GeneticsGenetics GeneticsGenetics is the scientific study is the scientific study

of heredity.of heredity.

Gregor Mendel born in 1822 Gregor Mendel born in 1822 was an Austrian monk who first was an Austrian monk who first formed the basic laws of formed the basic laws of heredity during the mid-1800’s. heredity during the mid-1800’s. He is credited with advancing He is credited with advancing the study of genetics through his the study of genetics through his good fortune, scientific method, good fortune, scientific method, careful record keeping and careful record keeping and application of mathematics to application of mathematics to biological studies.biological studies.

Mendel is known as the “ The Mendel is known as the “ The Father of Genetics” because his Father of Genetics” because his work laid the foundation to the work laid the foundation to the study of heredity.study of heredity.

The Good FortuneThe Good Fortune Mendel inherited a purebred stock of peas that produced identical Mendel inherited a purebred stock of peas that produced identical

offspring as a result of self pollination of pea plants. (male and female offspring as a result of self pollination of pea plants. (male and female parts on the same plant)parts on the same plant)

Mendel based his laws on his studies of the garden peas and was able Mendel based his laws on his studies of the garden peas and was able to observe differences in multiple traits over many generations to observe differences in multiple traits over many generations because pea plants reproduce rapidlybecause pea plants reproduce rapidly

He chose to study seven traits with just two contrasting characters He chose to study seven traits with just two contrasting characters (as opposed to intermediate forms)(as opposed to intermediate forms)

Good ScienceGood Science(Tall plants used as an example)(Tall plants used as an example)

Mendel noticed that some plants Mendel noticed that some plants always produced offspring that always produced offspring that had a form of a trait exactly like had a form of a trait exactly like the parent plant. He called these the parent plant. He called these plants “plants “purebredpurebred” plants.” plants.

Mendel cross pollinated purebred Mendel cross pollinated purebred plants with opposite forms of a plants with opposite forms of a trait. He called these plants the trait. He called these plants the parental generationparental generation; or ; or P P generation.generation.

He called the offspring the He called the offspring the F1 F1 generation; or first filial and he generation; or first filial and he observed that they were all tall, as observed that they were all tall, as if short trait had disappeared.if short trait had disappeared.

Good ScienceGood Science(Tall plants used as an example)(Tall plants used as an example)

Since the F1 offspring plants received Since the F1 offspring plants received one tall and one short gene from the one tall and one short gene from the parents plants then they are said to be parents plants then they are said to be ““hybridhybrid” for that trait. (But why were ” for that trait. (But why were all the F1 plants tall if they had all the F1 plants tall if they had inherited one tall gene and one short inherited one tall gene and one short gene?)gene?)

Mendel then crossed two of the Mendel then crossed two of the offspring tall plants produced in the F1 offspring tall plants produced in the F1 generation.generation.

He called this second generation of He called this second generation of plants the second filial; or F2 plants the second filial; or F2 generation.generation.

To his surprise he observed that this To his surprise he observed that this generation had a mix of tall and short generation had a mix of tall and short plants even though none of the F1 plants even though none of the F1 parents were short.parents were short.

Mendel’s Law of SegregationMendel’s Law of Segregation

Mendel’s first law, the Mendel’s first law, the Law of SegregationLaw of Segregation, has three parts. , has three parts. From his experiments he concluded:From his experiments he concluded:

1.1. Plant traits are handed down through “Plant traits are handed down through “hereditary hereditary factorsfactors” ” in the sperm and egg. in the sperm and egg.

2.2. Because offspring obtain hereditary factors from both Because offspring obtain hereditary factors from both parents, each plant must contain two factors for every parents, each plant must contain two factors for every trait.trait.

3.3. The factors in a pair segregate (separate) during the The factors in a pair segregate (separate) during the formation of sex cells (meiosis), and each sperm or egg formation of sex cells (meiosis), and each sperm or egg receives only one member of the pair.receives only one member of the pair.

We now call the “hereditary factors” We now call the “hereditary factors” genesgenes..

Dominant and Recessive GenesDominant and Recessive Genes In the first experiment when In the first experiment when

Mendel crossed a purebred tall Mendel crossed a purebred tall with a purebred short, all the with a purebred short, all the offspring were tall.offspring were tall.

Mendel reasoned that one factor Mendel reasoned that one factor (gene) in a pair may mask, or hide, (gene) in a pair may mask, or hide, the other factor. the other factor.

