Unit 3: DNA and GeneticsUnit 3: DNA and Genetics

Module 8: GeneticsModule 8: Genetics

I.I. How are traits passed from parent to How are traits passed from parent to offspring?offspring?

A.A. TraitsTraits

1.1. Traits are physical or Traits are physical or physiological characteristics of an physiological characteristics of an organismorganism. .

Ex. Ex. height or blood typeheight or blood type

2.2. The term The term phenotypephenotype is used to is used to describe the physical expression of the describe the physical expression of the traittrait. .

Ex. short/tall or Type A/Type BEx. short/tall or Type A/Type B

B.B.Chemical basis of traitsChemical basis of traits

1.1. DNADNA is the molecule that is the molecule that contains the contains the information to make proteins, which control our information to make proteins, which control our traitstraits. .

2.2. A section of DNA that is used to make a A section of DNA that is used to make a protein is called a geneprotein is called a gene. There are many genes . There are many genes (hundreds) on a single chromosome. (hundreds) on a single chromosome.

3.3. Eukaryotic organism’s Eukaryotic organism’s chromosomes exist chromosomes exist in pairs. One is inherited from the sperm and in pairs. One is inherited from the sperm and one is inherited from the egg. Each one is inherited from the egg. Each chromosome, in a pair, contains genes for the chromosome, in a pair, contains genes for the same traits. This is why we call them same traits. This is why we call them homologous pairshomologous pairs. .

4.4. Although the genes on homologous Although the genes on homologous chromosomes may code for the same trait, chromosomes may code for the same trait, slight slight differences in the DNA sequences may lead to differences in the DNA sequences may lead to different forms of the proteindifferent forms of the protein. This creates . This creates slightly different versions of the same trait. slightly different versions of the same trait. Each Each version is called an alleleversion is called an allele. .

Ex. Blue and brown are two alleles of the Ex. Blue and brown are two alleles of the eye color trait.eye color trait.

5.5. GenotypeGenotype is the term used to is the term used to describe the describe the combination of alleles present in an organism’s combination of alleles present in an organism’s chromosomeschromosomes. An allele is usually represented . An allele is usually represented by a by a single lettersingle letter. Thus, a . Thus, a genotypegenotype is usually is usually represented by represented by two letterstwo letters. .

a.a. If an individual inherits If an individual inherits identical identical copiescopies from each parent the individual is from each parent the individual is considered considered homozygoushomozygous (pure breeding). (pure breeding).

Ex. Ex. AA, aaAA, aa

b.b. If an individual inherits a If an individual inherits a different copydifferent copy from each parent the from each parent the individual is considered individual is considered heterozygousheterozygous (hybrid). (hybrid).

Ex. Ex. AaAa

II.II. How was the path of inheritance discovered in a How was the path of inheritance discovered in a garden in Austria?garden in Austria?

A.A. Gregor Mendel – The Gregor Mendel – The father of geneticsfather of genetics – – using using pea plantspea plants, Mendel , Mendel proved experimentally proved experimentally the link between meiosis, genes, and inheritance the link between meiosis, genes, and inheritance (long before we knew about DNA!). He (long before we knew about DNA!). He developed 3 basic conclusions:developed 3 basic conclusions:

1.1. The The principle of dominanceprinciple of dominance

Certain allelesCertain alleles (forms of a trait) (forms of a trait) can can hide/mask other alleleshide/mask other alleles. These alleles are . These alleles are called called dominantdominant alleles and are represented alleles and are represented by by a a capital lettercapital letter (A). The (A). The alleles that may alleles that may be be hidden are called recessive alleleshidden are called recessive alleles and and are are represented by the represented by the lower case of the lower case of the same same letterletter (a). Thus, homozygous (a). Thus, homozygous dominant is dominant is AAAA and will express the and will express the dominantdominant phenotype. Heterozygous phenotype. Heterozygous individuals are individuals are AaAa and will also express the and will also express the dominantdominant phenotype. Only homozygous phenotype. Only homozygous recessive recessive (aa) individuals will express the (aa) individuals will express the recessiverecessive phenotype. phenotype.

