Mendel and the gene idea l.jpg
This presentation is the property of its rightful owner.
Sponsored Links
1 / 108

Mendel and the Gene Idea PowerPoint PPT Presentation


  • 147 Views
  • Uploaded on
  • Presentation posted in: General

Mendel and the Gene Idea. Inheritance. The passing of traits from parents to offspring. Humans have known about inheritance for thousands of years. Genetics. The scientific study of the inheritance. Genetics is a relatively “new” science (about 150 years). Genetic Theories.

Download Presentation

Mendel and the Gene Idea

An Image/Link below is provided (as is) to download presentation

Download Policy: Content on the Website is provided to you AS IS for your information and personal use and may not be sold / licensed / shared on other websites without getting consent from its author.While downloading, if for some reason you are not able to download a presentation, the publisher may have deleted the file from their server.


- - - - - - - - - - - - - - - - - - - - - - - - - - E N D - - - - - - - - - - - - - - - - - - - - - - - - - -

Presentation Transcript


Mendel and the gene idea l.jpg

Mendel and the Gene Idea


Inheritance l.jpg

Inheritance

  • The passing of traits from parents to offspring.

  • Humans have known about inheritance for thousands of years.


Genetics l.jpg

Genetics

  • The scientific study of the inheritance.

  • Genetics is a relatively “new” science (about 150 years).


Genetic theories l.jpg

Genetic Theories

1. Blending Theory -

traits were like paints and mixed evenly from both parents.

2. Incubation Theory -

only one parent controlled the traits of the children.

Ex: Spermists and Ovists


Slide5 l.jpg

3. Particulate Model -

parents pass on traits as discrete units that retain their identities in the offspring.


Gregor mendel l.jpg

Gregor Mendel

  • Father of Modern Genetics.


Slide7 l.jpg

  • Mendel’s paper published in 1866, but was not recognized by Science until the early 1900’s.


Reasons for mendel s success l.jpg

Reasons for Mendel's Success

  • Used an experimental approach.

  • Applied mathematics to the study of natural phenomena.

  • Kept good records.


Slide9 l.jpg

Mendel was a pea picker.

He used peas as his study organism.


Why use peas l.jpg

Why Use Peas?

  • Short life span.

  • Bisexual.

  • Many traits known.

  • Cross- and self-pollinating.

  • (You can eat the failures).


Cross pollination l.jpg

Cross-pollination

  • Two parents.

  • Results in hybrid offspring where the offspring may be different than the parents.


Self pollination l.jpg

Self-pollination

  • One flower as both parents.

  • Natural event in peas.

  • Results in pure-bred offspring where the offspring are identical to the parents.


Mendel s work l.jpg

Mendel's Work

  • Used seven characters, each with two expressions or traits.

  • Example:

  • Character - height

    • Traits - tall or short.


Monohybrid or mendelian crosses l.jpg

Monohybrid or Mendelian Crosses

  • Crosses that work with a single character at a time.

    Example - Tall X short


P generation l.jpg

P Generation

  • The Parental generation or the first two individuals used in a cross.

    Example - Tall X short

  • Mendel used reciprocal crosses, where the parents alternated for the trait.


Offspring l.jpg

Offspring

  • F1 - first filial generation.

  • F2 - second filial generation, bred by crossing two F1 plants together or allowing a F1 to self-pollinate.


Another sample cross l.jpg

Another Sample Cross

P1 Tall X short (TT x tt)

F1 all Tall (Tt)

F2 3 tall to 1 short

(1 TT: 2 Tt: 1 tt)


Results summary l.jpg

Results - Summary

  • In all crosses, the F1 generation showed only one of the traits regardless of which wasmaleorfemale.

  • The other trait reappeared in the F2 at ~25% (3:1 ratio).


Mendel s hypothesis l.jpg

Mendel's Hypothesis

1. Genes can have alternate versions called alleles.

2. Each offspring inherits two alleles, one from each parent.


Mendel s hypothesis24 l.jpg

Mendel's Hypothesis

3. If the two alleles differ, the dominant allele is expressed. The recessive allele remains hidden unless the dominant allele is absent.

Comment - do not use the terms “strongest” to describe the dominant allele.


Mendel s hypothesis25 l.jpg

Mendel's Hypothesis

4. The two alleles for each trait separate during gamete formation. This now called: Mendel's Law of Segregation


Law of segregation l.jpg

Law of Segregation


Mendel s experiments l.jpg

Mendel’s Experiments

  • Showed that the Particulate Model best fit the results.


