Mrs. Earland's Class Resources - Home - 3.4.U1 Mendel ... · Web viewInheritance of cystic fibrosis and Huntington’s disease. Read p. 178-179 in Textbook 3.4.A4 Consequences of

3.2 - InheritanceUnderstandings, Applications and Skills (This is what you maybe assessed on)

Statement Guidance

3.4.U1 Mendel discovered the principles of inheritance with experiments in which large numbers of pea plants were crossed.

Workbook Activity 86-89

3.4.U2 Gametes are haploid so contain only one allele of each gene.

3.4.U3 The two alleles of each gene separate into different haploid daughter nuclei during meiosis.

3.4.U4 Fusion of gametes results in diploid zygotes with two alleles of each gene that may be the same allele or different alleles.

3.4.U5 Dominant alleles mask the effects of recessive alleles but co-dominant alleles have joint effects.

Workbook Activity 90

3.4.U6 Many genetic diseases in humans are due to recessive alleles of autosomal genes, although some genetic diseases are due to dominant or co-dominant alleles.


3.4.U7 Some genetic diseases are sex-linked. The pattern of inheritance is different with sex-linked genes due to their location on sex chromosomes.

Workbook Activity 93Alleles carried on X chromosomes should be shown as superscript letters on an upper case X, such as Xh.

3.4.U8 Many genetic diseases have been identified in humans but most are very rare.

3.4.U9 Radiation and mutagenic chemicals increase the mutation rate and can cause genetic diseases and cancer.

3.4.A1 Inheritance of ABO blood groups. The expected notation for ABO blood group alleles: O = i, A=IA, B = IB.

3.4.A2 Red-green colour blindness and hemophilia as examples of sex-linked inheritance.

Read p. 180-181 in Textbook

3.4.A3 Inheritance of cystic fibrosis and Huntington’s disease. Read p. 178-179 in Textbook

3.4.A4 Consequences of radiation after nuclear bombing of Hiroshima and accident at Chernobyl.

Read p. 184-185 in TextbookDBQ 1-4p. 186

3.4.S1 Construction of Punnett grids for predicting the outcomes of monohybrid genetic crosses.


3.4.S2 Comparison of predicted and actual outcomes of genetic crosses using real data.

DBQ p 176-177 #1-3

3.4.S3 Analysis of pedigree charts to deduce the pattern of inheritance of genetic diseases.

workbook Activity 96DBQ 1-2 p. 183

3.4.U1 Mendel discovered the principles of inheritance with experiments in which large numbers of pea plants were crossed.

Gregor Mendel was an Austrian monk who developed the principles of inheritance by performing experiments on pea plants

First, he crossed different varieties of purebred pea plants, then collected and grew the seeds to determine their characteristics

Next, he crossed the offspring with each other (self-fertilization) and grew their seeds to similarly determine their characteristics

These crosses were performed many times to establish reliable data trends (over 5,000 crosses were performed)

As a result of these experiments, Mendel discovered the following things:

1. When he crossed two different purebred varieties together the results were not a blend – only one feature would be expressed

E.g. When purebred tall and short pea plants were crossed, all offspring developed into tall growing plants

2. When Mendel self-fertilized the offspring, the resulting progeny expressed the two different traits in a ratio of ~ 3:1

E.g. When the tall growing progeny were crossed, tall and short pea plants were produced in a ratio of ~ 3:1

P1

P2

P3

From these findings, Mendel drew the following conclusions: ______________________: Organisms have discrete factors that determine its features ______________________: Organisms possess two versions of each factor ______________________:Each gamete contains only one version of each factor ______________________:Parents contribute equally to the inheritance of offspring as a result of the fusion

between randomly selected egg and sperm ______________________:For each factor, one version is dominant over another and will be completely

expressed if present

While there are caveats to Mendel’s conclusions, certain rules can be established:1. Law of Segregation: ____________________________________________________________________________________________

______________________________________________________________________________________________________________________2. Law of Independent Assortment: ________________________________________________________________________

