CHARACTERISTICS OF LIFE

All Living Things reproduce!!!!!

All Living Things Have DNA!!!!

Cladogram

WHY ARE WE ALL DIFFERENT?

We all inherited different genes from our parents which determines our traits.

Heredity – Passing on of traits from parentsto offspring.

23 chromosomes from each parent.

Autosomal vs. Sex Chromosomes

• ALL OF THE TRAITS THAT MENDEL STUDIED WERE AUTOSOMAL TRAITS. THAT IS WHY PEA PLANT WAS AN EASY STUDY. NO WEIRD TRAITS LIKE BLENDING!!!

Genes – Pieces of DNA that carry heredityinstructions and are passed from parents.

Traits – A distinguishing characteristic that is passed from parents to offspring.

Genetics – Study of heredity(passingon of genes)

JOHANN Gregor Mendel was born July 22, 1822. Mendel became a friar at the Augustinian monastery in Brno, Czechoslovakia. From 1868 until his death, Mendel was the abbot of the monastery.

Mendel was experimenting with flowers in the monastery's gardens. He wondered how traits were passed from parent to offspring. He studied the relations between parents and children with mathematical symbols.

Father of Modern Genetics

•The first person to trace the characteristics of successive generations of a living thing

•He was not a world-renowned scientist of his day.• Rather, he was an Augustinian monk who taught natural

science to high school students.

• Second child of Anton and Rosine Mendel

• They were farmers in Brunn• They couldn’t afford for him to attend

college• Gregor Mendel then attended the

Augustinian Monastery and became a monk

Gregor J. Mendel, O.S.A., experimental garden (35x7 meters) in the grounds of the Augustinian Monastery in Old Brno.Its appearance before 1922. Courtesy of Villanova University Archives.

The Monastery Garden with the greenhouse whichGregor J. Mendel, O.S.A., had built in 1870. Its appearance before 1902.Courtesy of

Villanova University Archives.

The Birth of the idea: Heredity

• On a walk around the monastery, he found an atypical variety of an ornamental plant.

• He took it and planted it next to the typical variety.

• He grew their progeny side by side to see if there would be any approximation of the traits passed on to the next generation.

• This experiment was "designed to support or to illustrate Lamarck's views concerning the influence of environment upon plants.“

GREGOR MENDAL

He chose to study 7 different traits,only one at a time, so he could understand the mathematical results.(tall, flower color and position, pod color and shape, etc.)He learned that each plant had two genes for each trait. One from each parent.

He Argued!!!!

• Parents pass on their offspring heritable traits(genes) SO two alleles for every trait. One from each parent!!!

• Genes retain their individuality. There is no blending.

Why Did He Chose Peas?

• Short generation times

• Large number of offspring

• Many different traits(varieties)

Why did Mendal work with peas? •Good choice for environment of monastery(food)

•Network provided unusual varieties for testing- several traits.

•Obligate self-pollination reproductive system

•Crosses easy to document

•Short life cycle

•Easy to track he traits.

Character vs. trait

• Character – heritable trait varies that varies among individual. Hair color, eye color, etc

• Trait – Variant for a character – brown , black, blonde hair

Self- pollination Vs. Cross Pollination

Self – pollination – plant pollinates itself. Peas do this. Mendel could decide on the test crosses.

Cross pollination – Mendel crossed one plant with another by taking pollen from one type of plant and placing it on the other.

Mendel cross-pollinated pea

plants• He cut away the male

parts of one flower, then dusted it with pollen from another

• He found that the plants' respective offspring retained the essential traits of the parents, and therefore were not influenced by the environment.

Mendel’s 4 Conclusion

1. There are alternative versions of gene that account for variations in inherited characters.

Alleles: Alternate versions of a gene!!!

Mendel’s 4 Conclusion

2. For each character, an organism inherits two alleles. They can be the same or different.

Homozygous – identical alleles

Heterozygous – two different alleles.

Mendel’s 4 Conclusion

3. If the 2 alleles of an inherited pair differ, then one determines the organism’s appearance. It is called DOMINANT.

Recessive – no affect on organism unless dominant is not present.

Mendel’s 4 conclusions• A sperm or egg carries only one allele

for each inherited character because allele pairs separate from each other during gamete formation.

• Law of segregation – Sperm and egg carries only one allele which separate during meiosis.