Vocabulary l.jpg

Vocabulary

  • Phenotype - the physical appearance of the organism.

  • Genotype - the genetic makeup of the organism, usually shown in a code.

    • T = tall

    • t = short


Helpful vocabulary l.jpg

Helpful Vocabulary

  • Homozygous - When the two alleles are the same (TT/tt).

  • Heterozygous- When the two alleles are different (Tt).


6 mendelian crosses are possible l.jpg

6 Mendelian Crosses are Possible

CrossGenotypePhenotype

TT X tt all Tt all Dom

Tt X Tt 1TT:2Tt:1tt 3 Dom: 1 Res

TT X TT all TT all Dom

tt X tt all tt all Res

TT X Tt 1TT:1Tt all Dom

Tt X tt 1Tt:1tt 1 Dom: 1 Res


Test cross l.jpg

Test Cross

  • Cross of a suspected heterozygote with a homozygous recessive.

  • Ex: T_ X tt

    If TT - all dominant

    If Tt - 1 Dominant: 1 Recessive


Dihybrid cross l.jpg

Dihybrid Cross

  • Cross with two genetic traits.

  • Need 4 letters to code for the cross.

    • Ex: TtRr

  • Each Gamete - Must get 1 letter for each trait.

    • Ex. TR, Tr, etc.


Number of kinds of gametes l.jpg

Number of Kinds of Gametes

  • Critical to calculating the results of higher level crosses.

  • Look for the number of heterozygous traits.


Equation l.jpg

Equation

The formula 2n can be used, where “n” = the number of heterozygous traits.

Ex: TtRr, n=2

22 or 4 different kinds of gametes are possible.

TR, tR, Tr, tr


Dihybrid cross37 l.jpg

Dihybrid Cross

TtRr X TtRr

Each parent can produce 4 types of gametes.

TR, Tr, tR, tr

Cross is a 4 X 4 with 16 possible offspring.


Results l.jpg

Results

  • 9 Tall, Red flowered

  • 3 Tall, white flowered

  • 3 short, Red flowered

  • 1 short, white flowered

    Or: 9:3:3:1


Law of independent assortment l.jpg

Law of Independent Assortment

  • The inheritance of 1st genetic trait is NOT dependent on the inheritance of the 2nd trait.

  • Inheritance of height is independent of the inheritance of flower color.


Comment l.jpg

Comment

  • Ratio of Tall to short is 3:1

  • Ratio of Red to white is 3:1

  • The cross is really a product of the ratio of each trait multiplied together. (3:1) X (3:1)


Probability l.jpg

Probability

  • Genetics is a specific application of the rules of probability.

  • Probability - the chance that an event will occur out of the total number of possible events.


Genetic ratios l.jpg

Genetic Ratios

  • The monohybrid “ratios” are actually the “probabilities” of the results of random fertilization.

    Ex: 3:1

    75% chance of the dominant

    25% chance of the recessive


Rule of multiplication l.jpg

Rule of Multiplication

  • The probability that two alleles will come together at fertilization, is equal to the product of their separate probabilities.


Example ttrr x ttrr l.jpg

Example: TtRr X TtRr

  • The probability of getting a tall offspring is ¾.

  • The probability of getting a red offspring is ¾.

  • The probability of getting a tall red offspring is ¾ x ¾ = 9/16


Comment47 l.jpg

Comment

  • Use the Product Rule to calculate the results of complex crosses rather than work out the Punnett Squares.

  • Ex: TtrrGG X TtRrgg


Solution l.jpg

Solution

“T’s” = Tt X Tt = 3:1

“R’s” = rr X Rr = 1:1

“G’s” = GG x gg = 1:0

Product is:

(3:1) X (1:1) X (1:0 ) = 3:3:1:1


Tips for dihybrid problems l.jpg

Tips for Dihybrid Problems

  • Identify all of the alleles that can be identified from the phenotypes of the parents or kids.

  • Work from the monohybrid ratios to solve for the missing alleles.


Variations on mendel l.jpg

Variations on Mendel

1. Incomplete Dominance

2. Codominance

3. Multiple Alleles

4. Epistasis

5. Polygenic Inheritance


Incomplete dominance l.jpg

Incomplete Dominance

  • When the F1 hybrids show a phenotype somewhere between the phenotypes of the two parents.

