene for round pea (R) is dominant over the gene for wrinkled pea (r) and only three genotypes are possible: RR, Rr and rr. These three genotypes produce only two phenotypes: Round (RR and Rr) and wrinkled (rr). There are no intermediate traits between round and wrinkled. If all human characteristics were controlled by simple pairs of dominant and recessive alleles like the one Mendel studied, we would have tall and short people with no intermediates. Therefore for some traits, especially with ones involved polygenic inheritance/multiple gene inheritance, there is a secondary gene that controls a trait. Human skin color is a good example of polygenic (multiple gene) inheritance. Assume that three "dominant" capital letter genes (A, B and C) control dark pigmentation because more melanin is produced. The "recessive"alleles of these three genes (a, b & c) control light pigmentation because lower amounts of melanin are produced. The words dominant and recessive are placed in quotation marks because these pairs of alleles are not truly dominant and recessive as in some of the garden pea traits that Gregor Mendel studied. A genotype with all "dominant" capital genes (AABBCC) has the maximum amount of melanin and very dark skin. A genotype with all "recessive" small case genes (aabbcc) has the lowest amount of melanin and very light skin. Each "dominant" capital gene produces one unit of color, so that a wide range of intermediate skin colors are produced, depending on the number of "dominant" capital genes in the genotype. For example, a genotype with three "dominant" capital genes and three small case "recessive" genes (AaBbCc) has a medium amount of melanin and an intermediate skin color Q: A gene for feather colour in chickens is carried on an autosome. This gene has two alleles, black (CB) and splashed-‐white (CW). When a male chicken with black feathers is mated with a female chicken with splashed-‐white feathers, all the offspring have blue feathers. This also occurs when a male chicken with splashed-‐white feathers is crossed with a female with black feathers. Another gene may cause stripes on feathers (barred feathers). This gene is carried on the X chromosome. The allele for barred feathers (XA) is dominant to the allele for nonbarred feathers (Xa). In chickens the male is homogametic and has two X chromosomes while the female is heterogametic and has one X chromosome and one Y chromosome. Own notes


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A male chicken with black, non-‐barred feathers was crossed with a female chicken with splashed-‐white, barred feathers. All the offspring had blue feathers, but the males were barred and the females were non-‐barred. Q: Draw a genetic diagram to explain this cross. (d) use genetic diagrams to solve problems involving dihybrid cross Key points: A dihybrid cross is a breeding experiment between parental generation organisms that differ in two traits.

(e) use genetic diagrams to solve problems involving test crosses. Key points: The test cross is another one of the fundamental tools devised by Gregor Mendel. In its simplest form this is an experimental cross of an individual organism of dominant phenotype but unknown genotype to an organism with a homozygous recessive genotype (and phenotype). Q: A gene for feather colour in chickens is carried on an autosome. This gene has two alleles, black (CB) and splashed-‐white (CW). When a male chicken with black feathers is mated with a female chicken with splashed-‐white feathers, all the offspring have blue feathers. This also occurs when a male chicken with splashed-‐white feathers is crossed with a female with black feathers. Another gene may cause stripes on feathers (barred feathers). This gene is carried on the X chromosome. The allele for barred feathers (XA) is dominant to the allele for nonbarred feathers (Xa). In chickens the male is homogametic and has two X chromosomes while the female is heterogametic and has one X chromosome and one Y chromosome. A male chicken with black, non-‐barred feathers was crossed with a female chicken with splashed-‐white, barred feathers. All the offspring had blue feathers, but the males were barred and the females were non-‐barred. Q: Explain how a farmer could use a breeding programme to find out the genotype of a male chicken with blue, barred feathers Own notes

Peter Ting � 12/2/12 8:27 AMComment [22]: Peter Ting � 12/1/12 5:39 PMComment [23]: Pure breeding organism describes that the trait possessed came from alleles which are homozygous.


