3823) Which of the following genes have been implicated in hereditary forms of breast cancer? BRCA1, b) BRCA2, c) RB, d) phMSH2, e) BRCA1 and BRCA2 1123)

3823) Which of the following genes have been implicated in hereditary forms of breast cancer? BRCA1, b) BRCA2, c) RB, d) phMSH2, e) BRCA1 and BRCA2

1123) Which of the following properties is not characteristic of a malignant cell?

a) It no longer undergoes cell cycle regulation and growth arrest.

b) It has undergone mutations in a c-onc and in other genes.

c) It cannot leave its site of growth in the tumor.d) It may have undergone a chromosome

rearrangement.e) All of these are correct.

Answer: e

Answer: c

4353) Which of the following can be determined using a cloned gene?1. A gene’s nucleotide sequence2. A gene’s function3. A gene’s amino acid sequencea) 1, b) 2, c) 3, d) 1 and 2, e) All of these

1009) What method allows bacteria to protect endogenous restriction sites from being cleaved by restriction enzymes?

a) Methylationb) Amylationc) Glycosylationd) Methylation and Amylatione) None of these

Answer: e

Answer: a

Chapter 3Mendelism: The Basic Principles

of Inheritance

© John Wiley & Sons, Inc.

Chapter 23

--The theory of allele frequency

--Random genetic Drift

Chapter 24

--Genetic variation

--Molecular

--Speciation

Chapter Outline

Mendel’s Study of HeredityApplications of Mendel’s PrinciplesTesting Genetic HypothesesMendelian Principles in Human

Genetics


The Garden Pea: true-breeding


Pisum Sativum--anther: sperm-pollen--ovary: eggs

Petals of the flowers are close down--self-fertilization ----inbreeding and uniform

Cross-fertilizationTwo plants with differentcharacteristics(Tall and short)

Monohybrid Crosses: single phenotype


Heritable (genetic) factors (genes)

--Dominant (expressed)

--Recessive (latent or not expressed)

(Alleles)

--parental strain: two copies of a gene (diploid and homozygous)

--gametes has a single copy

(haploid)

--offspring strain: two different copies of a gene (heterozygous)

hybrid


Phenotype: physical appearance

Genotype: allelic constitution of each strainD allele of dominant gene d allele of recessive gene

Ratio of progeny ~3:1

Vocabulary for Monohybrid Crosses True-breeding Cross-fertilize Monohybrid cross Dominant Recessive Gene, genetic factor ( fragment of DNA) that

determines a characteristic.

Allele,alternative forms of a gene

Parental Filial Segregate Characteristic, an attribute or feature of a

particular gene

Homozygous, an individual organism possessing two of the same alleles at a locus

Heterozygous, an individual organism possessing two different alleles at a locus

Genotype, set of alleles that an individual organism possesses

Phenotype (trait), the appearance or manifestation of a character

Locus, specific place on a chromosome occupied by an allele


Symbolic Representation of a Monohybrid Cross


22

75%

Mendel’s Principles

The Principle of Dominance: In a heterozygote, one allele may conceal the presence of another. (This means the dominant allele is observed in the phenotype)

The Principle of Segregation: In a heterozygote, two different alleles segregate from each other during the formation of gametes. (This means that the pair of alleles encoding the traits in each parental plant had separated or segregated from one another during meiosis)

The Principle of Dominance: In a heterozygote, one allele may conceal the presence of another.

--genetic function--control phenotype--regulate physiological consequences

The Principle of Segregation: In a heterozygote, two different alleles segregate from each other during the formation of gametes.

--genetic transmission-- may control phenotype--may regulate physiological consequences

Dihybrid Crosses


How are genes transmitted?


Diploid

Haploid

25%

2

75%

Comparison of Observed and Expected Results in the F2


Mendel’s PrinciplesThe Principle of Independent

Assortment: The alleles of different genes segregate,(assort) independently of each other (The traits in the offspring of this crosses did not always match the combinations of traits in the parental organisms).


In humans, diploid cells contain 46 chromosomes, 23 female chromosomes23 male chromosomesDuring meiosis, the pairs of similar homologous chromosome are divided in half to form haploid cells, and this separation is random.

Recombination scrambles pieces of maternal and paternal genes, which ensures that genes assort independently from one another, except genetic linkage

The Principle of Dominance

The Principle of Segregation

Applications of Mendel’s Principles

Mendel’s principles can be used to predict the outcomes of crosses between different strains of organisms.

Three methods to predict outcomes– The Punnett Square Method– The Forked-Line Method– The Probability Method



AlleleAa

The Punnett Square Methodone or two genes

The Forked-Line Method for an Intercross two or more genes


Trihybrid heterozygous cross …. --independent sorting--monohybrid cross…Dd x Dd....Ratio 3:1

The Forked-Line Method for a Testcross


Heterozygous vs homozygous recessive

Dd x dd

D d

d Dd dd

d Dd dd

Ratio 1:1

Probability The probability of an event is the frequency of that event in the sample. Express the likelihood of the occurrence of a particular event. For a coin toss:

– The probability of heads is 1/2. =0.5

– The probability of tails is 1/2.

For two heterozygotes (Gg) producing an offspring:– The probability of the incorporation of G in each gamete in GG zygote is

1/2 and 1/2. 1/2 x 1/2=1/4

– The probability of the incorporation of G or g in Gg is 1/2 because there two possible ways “Gg or gG”... 1/4+1/4= 1/2 but not in the context of the total probability (4)= 1/4

– The probability of gg is 1/4. (1/2 x1/2)


Two rules of probabilityThe Multiplicative (Product) Rule If the events A and B are independent, the

probability that they will occur together, denoted P(A and B), is P(A) P(B).