2.2.The The principle of segregationprinciple of segregation

Alleles are not passed in pairs from one Alleles are not passed in pairs from one parent to an offspring. parent to an offspring. Each parent only Each parent only donates half of each offspring’s genotypedonates half of each offspring’s genotype (typically one allele per trait). This is (typically one allele per trait). This is because because during meiosis only one of each during meiosis only one of each homologous pair of chromosomes is homologous pair of chromosomes is passed to the gametepassed to the gamete (sperm or egg). (sperm or egg).

3.3. The principle of The principle of independent assortmentindependent assortment

The way one pair of chromosomes is separated The way one pair of chromosomes is separated during meiosis does not affect the way the next during meiosis does not affect the way the next pair separates. A gene for one trait is only pair separates. A gene for one trait is only passed in connection with a gene for a different passed in connection with a gene for a different trait if the two genes are on the same trait if the two genes are on the same chromosome. chromosome. Genes on separate Genes on separate chromosomes are passed independently of each chromosomes are passed independently of each otherother. .

III.III. Does the environment affect the traits of Does the environment affect the traits of organisms? organisms?

A.A. Nature vs. NurtureNature vs. Nurture

1.The 1.The environment does influence environment does influence the expression of genesthe expression of genes by chemically by chemically interacting with DNA or the cell, or by interacting with DNA or the cell, or by limiting available resources the organism limiting available resources the organism requires to express the gene.requires to express the gene.

Ex. The gene for the dark pigment Ex. The gene for the dark pigment (protein) for coat color in Siamese cats (protein) for coat color in Siamese cats is activated by colder temperaturesis activated by colder temperatures

2.2. Environmental hazards can create Environmental hazards can create genetic mutationsgenetic mutations, turning off or altering the , turning off or altering the expression of a gene. These hazards are expression of a gene. These hazards are called called mutagensmutagens. .

Ex. Many environmental toxins mimic Ex. Many environmental toxins mimic human hormones such as estrogen human hormones such as estrogen and and therefore inhibit the production of therefore inhibit the production of that that hormone by the cells. hormone by the cells.

B.B. Identical twins are often used to study the Identical twins are often used to study the effects of the environment on gene expressioneffects of the environment on gene expression. . This is because identical twins have identical This is because identical twins have identical genes but are often exposed to different genes but are often exposed to different environments. environments.

Twins: Is it All in the Genes? - Our America with Lisa Ling - Oprah Winfrey Network - YouTubeTwins: Is it All in the Genes? - Our America with Lisa Ling - Oprah Winfrey Network - YouTube

C. There is a cause-and-effect relationship between environmental factors and expression of a particular genetic trait:

1.Lung/mouth cancer is linked to tobacco use. All tobacco products contain toxins and carcinogens. Carcinogens can change the DNA, causing uncontrolled division (cancer).

2. Skin cancer, sun exposure, vitamin D production, and folic acid share a complex relationship.

a. Skin cancer is directly linked to sun exposure. UV rays mutate the DNA, causing cancer. b.When absorbed by the skin, sunlight also destroys folate (folic acid). Folic acid is key to DNA repair of mutations (like those caused by the sun). Folic acid deficiency is a contributor to skin cancer risks. Folic acid can be supplemented with food or vitamins. c.However, sun exposure is also one of the ways our body can gain vitamin D, a vitamin that helps protect us from heart disease among other health benefits. When the sun’s UV-B rays hit the sun, it causes a chemical reaction that produces vitamin D. You only need about 10 minutes of exposure a day, at most, and can also supplement with food and vitamin pills.

3. Diabetes (especially Type 2 Diabetes) is linked to diet/exercise with genetic interaction. It is possible to delay or prevent type 2 diabetes by exercising and losing weight, even if there is a strong family history.

4. Heart disease is also linked to diet/exercise with genetic interaction. Different genes or gene combinations respond differently to changes in diet, health choices such as smoking, and exercise. So far, 40 or more genes have been identified that are linked to cardiovascular health.

IV.IV. How can I predict the appearance of offspring How can I predict the appearance of offspring based on the traits of the parents?based on the traits of the parents?A.A. Two kinds of inheritanceTwo kinds of inheritance

1.1.Mendelian inheritanceMendelian inheritance includes any includes any trait trait which has only a which has only a pair of contrasting pair of contrasting alleles alleles and one of the alleles is dominant and one of the alleles is dominant to the to the other alleleother allele. These traits will follow . These traits will follow Mendel’s Mendel’s principles of heredity. principles of heredity.