_______________________________________________________________________________________________________________*3. Principle of Dominance: _____________________________________________________________________________________†

* The law of independent assortment does not hold true for genes located on the same chromosome (i.e. linked genes)† Not all genes show a complete dominance hierarchy – some genes show co-dominance or incomplete dominance

RECALL:

3.4.U2 Gametes are haploid so contain only one allele of each gene. / 3.4.U3 The two alleles of each gene separate into different haploid daughter nuclei during meiosis. Gametes are ___________________________________________ formed by the process of meiosis – males produce sperm and females produce ova

During meiosis I, __________________________________________________ into different nuclei prior to cell division

As homologous chromosomes carry the same genes, segregation of the chromosomes ___________________ __________________________________________________Consequently, as gametes contain only one copy of each chromosome they therefore carry only one _________________________________________________

3.4.U4 Fusion of gametes results in diploid zygotes with two alleles of each gene that may be the same allele or different alleles.Gametes are haploid male and female gametes fuse during fertilization, resulting zygote will contain two alleles for each gene.

Exception: Males have only one allele for each gene located on a sex chromosome, as these chromosomes aren’t paired (XY)

For any given gene, the combination of alleles can be categorized as follows:• If the maternal and paternal alleles are the same, the offspring is said to be _______________________________

for that gene• If the maternal and paternal alleles are different, the offspring is said to be ________________________________

for that gene• Males only have one allele for each gene located on a sex chromosome are _________________________________

for that gene

3.4.U5 Dominant alleles mask the effects of recessive alleles but co-dominant alleles have joint effects.

Complete Dominance Incomplete Dominance Co-DominanceDefinition

Heterozygote state

Symbols

Example

3.4.A1 Inheritance of ABO blood groups.

The _____________________ classification system uses the presence or absence of certain ______________ on red blood cells to categorize blood into ______________types.

Distinct molecules called agglutinogens (a type of antigen) are attached to the surface of red blood cells. There are two different types of agglutinogens, type "A" and type "B”.

TRY THIS A man with group A blood marries a woman with group B blood. Their child has group O blood. What are the genotypes of these individuals?

What other genotypes and in what frequencies, would you expect in offspring from this marriage?

3.4.S1 Construction of Punnett grids for predicting the outcomes of monohybrid genetic crosses.A monohybrid cross determines the allele combinations for potential offspring for one gene only

Monohybrid crosses can be calculated according to the following steps: Step 1: Designate letters to represent alleles (dominant = capital letter ; recessive = lower case ; co-

dominant = superscript) Step 2: Write down the genotype and phenotype of the prospective parents (this is the P generation) Step 3: Write down the genotype of the parental gametes (these will be haploid and thus consist of a single

allele each) Step 4: Draw a grid with maternal gametes along the top and paternal gametes along the left (this is a

Punnett grid) Step 5: Complete the Punnett grid to determine potential genotypes and phenotypes of offspring (this is

the F1 generation)

Explain This: When Mendel crossed two yellow pea plants 25% of the offspring were green

F1 _________ x _________

Punnet Square OffspringGenotype Ratios

Phenotype Ratios

Try This: What is the expected outcome of crossing two green pea plants that are both homozygous

F1 _________ x _________


Phenotype Ratios

Try This: What is the expected outcome of crossing a green pea plant with a heterozygous yellow plant

F1 _________ x _________


Phenotype Ratios

Try This: Would you expect to have any green peas if you crossed a homozygous yellow pea with a heterozygous yellow pea

F1 _________ x _________


Phenotype Ratios

TRY THIS: A test cross is where an unknown genotype is breed with a homozygous recessive individual. Explain how a test cross could be used to determine the genotype of a yellow pea.


In the F2 generation of a Mendelian cross, in flowers where purple is dominant to white, there were 1-5 purple flowers and 45 white flowers. Does this support the hypothesis that the F1 parents were in fact heterozygous?