MENDAL’S EXPERIMENT

PART 1- He bred a pure tall peaplant with a pure short pea plant. ALL the offspring wereTALL.TT X tt = Tt

PART 2 - F1He crossed 2 of the offspring from the abovecross.Results – 75% Tall

25% ShortTt X Tt = TT, Tt, tt

Mendelian genetics

• Character (heritable feature, i.e., fur color)

• Trait (variant for a character, i.e., brown)• True-bred (all offspring of same variety)• Hybrid (crossing of 2 different true-

breds)• P generation (parents)• F1 generation (first filial generation)

Parent Generation

F1 Generation

F2 Generation, 3:1 ratio

Three Conclusions to His Research1. Principle of Dominance and Recessiveness

One allele in a pair may mask the effect of the other

2. Principle of SegregationThe two alleles for a characteristic separate

during the formation of eggs and sperm3. Principle of Independent Assortment

The alleles for different characteristics are distributed to reproductive cells independently of the other genes on the chromosome.

Independent Assortment

Bb

diploid (2n)

B

b

meiosis I

B

B

b

b

sperm

haploid (n)

meiosis II

• Chromosomes separate independently of each other

Bb

Ff

B

F

B

f

b

f

B

F

Bb

Ff

Bb

Ff

This means all gametes will be different!

Independent Assortment• Genes for different traits can segretate

independently during the formation of gametes without influencing eachother

• Question: How many gametes will be produced for the following allele arrangements?

• Remember: 2n (n = # of heterozygotes1. RrYy

2. AaBbCCDd

3. MmNnOoPPQQRrssTtQq

Mendal’s Death

• Died in 1884 of Nephritis(kidney inflammation). After his death, his papers were burnt by his abbott because they went against beliefs of the times.

• His work was lost for 50 years!!

Genetic vocabulary…….• Punnett square: • Gene: point on a chromosome

that controls the trait• Allele: an alternate form of a

gene A or a• Homozygous: identical alleles

for a character• Heterozygous: different alleles

for a gene• Phenotype: physical traits• Genotype: genetic makeup• Testcross: breeding of a

recessive homozygote X dominate phenotype (but unknown genotype)

Vocabulary• Diploid – Full number of chromosomes in a

somatic cell

• Haploid – Half number of chromosomes in a gamete.

Dominant and Recessive alleles

Dominant alleles – upper-case a. homozygous dominant

(BB – Brown eyes)

Recessive alleles – lower casea. homozygous recessive

(bb – blue eyes)b. Heterozygous (Bb – Brown eyes)

Dominant gene – Stronger of the two traits and masked(hides) the recessive trait.Recessive gene – Weaker trait.

For these reasons, he is called the Father of Genetics.

GENETICS RULES

Capital Letters – Represents dominanttrait.Lower Case Letters – Represents recessivetrait.

GENETIC SYMBOLS

Use symbols to represent different forms of agene.

Examples- B – Brown eyes b – blue eyes

GENETIC RULES

Every organism has TWO forms of every gene.One from each parent. Each form is calledan ALLELE. You could have got a blue eye genefrom mom and a brown eye gene from dad.

Examples – Bb, WW, gg, Rr

An organism can have the same gene for thetrait or they can have two different genes.

If the genes are the same, then they are called HOMOZYGOUS or purebred.Examples – aa(one antenna), AA(2 antenna), LL(different colored legs), ll(clear legs), TT(curly Tail), tt(straight tail)

If the genes are different, then they are called HETEROZYGOUS or hybrid

Examples – Aa(2 antenna), Ll(different color leg), Tt(curly tail)

Phenotype vs. Genotype

• Outward appearance• Physical

characteristics

• Examples:1.Brown eyes2.blue eyes

• Arrangement of genes that produces the phenotype

• Exmple:1. TT, Tt2. tt

GENETIC PROBABILITY

Mendal crossed yellow and green pea plantsand discovered that 1 out of 4 were green.

He was using probability.

Probability – The possibility or likelihood thata particular event will occur.

Used to predict – the results of geneticscrosses.

The squares contain the gene combinationsthat could occur in the cross.

The genotype is the letter combination or gene combinations in the squares.

Example – Tt, Aa, bb,or Ll

The phenotype is the actual appearance ofthe organism.