2.2.Non-Mendelian inheritanceNon-Mendelian inheritance includes includes

traits traits which may which may share dominance, be linked share dominance, be linked with with a second traita second trait (such as sex), (such as sex), rely on rely on multiple multiple genes within the chromosomes, or genes within the chromosomes, or have have multiple formsmultiple forms (alleles) which may be (alleles) which may be

inherited. These traits do not follow all inherited. These traits do not follow all of of Mendel’s principles of inheritance. Mendel’s principles of inheritance.

B.B. Probability and InheritanceProbability and Inheritance

1. Punnett developed a 1. Punnett developed a graphical method graphical method to predict the results of a crossto predict the results of a cross between between two parent organisms. These are called two parent organisms. These are called Punnett squaresPunnett squares. A Punnett square . A Punnett square shows all of the possible outcomes each shows all of the possible outcomes each time gametes from the two parents time gametes from the two parents combinecombine. .

punnetsquarespunnetsquares

2.2. Steps to solving a Punnett square:Steps to solving a Punnett square:

a.a. Assign each alleleAssign each allele (form of the (form of the trait) trait) a lettera letter. .

Problem: Tongue rolling is dominant to non-rolling. Problem: Tongue rolling is dominant to non-rolling.

Tongue rolling – R ; Non-rolling – rTongue rolling – R ; Non-rolling – r

b.b. Determine the genotype of each Determine the genotype of each parentparent based on the information in based on the information in the problem.the problem.

Problem: Cross two heterozygous individuals. Problem: Cross two heterozygous individuals.

Parent 1 – Parent 1 – RrRr ; Parent 2 – ; Parent 2 – RrRr

c.c. Set up the Punnett square by putting one Set up the Punnett square by putting one parent’s genotype across the top and the parent’s genotype across the top and the other down the side of the squareother down the side of the square. . These represent possible gametes. These represent possible gametes.

RR rr

RR

rr

d.d. Complete the Punnett squareComplete the Punnett square by by recording the letter on top of the column recording the letter on top of the column and on the side of the row. Always put and on the side of the row. Always put the capital letter first. the capital letter first.

RR r r

R RRR RR Rr Rr

r Rrr Rr rr rr

e.e. Use the laws of probability and the Use the laws of probability and the Punnett square to Punnett square to answer any question answer any question posed in the problemposed in the problem. . Problem 1: What is the genotype ratio? Problem 1: What is the genotype ratio? Answer: 1 Answer: 1 RR, 2 Rr, 1 rrRR, 2 Rr, 1 rr

1 : 2 : 11 : 2 : 1Problem 2: What is the phenotype ratio?Problem 2: What is the phenotype ratio?Answer: Answer: 3 Tongue rolling , 1 Non-rolling3 Tongue rolling , 1 Non-rolling

3 : 13 : 1Problem 3: What is the chance the Problem 3: What is the chance the

couple will have a non-rolling child? couple will have a non-rolling child? Answer: Answer: 1 / 4 or 25%1 / 4 or 25%

3.3. Punnett squares can be used to solve Punnett squares can be used to solve crosses involving only crosses involving only one traitone trait (called a (called a monohybridmonohybrid cross) or crosses involving cross) or crosses involving two traitstwo traits (called a (called a dihybriddihybrid cross). The cross). The monohybrid cross requires four squares monohybrid cross requires four squares to represent all possible gamete to represent all possible gamete combinations. The dihybrid cross combinations. The dihybrid cross requires sixteen squares to represent all requires sixteen squares to represent all possible gamete combinations.possible gamete combinations.

V.V. What are the different patterns of inheritance? What are the different patterns of inheritance? A.A. Mendelian/simple dominanceMendelian/simple dominance

1.1. MonohybridMonohybridProblem: Tall pea plant height is dominant to Problem: Tall pea plant height is dominant to

short short pea plant height. Cross a pure pea plant height. Cross a pure breeding tall breeding tall pea plant with a pure breeding pea plant with a pure breeding short pea short pea plant. Give the genotypic and plant. Give the genotypic and phenotypic phenotypic ratio. ratio. Solution: Solution: a. Tall – a. Tall – HH , short - , short - hhb. Parent 1 – b. Parent 1 – HHHH , Parent 2 – , Parent 2 – hhhhc/d. c/d. HH HH

hh HhHh Hh Hh

hh HhHh HhHh

e. Genotypic ratio: HH , Hh, hh 0 : 4

: 0Phenotypic ratio: tall , short

4 : 0

Paths of InheritancePaths of InheritancePath TypePath Type CharacteristicsCharacteristics