States that the probability of two or more independent events occurring together is calculated by multiplying their independent probabilities

Example: probability of drawing the ace of hearts [an ace (A) AND a heart (H)], P(A and H)P(A) = 4/52 P(H) = 1/4

P(A) P(H) = 4/52 1/4 = 1/52

The Additive (Addition) Rule

If the events A and B are independent, the probability that at least one of them occurs, denoted P(A or B), is given by P(A) + P(B)

States that the probability of any one of two or or mutually exclusive events is calculated by adding their probabilities

Example: Probability of a drawing EITHER an ace OR a king, P(A or H)P(A) = 4/52 P(H) = 4/52P(A or H) = (4/52) (4/52) = 8/52



What is the change of zygote to be AA?1/2 x 1/2= 1/4

What is the change of zygote to be aa?1/2 x 1/2= 1/4

PhenotypeRecessive 1/4Dominant 1/2 +1/4=3/4


What fraction of progeny will be homozygous for all four recessive genes?

1/4 x 1/4 x 1/4 x 1/4= 1/256

What fraction of progeny will be homozygous for all four genes?

D and d

1/2 x 1/2 x 1/2 x 1/2= 1/16

Mathematical definition of probability

P: a/n

where a = the outcome of interest n = the number of possible outcomes.

Examples• P(getting a head on a coin toss) = 1/2• P(rolling a 1 on a die) = 1/6• P(drawing the ace of spades) = 1/54• P(dominant offspring from the cross Aa x Aa) = 3/4

• If P = 0, the event is impossible• P(rolling a 7 on a standard die) = 0

• If P = 1, the event is certain• P(rolling a number less than 10) = 1

Definition of binomial formula(hybrid-heterozygous)

P: n! ps qt

s!t!• n = total number of events• s = number of type A events• t = number of type B events• p = probability of type A event• q = probability of type B event• Always true: s + t = n, p + q = 1 ! Factorial

Example 3!= 3x2x1

Testing Genetic Hypotheses

Hypothesis: a well-formulated scientific idea

Data collected from observations or from experimentation enable scientists to test hypotheses.

Genetics: Are the results of a cross consistent with a hypothesis?


The Chi-Square Test

Predict Expected numbers based on hypothesis. Determine the degrees of freedom. (n-1: different

expected phenotype) Compare the 2 statistic to the critical value


Example:Mendel’s Dihybrid Cross



Example: A Dihybrid Cross with Campion (Hugo deVries)




P: 0.05%

Comparison to the Critical Value Mendel’s Dihybrid Cross:

2 = 0.51 Degrees of Freedom = 4 1 = 3 Critical Value = 7.815 Hypothesis?

DeVries’ Dihybrid Cross: 2 = 22.91 Degrees of Freedom = 4 1 = 3 Critical Value = 7.815 Hypothesis ?


Comparison to the Critical Value Mendel’s Dihybrid Cross:

2 = 0.51 Degrees of Freedom = 4 1 = 3 Critical Value = 7.815 Hypothesis is correct

DeVries’ Dihybrid Cross: 2 = 22.91 Degrees of Freedom = 4 1 = 3 Critical Value = 7.815 Reject the Hypothesis


Mendelian Principles in Human Genetics

Obstacles to Human Genetic Analysis– Incomplete family records– Small number of progeny– Uncontrolled environment

Despite these obstacles, many human genetic traits have been described.



Pedigree Conventions

Pedigrees are diagrams that show the relationships among the members of a family.


Inheritance of a Dominant Trait

Every individual who carries the dominant allele manifests the trait.

Every affected individual is expected to have at least one affected parent.

If a dominant trait is associated with reduced viability or fertility, most people who show the trait are heterozygous, and half their children should inherit the condition.


Inheritance of a Recessive Trait

Recessive traits may occur in individuals whose parents are not affected.


Mendelian Segregation in Human Families

Binomial probabilities: affected and unaffected

Definition of binomial formula

P: n! ps qt

s!t!• n = total number of events• s = number of type A events• t = number of type B events• p = probability of type A event• q = probability of type B event• Always true: s + t = n, p + q = 1 ! Factorial

Example 3!= 3x2x1

Genetic Counseling:

Non-polypoid Colorectal Cancer--dominant mode of the disease


Albinism--recessive mode of the disease


1/4 albinism3/4 no-diseaseExample 1: 3 children with diseaseP=(1/4)3=1/64Example 2: 3 children 1 with disease2 normalP= 3/2 (3/4)2 (1/4)=0.21Example 3:5 children 2 with disease3 normalP= 10 (3/4)3 (1/4) 2 =0.26

4093) A recessive trait is one that is:a) Masked by a dominant trait, if a dominant trait is present in the genotypeb) Not masked by any other trait present in the genotypec) Masked by another recessive trait, if another recessive trait is present in the Genotyped) All of thesee) None of these

5097) A monohybrid cross is one in which:a) Two traits are being studied at the same timeb) One trait is being studiedc) Two organisms are being studied at the same timed) One organism is being studiede) None of these

Answer: a

Answer: b


Determine P for :

1- Is R heterozygous carrier? 2/3

R ST

Documents

3823) Which of the following genes have been implicated in hereditary forms of breast cancer? BRCA1, b) BRCA2, c) RB, d) phMSH2, e) BRCA1 and BRCA2 1123)