Although the F1 offspring all had Although the F1 offspring all had both tall and short factors, they both tall and short factors, they only displayed the tall factoronly displayed the tall factor

He concluded that the tallness He concluded that the tallness factor masked the shortness factor.factor masked the shortness factor.

Today scientists refer to factors that control traits as Today scientists refer to factors that control traits as genesgenes..

The different forms of a gene are called The different forms of a gene are called allelesalleles.. Dominant allelesDominant alleles are the alleles that mask or hide are the alleles that mask or hide

other alleles, such as the tall allele.other alleles, such as the tall allele. Recessive allelesRecessive alleles, such as the short allele, that are , such as the short allele, that are

masked, or covered up (hidden), whenever the masked, or covered up (hidden), whenever the dominant allele is present.dominant allele is present.

Mendel’s Mendel’s Principle of dominancePrinciple of dominance states that one states that one factor in a pair may prevent the other from being factor in a pair may prevent the other from being expressed. The expressed. The dominantdominant gene masks the expression gene masks the expression of the of the recessiverecessive gene. gene.

Dominant and Recessive Genes, cont.Dominant and Recessive Genes, cont.

P generation plants in this experiment were both P generation plants in this experiment were both purebreds with the same type of genepurebreds with the same type of gene

TT (tall ) and tt (short)TT (tall ) and tt (short) Capital letter of the dominant trait is used for the Capital letter of the dominant trait is used for the

dominant factor and the lower case letter is used for dominant factor and the lower case letter is used for the recessive traitthe recessive trait

The purebred dominant is called The purebred dominant is called homozygous dominant-TT homozygous dominant-TT The pure bred recessive is called The pure bred recessive is called homozygous recessive- tthomozygous recessive- tt The F1 plants in this study had one factor from each The F1 plants in this study had one factor from each

purebred parent and are called purebred parent and are called heterozygousheterozygous - Tt or - Tt or hybrid hybrid

To explain the expression of traits in the F2 plants To explain the expression of traits in the F2 plants Mendel developed two more principalsMendel developed two more principals

The principle of segregation states that the members The principle of segregation states that the members of each pair of genes separates ,or segregate, when of each pair of genes separates ,or segregate, when gametes are formedgametes are formed

The principle of independent assortment states that The principle of independent assortment states that two or mores pairs of genes segregate independently two or mores pairs of genes segregate independently of one another during the formation of gametes.of one another during the formation of gametes.

The process of meiosis is the mechanism for these The process of meiosis is the mechanism for these principlesprinciples

More TermsMore Terms Allele Allele is the term used to describe either member of a pair of is the term used to describe either member of a pair of

genes that determines a single trait.genes that determines a single trait. T is the dominant alleleT is the dominant allele t is the recessive allelet is the recessive allele GGenotype is the genetic makeup of the organism. It’s gene-enotype is the genetic makeup of the organism. It’s gene-

type (type (ggenes it received)enes it received) PPhenotype is the trait that’s actually expressed in an henotype is the trait that’s actually expressed in an

organism’s appearance. (organism’s appearance. (pphysical appearance)hysical appearance)

I t is important to note that Mendel made all I t is important to note that Mendel made all his observations, developed his experimental his observations, developed his experimental methods and mathematical conclusions before methods and mathematical conclusions before detailed knowledge of cell structure and detailed knowledge of cell structure and division had been discovered .division had been discovered .

Genetics and ProbabilityGenetics and Probability ProbabilityProbability – is the likelihood that – is the likelihood that

a particular event will occur.a particular event will occur. Example: If you flip a coin it may Example: If you flip a coin it may

land heads up or tails up. The land heads up or tails up. The chance, or probability, of either chance, or probability, of either outcome are equal. Therefore, the outcome are equal. Therefore, the probability that a single coin flip will probability that a single coin flip will come up heads is 1 chance in 2 , that come up heads is 1 chance in 2 , that is ½ , or 50%. is ½ , or 50%.

If you flip the coin 3 times in a row If you flip the coin 3 times in a row the probability each time is still ½ the probability each time is still ½ So ½ X ½ X ½ = 1/8So ½ X ½ X ½ = 1/8

The The principles of probabilityprinciples of probability can can be used to predict the outcomes of be used to predict the outcomes of genetic crosses.genetic crosses.

Punnett SquarePunnett Square

Developed in the early Developed in the early 1900’s by Reginald 1900’s by Reginald Punnett, the Punnett Punnett, the Punnett square is a useful tool square is a useful tool in visualizing the in visualizing the outcome of various outcome of various types of gene types of gene combinations.combinations.

