Chapter 11: Genetics. Understanding Genetics Genetics – the branch of biology that studies heredity (the passing on of traits from parent to offspring)

Chapter 11: GeneticsChapter 11: Genetics

Understanding Genetics

Genetics – the branch of biology that studies heredity (the passing on of traits from parent to offspring)

11-1: The Work Of Gregor Mendel-1: The Work Of Gregor Mendel

• a.k.a. “Father of Genetics”• Founded Modern Genetics• Monk who worked in a

monastery ; in charge of the garden

• Grew over 28,000 pea plants (Pistum sativum) and studied their unique characteristics passed from one generation to the next.

• See pg 309 in Macaw Biology book for further details

Before we continue…

It is important to remember that we get half our genetic material from MOM and the other half from DAD.

Therefore, we have two genes* for each trait we have.

We presently know this because of Mendel.

*Sometimes we have more than two genes for each trait but we’ll talk about that later.

Homozygous/Heterozygous

• The two genes for the same trait are called alleles.

• These alleles can have the same form or contrasting forms.

• If the alleles are the same, they are called HOMOZYGOUS or Pure for that trait

• If the alleles are contrasting, they are called HETEROZYGOUS or Hybrid for that trait.

Dominant and Recessive Genes

• Some alleles can be dominant meaning they code for the more influential trait.

• Some alleles can be recessive meaning they code for the more subtle trait.

• For example: Brown eyes are dominant over green or blue eyes.

Applying Mendel’s Genetics

There are two factors that determine everything about an organism:

1) HeredityHeredity - - what you inheritwhat you inheritExamples of thing you inherit: Color of hair, skin, eyes, height, frame size, handedness, disease/disorder, tongue-rolling, IQ, shape of teeth, athleticism, vision, # of digits.

2. EnvironmentEnvironment - what you acquire - what you acquire

• Examples of things you acquire: Ability to play an instrument, skills of a sport, disability/illness, job skills.

• Things you inherit can sometimes be influenced by your environment.

• Ex. You can inherit strong bones but if you do not get the proper nutrition, your bones may become weak and brittle.

Twins reared apart• Both wear rubber bands around their left wrist

• Both married “Lindas” and divorced then married “Marys”

• Both read magazines from back to front

• Both had miscarriage same day & year

• Both drove the same car

• Both had the same occupation (gym owners)

• Both had short mustaches

• Both cross their eyes when they laugh

• Both dance the same and have same mannerisms

Traits - features or characteristics that organisms have. There two basic types of traits:

1)1) Species TraitsSpecies Traits - common to all members of a species.

Ex. Feathers on birds, # of legs, chromosomes, appendages, body form.

2)2) Individual Traits Individual Traits - differences among members of a species. Ex. Color of feathers, size of legs, location and texture of fur/hair, pigmentation, athletic ability, IQ.

Watchung Reservation Nov. 15, 2008

ProbabilityProbability - is the likelihood that a particular event will occur.

• Formula:

P = The number of times a particular event occurs The number of total trials

• Ex. Flipping a coin

• What is the probability of getting “tails”?

1/2 or 1:1

Important Rules of Probability:

• The previous event has NO impact on future outcomes. Each event is a separate, independent event.

• The larger the number of trials, the closer you get to the expected ratios.

4 box Punnett square word problems

Right-handedness is dominant over left-handedness.

Cross a male who is homozygous (pure) right-handed with a female who is lefty. What are the phenotypic and genotypic ratios and percentages of the possible offspring?

Phenotype/Genotype

• Phenotype: % of the appearance of an individual. (two categories: Dom. Vs. Rec)

• Ex. Righty vs. Lefty

• Genotype: % of the genetic possibilities of the individual (3 categories: pure dom., hybrid, rec.)

• Ex. Pure Righty vs. Hybrid Righty vs. Lefty

How To Do A Genetics Problem

1. Show a keyShow a key:

• The first letter of the dominant trait is capitalized to represent the trait.