    Ex. Red X White snapdragons

    F1 = all pink

    F2 = 1 red: 2 pink: 1 white


Result l.jpg

Result

  • No hidden Recessive.

  • 3 phenotypes and 3 genotypes (Hint! – often a “dose” effect)

    • Red = CR CR

    • Pink = CRCW

    • White = CWCW


Another example l.jpg

Another example


Codominance l.jpg

Codominance

  • Both alleles are expressed equally in the phenotype.

  • Ex. MN blood group

    • MM

    • MN

    • NN


Result56 l.jpg

Result

  • No hidden Recessive.

  • 3 phenotypes and 3 genotypes (but not a “dose” effect)


Multiple alleles l.jpg

Multiple Alleles

  • When there are more than 2 alleles for a trait.

  • Ex. ABO blood group

    • IA - A type antigen

    • IB - B type antigen

    • i - no antigen


Result58 l.jpg

Result

  • Multiple genotypes and phenotypes.

  • Very common event in many traits.


Alleles and blood types l.jpg

Alleles and Blood Types

TypeGenotypes

A IA IA or IAi

B IB IB or IBi

AB IAIB

O ii


Comment62 l.jpg

Comment

  • Rh blood factor is a separate factor from the ABO blood group.

  • Rh+ = dominant

  • Rh- = recessive

  • A+ blood = dihybrid trait


Epistasis l.jpg

Epistasis

  • When 1 gene locus alters the expression of a second locus.

  • Ex:

  • 1st gene: C = color, c = albino

  • 2nd gene: B = Brown, b = black


Gerbils l.jpg

Gerbils


In gerbils l.jpg

In Gerbils

CcBb X CcBb

Brown X Brown

F1 = 9 brown (C_B_)

3 black (C_bb)

4 albino (cc__)


Result66 l.jpg

Result

  • Ratios often altered from the expected.

  • One trait may act as a recessive because it is “hidden” by the second trait.


Epistasis in mice l.jpg

Epistasis in Mice


Problem l.jpg

Problem

  • Wife is type A

  • Husband is type AB

  • Child is type O

    Question - Is this possible?

    Comment - Wife’s boss is type O


Bombay effect l.jpg

Bombay Effect

  • Epistatic Gene on ABO group.

  • Alters the expected ABO outcome.

  • H = dominant, normal ABO

  • h = recessive, no A,B, reads as type O blood.


Genotypes l.jpg

Genotypes

  • Wife: type A (IA IA , Hh)

  • Husband: type AB (IAIB, Hh)

  • Child: type O (IA IA , hh)

    Therefore, the child is the offspring of the wife and her husband (and not the boss).


Bombay detection l.jpg

Bombay - Detection

  • When ABO blood type inheritance patterns are altered from expected.


Ap biology l.jpg

AP Biology

Best Looking Bio Teacher EVER.

Who’s Hungry?

It Came From Space!

He Made New Friends.

FEED ME!

This Isn’t a Human at All!

Zachary - IASMH


Homework l.jpg

Homework

  • Readings – Chapters 14, 47

  • Lab – changed to Chi Square and other genetics.

  • Chapter 47 – Wed. 12/1

  • Chapter 14 – Fri. 12/3


New 1 800 l.jpg

New 1-800

  • You can now reach my office directly 24/7 by calling:

    1-800-316-3163 ext. 31


Polygenic inheritance l.jpg

Polygenic Inheritance

  • Factors that are expressed as continuous variation.

  • Lack clear boundaries between the phenotype classes.

  • Ex: skin color, height


Genetic basis l.jpg

Genetic Basis

  • Several genes govern the inheritance of the trait.

  • Ex: Skin color is likely controlled by at least 4 genes. Each dominant gives a darker skin.


Result78 l.jpg

Result

  • Mendelian ratios fail.

  • Traits tend to "run" in families.

  • Offspring often intermediate between the parental types.

  • Trait shows a “bell-curve” or continuous variation.


Genetic studies in humans l.jpg

Genetic Studies in Humans

  • Often done by Pedigree charts.

  • Why?

    • Can’t do controlled breeding studies in humans.

    • Small number of offspring.

    • Long life span.


