FUNDAMENTALS OF GENETICS

USEFUL MATERIALS Video- Garden of Inheritance Guinea Pig Work sheetText pages 159-176Worksheet and word search

Vocabulary

• 75. Independent assortment

• Monohybrid cross• True breeding• Cross pollination• Self pollination• Alleles• Homozygous

dominant

• Heterozygous• Homozygous

recessive• Genotype• Phenotype• Test cross

Read: 159-170

Remember this about chromosomes?

• X = shorthand for chromosomes• 46 total – 23 from mom and 23 from dad

(23 pairs)

centromere

Chromatids (2)

Types of Chromosomes• Autosomes – do not determine sex (1-22)• Sex Chromosomes – determine sex (X

and Y) = 23rd

–XY – male–XX - female

Hereditary Terms• Trait – genetic characteristic of an

organism• Gene – DNA sequence that codes for a

protein (may lead to a trait)• Allele – different forms of a gene

I. Principles of Heredity

• There are two factors which determine what and who you are, or what an organism looks like and how it behaves.– HEREDITY - the genetic make-up – ENVIRONMENT- conditions during

development • Is it “NATURE OR NURTURE” that

determines the ultimate product?– Studies on TWINS are inconclusive

II. PARADOX OF HEREDITY• A paradox is a seeming contradiction.

– “Success is measured sweetest by those who never succeed.” – Dickens

– “We are most lonely at times when we are among many men” H. D. Thoreau

– Consider a situation in which a father and his son are driving down the road. The car collides with a tree and the father is killed. The boy is rushed to the nearest hospital where he is prepared for emergency surgery. On entering the surgery suite, the surgeon says, "I can't operate on this boy. He's my son."

So what is the paradox of heredity?

• Why are some characteristics inherited exactly and others are variable?– Species Characteristics: 5 fingers,

walk erect, nervous system, appendix, 2 eyes

– Individual Characteristics: height, hair color, skin color, hair line

Diagram 2 homologous pairs of chromosomes with alleles on each pair

X XX X

Useful Terms• Phenotype- observable feature (eye color,

hair color, blood type)• Genotype- arrangement of alleles (Aa, Tt,

Bb Gg)

III. History• Gregor Mendel: Austrian Monk (1822-

1884)– Published the results of scientific research on

Garden Peas (Pisium sativum) in 1865.

Why study peas?– Great natural variation- stem length, seed

color, pod shape ,pod color, small, edible, easy to grow, many offspring, easy to cross fertilize, grow well in tne climate

Floral Anatomy• pollination• fertilization

Floral Anatomy

More Useful Terms

• P generation (parental): true breeding• F1 (first filial) offspring of P generation

• F2 (second filial) offspring from F1 cross

IV. EXPERIMENTAL CROSSES FOR INDIVIDUAL TRAITS

Must begin with PURE BREEDING parents:

HYBRID offspring F1 First Filia Generation

Cross Pollination P yellow X green tall X short wrinkled X round

F1 yellow tall round

these are TEST CROSSES to determine dominance and recessiveness

allowed to Self Pollination

F1 yellow X yellow Tall X Tall Round X Round

F2 3 yellow 1 green 3 tall 1 short 3 round 1 wrinkled

**Large sample sizes are needed to get an accurate picture of the frequency

P red X white

F1 red (self)

F2 705 red 224 white

P yellow X green F1 yellow

V. PUNNETT SQUAREMethod for determining possible allele combination for the offspring

Gametes outside

Offspring Inside

Who was Punnett?• REGINALD CRUNDALL

PUNNETT (1875-1967)was among the first English geneticists. He created the “Punnett Square” – a diagram to work out the possible allele combinations of the offspring of two parents.

How are gametes produced?• Meiosis!

– Where does this process happen in a flower?• If a person is a tongue roller with the

genotype Tt, what happens to the alleles during meiosis? Draw the process.

Draw summary and short hand of meiosis with 1 pair of chromosomes

Tongue Rolling

Chromosomes with alleles

Gene: tongue rolling

Alleles:

T- can roll

t – unable to rollX X

VI. TEST CROSSES• Monohybrid (one feature)

• Dihybrid (two features)

Some more terms…• Homozygous Dominant – TT – given two

dominant alleles from parents• Homozygous Recessive – rr – given two

recessive alleles from parents• Heterozygous – Gg – given one dominant

allele and one recessive allele from parents

Setting up a Punnett Square

B B

b

b

Bb Bb

Bb Bb

• Brown eyes (B) are dominant to blue eyes (b)

• Cross a homozygous brown-eyed person with a blue-eyed person

• BB vs. bb

What is the probability of having an offspring with heterozygous brown eyes? 4/4 or 100%

Another Example

• Tongue rolling(T) is dominant to non-tongue rolling (t)

• Cross a homozygous tongue roller with a heterozygous tongue roller

• TT vs. Tt

T T

T

t

TT TT

Tt Tt

What are the genotype possibilities?2/4 or 50% TT and 2/4 or 50% Tt

Useful Terms• Phenotypic ratio- Pattern of offspring

distribution according to phenotype Usually written as a fraction. observable feature (eye color, hair color, blood type)

• Genotypic ratio- Pattern of offspring distribution according to genotype. Usually written as a fraction.