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(f) [PA] use the chi-‐squared test to test the significance of differences between observed and expected results Key points: The difference between an experiment and real life is that an experiment tries to reproduce the real life while actually the real life cannot be completely mimicked at all, even if you try as hard as you may. E.g. If you are experimenting on a subject, the results you get by repeating the experiment over and over again are not going to be the same. There’re bound to be differences, which could mean little or big. How far would you accept differences? A statistical test allows us to accept or reject the differences, depending on the results of the experiment and criteria of the test. If the difference is not large or significant, then the null hypothesis will be accepted. However, to accept a hypothesis does not mean that it is true, only that we do not have evidence to believe otherwise. There are many statistical test being used, however there are two which we will particularly study in the syllabus. There are the chi-‐squared test and the t-‐test. Knowing the function of each test is important because we cannot simply employ a test that is not meant for certain data. The requirements to use each test are as follows; Chi-‐Squared Test

• When data acquired is discontinuous/categorical/discreet • When the results involve an expected number and observed number

T-‐Test • When data acquired is continuous/normal • When the results involve means between TWO groups

Chi-‐Squared Test As part of an investigation into the foraging habits of bees (Bombus monticola), the number of visits made to two types of plant, Vaccinium vitis-‐idaea and Erica tetralix, were recorded in the table below; these numbers are called the observed frequencies (O).

The researchers wished to test for a significant difference in the number of visits to the two plants, i.e. whether Bombus monticola has a feeding preference. Step 1: State your null hypothesis, H0

Null hypothesis: There will be no difference in the number of visits to each type of plant.

Own notes

Peter Ting � 12/2/12 12:38 AMComment [24]: You know what is a hypothesis is right? A null hypothesis describes how it behaves positively towards the differences in the results of the experiment. Means to say that there is no big difference at all, despite how big or small. Usually we doubt this to be true, which is why we carry out the statistical test. If proven true that NH can’t be used, then we will believe in the alternative hypothesis instead.


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Step 2: Calculate the expected frequencies,

Step 3: Calculate the differences between the observed frequencies (O) and expected frequencies (E)

Step 4: Square the differences , and divide each square by the corresponding expected frequency, E

Step 5: Calculate the test value

Therefore 2.29 + 2.29 = 4.58 Step 6: Calculate the number of degrees of freedom, df using the formula below D.O.F = (number of columns) – 1 = 2 – 1 = 1 Use the table below, to find the critical value, corresponding to 1 degree of freedom and 5% level of significance. REMINDER: Please use 5% significance level if the question doesn’t indicate you to do otherwise.

Own notes

Peter Ting � 12/2/12 1:42 AMComment [25]: The critical region encompasses those values of the test statistic that lead to a rejection of the null hypothesis. Based on the distribution of the test statistic and the significance level, a cut-‐off value for the test statistic is computed. Values either above or below or both (depending on the direction of the test) this cut-‐off define the critical region. Peter Ting � 12/2/12 1:37 AMComment [26]: The significance level, defines the sensitivity of the test. A value of = 0.05 means that we inadvertently reject the null hypothesis 5% of the time when it is in fact true. This is also called the type I error. The choice of significance level is somewhat arbitrary, although in practice values of 0.1, 0.05, and 0.01 are commonly used.


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Critical value = 3.84 Step 7: Reject the null hypothesis and accept the alternative hypothesis if the test value, Χ2 is greater than the critical value. Step 8: State the smallest level of significance for which the null hypothesis is rejected.

