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Genetic Inheritance

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http://fi.wikipedia.org/wiki/Gregor_Mendel. http://www.personal.psu.edu/staff/d/c/dcw1/graphics/pea_plant.jpg. Genetic Inheritance. Father of Modern Genetics. The first person to trace the characteristics of successive generations of a living thing. - PowerPoint PPT Presentation

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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.

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• 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

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Where Mendel Studied

• He was later sent to the University of Vienna to study. By both his professors at University and his colleagues at the monastery, Mendel was inspired to study variance in plants

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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.

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How Mendel Got Started

• Mendel's attraction to research was based on his love of nature.

• He was not only interested in plants, but also in meteorology and theories of evolution.

• Mendel often wondered how plants obtained atypical characteristics.

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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.“

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

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Mendel's research reflected his personality.

Once he crossed peas and mice of different varieties "for the fun of the thing," and the phenomena of dominance and segregation "forced themselves upon notice."

He saw that the traits were inherited in certain numerical ratios.

He then came up with the idea of dominance and segregation of genes and set out to test it in peas.

It took seven years to cross and score the plants to the thousand to prove the laws of inheritance!

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Mendel's work became the foundation for modern genetics.

• The impact of genetic theory is no longer questioned in anyone's mind.

• Many diseases are known to be inherited• and pedigrees are typically traced to

determine the probability of passing along an hereditary disease.

• Plants are now designed in laboratories to exhibit desired characteristics.

• The practical results of Mendel's research has not only changed the way we perceive the world, but also the way we live in it.

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• Took seven years to prove laws of inheritance

• -Basic Laws-• Heredity Factors do not combine• Each member of a parental

generation transfers only one half of its heredity factors to each offspring

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• Mendel’s works became the foundation of modern genetics

• Later crossed mice and pea plants• Noticed traits were inherited in certain

numerical ratios• Came up with idea of dominance and

segregation of genes and set out to test it in peas

• Love of nature encouraged his interest in research

• Also interested in meteorology and theories of evolution

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• Is the study of heredity

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• Heredity: the transmission of traits from one generation to the next


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Its all in our genes

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• You have already learned about chromosomes as compact carriers of DNA.

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• “A discrete unit of hereditary information consisting of a specific nucleic sequence in DNA (or RNA in some viruses)”

• -Campbell Biology

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• Locus: a gene’s specific location on a chromosome ( the plural is loci)

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• Homologous Chromosomes: alike chromosomes carrying genes for the same heritable characteristics

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Homologous Chromosomes


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• Allele: an alternate form of a gene• Ie. One coding for blue eyes and one for



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• The joining point of 2 sister chromatids

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• telomere: the protective structure at the end of the chromosome (protects DNA when it is copied)

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Sister chromatids

• Replicated forms of a chromosome jointed together by the centromere and eventually separated by mitosis or meiosis 2

(Don’t worry we’ll be learning about mitosis and meiosis on Monday)

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Parts of a Chromosome


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• Character: a feature that can be inherited by offspring from a parent (i.e. blue eyes)


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• Trait: a variation of a character

I.e. blue or green brown eyes are traits


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What Mendel did

• He took true breeding pea plants

• Meaning the parents only produced offspring with the same combination of traits that they had.


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The parents possessed a combination of traits below


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For now we will examine one trait set at a time

• This is called monohybridization or a monohybrid cross

• The crossing of a single trait

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• The parents generation is the P generation

• The first generation of offspring is the F1 generation

• The second generation of offspring is the F2 generation

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• The following is adapted from: http://www.borg.com/~lubehawk/mendel.htm#Law%202%20Seg

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• 1. the Law of Dominance 2. the Law of Segregation 3. the Law of Independent Assortment

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The Law of Dominance

• “In a cross of parents that are pure for contrasting traits, only one form of the trait will appear in the next generation.  Offspring that are hybrid for a trait will have only the dominant trait in the phenotype.”

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• A dominant trait will mask or cover up a recessive trait

• A recessive trait is only seen if the offspring receive a copy of it from each parent

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• Dominant DOES NOT = better


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• A Dominant trait is expressed as a capital letter i.e. A

• A Recessive trait is expressed as a lowercase letter i.e. a

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The Law of Segregation

“During the formation of gametes (eggs or sperm), the two alleles responsible for a trait separate from each other.  Alleles for a trait are then

"recombined" at fertilization, producing the genotype for the traits of the offspring. “

(more about this on Monday)

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The Law of Independent Assortment

“Alleles for different traits are distributed to sex cells (& offspring) independently of one another.”