Example – curly tail, 2 antennas, 3 body Segments, different color legs

PUNNETT SQUARES

A Punnett square is a special chart used to show the possible gene combinations in a cross between 2 organisms.

Developed by an English genetists by the name of Reginald Punnett.

5 Steps of Punnett Square1. Determine the genotypes of parents.

2. Set up your Punnett Square. Dad’s genotype on top and Mom’s on side.

3. Fill in squares by combining sperm with egg.

4. Write out possible combos(genotype).

5. Determine phenotype ratio.

How does a Punnett Square Work?

1. Draw a square and divideit into 4 sections. 2. Write the gene pairs across the top of the box, then the other down the side3. In each box, place the correct gene to see the possible combinations.

Each square represents a 25%possibility of getting that trait.

PARTS OF A PUNNETT SQUARE

Male Genes

FemaleGenes

Offspring Combinations

Tt Tt

Tt Tt

Cross betweenhomozygous dominant and recessive.

What are the percent of the offspring?What are the genotypes?What are the phenotypes?

Cross betweentwo heterozygous

parents.

What are the percentages of offspring?What are the genotypes?What are the phenotypes?

TT Tt

Tt tt

Mathematical Computations

In a Punnett Square where both parents are Hybrids the percents are listed below:

25% purebred(homozygous) black – BB

50% hybrid(heterozygous) black - Bb

25% purebred(homozygous) white - bb

% of same genotype as parents - 50 %

% of same phenotype as parents -

75%

What about 2 Traits?• BbTt x BbTt• The Gametes contain one of each of the

alleles. (BT).• Each of the offspring contain four alleles

exactly like the parents.(BbTt).• Notice the number of possible offspring

has increased.• The phenotypic ratio is 9:3:3:1

Steps of Dihybrid Cross

Dihybrid Cross

Dihybrid Cross

RYRY RyRy rYrY ryry

RYRY

RyRy

rYrY

ryry

Dihybrid Cross

RRYY

RRYy

RrYY

RrYy

RRYy

RRyy

RrYy

Rryy

RrYY

RrYy

rrYY

rrYy

RrYy

Rryy

rrYy

rryy

Round/Yellow: 9

Round/green: 3

wrinkled/Yellow: 3

wrinkled/green: 1

9:3:3:1 phenotypic ratio

RYRY RyRy rYrY ryry

RYRY

RyRy

rYrY

ryry

Dihybrid Cross

• Example: cross between round and yellow heterozygous pea seeds.

R = round

r = wrinkled

Y = yellow

y = greenRY Ry rY ry RY Ry rY ry x RY Ry rY ryRY Ry rY ry possible gametes produced

RrYyRrYy x RrYyRrYy

Genetics Beyond Mendel

• Sex linked

• Incomplete dominance

• Codominance

• Pedigrees

Incomplete Dominance• One allele is not

completely dominant over another. THEY BLEND TOGETHER!!

RW

RW

RW

RW

W

W

R R

All Rr = pink(heterozygous pink)

produces theFF11 generation generation

INCOMPLETE DOMINANCESometimes, you may notice that traits can blend Together. The blending of two traits is call incompletedominance. Two capital letters are used. For example, from baby marmellow RY = orange nose, RR = red nose, and RY = yellow nose

Examples – palomino in horses, pink color in flowers are red and white combined.

Cat Examples

• Black cat mated to a white cat can get a gray cat!!!

What is meant by MULTIPLE ALLELES?

• A trait that is controlled by more than two alleles is said to be controlled by multiple alleles

• Traits controlled by multiple alleles produce more than three phenotypes of that trait.

• Codominance – situation where both alleles are expressed.

Multiple Alleles and Codominance

• Ex )Blood type• Blood type A and B are co-dominant,

while O is recessive.• Forms possible blood types of A, B, AB,

and O.

Codominance• Both alleles are

expressed

1. type A= IAIA or IAi

2. type B= IBIB or IBi

3. type AB= IAIB

4. type O= ii

Black cow + white cow = spotted cow

Blood Also Shows Codominance

http://en.wikipedia.org/wiki/File:ABO_blood_type.svg

Where are Disorders Located?

• Autosomal chromosomes: 1 - 22– The disorder is caused by a gene or

nondisjunction of chromosomes 1 - 22.

* Sex Linked disorders: Located on the X or Y chromosomes.