• arrangement of alleles (Aa, Tt, Bb Gg)

Practice Problems• Pea Plants: green – G yellow – g• GG x gg• GG x Gg• Gg x gg• Gg x Gg

Genotypic/phenotypic ratios:

GG x Gg

Gg x gg

Gg x Gg

Albinism is the result of the expression of a

recessive allele for skin pigment

There are several forms

of albinism

• A normal pigmented male (who has an albino mom) and an albino female get married and have two children. What are the phenotypic ratios and genotypic ratios? What alleles will you use?

Genotypic Ratio:

Phenotypic Ratio:

Some more practice problems:• Two “normal” heighted but heterozygous

people have a child who is a midget. The wife is pregnant. What is the chance that their second child will be of normal height? What alleles will you use?

Genotypic Ratio:

Phenotypic Ratio:

• Dimples is a dominant trait. A heterozygous mom and a homozygous recessive dad have a child. What is the phenotypic ratio and genotypic ratio of the possible offspring? What is the genotype and phenotype of the parents?

Finding phenotypes and genotypes for 2 traits.

• Read lab• Observed ratio- a record of the results of

an event that has occurred• Expected ratio- mathematically calculated

results of an event prior to it occurring

Finding phenotypes and genotypes for 2 traits.

• Chance- not planned, accidental, not expected

• Sample Size- number of events recordedlarge sample side is needed to reduce the influence of chance and allow the true patterns to emerge.

Dihybrid CrossCross 2 pea plants that are both heterozygous purple flowered and heterozygous for smooth seeds.P= purple p= whiteN= non-wrinkled (smooth) n= wrinkled

•Step 1: Figure out the different gametes for each parent•Step 2: Set-up the cross and complete•Step 3: Calculate the genotypic and phenotypic ratios

Example of Ratios

Data summary from dihybrid lab

Data summary from dihybrid lab

VII. Mendel’s LawsMendel was a patient and keen observer.• Some characteristics mask others yet

reappear.– Principle of Dominance and Recessiveness

• Features can skip a generation.• Theorized there were 2 factors for each

trait.– Principle of Segregation of Alleles

• Pairs of factors separate into gametes without influenceing each other. – Principle of Independent Assortment

Quiz Topics –FRIDAY 3/5

Read: 159-170• Vocab 90-101• Worksheets (pg 127 and pg 129)• Mendel and his laws• Terminology (P, F1, F2, heterozygous,

homozygous dom, homozygous rec, phenotype, genotype, trait, gene, allele)

• Monohybrid vs Dihybrid crosses• Doing monohybrid problems

Review Questions

• RRTT• RrTt• RRtt• Rrtt

• List gametes possible from these parents

• (T) is the allele for tall humans and is dominant over the allele (t) for short humans. The allele for widows peak (W) is dominant over (w) non-widows peak hairlines.

What are the phenotypes for the following parents?

TtWw - _________________

TTww - _________________ What are the possible gametes formed by the

parents listed above?

AND

• 1. A woman with free ear lobes marries a man with attached ear lobes. Two of their children have attached ear lobes and two have free ear lobes. The alleles are (E) - free (e) - attached

• A. what is the genotypes of the woman?

• B. what is the genotype of the man?• C. What are the chances of the 5th

child having free ear lobes?

• (F) striped fur is dominant over (f) white fur in Australian cats.What is the result of a cross between a homozygous recessive parent and a heterozygous parent? Give phenotypic ratios and genotypic ratios.

Genotypic Ratio:

Phenotypic Ratio:

PTC tasting

Reality Show?Reality Show?

Do you recognize this family?

*Hint: They are from a TV show

• They are the Roloff family from TLC’s show Little People Big World

• How are the members of this family the same?

• How are they different?

• Great! You probably noticed that the family members share facial features, hair color etc.

• They are different because of their height

• Some family members (including the parents) exhibit the characteristic short stature of Achondriplasia, a dominant genetic disorder that results in a form of dwarfism.

• How is it possible for Matt and Amy (the parents) to have a child like Zach with Achondriplasia and three children who do not have the disease?

• The key is understanding dominant and recessive genes and the concept of segregation

• Zach and Jeremy are Fraternal Twins – what does that tell us about their genes?

• Fraternal twins have genes that are different - genetically, they are no more similar than any other set of siblings.

• If Zach and Jeremy were Identical Twins, how would this picture change?

• Both boys would either display the short stature of Achondriplasia or be of normal height – Identical twins have identical genes!

Zach

Jeremy