Monohybrid Cross

A A monohybridmonohybrid cross is cross is one involving just one one involving just one traittrait

A A dihybriddihybrid cross cross involves two traitsinvolves two traits

In a test cross the In a test cross the unknown genotypeunknown genotype of a dominant of a dominant phenotype can be phenotype can be determined by determined by crossing it with a crossing it with a homozygous homozygous recessiverecessive (recessive (recessive phenotype)phenotype)

Genetics and ProbabilityGenetics and Probability

The The genotypicgenotypic ratio for the F2 ratio for the F2 offspring is just offspring is just like our coins like our coins 1:2:11:2:1

The The phenotypicphenotypic ratio is 3:1ratio is 3:1

Genetics and ProbabilityGenetics and Probability

The The phenotypicphenotypic ratio for the F2 offspring in a ratio for the F2 offspring in a dihybriddihybrid cross is 9:3:3:1 cross is 9:3:3:1

Steps To Working Genetic CrossesSteps To Working Genetic Crosses

1. Set up A Legend1. Set up A Legend 2. Set-up Parental Genotype.2. Set-up Parental Genotype. 3. Construct a Punnett 3. Construct a Punnett

SquareSquare 4. Align Parentals Genotype4. Align Parentals Genotype 5. Fill in Punnett Square.5. Fill in Punnett Square. 6. Record Results. 6. Record Results.

1.) Setting Up A Legend1.) Setting Up A Legend

A legend is an explanatory list of the A legend is an explanatory list of the symbols on a map or chart symbols on a map or chart

Setting Up A LegendSetting Up A Legend

Your legend for genetic Your legend for genetic crosses will show both crosses will show both the phenotype and the phenotype and genotype.genotype.

The The PhPhenotype enotype ((PhPhysical appearance) ysical appearance) will be on the left. will be on the left.

The The GeGenotype (notype (gegenetic netic make-up) will be on the make-up) will be on the right.right.

Tall = TT TtTall = TT Tt Short = ttShort = tt (phenotype) (genotype)(phenotype) (genotype)

oror

Red = RR RrRed = RR Rr White = rrWhite = rr

2.) Set-up2.) Set-up parental genotypesparental genotypes

WWrite down your rite down your "cross"(mating)."cross"(mating).    Write the Write the genotypes of the genotypes of the parents in the parents in the form of letters form of letters

Tt x tt

3.) Setting Up A PUNNETT SQUARE3.) Setting Up A PUNNETT SQUARE

When given enough info about two parent organisms, we can use this window pane to predict the genotypes & phenotypes of their offspring.

4.) Align Parentals Genotype4.) Align Parentals Genotype11stst Parent Parent

Take the Take the genotype letters genotype letters of one parent, of one parent, split them and split them and put them on the put them on the left, outside the left, outside the rows of the rows of the punnett squarepunnett square

Align Parental GenotypeAlign Parental Genotype22ndnd Parent Parent

Now take the two Now take the two letters of the second letters of the second parent's genotype, parent's genotype, split 'em up, and split 'em up, and place them above place them above each of the two each of the two columns of the columns of the punnett square.punnett square.

Fill in Punnett SquareFill in Punnett Square Filling in the top-left boxFilling in the top-left box::

One from the One from the left, one from left, one from the top.the top.

Filling in the bottom-left boxFilling in the bottom-left box::

One from the One from the left, one from left, one from the top.the top.

Filling in the top-right boxFilling in the top-right box::

One from the One from the left, one from left, one from the top.the top.

Filling in the bottom-right boxFilling in the bottom-right box::

One from the One from the left, one from left, one from the top.the top.

5.) Record Results5.) Record Results

Show Phenotype and Show Phenotype and Genotype in your Genotype in your resultsresults

Phenotype: Show the Phenotype: Show the results as Percent (%)results as Percent (%)

and ratio.and ratio.

Genotype: Show the Genotype: Show the results for each different results for each different genotype.genotype.

Phenotype: 50% Tall,50% Short (2:2)

Genotype: 2Tt, 2tt

It was Walter Sutton in 1903 who made It was Walter Sutton in 1903 who made the link between Mendel's principles and the link between Mendel's principles and his own observation of meiosis in his own observation of meiosis in grasshoppers.grasshoppers.

