Background VocabularyBackground Vocabulary

True-breeds: pure gene lines – offspring match parent

Self-pollination: pollen from flower fertilizes the same plant

Cross-pollination: pollen will fertilize a different plant

Hybrid: Cross between organisms with different traits (blonde hair & brown hair)

Trait: Physical characteristics

Gregor Mendel

• Austrian monk

• “Father of Modern Genetics”

• Famous for his work with peas

Mendel’s PeasMendel’s Peas

Cross-PollinatingCross-Pollinating

Mendel’s CrossesMendel’s Crosses

TRAIT 1: Seed Shape

P Cross: Round v. Wrinkled

F1 Phenotype: Round

Mendel’s CrossesMendel’s Crosses

TRAIT 2: Seed Color

P Cross: Green v. Yellow

F1 Phenotype: Yellow

Mendel’s CrossesMendel’s Crosses

TRAIT 3: Flower Color

P Cross: Purple v. White

F1 Phenotype: Purple

Mendel’s CrossesMendel’s Crosses

TRAIT 4: Pod Shape

P Cross: Inflated v. Pinched

F1 Phenotype: Inflated

Mendel’s CrossesMendel’s Crosses

TRAIT 5: Pod Color

P Cross: Green v. Yellow

F1 Phenotype: Green

Mendel’s CrossesMendel’s Crosses

TRAIT 6: Flower Position

P Cross: Axial v. Terminal

F1 Phenotype: Axial

Mendel’s CrossesMendel’s Crosses

TRAIT 7: Plant Height

P Cross: Tall v. Short

F1 Phenotype: Tall

Mendel’s ConclusionsMendel’s Conclusions

• Biological inheritance is determined by Biological inheritance is determined by chemical factors passed from one chemical factors passed from one generation to the next generation to the next (Particulate (Particulate hypothesis)hypothesis)

– Geneticists now refer to these factors as Geneticists now refer to these factors as genesgenes

– Genes can come in more than one form, each Genes can come in more than one form, each form is an form is an alleleallele

ex. B or b ex. B or b (The “B” gene w/ 2 alleles)(The “B” gene w/ 2 alleles)

The Principle of The Principle of DominanceDominance

1.1. Certain alleles will be expressed Certain alleles will be expressed over othersover others

2.2. The expressed alleles are The expressed alleles are dominantdominant to the unexpressed to the unexpressed recessiverecessive allelesalleles

• How does Mendel’s particulate hypothesis differ from the blending hypothesis of inheritance?

• What is the difference between self-pollination and cross-pollination?

• Describe a pattern of inheritance shown in Mendel’s crosses that contradicts the blending hypothesis.

Self-Assessment:

The FThe F11 Cross Cross

• Mendel’s experiment:– Allow the F1 plants to self pollinate

• The results:– The dominant trait was expressed 75%

of the time– The recessive trait was expressed 25%

of the time

The Explanations:The Explanations:

1. The recessive allele was still present in the F1 plants

2. Principle of Segregation: Each individual inherits two alleles for each gene.

Probability Probability

• The likelihood of an event happening• How is it determined:

– Likelihood of rolling heads = 50% (1 of 2 possibilities)

– Rolling heads twice? • 50% x 50% = 25%

• To predict outcomes of genetic crosses we use punnett squarespunnett squares

More genetics More genetics vocabulary…vocabulary…

• Homozygous: two identical alleles (AA or aa)

• Heterozygous: two different alleles (Aa)

• Phenotype: Physical appearance • Genotype: Genetic make-up

– Homozygous dominant (AA)– Homozygous recessive (aa)– Heterozygous (Aa)

The Test Cross• In order to determine whether an individual

expressing a dominant trait is homozygous or heterozygous, it can be crossed with an organism expressing the recessive trait.

• If R = round seeds and r = wrinkled seeds, show how the results of a test cross for seed shape will differ for homozgygous v. heterozgous genotypes for round seeds.

Self-Assessment

• What are the two possible gametes produced by a plant that has the genotype Aa? What is the probability of each type of gamete?

• Use a Punnett square to predict the genetypes produced if the plant above is self-fertilized.

Monohybrid (1-factor) Cross PracticeKEY: G = green pods, g = yellow pods

P = purple flowers, p = white flowersT = tall plants, t = short plants

Show a cross a plant heterozygous for green pods with a plants with yellow pods. What are the expected genotype and phenotype ratios?

Show a cross of a homozygous tall plant with a heterozygous tall plant. What are the expected genotype and phenotype ratios?

Show a cross of two heterozygous purple flowered plants. What are the expected genotype and phenotype ratios?