Observed Expected (O-E) (O-E)^2 (O-E)^2/E

Try This: A scientist predicts that the kittens born with a congenital birth defect will be 25% based on the hypothesis that it is caused be a recessive gene in that breed of cat. After surveying several litters, he found that 44 out of 125 kittens had the defect. Is his hypothesis correct?

Observed Expected (O-E) (O-E)^2 (O-E)^2/E

3.4.U8 Many genetic diseases have been identified in humans but most are very rare. There are over 4,000 identified single gene defects that lead to genetic disease, but most are very rare

Any allele that adversely affects survival and hence the capacity to reproduce is unlikely to be passed on to offspring

______________________________ tend to be more common, as the faulty allele can be present in carriers without causing disease______________________________ may often have a late onset, as this does not prevent reproduction and the transfer of the faulty allele

3.4.A3 Inheritance of cystic fibrosis and Huntington’s disease. Cyctic Fibrosis

Cystic fibrosis is an ______________________________ caused by a mutation to the CFTR gene on chromosome 7 Individuals with cystic fibrosis produce ______________which is unusually thick and sticky. This mucus clogs the airways and secretory ducts of the digestive system, leading to respiratory failure and

pancreatic cysts Heterozygous carriers who possess one normal allele __________________________ disease symptoms

What is the probability of two parents who are both carriers of the recessive allele producing children affected by CF?

Huntington’s Disease Huntington’s disease is an ________________________ caused by a mutation to the Huntingtin (HTT) gene on

chromosome 4 The HTT gene possesses a repeating trinucleotide sequence (CAG) that is usually present in low amounts (10 –

25 repeats) More than 28 CAG repeats is unstable and causes the sequence to amplify (produce even more repeats) When the number of repeats exceeds ~40, the huntingtin protein will misfold and cause neurodegeneration This usually occurs in late adulthood and so symptoms usually develop noticeably in a person’s middle age (~40

years) Symptoms of Huntington’s disease include uncontrollable, spasmodic movements (chorea) and dementia

3.4.U6 Many genetic diseases in humans are due to recessive alleles of autosomal genes, although some genetic diseases are due to dominant or co-dominant alleles.

• Genetic diseases are caused when mutations to a gene (or genes) abrogate normal cellular function, leading to the development of a disease phenotype

• Genetic diseases can be caused by recessive, dominant or co-dominant alleles

An autosomal __________________genetic disease will only occur if ______________ alleles are faulty• Heterozygous individuals will possess one copy of the faulty allele but not develop disease symptoms

(they are carriers)• An example of an autosomal recessive genetic disease is __________________________________

An autosomal __________________genetic disease only requires __________________ of a faulty allele to cause the disorder

• Homozygous dominant and heterozygous individuals will both develop the full range of disease symptoms

• An example of an autosomal dominant genetic disease is ________________________________

If a genetic disease is caused by ______________________ alleles it will also only require _______________ of the faulty allele to occur

• However, heterozygous individuals will have __________________________ due to the moderating influence of a normal allele

• An example of a genetic disease that displays co-dominance is ________________________________________________

Recall Sickle Cell

What is the chance of a carrier and a person who is unknown geneotype having a child that has complete disease?


Key: female male

affected

NotAffected

deceased

Deduce the genotypesof these individuals: A & B C D

Genotype

Reason

a. Male $ is healthy but of unknown genotype. Calculate the likelihood of any children produced with female D having sickle cell anemia. Show all working.

b. Calculate the likelihood of any further children produced by E and her # having sickle cell anemia.

c. Male $ is healthy but of unknown genotype. Calculate the likelihood of any children produced with female D having sickle cell anemia. Show all working.

3.4.U7 Some genetic diseases are sex-linked. The pattern of inheritance is different with sex-linked genes due to their location on sex chromosomes. AND 3.4.A2 Red-green colour blindness and haemophilia as examples of sex-linked inheritance. The sex chromosomes are non-homologous. There are many genes on the X-chromosome which are not present on the Y-chromosome.

Sex-linked traits are those which are carried on the X-chromosome in the non-homologous region.

Alleles in this regions are expressed whether they are dominant or recessive, as there is no alternate allele carried on the Y chromosome. Therefore sex-linked genetic disorders are more common in males.