Pedigree chart symbols l.jpg

Pedigree Chart Symbols

Male

Female

Person with trait


Sample pedigree l.jpg

Sample Pedigree


Slide82 l.jpg

Recessive Trait

Dominant Trait


Human recessive disorders l.jpg

Human Recessive Disorders

  • Several thousand known:

    • Albinism

    • Sickle Cell Anemia

    • Tay-Sachs Disease

    • Cystic Fibrosis

    • PKU

    • Galactosemia


Sickle cell disease l.jpg

Sickle-cell Disease

  • Most common inherited disease among African-Americans.

  • Single amino acid substitution results in malformed hemoglobin.

  • Reduced O2 carrying capacity.

  • Codominant inheritance.


Tay sachs l.jpg

Tay-Sachs

  • Eastern European Jews.

  • Brain cells unable to metabolize type of lipid, accumulation of causes brain damage.

  • Death in infancy or early childhood.


Cystic fibrosis l.jpg

Cystic Fibrosis

  • Most common lethal genetic disease in the U.S.

  • Most frequent in Caucasian populations (1/20 a carrier).

  • Produces defective chloride channels inmembranes.


Recessive pattern l.jpg

Recessive Pattern

  • Usually rare.

  • Skips generations.

  • Occurrence increases with consaguineous matings.

  • Often an enzyme defect.

  • Affects males and females equally.


Human dominant disorders l.jpg

Human Dominant Disorders

  • Less common then recessives.

  • Affects males and females equally.

  • Ex:

    • Huntington’s disease

    • Achondroplasia

    • Familial Hypercholesterolemia


Inheritance pattern l.jpg

Inheritance Pattern

  • Each affected individual had one affected parent.

  • Doesn’t skip generations.

  • Homozygous cases show worse phenotype symptoms.

  • May have post-maturity onset of symptoms.


Genetic screening l.jpg

Genetic Screening

  • Risk assessment for an individual inheriting a trait.

  • Uses probability to calculate the risk.


General formal l.jpg

General Formal

R = F X M X D

R = risk

F = probability that the female carries the gene.

M = probability that the male carries the gene.

D = Disease risk under best conditions.


Example l.jpg

Example

  • Wife has an albino parent.

  • Husband has no albinism in his pedigree.

  • Risk for an albino child?


Risk calculation l.jpg

Risk Calculation

  • Wife = probability is 1.0 that she has the allele.

  • Husband = with no family record, probability is near 0.

  • Disease = this is a recessive trait, so risk is Aa X Aa = .25

  • R = 1 X 0 X .25

  • R = 0


Risk calculation95 l.jpg

Risk Calculation

  • Assume husband is a carrier, then the risk is:

    R = 1 X 1 X .25

    R = .25

    There is a .25 chance that every child will be albino.


Common mistake l.jpg

Common Mistake

  • If risk is .25, then as long as we don’t have 4 kids, we won’t get any with the trait.

  • Risk is .25 for each child. It is not dependent on what happens to other children.


Carrier recognition l.jpg

Carrier Recognition

  • Fetal Testing

    • Amniocentesis

    • Chorionic villi sampling

  • Newborn Screening


Fetal testing l.jpg

Fetal Testing

  • Biochemical Tests

  • Chromosome Analysis


Amniocentesis l.jpg

Amniocentesis

  • Administered between 11 - 14 weeks.

  • Extract amnionic fluid = cells and fluid.

  • Biochemical tests and karyotype.

  • Requires culture time for cells.


Chorionic villi sampling l.jpg

Chorionic Villi Sampling

  • Administered between 8 - 10 weeks.

  • Extract tissue from chorion (placenta).

  • Slightly greater risk but no culture time required.


Newborn screening l.jpg

Newborn Screening

  • Blood tests for recessive conditions that can have the phenotypes treated to avoid damage. Genotypes are NOT changed.

  • Ex. PKU


Newborn screening104 l.jpg

Newborn Screening

  • Required by law in all states.

  • Tests 1- 6 conditions.

  • Required of “home” births too.


Multifactorial diseases l.jpg

Multifactorial Diseases

  • Where Genetic and Environment Factors interact to cause the Disease.


Ex heart disease l.jpg

Ex. Heart Disease

  • Genetic

  • Diet

  • Exercise

  • Bacterial Infection


Summary l.jpg

Summary

  • Know the Mendelian crosses and their patterns.

  • Be able to work simple genetic problems (practice).

  • Watch genetic vocabulary.

  • Be able to read pedigree charts.


Summary108 l.jpg

Summary

  • Be able to recognize and work with some of the “common” human trait examples.


  • Login