Sex Linked GenesSex Linked Traits or Disorders - The X and

Y chromosomes carry the genes that determine gender traits so the genes located on X and Y are called sex linked.

• X – 1098 genes

• Y – 26 genes much smaller!!!

Sex Linked Genes• The genes that are on the X are expressed in

the phenotype of the male because it is the only gene they carry. If the gene is a recessive for a disorder, the male will have the disorder.

• Ex: hemophilia, duchene muscular, fragile-X syndrome, high blood pressure(some), night blindness, and red-green color blindnesss.

Sex-Linked Inheritance

• Traits that are only found on the X chromosome

• Colorblindness and Hemophilia are examples of sex-linked traits.

• These genes are recessive and found only on the X chromosome.

How Would a Female Have a Sex Linked Disorder?

• She would have to receive a recessive gene from both parents.

Queen Victoria of England

• Carrier of hemophilia

• X-linked traits to one of her sons. He died but all of her daughters were carriers.

• They married into the Russia royal families and spread it to the Russian royality.

• By 20th century, 20 of her descendants had hemophilia.

History

• Her daughter Alexandra married Tsar Nicholas of Russian. Finally had a son Alexei. He had hemophilia. He was the only son and only heir to become Tsar. To keep people from learning of his disease, they withdrew from society. The people mistook this as they did not care. Alexei had som internal bleeding and a man by the name of Rasputin stopped the bleeding. He was let into the inner circle. Many thought he led to revolution.

Why do Pedigrees?

• Punnett square tests work well for organisms that have large numbers of offspring and controlled matings, but humans are quite different:

1. small families. Even large human families have 20 or fewer children.

2. Uncontrolled matings, often with heterozygotes.

3. Failure to truthfully identify parentage.

Today... Pedigree analysis

In humans, pedigree analysis is an important tool for studying inherited diseases

Pedigree analysis uses family trees and information about affected individuals to:

figure out the genetic basis of a disease or trait from its inheritance pattern

predict the risk of disease in future offspring in a family (genetic counseling)

Goals of Pedigree Analysis

• 1. Determine the mode of inheritance: dominant, recessive, partial dominance, sex-linked, autosomal, mitochondrial, maternal effect.

• 2. Determine the probability of an affected offspring for a given cross.

Basic Symbols

More Symbols

Today... Pedigree analysis

How to read pedigrees

Basic patterns of inheritanceautosomal, recessiveautosomal, dominantX-linked, recessiveX-linked, dominant (very rare)

Applying pedigree analysis - practice

Sample pedigree - cystic fibrosis

femalemale

affected individuals

Dominant vs. Recessive

• Is it a dominant pedigree or a recessive pedigree?• 1. If two affected people have an unaffected child, it must

be a dominant pedigree: D is the dominant mutant allele and d is the recessive wild type allele. Both parents are Dd and the normal child is dd.

• 2. If two unaffected people have an affected child, it is a recessive pedigree: R is the dominant wild type allele and r is the recessive mutant allele. Both parents are Rr and the affected child is rr.

• 3. If every affected person has an affected parent it is a dominant pedigree.

Assigning Genotypes for Dominant Pedigrees

• 1. All unaffected are dd. • 2. Affected children of an affected parent and an

unaffected parent must be heterozygous Dd, because they inherited a d allele from the unaffected parent.

• 3. The affected parents of an unaffected child must be heterozygotes Dd, since they both passed a d allele to their child.

• 4. Outsider rule for dominant autosomal pedigrees: An affected outsider (a person with no known parents) is assumed to be heterozygous (Dd).

• 5. If both parents are heterozygous Dd x Dd, their affected offspring have a 2/3 chance of being Dd and a 1/3 chance of being DD.

Autosomal Dominant

• Assume affected outsiders are assumed to be heterozygotes.

• All unaffected individuals are homozygous for the normal recessive allele.

Autosomal dominant pedigrees

• Trait is common in the pedigree

• Trait is found in every generation

• Affected individuals transmit the trait to ~1/2 of their children (regardless of sex)

1 2 3 4 5 6 7 8 9 10

1 2

I

1 2 3 4 5 6

II

III

Dominant Autosomal Pedigree

Autosomal dominant traits

There are few autosomal dominant human diseases (why?), but some rare traits have this inheritance pattern

ex. achondroplasia (a sketelal disorder

causing dwarfism)

Assigning Genotypes for Recessive Pedigrees

• 1. all affected are rr.• 2. If an affected person (rr) mates with an unaffected person, any

unaffected offspring must be Rr heterozygotes, because they got a r allele from their affected parent.