Exploring Mendelian Exploring Mendelian GeneticsGenetics

• Does segregation of one set of alleles influence the segregation of another pair of alleles?

• Mendel’s Two Factor Crosses– Followed two traits at a time.– Same method as his original single-factor

crosses– Cross-pollinated to produce the F1 and

allowed them to self-pollinate

The Parental CrossThe Parental Cross _________________________________

The F1 CrossThe F1 Cross _________________________________

A Summary of Mendel’s A Summary of Mendel’s PrinciplesPrinciples

• Dominance: a recessive allele will be masked by a dominant allele

• Segregation: alleles for each trait segregate (separate) during gamete formation

• Independent Assortment: Alleles for different traits do not influence each other’s segregation

Mendel’s Peas were ideal for Mendel’s Peas were ideal for learning about inheritance, but learning about inheritance, but they do not represent the norm… they do not represent the norm…

• Traits in pea plants are determined by just two alleles

• In peas, one allele is clearly dominant & the other is clearly recessive

• However, things aren’t always this clear-cut and simple in the world of genetics.

What if Mendel looked at mice?

If a female black mouse and a male white mouse were crossed, what will the offspring look like? - 100% are GREYGREY

If the F1 offspring were crossed, what will there offspring look like?- 25% black- 50% grey- 25% white

Incomplete DominanceIncomplete Dominance

• A cross between two organisms with different traits results in an offspring with a third phenotype that is a blending of the parental traits.

• It’s like mixing paints: – Red + White = Pink– Red does not totally block (dominate)

white, we end up with something in-between.

Inheritance in Inheritance in SnapdragonsSnapdragons

Let’s try crossing Let’s try crossing snapdragons…snapdragons…

What will the genotype and phenotype ratios be if a red plant is crossed with a pink plant?

(Use capital letters for alleles symbols; R & W)

G:

P:

One more….One more….

What will the genotype and phenotype ratios be if a red plant is crossed with a white plant?

G:

P:

What does the prefix “Co-” What does the prefix “Co-” mean?mean?

•Consider the meaning of the following words:

- Cooperate- Coexist- Cohabitat

•What about “Codominance”?

Let’s look at cattle….Let’s look at cattle….This cow resulted from a cross between a cow with red fur and a cow with white fur.

This is called ‘roan’ fur; red & white fur together.

CodominanceCodominance

• Similar to incomplete dominance in that there is a 3rd phenotype

• In COdominance, the “recessive” and “dominant” alleles appear together in the phenotype of hybrid organisms.

• Red x White = red & white

Let’s try crossing Let’s try crossing cattle….cattle….

What will the gentype and phenotype ratios be if a red cow is crossed with a white cow?

G:

P:

One more….One more….

What will the ratios be if a red cow is crossed with a roan cow?

G:

P:

Polygenic (Multifactorial) Traits

• Phenotype is determine by more than one gene

• Often results in gradations, where each gene has an additive effectEx) If 10 gene loci are turned on plant will be 20cm tall, if only 5 loci are turned on plant will be 10cm tall

• Results in a bell-shaped curve – Skin color & Height are examples in humans

Phenotype Distribution:Polygenic Traits

Full color: CC, Ccch, Cch, or CcChinchilla: cchch, cchcch, or cchcHimalayan: chc, or chchAIbino: cc

KEY

C = full color; dominant to all other alleles

cch = chinchilla; partial defect in pigmentation; dominant to ch and c alleles

ch = Himalayan; color in certain parts of the body; dominant to c allele

c = albino; no color; recessive to all other alleles

Multiple Alleles• More than 2 alleles for a particular trait

ABO Blood Types

• In addition to having multiple alleles, ABO blood type also exhibits codominance

• ‘IA’ & ‘IB’ are codominant• ‘i’ is recessive

ABO Blood TypingABO Blood Typing

Genotype Blood Type

IA IA or IA i

IB IB or IB i

IAIB

ii

ABO Blood TransfusionsABO Blood Transfusions

Blood Type

Can receive:

A

B

AB*

O*

What does your ABO blood type mean?

Remember the ‘flags’ on our cell membranes? They help cells to recognize each other.

Some of those flags ‘announce’ your blood type. We call these flags antigens

Blood

Type

Antigen

A

B

AB

O

Summary of ABO Blood Types

Rh FactorRh Factor• Blood can also be categorized as + or –

• This refers to the presence (dominant) or absence (recessive) of the Rh antigen

Phenotype Genotype(s) Antigen

Rh+

Rh-

Rh Factor & Pregnancy

Rh Disease• Mother's antibodies cross the placenta to fight the Rh positive cells in the baby's body.