Examples of sex-linked genetic disorders:

- haemophilia- colour blindness

What chance of a colour-blind child in the cross between a normal male and a carrier mother?

How can you tell from a Pedigree Chart, the pattern of inheritance?

3.4.U9 Radiation and mutagenic chemicals increase the mutation rate and can cause genetic diseases and cancer.A gene mutation is a change to the base sequence of a gene that can affect the structure and function of the protein it encodes

• Mutations can be spontaneous (caused by copying errors during DNA replication) or induced by exposure to external elements

Examples of factors which can induce mutations include:• ________________– e.g. UV radiation from the sun, gamma radiation from radioisotopes, X-rays from medical

equipment• ________________– e.g. reactive oxygen species (found in pollutants), alkylating agents (found in cigarettes)• ________________ – e.g. bacteria (such as Helicobacter pylori), viruses (such as human papilloma virus)

Agents which increase the rate of genetic mutations are called mutagens, and can lead to the formation of genetic diseases

• Mutagens which lead to the formation of cancer are more specifically referred to as carcinogens


Compare and Make Notes below:

Practice:3.4.U1 Mendel discovered the principles of inheritance with experiments in which large numbers of pea plants were crossed.

2. Mendel is known as the father of genetics for his extensive experimental work with peas. His findings enabled him to form the principles of inheritance. Find out about Mendel: http://knowgenetics.org/mendelian-genetics/ and read pg. 169 in your text book

http://knowgenetics.org/mendelian-genetics/

a. State the range of the number of seeds used in each trial.

b. List three examples of traits Mendel investigated.

c. Explain what is meant by the term ‘pure-bred’.

d. Describe the key experimental finding that led to the establishment of the principles of inheritance.

Nature of science: Making quantitative measurements with replicates to ensure reliability. Mendel’s genetic crosses with pea plants generated numerical data.

3. To reach valid conclusions often statistical tests are used to help analyse the data collected. Outline why large sample sizes are preferable to smaller ones.

3.4.U2 Gametes are haploid so contain only one allele of each gene. 3.4.U3 The two alleles of each gene separate into different haploid daughter nuclei during meiosis. 3.4.U4 Fusion of gametes results in diploid zygotes with two alleles of each gene that may be the same allele or different alleles.

4. State definitions of the following:

Genotype

Phenotype

Dominant allele

Recessive allele

Codominant alleles

Homozygous

Heterozygous

Carrier

Phenotype

Autosomal genes

Sex-linked inheritance

3.4.A1 Inheritance of ABO blood groups. AND 3.4.U5 Dominant alleles mask the effects of recessive alleles but co-dominant alleles have joint effects.

5. Human ABO blood types follow a codominant inheritance pattern.a. Describe what is meant by “some genes have multiple alleles.”

b. Complete the table (both genotype and phenotype) below to show how blood type is inherited.

alleles i IA IB

i

IA

IB

State the genotype and phenotype which is an example of codominance.

6. Explain why the identified genotype above is an example of codominance.

3.4.S1 Construction of Punnett grids for predicting the outcomes of monohybrid genetic crosses.

Explain why a type O person can donate blood to all other blood types but can only receive type O blood.

Blood typing has often been used as evidence in paternity cases, when the blood type of the mother and child may indicate that a man alleged to be the father could not possibly have fathered the child. For the following mother and child combinations, indicate which blood groups of potential fathers would be exonerated.

Blood Group of Mother

Blood Group of Child

Blood Group that would Exonerate Man

AB A a.

O B b.

A AB c.

O O d.

B A e.

Discuss

28.

Fred has type AB blood, Wilma has type B blood, and Pebbles, their daughter has type A blood. Betty has type B blood, Barney has type A blood, and their son Bam Bam has type O blood. In the bloodiest fight ever witnessed in Bedrock, BCE, Barney accused Betty of having an affair with Fred. Barney also claimed that Fred is Bam Bam’s father, sighting evidence from the new field of Geneticsrock. Could Barney be right? Could Fred be Bam Bam’s father? Support your answer.Discuss

29.