MendelianMendelian 1 allele is dominant and 1 allele 1 allele is dominant and 1 allele is recessiveis recessive

CodominantCodominant 2 alleles – both are equally 2 alleles – both are equally expressedexpressed

Incomplete Incomplete dominancedominance

2 alleles – if heterozygous, 2 alleles – if heterozygous, alleles blend togetheralleles blend together

Multiple allelesMultiple alleles More than 2 alleles possible for More than 2 alleles possible for a trait (but each person gets 2)a trait (but each person gets 2)

PolygenicPolygenic A traits is controlled by more A traits is controlled by more than one gene in a personthan one gene in a person

2.2. DihybridDihybridProblem: In guinea pigs black fur is dominant to white fur and Problem: In guinea pigs black fur is dominant to white fur and rough fur is dominant to smooth fur. Cross two heterozygous rough fur is dominant to smooth fur. Cross two heterozygous black, rough guinea pigs. Give the phenotypic ratio. black, rough guinea pigs. Give the phenotypic ratio.

a.a. Black fur – Black fur – BB, white fur – , white fur – bb Rough fur – Rough fur – RR, smooth fur - , smooth fur - rrb.b. Parent 1 – Parent 1 – BbRrBbRr, Parent 2 - , Parent 2 - BbRrBbRr

c/dc/d BR BR Br Br bR bR br br

BBRR BBRr BbRR BBRR BBRr BbRR BbRrBbRr

BBRrBBRr BBrrBBrr BbRr Bbrr BbRr Bbrr

BbRR BbRr BbRR BbRr bbRRbbRR bbRr bbRr

BbRrBbRr Bbrr Bbrr bbRr bbRr bbrrbbrr

e. e. Black, rough: Black, smooth: White, rough: White, smoothBlack, rough: Black, smooth: White, rough: White, smooth 9 :9 : 3 : 3 : 3 : 3 : 1 1

BRBR

BrBr

bRbR

brbr

B.B. Non-mendelian – 5 possible paths of Non-mendelian – 5 possible paths of inheritanceinheritance

1.1. CodominanceCodominance – Both alleles are – Both alleles are equally dominantequally dominant and so both are and so both are equally equally expressedexpressed. To represent the equal dominance . To represent the equal dominance each allele is assigned a each allele is assigned a different capital letterdifferent capital letter. . Problem: Black feathers and white feathers Problem: Black feathers and white feathers are codominant in chickens. Cross a chicken are codominant in chickens. Cross a chicken with black and white feathers and a chicken with black and white feathers and a chicken with only black feathers. What is the chance with only black feathers. What is the chance they will have a chick with only white feathers?they will have a chick with only white feathers?a.a. Black Feathers – Black Feathers – BB, White Feathers – , White Feathers – WWb.b. Parent 1 (black and white) – Parent 1 (black and white) – BWBW, ,

Parent 2 – Parent 2 – BBBB

c/dc/d BB WW

BBBB BWBW

BBBB BWBW

e. e. 0% chance of chick with white feathers0% chance of chick with white feathers

BB

BB

2. 2. Incomplete dominanceIncomplete dominance – – Neither allele is Neither allele is sufficiently dominantsufficiently dominant to mask the other to mask the other allele. When both alleles are present in allele. When both alleles are present in an individual’s genotype (an individual’s genotype (heterozygousheterozygous) ) an entirely different, an entirely different, blended phenotypeblended phenotype appears. To represent the incomplete appears. To represent the incomplete dominance both share the same capital dominance both share the same capital letter, but one is assigned a “letter, but one is assigned a “primeprime” ” symbol. symbol.

Problem: In four o’clock flowers red petals and Problem: In four o’clock flowers red petals and white petals are incompletely dominant. Cross white petals are incompletely dominant. Cross a red flower and a white flower. What is the a red flower and a white flower. What is the resulting phenotype of all offspring? resulting phenotype of all offspring?

a.a. Red – Red – RR, White – , White – RR’’

b.b. Parent 1 (Red) – Parent 1 (Red) – RRRR, Parent 2 – , Parent 2 – R’RR’R’’

c/d c/d RR RR

RRRR’ ’ RRRR’’

RRRR’ ’ RRRR’’

e. e. All offspring are pinkAll offspring are pink..