Ex. Right-handedness = R

• The small (lowercase) letter of the dominant trait is used to represent the recessive trait. Ex. Left-handedness = r

R

r

KEY:

• RR = Right handed, dominant pure (homozygous)

• Rr = Right handed, dominant hybrid (heterozygous)

• rr = Left handed, recessive, (always pure/homozygous)

2. Show the parent’s traits:parent’s traits:

RR rrX

3. Show segregationsegregation (into sex cells)

R R r r

R R r r

4. Punnett’s SquarePunnett’s Square

R R

r

r

Rr Rr

RrRr

5. Ratio of offspringRatio of offspring:

Phenotype - the outward appearance of the organism. (dominant or recessive)

Phenotypic % and Ratio= 4 righty : 0 lefty(4:0) or 100% to 0%

Genotype - the genetic mix of genes. (pure dominant, hybrid dominant, or recessive)

Genotypic % and ratio = 0 pure/righty: 4 hybrid/righty: 0 lefty (0:4:0) or

0% : 100% : 0%

Problem: Crossing the F1 generation:

Right-handedness is dominant over left-handedness. Cross a female and male who are both hybrid right-handed. What are the phenotypic and genotypic ratios of their possible offspring?

1. Key:

RR = pure/dominant righty

Rr = hybrid/dominant righty

rr = pure/recessive lefty

2. Parents: Rr X Rr

3. Segregation: R r R r

4. Punnett

5. Ratio & Percentage:Phenotype: 3: 1 or 75% : 25%Genotype: 1:2:1 or 25% : 50% : 25%

A cross between two hybrids is called a monohybrid cross and it will always have the same ratio & % as the problem above.

R

R

r

r

RR

Rr

Rr

rr

Monohybrid 4 box Punnett Square Problem

Problem: Long horns is dominant over shorthorns in cattle. Cross a male and female who are both heterozygous for this trait.

1. KEY:• LL = pure dominant long horns• Ll = hybrid dominant long horns• ll = recessive short horns2. PARENTS:

Ll X Ll

3-4. Punnett:

LL Ll

Ll ll

L l

L

l

Phenotype: 3 : 1 or 75%: 25%

Genotype: 1: 2: 1 or 25%: 50%; 25%

• Testcross – – crossing an individual of unknown genotype with

a recessive individual (which is always pure) to determine the genotype of the unknown.

Problem: Black fur is dominant over white fur in rats. If you have a black rat, how can you find out if she is homozygous (BB) or heterozygous (Bb)?

Answer: Mate her with a recessive colored rat and then check the ratio of the offspring!2 possible genotypes for your pet rat are:

BB or Bb

B B b Bb Bbb Bb Bb

B bb Bb bb

b Bb bb

Testcross Results

BB X bb = Bb X bb =

• Phenotype: 4:0 Phenotype: 2:2

• Genotype: 0:4:0 Genotype: 0:2:2

• If your black rat has 100% black offspring, she is BB. If she has any white offspring, she must be Bb.

Co-dominance

Roan colored fur

• In horses, fur color is co-dominant. Cross a brown colored horse and a white colored horse. What is the phenotypic % of the offspring?

• Key:BB= Brown fur

B = Roan Fur

Cross the F1 generation. What is the phenotypic % of the F2 generation of offspring?

Incomplete Dominancea.k.a. Blending

• In parakeets, feather color exhibits incomplete dominance. Cross a blue parakeet with a yellow parakeet. What is the phenotypic % of the offspring?

• Key:

BB= blue feathers

YY= yellow feathersYY= yellow feathers

BY = green feathers

Both co-dominant and incomplete dominance

Parakeets can also exhibit co-dominance AND incomplete dominance so sometimes they exhibit multi-colors.

Multiple Alleles

Each person can have only two versions of a multiple allele trait in their genome at one

time, but in the population there are 3

forms.

Example: Blood types ( A, B,& O)

• Karl Lansteiner (1868 -1943) won the Nobel Prize in 1930 for his discovery of blood groups.

Blood Typing

Antigens• Antigens are proteins that can be found on your

Red Blood Cells (RBC).

• If you have antigen A, you have Type A blood.

• If you have antigen B, you have Type B blood.

• If you have both antigen A and B, you have Type AB blood.

• If you do not have either antigen A or B, you have Type O blood.

Four Types of Blood

• Type A

• Type AB

Type B

Type O

Rh FactorSeveral years later, Landsteiner found another antigen on the RBC while studying Rhesus monkey blood.

He named the protein after the monkey calling it the Rh factor.If you have the Rh factor you are considered Rh+. If you don’t have it, you’re Rh-.

Rh factor in pregnanciesThe Rh- mother will produce anti-Rh antibodies.Causing hemolytic disease of the newborn this can lead to brain damage, mental retardation, and even death.