• 3. If two unaffected mate and have an affected child, both parents must be Rr heterozygotes.

• 4. Recessive outsider rule: outsiders are those whose parents are unknown. In a recessive autosomal pedigree, unaffected outsiders are assumed to be RR, homozygous normal.

• 5. Children of RR x Rr have a 1/2 chance of being RR and a 1/2 chance of being Rr. Note that any siblings who have an rr child must be Rr.

• 6. Unaffected children of Rr x Rr have a 2/3 chance of being Rr and a 1/3 chance of being RR.

Autosomal Recessive

• All affected are homozygotes.

• Unaffected outsiders are assumed to be homozygous normal

• Consanguineous matings are often (but not always) involved.

Autosomal recessive traits

• Trait is rare in pedigree

• Trait often skips generations (hidden in heterozygous carriers)

• Trait affects males and females equally

Recessive Autosomal Pedigree

Autosomal recessive diseases in humans

Most common ones • Cystic fibrosis • Sickle cell anemia• Phenylketonuria (PKU)• Tay-Sachs disease

For each of these, overdominance (heterozygote superiority) has been suggested as a factor in maintaining the disease alleles at high frequency in some populations

Y-Linked Inheritance

• We will now look at how various kinds of traits are inherited from a pedigree point of view.

• Traits on the Y chromosome are only found in males, never in females.

• The father’s traits are passed to all sons.

• Dominance is irrelevant: there is only 1 copy of each Y-linked gene (hemizygous).

X-linked recessive pedigrees

• Trait is rare in pedigree

• Trait skips generations

• Affected fathers DO NOT pass to their sons,

• Males are more often affected than females

X-linked recessive traits

ex. Hemophilia in European royalty

X-linked recessive traits

ex. Glucose-6-Phosphate Dehydrogenase deficiency

• hemolytic disorder causes jaundice in infants and (often fatal) sensitivity to fava beans in adults

• the most common enzyme disorder worldwide, especially in those of Mediterranean ancestry

• may confer malaria resistance

X-linked recessive traits

ex. Glucose-6-Phosphate-Dehydrogenase deficiency

X-linked dominant pedigrees

• Trait is common in pedigree

• Affected fathers pass to ALL of their daughters

• Males and females are equally likely to be affected

Sex-Linked Dominant

• Mothers pass their X’s to both sons and daughters

• Fathers pass their X to daughters only.

• Normal outsider rule for dominant pedigrees for females, but for sex-linked traits remember that males are hemizygous and express whichever gene is on their X.

• XD = dominant mutant allele• Xd = recessive normal allele

Sex-Linked Recessive

• males get their X from their mother

• fathers pass their X to daughters only

• females express it only if they get a copy from both parents.

• expressed in males if present• recessive in females• Outsider rule for recessives

(only affects females in sex-linked situations): normal outsiders are assumed to be homozygous.

X-linked dominant diseases

• X-linked dominant diseases are extremely unusual

• Often, they are lethal (before birth) in males and only seen in females

ex. incontinentia pigmenti (skin lesions)

ex. X-linked rickets (bone lesions)

Pedigree Analysis in real life: complications

Incomplete Penetrance of autosomal dominant traits=> not everyone with genotype expresses trait at all

Ex. Breast cancer genes BRCA-1 and BRCA-2 & many “genetic tendencies” for human diseases

What is the pattern of inheritance?What are IV-2’s odds of being a carrier?

What is the inheritance pattern?What is the genotype of III-1, III-2, and II-3?What are the odds that IV-5 would have an affected son?

Sample pedigree - cystic fibrosis

What can we say about I-1 and I-2?

What can we say about II-4 and II-5?

What are the odds that III-5 is a carrier?

What can we say about gene frequency?

III-1 has 12 kids with an unaffected wife 8 sons - 1 affected4 daughters - 2 affected

Does he have reason to be concerned about paternity?

Breeding the perfect Black Lab

black individuals = fetch wellgrey individuals = don’t drool

How do we get a true-breeding line for both traits??