In other words the traits can be in any combinations in offspring it doesn't have to be all from the mother or all from the father.

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Sweet picture I found on the internet

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• Homozygous : having identical alleles for the same character “AA or aa”

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• Heterozygous: having 2 different alleles for the same character “Aa”

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Genotype: what the genetic code of the organism is

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Phenotype: what is actually expressed (seen)

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• Expressed traits: the phenotype what is seen

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How do we do this?


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Parents Tt & tt

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Try this one


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Now try this

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One step further comparing two traits at once

• dihybrid cross: comparing two traits simultaneously

YYRR yyrr

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F1 generation

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• Incomplete dominance- a blending of characters. No dominant or recessive

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Good site for help



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Try these

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• Taken from http://anthro.palomar.edu/synthetic/synth_2.htm

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• “This definition of evolution was developed largely as a result of independent work in the early 20th century by Godfrey Hardy, an English mathematician, and Wilhelm Weinberg, a German physician.  Through mathematical modeling based on probability, they concluded in 1908 that gene pool frequencies are inherently stable but that evolution should be expected in all populations virtually all of the time.  They resolved this apparent paradox by analyzing the net effects of potential evolutionary mechanisms. “

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• They originally wrote it in a restaurant ton a napkin after a conversation about the topic.

• Don’t you wish you were that smart

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The 7 conditions need to use the equation

• 1.   mutation is not occurring

• 2.  natural selection is not occurring

• 3.  the population is infinitely large

• 4.  all members of the population breed

• 5.  all mating is totally random

• 6.  everyone produces the same number of offspring

• 7.  there is no migration in or out of the population

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• “used to discover the probable genotype frequencies in a population and to track their changes from one generation to another “

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Hardy-Weinberg equilibrium equation

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What the letter mean

• p is defined as the frequency of the dominant allele

• q as the frequency of the recessive allele • p² is the predicted frequency of

homozygous dominant (AA) • 2pq is the predicted frequency of

heterozygous (Aa) • q² is the predicted frequency of

homozygous recessive (aa)

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• Those who express the trait in their phenotype could be either homozygous dominant (p²) or heterozygous (2pq).

• The dominant phenotype is p = 1 - q

• The recessive phenotype is q

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• Albinism is a rare genetically inherited trait that is only expressed in the phenotype of homozygous recessive individuals (aa). The average human frequency of albinism in North America is only about 1 in 20,000.


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• Referring back to the Hardy-Weinberg equation (p² + 2pq + q² = 1), the frequency of homozygous recessive individuals (aa) in a population is q².  Therefore, in North America the following must be true for albinism:

• q² = 1/20,000 = .00005

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• By taking the square root of both sides of this equation, we get:    (Note: the numbers in this example are rounded off for simplification.)

• q = .007     

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• In other words, the frequency of the recessive albinism allele (a) is .00707 or about 1 in 140.  Knowing one of the two variables (q) in the Hardy-Weinberg equation, it is easy to solve for the other (p).

• p = 1 - qp = 1 - .007p = .993• The frequency of the dominant, normal allele (A)

is, therefore, .99293 or about 99 in 100.

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• The next step is to plug the frequencies of p and q into the Hardy-Weinberg equation:

• p² + 2pq + q² = 1

• (.993)² + 2 (.993)(.007) + (.007)² = 1

• .986 + .014 + .00005 = 1

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This gives us the frequencies for each of the three genotypes for this

trait in the population:• p² =

predicted frequencyof homozygousdominant individuals = .986 = 98.6%

• 2pq =predicted frequencyof heterozygousindividuals = .014 = 1.4%

• q² =predicted frequencyof homozygousrecessive individuals (the albinos)

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• With a frequency of .005% (about 1 in 20,000), albinos are extremely rare.  However, heterozygous carriers for this trait, with a predicted frequency of 1.4% (about 1 in 72), are far more common than most people imagine.  There are roughly 278 times more carriers than albinos.  Clearly, though, the vast majority of humans (98.6%) probably are homozygous dominant and do not have the albinism allele. why?

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• expressed, homozygous, heterozygous, monohybrid cross, dihybrid cross, plieotrophy, complete dominance, multiple alleles, hardy-weinberg, ratios ecological effect p435

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Sites for practice

• http://www.changbioscience.com/genetics/punnett.html

• http://science.nhmccd.edu/biol/dihybrid/dihybrid.html

• http://www.athro.com/evo/gen/punexam.html#monohybrid