What’s your Type?

Ready for Multiple Allele

Punnett

squares?

Genotypes

• When writing the genotypes of multiple alleles , you use the letter “I” for the dominant and letter “i” for the recessive.

• The A, &/or B is shown as a superscript.

• The “I” stands for "isoagglutinogen". This is another word for a blood group antigen in the ABO system.

How to write genotypes for Blood type genetics problems

This is always your key!

• IA IA = type A blood, pure dominant• IA i = type A blood, hybrid dominant• IB IB = type B blood, pure dominant• IB i = type B blood, hybrid dominant• IA IB = type AB blood, co-dominant• i i = type O blood, recessive

Multiple Allele Problems

• A man with Type AB blood marries a woman with type O blood.

• Using a key & Punnett square, show the cross between these two parents and give the phenotypic % of their possible offspring.

Pedigree Analysis

Genetics

What is a Pedigree?A pedigree is a diagram of family

relationships that uses symbols to represent people and lines to represent genetic relationships.

These diagrams make it easier to visualize relationships within families, particularly large extended families. Pedigrees are often used to determine the mode of inheritance (dominant, recessive, etc.) of genetic diseases.

• In a pedigree, males are represented by squares and females by circles .

• An individual who exhibits the trait in question, for example, is represented by a filled symbol or

In the pedigree here, the grandparents had two children, a son and a daughter. The son had the trait in question. One of the son’s children also had the trait.

Vertical lines extending downward from a couple represent their children. Subsequent generations are therefore written underneath the parental generations and the oldest individuals are found at the top of the pedigree.

Oldest individuals

Oldest individuals

All 4 are the youngest generation

Again…

For Example

Dominant and Recessive Traits

Using genetic principles, the information presented in a pedigree can be analyzed to determine whether a given physical trait is either dominant or recessive.

Dominant Traits : Characteristics of a dominant pedigree

are: 1) Every affected individual has at least one affected parent; 2) Affected individuals who mate with unaffected individuals have a 50% chance of transmitting the trait to each child; and 3) Two affected individuals may have unaffected children.

A dominant trait is passed on to a son or daughter from only one parent.

Recessive Traits• Recessive traits are passed on to children from both

parents, although the parents may seem perfectly "normal."

• Characteristics of recessive pedigrees are: – 1) An individual who is affected may have parents who

are not affected; – 2) All the children of two affected individuals are

affected; and – 3) In pedigrees involving rare traits, the unaffected

parents of an affected individual may be related to each other.

Outsider Rules• In any pedigree there are people whose parents are unknown. These

people are called “outsiders”, and we need to make some assumptions about their genotypes.

• Outsider rule for dominant pedigrees: affected outsiders are assumed to be hybrid.

• Outsider rule for recessive pedigrees: unaffected (normal) outsiders are assumed to be homozygotes.

• Both of these rules are derived from the observation that mutant alleles are rare.

Sample Pedigree Problems------------------ ------------------

1.The pedigree below is studying the incidence of blonde hair in a family. In humans, dark hair (B) is dominant to blonde hair (b). In this case, individuals who are shaded in are homozygous recessive. Individuals who have clear circles and squares have at least one dominant gene.                                                                  

What are the genotypes of persons A through F above?

Answer

• Explanation: • Person B is blonde, because they are shaded in. They are thus

homozygous recessive (hh).• Persons C through F must have at least dominant allele (H). Without

more information, this would make them HH or Hh.• Person B can only provide the h alleles to its eggs, so persons C-F

must be heterozygous (Hh).• Without more information, Person A who is dominant must be HH or

Hh.

Interesting Fact:The Story of Hemophilia

• Late in the summer of 1818, a human sperm and egg united to form a human zygote. One of those gametes, we don't know which, was carrying a newly mutated gene. A single point mutation in a nucleotide sequence coding for a particular amino acid in a protein essential for blood clotting. The zygote became Queen Victoria of England and the new mutation was for hemophilia, bleeder's disease, carried on the X chromosome.

• A century later, after passing through three generations, that mutation may have contributed to the overthrow of the Tsar and the emergence of communism in Russia. Victoria passed the gene on to some of her children and grandchildren, including Princess Alexandra, who married Nicholas II, Tsar of Russia, in 1894.