•As the antibodies destroy the red blood cells, the baby can become anemic.

•The anemia can lead to other complications including jaundice and organ enlargement

•With amniocentesis, the amniotic fluid may have a yellow coloring and contain bilirubin.

•Ultrasound of the fetus shows enlarged liver, spleen, or heart and fluid build up in the fetus' abdomen.

Gene Linkage & Mapping Chromosomes• Genes on the same chromosome are more likely to be

inherited together• Crossing over helps to increased variation, but the

closer two genes are on a chromosome the more likely they are to be “linked”

Sex Chromosomes & Autosomes

• Two of the 46 human chromosomes are known as sex chromosomes, because they determine the individual’s sex.– Females have two copies of an X

chromosome.– Males have one X chromosome and one Y

chromosome.• The remaining 44 chromosomes are

known as autosomal chromosomes or autosomes.

Sex-Linked GenesSex-Linked Genes

• Located on one of the sex chromosomes

(X or Y)• Since the X

chromosome is longer, it has many genes not found on the Y chromosome.

• Most sex-linked genes are X-linked genes.

Sex-Linked Genes

X-Linked InheritanceX-Linked Inheritance• Examples:

– Hemophilia• The protein necessary for normal blood clotting is

missing

– Colorblindness• Defective version of one or all of the 3 genes

responsible for color vision

– Male Pattern Baldness• Hair loss

– Duchenne Muscular Dystrophy• Weakening and loss of skeletal muscle

• These traits are recessive & more common in males. Why?

Possible Inheritance of Colorblindness Allele

Pedigree Analysis of Traits

Sex-Linked Pedigree Analysis

Complete the following sex-linked crosses:

Eva and Paul just had a son, Michael. Paul is has normal color vision, but Eva’s father was colorblind. What is the likelihood that Michael is colorblind?

Laura and Steve are expecting their first child. They are concerned about the chances their child might be hemophiliac because both Steve and Laura’s father are hemophiliac. What is the probability of Laura and Steve having a hemophiliac child?

Complete the following pedigrees. Which is for a sex-linked trait? How do you know?

Chromosomal DisordersChromosomal Disorders• The most common error in meiosis

occurs when homologous chromosomes fail to separate.

• This is known as nondisjunction, which means “not coming apart”

• If nondisjunction occurs, abnormal numbers of chromosomes may find their way into gametes and a disorder of chromosome numbers may occur.

• A monosomy results if an entire chromosome is missing and a trisomy results if there is an additional copy of a chromosome

Other Chromosomal Mutations

Jumping Genes• In the 1940’s, while

studying corn, Barbara McClintock discovered that sometimes genes could move from one location to another in a chromosome or even to other chromosomes.

• The movement could result in the genes landing in the middle of another gene and disrupting them.

• These “jumping genes” are now called transposons.

Amniocentesis: Detecting Chromosomal

Disorders

Karyotypes:Detecting Monsomies, Trisomies & Translocations

Down Syndrome

• Trisomy 21• Produces mild to

severe mental retardation

• Characterized by:– Increased susceptibility

to many diseases– Higher frequency of

some birth defects.

Turner Syndrome

• Monosomy X• Result of

nondisjunction in females

• Characteristic physical abnormalities, such as short stature, broad chest, low hairline, low-set ears, and webbed neck

Klinefelter Syndrome• Karyotype 47, XXY• Extra X chromosome

interferes with meiosis and usually prevents these individuals from reproducing

• Most common sex chromosome disorder, second most common disorder due to the presence of an extra chromosome

Genes & The Environment• Some obvious human traits are almost

impossible to associate with a single gene.• These traits, such as the shape of your eyes

or ears, polygenic meaning they are controlled by many genes.

• Many of your personal traits are only partially governed by genetics.

• epigenetics is the study of heritable changes in gene expression or cellular phenotype caused by mechanisms other than changes in the underlying DNA sequence

Epigenetics

NOVA Video (13min)

The Genetic Basis of Cancer• You already know that cancer results when controls on the cell

cycle do not work properly and cells grow and divide too quickly.

• Two classes of genes direct the production of proteins that regulate cell growth and division:

– one produces growth factors to initiate cell division (can mutate to an oncogene & result in too much growth factor)

– the other produces proteins to stop cell division (tumor suppressor genes)

• Cancer is always a genetic disease in that it results from changes in DNA: – Since the mutations do not usually arise in gametes, cancer is not

usually passed from parent to child– However some mutations do arise in the ovaries or testes which can

give rise to gametes and result in the inheritance of cancer genes.