The chromosome theory he proposed The chromosome theory he proposed states that hereditary factors or genes, are states that hereditary factors or genes, are carried on chromosomes.carried on chromosomes.

The pairing of homologous chromosomes The pairing of homologous chromosomes followed by their independent segregation followed by their independent segregation during meiosis explained all of Mendel's during meiosis explained all of Mendel's observations.observations.

Dihybrid Crosses: Setting Up Dihybrid Crosses: Setting Up Punnett SquarePunnett Square

Go to Dihybrid pwptGo to Dihybrid pwpt

Incomplete Dominant CrossesIncomplete Dominant Crosses Not all Phenotypes are the Not all Phenotypes are the

result of dominant or result of dominant or recessive genes . recessive genes .

Incomplete DominanceIncomplete Dominance is the is the incomplete expression of the incomplete expression of the dominant allele in a dominant allele in a heterozygote, where both heterozygote, where both alleles are expressed in the alleles are expressed in the phenotype.phenotype.

That is, there is a blending of That is, there is a blending of traits where the alleles act traits where the alleles act together to yield an together to yield an intermediateintermediate phenotype phenotype

Flower Color in Snapdragons: Incomplete Dominance

Red flowers - two alleles allow them to make a red pigment

White flowers - two mutant alleles; can’t make red pigment

Pink flowers - have one normal and one mutant allele; make a smaller amount of red pigment

Flower Color in Snapdragons: Incomplete Dominance

Red-flowered plant X White-flowered plant

(homozygote) (homozygote)

Pink-flowered F1 plants

(heterozygote)

Flower Color in Snapdragons: Incomplete Dominance

Pink-flowered plant X Pink-flowered plant

(heterozygote) (heterozygote)

White-, pink-, and red-flowered plants

in a 1:2:1 ratio

R = allele for red flowers W = allele for white flowers

red x white ---> pink

Legend: Red = RR

White= WW

Pink= RW

RR x WW

Phenotype: 0% Red, 100% Pink, 0% White(0:4:0) (R:P:W)Genotype: 4RW

Non Mendalian GeneticsNon Mendalian Genetics

Codominance is Codominance is a condition a condition when both when both alleles are alleles are expressed expressed neither one is neither one is dominantdominant

BBxWW = BW

Example of Co-DominanceExample of Co-Dominance

Black\white spottedBlack\white spotted crossed withcrossed with

Multiple Allele TraitsMultiple Allele Traits

Many traits have more then two alleles in the Many traits have more then two alleles in the populationpopulation

One important multiple allele trait is blood typeOne important multiple allele trait is blood type Type A is Codominant with type BType A is Codominant with type B Type O is recessive to both A and BType O is recessive to both A and B Resulting in: Type A = AA or AOResulting in: Type A = AA or AO Type B = BB or BOType B = BB or BO Type AB = ABType AB = AB Type O = OOType O = OO

Human ABO Blood Groups

Gene “I” specifies which sugar is found on the outside of red blood cells

3 common alleles are present in the human population: IA = N-acetyl-galactosamine IB = galactose i (also referred to as o) = no sugar present

6 possible genotypes

AA AO BB BO OO AB or IAIA IAi IBIB IBi ii IAIB

Immunology 101

Sugar on the blood cell is an antigen* (A, B, A and B, or none)

Your immune system thinks your own antigens are fine

Your immune system makes antibodies against non-self antigens

Antibodies recognize and target cells with antigens for destruction

*something that elicits an immune response

Legend: Type A = IAIA or IAi Type B = IBIB or IBi

Type AB = IAIB

Type 0 = ii

Example: IAi x IAIB

Phenotype = 50% Type A;25% Type AB; 25% Type B 0% Type O

(2:1:1:0)(A:B:AB:O)Genotype = 1IAIA; 1IAi; 1IAIB; 1IBi

IA i

IA

IB

IAIA IAi

IAIB IBi

Polygenic TraitsPolygenic Traits

PolygenicPolygenic traits are those traits that are traits are those traits that are determined by several genes.determined by several genes.

Examples of these are skin color, eye color Examples of these are skin color, eye color and heightand height

Drosophila melanogasterDrosophila melanogaster

Thomas Hunt Morgan working with genetics most Thomas Hunt Morgan working with genetics most famous animal, the fruit fly ,was the first to famous animal, the fruit fly ,was the first to demonstrate that a specific gene was located on a demonstrate that a specific gene was located on a specific chromosome.specific chromosome.