RR’’

RR’’

3.3. Multiple AllelesMultiple Alleles – – More than two alleles existMore than two alleles exist within the population for the given trait. within the population for the given trait. However, However, each individual may only inherit twoeach individual may only inherit two of the possible alleles. To represent the of the possible alleles. To represent the multiple alleles a multiple alleles a base letterbase letter is used for each is used for each allele and the allele is represented by a unique allele and the allele is represented by a unique superscriptsuperscript letter. letter.

Problem: Blood type in humans is determined by Problem: Blood type in humans is determined by multiple alleles: IA, IB, i. In addition, IA and multiple alleles: IA, IB, i. In addition, IA and IB are codominant, while i is recessive to both. IB are codominant, while i is recessive to both. Below is a chart representing all the possible Below is a chart representing all the possible genotypes and resulting phenotypes. genotypes and resulting phenotypes.

Blood Type (Phenotype)Blood Type (Phenotype) Possible GenotypesPossible Genotypes

Type AType A I IAAIIAA or I or IAAii

Type BType B I IBBIIBB or I or IBBii

Type ABType AB I IAAIIBB

Type OType O ii ii

Cross a heterozygous Type A female with a Type Cross a heterozygous Type A female with a Type O male. What are all the possible blood types O male. What are all the possible blood types of the offspring?of the offspring?

a/b Parent 1 – Ia/b Parent 1 – IAAi, Parent 2 – iii, Parent 2 – iic/dc/d

IIAA ii

IIAAii ii ii

IIAAii ii ii

e. Type A and Type O are the possible blood e. Type A and Type O are the possible blood types.types.

i

i

4. 4. Sex-linkageSex-linkage – One of the pairs of chromosomes – One of the pairs of chromosomes in an organism determines the sex. This pair in an organism determines the sex. This pair is called the sex chromosomes. In humans is called the sex chromosomes. In humans the the two types of sex chromosomes are two types of sex chromosomes are represented by an X and a Yrepresented by an X and a Y. Inheriting . Inheriting two Xtwo X chromosomes makes a chromosomes makes a femalefemale; inheriting an ; inheriting an X X and a Yand a Y chromosome makes a chromosome makes a malemale. . The The genes located on a sex chromosomegenes located on a sex chromosome (almost (almost always the X chromosome) are called always the X chromosome) are called sex-sex-linked geneslinked genes. Thus, . Thus, females inherit two alleles females inherit two alleles for the trait while males only inherit one allele for the trait while males only inherit one allele for the traitfor the trait. .

Problem: Colorblindness is a recessive sex-linked Problem: Colorblindness is a recessive sex-linked trait. A colorblind man has a child with a trait. A colorblind man has a child with a woman who is a carrier (heterozygous) for woman who is a carrier (heterozygous) for colorblindness. What is the chance they will colorblindness. What is the chance they will have a colorblind son? have a colorblind son?

a.a. “Normal” vision – “Normal” vision – XXBB, Colorblind - , Colorblind - XXbb

b.b. Parent 1 – Parent 1 – XXbbYY, Parent 2 - , Parent 2 - XXBBXXbb

c/dc/d XbXb YY

XXBBXXb b XXBBYY

XXbbXXbb XXbbYY

e. e. There is a 25% chance they will have a There is a 25% chance they will have a colorblind soncolorblind son

XXBB

XXbb

5. 5. PolygenicPolygenic inheritance – Many traits inheritance – Many traits actually actually depend on several genesdepend on several genes. The . The interaction of the many genes within one interaction of the many genes within one individual individual creates a range of phenotypescreates a range of phenotypes. . For example For example height, skin color and the height, skin color and the size of your footsize of your foot depend on the total depend on the total number of dominant alleles inherited for number of dominant alleles inherited for these traits. This means someone with these traits. This means someone with four dominant alleles will have a slightly four dominant alleles will have a slightly bigger foot than someone with three bigger foot than someone with three dominant alleles. This results in a dominant alleles. This results in a characteristic graphical patterncharacteristic graphical pattern seen seen below: below: