Bellwork : Which fact interests you the most and why?

Bellwork: Which fact interests you the most and why?

Genetics

Mendelian Genetics & Patterns of Inheritance

Biology And Society: Testing Before Birth

– Genetic testing Allows expectant parents to test for possibilities in their

unborn child. Includes amniocentesis and CVS. Has risks associated with it.

The Role of Environment

– Many human characteristics result from a combination of heredity and environment.

The Chromosomal Basis of Inheritance

– The chromosome theory of inheritance states that

Genes are located at specific positions on chromosomes.

The behavior of chromosomes during meiosis and fertilization accounts for inheritance patterns.

Figure 9.23

Linked Genes

– Linked genes Are located close together on a

chromosome. May be inherited together.

– Sex chromosomes Influence the inheritance of

certain traits. Due to linkage

Gregor Mendel1822-1884

The father of

genetics

Gregor Mendel

He was an Austrian monk. He is important because carried out the first important studies of heredity. He studied plants because plants have male & female parts so that they can reproduce sexually.

Was the first person to analyze patterns of inheritance.

Deduced the fundamental principles of genetics

Peas In an Abbey Garden

– Mendel studied garden peas because

These plants are easily manipulated.

These plants can self-fertilize.

– Mendel carried out some cross-fertilization.

– He also created true-breeding varieties of plants.

– Mendel then crossed two different true-breeding varieties.


– Mendel performed many experiments.

– He tracked several characteristics in pea plants from which he formulated several hypotheses.


Heredity

The passing on of characteristics from parents to children (offspring).

Genetics

The branch of biology that studies heredity.

Traits

Inherited characteristics

Often represented by single letters.

ExamplesTall plant = TShort plant = tPurple flowers = FWhite flowers = f

Allele

The different forms of a gene for the same trait. For example if we look at a particular plant’s flower color we have two possibilities F (for purple flowers) and f (for white flowers). One allele comes from the female parent, one comes from the male parent.

Homozygous

Two alleles of the same trait are the same

Example: TT or tt

Heterozygous

Two different alleles for the same trait

Example Tt

Dominant

The allele that is always displayed in a mixed (heterozygous Tt) cross.

Represented by an upper case letter ex: T

Tongue curling is a dominant trait.

Recessive

A gene that is only displayed if both alleles are the same.

Represented by a lower case letter ex: t

The bent finger is dominant and the straight finger is recessive.

Question

Is “W” dominant or recessive? Is “w” dominant or recessive?

Genetic Alleles and Homologous Chromosomes

– Homologous chromosomes• Have genes at specific loci.• Have alleles of a gene at the same locus.

Phenotype

What the organism looks like. Memory trick: PH in “phenotype” is like the

PH in “photo” Example: red, white, furry, bald.

Genotype

The genetic constitution of the organism. In other words the genes of that organism.

Memory trick: GEN in “genotype” is like the GEN in “gene”

Example: RR, rr, Rr

Question

In a heterozygous cross of short plants and tall plants how would you represent the trait with letters?

Question

In a heterozygous flower if the dominant trait’s genotype was for a purple phenotype and the recessive trait’s genotype was for a yellow phenotype. What would the flower’s phenotype be?

P Generation

The parental generation These are true breeding plants. They will always

produce the same traits. They are homozygous for a trait YY or yy

F1 Generation The first generation. These result after a cross from two parents of the P

generation with different traits. Heterozygous Yy The F1 generation are often

referred to as hybrids as they will have mixed genotypes but the same phenotype.

F2 Generation These are the offspring of a cross between

the heterozygous F1 generation Yy X Yy These offspring will have

mixed genotypes andphenotypes.

Bellwork 11/18/10 - Week 15 Monohybrid Cross – 1 trait

Example: hair color

B (blue hair) dominant

b (white hair) recessive

Make A Punnett Square Genotype

Mother = BB What is the mother’s phenotype?

Father = bb What is the father’s phenotype?

Question

How do you set up a Punnett square for this cross?

Make a Punnett IMother BB

(take one B and put it over each box)

Fat

her

b

b

B B

bb

(colors used in genotypes to help you to see where each one goes in the box)

Fill in the genotypes for each offspring

B = blue hairb = white hair



Fat

her

b

b

B B

bb


bB bB

bBbB

What is the phenotype for each offspring?




Fat

her

b

b

B B

bb


bB bB

bBbB

Blue Hair Blue Hair

Blue Hair Blue Hair


Question

1. How many white haired offspring are there?

2. How many blue haired offspring are there?

Answer

1. 0

2. 4 or 4/4

Answer

Both parents are Bb They both have blue hair

Mendel’s First LawThis law states that allele pairs separate or segregate during the formation of eggs and sperm (gamete formation), and randomly come back together (unite) at fertilization.

The Law of Segregation

Mendel’s Second Law

Different traits are inherited separately (independently) of each other.

The Law Of Independent Assortment

Mendel’s Third Law

If a homozygous dominant parent (TT) is crossed with a homozygous recessive parent (tt) the offspring will ALWAYS be Tt, displaying the dominant phenotype.

The Law Of Dominance

Question

So how do we predict the probability of offspring types between two parents?

Think about how we predict a coin flip: With a coin flip.

1 in 2 that it will be heads.

Punnett Square

Used to show all possible combinations.

Question

There are two parents who are both heterozygous for hair color, where blue was B and white was b

What is the genotype for each parent? What is the phenotype for each parent?

Make a Punnett IIMother Bb


Fat

her

B

b

B b

bB


Fill in the genotypes for each offspring


What is the phenotype for each offspring?

Question

1. How many white haired offspring are there?

2. How many blue haired offspring are there?

Dihybrid Cross

Used for two traits

Example:

R (round) dominant Y (yellow) dominant

r (wrinkled) recessive y (green) recessive

Genotype

Mother = RyrY What is the mother’s phenotype?

Father = RyrY What is the father’s phenotype?

Dihybrid Cross

Used for two traits

Example:

R (round) dominant Y (yellow) dominant

r (wrinkled) recessive y (green) recessive

Genotype

Mother = RYry What is the mother’s phenotype?

Father = RYry What is the father’s phenotype?

Make a PunnettMother RrYy

(take one allele pair and put it over each box)

Fat

her

R

rYy

RY

R Y(colors used in genotypes to help you to see where each one goes in the box)

Fill in the genotypes & phenotypes for each offspring

R = round r =wrinkled Y = yellow y = green

r YR y

r y

rY Ry ry

Question

1. How many round & yellow peas are there?

2. How many round & green peas are there?

3. How many wrinkled & yellow peas are there?

4. How many wrinkles & green peas are there?

Using a Testcross to Determine an Unknown Genotype

– A testcross is a mating between An individual of unknown genotype and a homozygous

recessive individual.

– The rule of multiplication states that

• The probability of a compound event is the product of the separate probabilities of the independent events.

The Rules of Probability

Summary of Mendel’s lawsSummary of Mendel’s lawsLAWLAW PARENT PARENT

CROSSCROSS OFFSPRINGOFFSPRING

DOMINANCEDOMINANCE TT x ttTT x tt tall x shorttall x short

100% Tt 100% Tt talltall

SEGREGATIONSEGREGATION Tt x TtTt x Tt tall x talltall x tall

75% tall 75% tall (TT & Tt)(TT & Tt)25% short25% short (tt) (tt)

INDEPENDENT INDEPENDENT ASSORTMENTASSORTMENT

RrGg x RrGgRrGg x RrGg round & round & green x green x round & round & greengreen

9/16 round seeds & green 9/16 round seeds & green pods pods

3/16 round seeds & yellow 3/16 round seeds & yellow pods pods

3/16 wrinkled seeds & 3/16 wrinkled seeds & green pods green pods

1/16 wrinkled seeds & 1/16 wrinkled seeds & yellow podsyellow pods

Incomplete Dominance, Codominance, Sex-Linked

Traits & Multiple Alleles

Beyond Mendel

Variations On Mendel’s Laws

–Some patterns of genetic inheritance are not explained by Mendel’s laws.

Incomplete DominanceIncomplete Dominance

F1 hybrids F1 hybrids have an appearance somewhat in in betweenbetween the phenotypes phenotypes of the two parents.

Example:Example: snapdragons (flower)snapdragons (flower)red (RR) x white (rr)

RR = red flowerRR = red flowerrr = white flower r

r

R R


rr

rr

RR RR

All _____ =All _____ = pink pink(heterozygous pink)(heterozygous pink)

produces theproduces the_____ generation_____ generation

ABO Blood Type: An Example of Multiple Alleles and Codominance

– Multiple alleles are traits that are controlled by more than two alleles.

Multiple Alleles continued

Note: An individual can only have two alleles for any given trait, but the population can have many different alleles for that trait, sometimes over 100 different alleles for a single trait!

Examples: Rabbit coat color, feather color, human hair color.

Codominance

– Two of the human blood type alleles exhibit codominance.Both alleles are expressed in the

phenotype.

CodominanceCodominance

Two allelesTwo alleles are expressed ( are expressed (multiple multiple allelesalleles) in ) in heterozygous individualsheterozygous individuals..

Example:Example: blood type blood type1.1. type Atype A = I= IAAIIAA or I or IAAii2.2. type Btype B = I= IBBIIBB or I or IBBii3.3. type ABtype AB = I= IAAIIBB

4.4. type Otype O = ii= ii

Codominance ProblemCodominance Problem

Example: homozygous male Type B (IBIB)

x heterozygous female Type A (IAi)

IA

IB IB

i

Another Codominance ProblemAnother Codominance Problem

• Example:Example: male Type O (ii) x female type AB (IAIB)

CodominanceCodominance

QuestionQuestion::If a boy has a blood type O and his sister has If a boy has a blood type O and his sister has blood type AB, blood type AB, what are the genotypes and what are the genotypes and phenotypes of their parents?phenotypes of their parents?

boy - boy - type O (ii) type O (ii) X girl - X girl - type AB (Itype AB (IAAIIBB))

Polygenic Inheritance

– Polygenic inheritance is the additive effects of two or more genes on a single phenotype.