A man with group B blood marries a woman with group B blood. Their child has group O blood. What are the genotypes of these individuals? What other genotypes, and in what frequencies, would you expect in offspring from this marriage?


7. Cat genetics - How well does the piebald frequency in the offspring match the predictions made from our knowledge of the genes?

https://www.proprofs.com/discuss/q/350116/pebbles-daughter-barney-bloodiest-witnessed-bedrock-accused-




https://www.proprofs.com/discuss/q/410852/evidence-paternity-indicate-possibly-fathered-following-comb




Fo Generation: Phenotypes

Genotypes

Punnet Grid

F1 Generation:Genotypes

Phenotypes

Phenotypes Ratio

Observed – Cats surveyed, only 308 had no white on them and 937 had some white on them. How does this compare to the expected ratios

a. Complete the table to compare expected genotype ratio with the observed outcomes from the cross.

genotype observed expected

No white (ss)

Some White (Ss)

Mostly White (SS)

b. Use the chi squared formula and the critical values table to determine whether the actual outcome matches the predicted cross.

Chi-square value = =

Degrees of freedom (df) = Number of classes – 1 =

Is the hypothesis outlined by the theory of pielbald genetics and the expected cross outcomes supported by the data?(is Chi-square value < critical value)

df critical values at 5%

1 3.84

2 5.99

3 7.82

4 9.49

5 11.07

3.4.U8 Many genetic diseases have been identified in humans but most are very rare.

8. Explain why genetic diseases are very rare in humans.

9. Why is it that most human harmful alleles are either recessive or late-onsetting?

3.4.U6 Many genetic diseases in humans are due to recessive alleles of autosomal genes, although some genetic diseases are due to dominant or co-dominant alleles. AND 3.4.A3 Inheritance of cystic fibrosis and Huntington’s disease.

10. Cystic fibrosis (CF) is caused by a mutation in the CFTR gene. Secretions (e.g. mucus, sweat and digestive juices) which are usually thin instead become thick. The secretions block tubes, ducts and passageways. Lung problems in most CF sufferers leads to a early death.

a. Analyse the pedigree chart below and deduce whether CF is a recessive, dominant or codominant condition. Quote your evidence in your answer.

b. What is the probability of two parents who are both carriers of (one copy of) the recessive allele producing children affected by CF? Show your workings.

c. Deduce the genotypes of the selected individuals.

d. D and $ are planning to have another child. Using the information in the pedigree chart in the last question to calculate the % chance that the child will suffer from CF.

11. Huntington's Disease (HD) is a brain disorder that affects a person's ability to think, talk, and move. HD is caused by a mutation in a gene on chromosome 4.

12. Is this a dominant or recessive condition?

13. Is this disorder autosomal or sex-linked

14. Produce a punnett grid to explain the inheritance pattern seen in the offspring of a normal mother and a heterozygous affected father. Don’t forget to use a key to explain the genotypes and allele symbols used.

$

Individual Genotype

A

B

C

D

15. Sickle cell disease is another example of codominant inheritance. a. State the genotypes description, phenotypes and malaria protection of these individuals.

genotype HbAHbA HbAHbs HbsHbs

description

phenotype

Malaria protection?

Allele key: HbA produces normal haemoglobin, HbS produces fibrous haemoglobin that causes red blood cells to sickle.

b. Predict the phenotype ratios of offspring in the following crosses. Show all your working, and set it out as expected. Take care with notation.

i. Carrier mother with affected father.

ii. Affected father with unaffected mother.

iii. Carrier mother with carrier father.


16. The pedigree chart below shows a family affected by sickle cell:a. Deduce the genotype of each individual with a letter.

A FB GC HD $E #

b.b.b.b.b.

Calculate the likelihood of any further children produced by E and her # having sickle cell anemia.

c. Male $ is healthy but of unknown genotype. Calculate the likelihood of any children produced with female D having sickle cell anemia. Show all working.