The Sex ChromosomesThe Sex Chromosomes

Nettie Stevens was the first to propose Nettie Stevens was the first to propose

that the odd smaller Y chromosome that that the odd smaller Y chromosome that

paired with the X determined anpaired with the X determined an

organism's sex. organism's sex.

To be To be

male you must have male you must have

an X and a Y to be an X and a Y to be

female you need two X’s.female you need two X’s.

50% chance of Male, 50% chance of Female

The Sex ChromosomesThe Sex Chromosomes

The mismatched The mismatched chromosomes are called chromosomes are called the the sex chromosomessex chromosomes. . (note the smaller size of (note the smaller size of the Y)the Y)

All the other (usually All the other (usually homologous) homologous) chromosomes are called chromosomes are called autosomesautosomes..

Sex linked TraitsSex linked Traits A sex linked trait is one determined by alleles carried A sex linked trait is one determined by alleles carried

only on the X chromosomeonly on the X chromosome A sex linked trait has no corresponding allele on the A sex linked trait has no corresponding allele on the

Y chromosome.Y chromosome.

Sex-Linked TraitsSex-Linked Traits As with all organisms As with all organisms

humans have traits that are humans have traits that are only carried on the X only carried on the X chromosome.chromosome.

Examples of these are Examples of these are colorblindness and colorblindness and hemophilia, a disorder that hemophilia, a disorder that prevents normal blood prevents normal blood clottingclotting

Gene linkage is a situation in which two or more Gene linkage is a situation in which two or more genes occur on the same Chromosome and are thus genes occur on the same Chromosome and are thus inherited together.inherited together.

Crossing over is the exchange of alleles between two Crossing over is the exchange of alleles between two homologous chromosomes ( it is a useful tool in gene homologous chromosomes ( it is a useful tool in gene mapping)mapping)

Sex-linked TraitsSex-linked Traits

Traits (genes) located on the sex sex chromosomeschromosomes

Example:Example: fruit fliesfruit flies

(redred-eyed male) X (whitewhite-eyed female)

Sex-linked TraitsSex-linked Traits

Sex ChromosomesSex Chromosomes

XX chromosome - female XY chromosome - male

fruit flyeye color

Notice there is no gene on theY chromosome

Example:Example: fruit fliesfruit flies(red-eyed male) X (white-eyed female)

XRY * XrXr

Remember:Remember: the Y chromosomeY chromosome in males does not carry traits.

Legend: red eyed= RR Rrwhite eyed= rrMale= XYFemale= XX

XRXr XrY

XRXr XrY

Xr

Xr

YXR

Phenotype50% red eyed and female50% white eyed and male

Genotype2 XRXr, 2 XrY

PEDIGREE CHARTSPEDIGREE CHARTS

Pedigree charts show Pedigree charts show a record of the family a record of the family of an individual. It can of an individual. It can be used to study the be used to study the transmission of a transmission of a hereditary condition. It hereditary condition. It is particularly useful is particularly useful when there are large when there are large families and a good families and a good family record over family record over several generations.several generations.

= males and O = females

Autosomal PedigreesAutosomal Pedigrees

An An autosomal pedigreeautosomal pedigree is probably one of the is probably one of the most common pedigrees most common pedigrees that you will find.  If a that you will find.  If a (recessive) trait is (recessive) trait is inherited on any inherited on any chromosome except for chromosome except for the sex chromosomes the sex chromosomes (X or Y), then you are (X or Y), then you are studying an autosomal studying an autosomal pedigree.pedigree.

Symbols used in pedigree chartsSymbols used in pedigree charts

In a marriage with five children, two daughters and three sons. The second son is affected bythe condition.

Above is a pedigree chart of a family showing four generations. A total of 20 individuals.

Sex Linked PedigreesSex Linked PedigreesA sex linked pedigree deals with a trait that is

found on the X Chromosome. Since

males are XY, they will only carry one allele; therefore the allele that they possess will directly be reflected in the genotype. Females, on the bother hand, are XX, so they carry two alleles per trait.  A female who is heterozygous for a sex-linked trait is said to be a carrier.

Symbol Meaning

        Dominant Male

        Dominant Female

        Recessive Male

         Recessive Female

       Carrier Female (for a sex-linked trait)

Human GeneticsHuman Genetics A A pedigree pedigree is a graphical representation of a is a graphical representation of a

genetic inheritancegenetic inheritance

Key

Key

Tay Sachs DiseaseTay Sachs Disease

Key