“Null Hypothesis is rejected. The difference did not occur by chance for P < 0.05”

If null hypothesis is accepted;

“Null Hypothesis is accepted. The difference did occur by chance for P > 0.05”

If Χ2 is big/large, means that the P(O = E) becomes smaller, likewise if Χ2 = 0, means that the O = E, probability of Observed approaching Expected is 1, P(O = E) = 1. The graph tells us where is the cut-‐off point where we allow our data to deviate from the expected. The cut off point is saying, this is only where the observed is allowed to spread away from the expected. Beyond that point, I reject the null hypothesis. Which is why, when the Χ2 is falls in the area of rejection (more than critical value), means that the observed has already spread so much from the expected value that I can no longer accept its difference. That would also mean the P(O=E) drops significantly too, so it falls below 0.05, P < 0.05, Null hypothesis is then rejected. The differences are not due by chance. And Own notes


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if the Χ2 value falls in the area of acceptance (smaller than critical value), means that the observed has spread from the expected value within the level that you may ignore its difference. That would mean that the P(O=E) is high, higher than 0.05, P > 0.05. Null hypothesis is then accepted. The differences are due by chance. (h) explain, with examples, how the environment may affect the phenotype; Key points: Although genes have major effects on an organism’s phenotype, the organism’s environment can also have large effects. Lactase production in Escherichia coli The bacterium Escherichia coli has a gene that codes for the production of the enzyme lactase, which hydrolyses the disaccharide lactose to glucose and galactose. This gene is only expressed when the bacterium encounters lactose in its environment. Hair colour in cats Many different genes determine hair colour in cats. At least eight different genes., at different loci, are known to influence hair colour and it is thought that there are probably more. These are known as polygenes. Depending on the particular combination of allele that a cat has for each of these genes, it can have any of a very wide range of colours. Hair colour in cats is an example of continuous variation. This is variation in which there are no clear-‐cut categories. There is a continuous range of variation in colour between the very lightest and very darkest extremes. The cat hair colour genes exert their effect by coding for the production of enzymes. One such gene is found at the C locus. Siamese cats have two copies of recessive allele of this gene called cs. This gene codes for an enzyme, which is sensitive to temperature. It produces dark hair at the extremities of the paws, ears and tail where the temperature is lower, and light hair in warmer parts of the body. The colouring of a Siamese cat is therefore the result of interaction between gene and environment.

Own notes


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Human height Many different genes at different loci also affect human height. It is also affected by environment. Even if a person inherits alleles of these genes that give the potential to grow tall, he or she will not grow tall unless the diet supplies plenty of nutrients to allow this to happen. Poor nutrition, specially in childhood, reduces the maximum height that is attained.

Cancer The risk of developing cancer in influenced by both genes and environment. For example, a woman with particular alleels of the genes BRCA1 or BRCA2 has 50% to 80% chance of developing breast cancer at some stage in her life. This is a much higher risk than for people who do not have these alleles. The normal alleles of these genes protect cells from changes that could lead to them becoming cancerous. However, environment also affects this risk. Smoking, for example, increases the risk even further. Taking the drug tamoxifen can reduce the risk. Monoamine oxidase A Monoamine oxidase A (MAO-‐A) is an enzyme that is found associated with mitochondria in the nervous system, and also in the liver and digestive system. In the nervous system, it is involved in the inactivation of neurotransmitters including noradrenaline and serotonin. Own notes


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Some alleles of the monoamine oxidase gene produce low activity MAO-‐A, while others produce high activity of MAO-‐A. It has been found that children with the high activity form, if maltreated, are more likely to show antisocial behavior than similarly treated children with low activity form. Other behaviours, such as novelty seeking, also appear to be associated with particular alleles of this gene. However in all cases the environment also has large effect on bahaviour; behavior is produced by interaction between this gene (and probably others as yet unidentified) and the environment. (g) explain, with examples, how mutation may affect the phenotype; Key points: Refer to Genetic Control (i) explain how a change in the nucleotide sequence in DNA may affect the amino acid sequence in a protein and hence the phenotype of the organism; Key points: Refer to Genetic Control Own notes

Peter Ting � 12/2/12 8:26 AMComment [27]: Recall; -‐Genetic Codons -‐Primary structure of proteins -‐Replication error -‐Degenerate codon (prevents a change even if mutation occurs) -‐Sickle cell anemia

O - Inherited Change

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