Unit 10Unit 10GeneticsGenetics

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

Review Questions Review Questions 1. Give an example (not in the notes) of a human trait.1. Give an example (not in the notes) of a human trait.

examples: type of ears, tongue rolling, dimplesexamples: type of ears, tongue rolling, dimples2. What is a phenotype?2. What is a phenotype?

the physical expression of the trait, ex brown the physical expression of the trait, ex brown eyeseyes

3. From where did you get each of the chromosomes in 3. From where did you get each of the chromosomes in the homologous pair?the homologous pair?

One is inherited from the sperm and one is One is inherited from the sperm and one is inherited from the egginherited from the egg

4. What is an allele?4. What is an allele? different versions of the same traitdifferent versions of the same trait

5. What is a genotype? 5. What is a genotype? the combination of alleles present in an the combination of alleles present in an

organism’s chromosomesorganism’s chromosomes ex. AA, Aa or aa ex. AA, Aa or aa

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

1.1. Using statistical analysis and the Using statistical analysis and the scientific method, scientific method, Mendel uncovered predictable Mendel uncovered predictable patterns of inheritance in pea plantspatterns of inheritance in pea plants. He is . He is responsible for responsible for developing the basic principles of developing the basic principles of inheritanceinheritance. Luckily, . Luckily, pea plants were a good pea plants were a good choicechoice because they have traits in only two because they have traits in only two contrasting forms (green seeds or yellow seeds), contrasting forms (green seeds or yellow seeds), they are capable of self and cross pollination, they are capable of self and cross pollination, and each individual plant can quickly produce and each individual plant can quickly produce multiple offspring. multiple offspring.

2.2. Mendel’s three principles of inheritance:Mendel’s three principles of inheritance:a.a. The The principle of dominanceprinciple of dominance

i.i. 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 alleles and are

represented represented by a by a capital lettercapital letter (A). The (A). The alleles that may alleles that may be hidden are called recessive be hidden are called recessive allelesalleles and and are represented by the are represented by the lower case of lower case of the the same lettersame letter (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 (aa) individuals will express the recessive (aa) individuals will express the recessiverecessive phenotype. phenotype.

ii.ii. Mendel discovered this relationship when Mendel discovered this relationship when he noted that he noted that certain traits tended to skip certain traits tended to skip generationsgenerations and that sometimes two green and that sometimes two green seeded plants would produce yellow seeded plants would produce yellow seeded offspring in small proportions. seeded offspring in small proportions.

b.b.The The principle of segregationprinciple of segregation

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

ii.ii. Mendel noticed when he crossed a green Mendel noticed when he crossed a green seeded plant with a yellow seeded plant all seeded plant with a yellow seeded plant all offspring were green seeded offspring were green seeded (dominance). However, the yellow seeded (dominance). However, the yellow seeded allele had not disappeared entirely allele had not disappeared entirely because when two of these green seeded because when two of these green seeded offspring mated some of the offspring were offspring mated some of the offspring were yellow seeded. yellow seeded. This proved each parent This proved each parent had donated genes to the offspring for had donated genes to the offspring for each traiteach trait..

c.c. The principle of The principle of independent assortmentindependent assortment

i.i. A gene for one trait is only passed in A gene for one trait is only passed in connection with a gene for a different trait if the connection with a gene for a different trait if the two genes are on the same chromosome. two genes are on the same chromosome. Genes on separate chromosomes are passed Genes on separate chromosomes are passed independently of each otherindependently of each other. .

ii.ii. Mendel crossed plants with two sets of Mendel crossed plants with two sets of contrasting traits (seed color and seed shape). contrasting traits (seed color and seed shape). He suspected that the two traits would be He suspected that the two traits would be inherited independently of each other. inherited independently of each other. Statistically, he verified his hypothesisStatistically, he verified his hypothesis. .

Review QuestionsReview Questions1.1. Why is it fortunate Mendel choose pea plants Why is it fortunate Mendel choose pea plants

to study? to study? they have traits in only two contrasting they have traits in only two contrasting

forms (green seeds or yellow seeds), they are forms (green seeds or yellow seeds), they are capable of self and cross pollination, and each capable of self and cross pollination, and each individual plant can quickly produce multiple individual plant can quickly produce multiple offspringoffspring

2. Name Mendel’s three principles of heredity:2. Name Mendel’s three principles of heredity:Principle of dominancePrinciple of dominancePrinciple of segregationPrinciple of segregationPrinciple of independent assortmentPrinciple of independent assortment

3. What process allows the principle of 3. What process allows the principle of segregation to take place? segregation to take place?

The of principle of meiosisThe of principle of meiosis

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.

Review Questions:Review Questions:

1. Are genes “nature” or “nurture”? 1. Are genes “nature” or “nurture”?

Both nature (what you inherit) and Both nature (what you inherit) and nurture (the things you are exposed to) nurture (the things you are exposed to) effect your gene expressioneffect your gene expression

2. How can the environment affect genes?2. How can the environment affect genes?

by chemically interacting with DNA by chemically interacting with DNA or the cell, or by limiting available or the cell, or by limiting available resources the organism requires to resources the organism requires to express the geneexpress the gene

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 trait) (form of the trait) a lettera letter. .

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

Step a: Tongue rolling – R ; Non-rolling – rStep a: Tongue rolling – R ; Non-rolling – r

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

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

Step b: Parent 1 – Step b: 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.

Step c: Step c: 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 short pea Problem: Tall pea plant height is dominant to short pea

plant height. Cross a pure breeding tall pea plant with a pure plant height. Cross a pure breeding tall pea plant with a pure breeding short pea plant. Give the genotypic and phenotypic ratio. breeding short pea plant. Give the genotypic and phenotypic 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 HhHh

hh HhHh HhHhe.e. Genotypic ratio: Genotypic ratio: HH , Hh, hhHH , Hh, hh 0 : 4 : 00 : 4 : 0

Phenotypic ratio: Phenotypic ratio: tall , shorttall , short 4 : 04 : 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

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 are Problem: Black feathers and white feathers are codominant in chickens. Cross a chicken with 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 they only black feathers. What is the chance they will have a chick with only white feathers?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 , Parent 2 – 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 multiple

alleles: IA, IB, i. In addition, IA and IB are alleles: IA, IB, i. In addition, IA and IB are codominant, while codominant, while

i is recessive to both. Below is a chart i is recessive to both. Below is a chart representing all the possible genotypes and representing all the possible genotypes and resulting phenotypes. resulting phenotypes.

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

Type AType A IAIA or IAi IAIA or IAi

Type BType B IBIB or IBi IBIB or IBi

Type ABType AB IAIB IAIB

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 – IAi, Parent 2 – iia/b Parent 1 – IAi, 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:

Number of Individuals

Review Questions: 1. Name the five paths of non-mendelian inheritance.

incomplete dominance, co-dominance, sex linked, multiple alleles, and polygenic inheritance

2. Which pattern of inheritance results in a third, blended phenotype in heterozygous individuals?

incomplete dominance3. What two patterns of inheritance does human blood type

follow? Codominance and multiple alleles4. Where are sex-linked traits located?

On the X chromosome5.Name three traits that follow polygenic inheritance. Height, skin color, and size of your foot