3.4.U6 Many genetic diseases in humans are due to recessive alleles of autosomal genes, although some genetic diseases are due to dominant or co-dominant alleles. AND 3.4.A3 Inheritance of cystic fibrosis and Huntington’s disease.

Huntington's Disease (HD) is a brain disorder that affects a person's ability to think, talk, and move. HD is caused by a mutation in a gene on chromosome 4. Genetics review:

1. Is this a dominant or recessive condition?

2. Is this disorder autosomal or sex-linked

3. Produce a Punnett square to explain the inheritance pattern in the diagram.

What is the probability of an unaffected mother and a heterozygous affected father (for HD) producing children affected by HD?

3.4.U7 Some genetic diseases are sex-linked. The pattern of inheritance is different with sex-linked genes due to their location on sex chromosomes. AND 3.4.A2 Red-green colour blindness and hemophilia as examples of sex-linked inheritance.

17. Some inherited disorders are associated with gender. a. State two examples of sex-linked genetic disorders.

b. Explain why sex-linked disorders are more common in males than females.

c. Explain why human females can be homozygous or heterozygous for sex-linked genes, where males cannot.

d. The allele for colour blindness (n) is recessive to the allele for normal vision (N). This gene is carried in a non-homologous region on the X chromosome. Complete the table below to show the genotypes and phenotypes of individuals with regard to colour blindness.

Female Male

Normal XN XN

Affected

Carrier Not possible! Why?

e. In the space below, complete a punnet grid to show a cross between a normal male and a carrier female. What is the expected ratio of phenotypes?

18. Hemophilia is a blood-clotting disorder that is also recessive and sex-linked. a. State the normal function of the gene associated with hemophilia.

b. Describe the signs and symptoms of hemophilia.

c. Use the pedigree chart to deduce the possible genotype(s) of the named individuals.

Leopold

Helen

Alice

Mary

Rubert

Bob

Britney

d. Suggest reasons why the frequency of some disease-related alleles might be increasing in the population.

More Pedigree Practice:Recessive or Dominant Autosomal or Sex Linked?

Super Evil Past Test Question:

In this pedigree chart for hemophilia, what is the chance that offspring ? will be affected?A. 0%B. 12.5%C. 25%D. 50%

3.4.U9 Radiation and mutagenic chemicals increase the mutation rate and can cause genetic diseases and cancer.

Key: female male

affected

NotAffected

deceased

19. State the definition of a mutation.

20. Mutations can cause a change in a gene allele, which can be harmful. Occasionally mutations can be beneficial. Some changes however are ‘silent’, i.e. they don’t cause a change in the trait. Explain how this is possible.

21. Mutagens are agents that cause gene mutations. List three types of mutagen.

22. Distinguish between mutations that can affect an individual during their lifetime and those which can lead to genetic diseases.


23. Radiation releases into the environment by humans can causes major problems. Radiation pollution is commonly the result of an accident at a nuclear power station (Chernobyl) or a deliberate after affect caused by the release of a nuclear bomb (Hiroshima). Outline the impacts and evidence of them caused by each incident plus make notes on the limitations of evidence.

Accident at Chernobyl nuclear power station Release of a nuclear bomb at Hiroshima

Impacts and supporting evidence

Limitations of the evidence / what cannot be concluded*

*Not being able to reach a conclusion due to lack of or limitations in the evidence is not the same as saying there no link between the variables. It simply means that the current data is insufficient to allow a conclusion to be drawn.

Citations:

Allott, Andrew. Biology: Course Companion. S.l.: Oxford UP, 2014. Print.

Taylor, Stephen. "Essential Biology 4.3 Theoretical Genetics.docx" Web. 7 Sep. 2015. <http://www.slideshare.net/gurustip/essential-biology-43-theoretical-genetics>.

Documents

Mrs. Earland's Class Resources - Home - 3.4.U1 Mendel ... · Web viewInheritance of cystic fibrosis and Huntington’s disease. Read p. 178-179 in Textbook 3.4.A4 Consequences of