• By 1903, the couple had produced four daughters. The next year, the long awaited male heir appeared - His Imperial Highness Alexis Nicolaievich, Sovereign Heir Tsarevich, Grand Duke of Russia. From his father, the baby Alexis inherited the undisputed claim to the throne of all the Russias.

• From his mother, Alexis inherited an X chromosome carrying a copy of the mutant gene for hemophilia. Soon after his birth, signs of Alexis' mutant gene appeared. At six weeks, he experienced a bout of uncontrolled bleeding and by early 1905 the royal physicians had concluded that he was suffering from hemophilia.

Sex-linked Traits

Color vision is dominant over color deficiency and is sex linked.

Cross a female who is a carrier of the disorder but who has normal vision with a male who is colorblind.

Show the key, parents, punnett and phenotype and genotype percentages for all offspring. (Remember you must separate males from females)

•Traits carried on the X chromosome.

•More prevalent in males because they only have 1 X chromosome

Sex-linked Problem2

• Normal blood clotting is dominant over hemophilia and is sex linked. Cross a pure dominant female with a male hemophiliac. Show the key, parents, Punnett and phenotype and genotype percentages for their sons and daughters.

• If one of the sons (F1 generation) marries a woman who is a hemophiliac, what is the chance that his sons (F2 generation) will have normal blood? __________

• Why? ____________________________________________________________

Sex-linked: Hemophilia

Pedigree Problem 2: To the right is a

pedigree for an inherited lung disease.  Provide the genotypes of each of the individuals marked with lower case letters.

• Solution to Problem 2

• a) aa

• b) Aa

• c) Aa

• d) A?  (in other words AA or Aa)

16 Box Punnett Square Problem Set Up

Word Problem #1• Purple flowers are dominant over white flowers in pea plants.• Axial Flower growth is dominant over terminal

(top) flower growth.• Cross a “female” who has pure purple flowers

and is hybrid axial for flower growth with a “male’ who has white flowers and is a terminal (top) flower grower.

• What are the possible phenotypes of the offspring?

Step 1: Key

• PP = pure dom. Purple

• Pp = hybrid dom. Purple

• pp = recessive White

• AA = pure dom. Axial

• Aa = hybrid dom. Axial

• aa = rec. top growing

Step 2: Parents

PPAa ppaa

Step 3: Segregation

• Order Rule 1:

• Cross: 1 + 3 1 + 4 2 + 3 2 + 4

P P A a

1 2 3 4

PA Pa PA Pa

Step 4: Punnett Square

  PA Pa PA Pa

pa PpAa      

pa        

pa        

pa        

Step 4: Punnett Square

  PA Pa PA Pa

pa PpAa Ppaa PpAa Ppaa

pa        

pa        

pa        

  PA Pa PA Pa

pa PpAa Ppaa PpAa Ppaa

pa PpAa Ppaa PpAa Ppaa

pa        

pa        

  PA Pa PA Pa

pa PpAa Ppaa PpAa Ppaa

pa PpAa Ppaa PpAa Ppaa

pa PpAa Ppaa PpAa Ppaa

pa        

  PA Pa PA Pa

pa PpAa Ppaa PpAa Ppaa

pa PpAa Ppaa PpAa Ppaa

pa PpAa Ppaa PpAa Ppaa

pa PpAa Ppaa PpAa Ppaa

Phenotypic Ratio

• Order Rule 2:

• Categories:Dom. of trait 1 with dom. of trait 2Dom. of trait 1 with the rec. of trait 2Rec. of trait 1 with the dom. of trait 2Rec. of trait 1 with the rec. of trait 2

Phenotype:Trait 1: Purple flowers are dominant over

white flowers in pea plants.

Trait 2: Axial Flower growth is dominant over terminal (top) flower growth.

Purple and Axial:

Purple and Top:

White and Axial:

White and Top:

Dom. of trait 1 with dom. of trait 2Dom. Of trait 1 with the rec. of trait 2Rec. of trait 1 with the dom. of trait 2Rec. of trait 1 and rec. of trait 2

  PA Pa PA Papa PpAa Ppaa PpAa Ppaapa PpAa Ppaa PpAa Ppaapa PpAa Ppaa PpAa Ppaapa PpAa Ppaa PpAa Ppaa

Purple and Axial: Purple and Top:White and Axial:White and Top:

8

8

0

0

Phenotypic Ratio is 8:8:0:0