Bellwork Pre-AP Biology

A red flower (RR) is crossed with a white flower (rr).

1. In the case of codominance what is the phenotype of the offspring?

2. In the case of incomplete dominance what is the phenotype of the offspring?

3. What generation is the offspring?

Sex-linked TraitsSex-linked Traits

Traits (genes) located on the Traits (genes) located on the sex sex chromosomeschromosomes

Sex chromosomes are Sex chromosomes are X and YX and Y XXXX genotype for femalesgenotype for females XYXY genotype for males genotype for males Many Many sex-linked traitssex-linked traits carried on carried on XX

chromosomechromosome

Sex-Linked Genes

– Sex-linked genes Are any genes

located on a sex chromosome.

Were discovered during studies on fruit flies.

Sex-linked TraitsSex-linked Traits

Sex ChromosomesSex Chromosomes

XX chromosome - female Xy chromosome - male

fruit flyeye color

Example: Example: Eye color in fruit fliesEye color in fruit flies

Sex-linked Trait ProblemSex-linked Trait Problem

Example: Eye color in fruit flies (red-eyed male) x (white-eyed female)

XRY x XrXr

Remember: the Y chromosome in males does not carry traits. RR = red eyed Rr = red eyed rr = white eyed Xy = male XX = female XR

XR y

Xr

Sex-Linked Disorders in Humans

– A number of human conditions result from sex-linked (X-linked) genes.

Is characterized by a malfunction of light-sensitive cells in the eyes.

Red-Green Color Blindness

Is characterized by a progressive weakening and loss of muscle tissue.

Duchenne Muscular Dystrophy

Is a blood-clotting disease.

Hemophilia

Female CarriersFemale Carriers

What is a carrier? Why are females usually carriers?

Pedigree Charts

The family tree of genetics

Family Pedigrees

– Mendel’s principles apply to the inheritance of many human traits.

A family pedigree

Shows the history of a trait in a family.Allows geneticists to analyze human traits.

What is a Pedigree?

A pedigree is a chart of the genetic history of family over several generations.

Scientists or a genetic counselor would find out about your family history and make this chart to analyze.

Constructing a Pedigree

Male

Female

Connecting Pedigree Symbols

Fraternal twins

Identical twins

Examples of connected symbols:Examples of connected symbols:

Connecting Pedigree Symbols

Married Couple

Siblings

Examples of connected symbols:Examples of connected symbols:

Example

What does a pedigree chart look like?

Symbols in a Pedigree Chart

Has the traitX-linkedAutosomal carrierDeceased

Interpreting a Pedigree Chart

1. Determine if the pedigree chart shows an autosomal or X-linked disease.

– If most of the males in the pedigree are affected the disorder is X-linked

– If it is a 50/50 ratio between men and women the disorder is autosomal.

Example of Pedigree Charts

Is it Autosomal or X-linked?

Interpreting a Pedigree Chart

2. Determine whether the disorder is dominant or recessive.

– If the disorder is dominant, one of the parents must have the disorder.

– If the disorder is recessive, neither parent has to have the disorder because they can be heterozygous.

Example of Pedigree Charts

Dominant or Recessive?

Summary

Pedigrees are family trees that explain your genetic history.

Pedigrees are used to find out the probability of a child having a disorder in a particular family.

To begin to interpret a pedigree, determine if the disease or condition is autosomal or X-linked and dominant or recessive.

Pedigree Chart -Cystic Fibrosis

Human Disorders Controlled

by a Single Gene– Many human traits• Show simple inheritance patterns.• Are controlled by genes on autosomes.

Recessive Disorders

– Most human genetic disorders are recessive.Individuals can be carriers of these diseases.

Figure 9.14

Dominant Disorders

– Some human genetic disorders are dominant.

Achondroplasia is a form of dwarfism.

Huntington’s disease is another example of a dominant disorder

Evolution Connection:The Telltale Y Chromosome

– Sex chromosomesInfluence the inheritance of certain traits.The Y chromosome of human males is only

about one-third the size of the X chromosome.Biologists believe that X and Y were once a

fully homologous pair.Major episodes of change have rearranged

pieces of the Y chromosome.

– Researchers recently used comparisons of Y DNA to confirm that the Lemba tribe in Africa descended from ancient Jewish people.

Evolution Connection:The Telltale Y Chromosome

Off to the computer lab!!!!

A Tour of Genetics

Bellwork : Which fact interests you the most and why?

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