Origin of Genetics

All of your traits come from your parentsHair colorEye colorHeightWeight

Heredity is the passing down of traits from parent to child

Humans have always been interested in how traits are passed down English sheep dogs were bred to be

herders of sheep, goats and cattle

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Beagles were bred to be scent dogs to track rabbits, foxes etc.

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Alaskan Malamutes were bred to be sled dogs.

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Dogs have been owned and bred by humans for

thousands of years

Humans have bred them to have many different characteristics

Gregor Johann Mendel was interested in

heredityAustrian MonkBorn in 1822Parents were peasants Studied Theology and Science and

MathLearned to use Math to explain natural

phenomena

Mendel used T.A. Knights previous

experiments on Pea PlantsCrossed a variety of Purple Pea plant with

a White Pea Plant

Purple Pea plant + White Pea Plant

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When the second generation were crossed with themselves…

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Mendel counted his resulting pea plants

and he noticed a pattern

After 1 Cross Purple + White ALL OFFSPRING WERE PURPLE

After Crossing the second generation…

3 pea plants had purple flowers1 pea plant had white flowers

At the time counting scientific data was considered “cutting edge” technology

Why were Peas a good organism to study

heredity?Had traits that were easy to tell apartEasy to mate pea plantsGarden pea is small and grows quickly

Mendel’s first experiments were

Monohybrid crossesA cross that involves 1 pair of

contrasting traits Either purple or white pea plants

Mendel first formed true-breeding pea

plantsPURE purple plants --- if they were

crossed with themselves they only had purple offspring

PURE white plants --- if they were crossed with themselves they only had white pea plants

Once he was sure they were true breeding

They became his parent generation or P generation The p generation were they first two that e

bred

Then Medel crossed a true-beeding purple plant with a true

breeding white plantHe called the offspring plants his F1

generation

He counted how many F1 were purple and how many were white

Last he allowed his F1 generation to self

pollinateThis next generation was called F2He counted the number of purple and

white pea plants in the F2 group

Mendel’s Results:

After the first cross ALL the F1 generation were had purple flowers!!!

After the second cross 705 plants had purple flowers and 224 plants had white flowers… What is the ratio of purple:white flowers?

705 = 3.15

224

We can say that this was about a 3 ratio.

1

3:13 purple for every 1

white

Dr. Mendel studied other pea traits as

wellFlower color ---- purple or whiteSeed color----- yellow or greedSeed shape ---- round or wrinkledPod color----- green or yellowPlant height----- tall or dwarf

A monohybrid cross occurs when two plants with one different trait

are crossedExample: when a plant with purple flowers are crossed with a plant with white flowers

Mendel discovered that offspring are not just a

blend of traitsIf a tall and short plant are crossed the

result is NOT a plant with medium height

Mendel thought that each plant held an

“inheritable factor”What do you think these inheritable

factors are?

Genes!

Because we are diploid we each have two copies of each gene

When sex cells are formed during Meiosis, each cell only gets one

of these copies

When the two sex cells fuse the new zygote has two copies of each trait

Every person has two alleles One from mom and one from dad

There are alternative versions of genes

Gene for flower color can be purple or white Each VERSION of a gene is called an Allele

If a zygote has two different alleles one might not be expressed

When the purple flowers were matched with White flowers, the resulting offspring were all purple

The white allele did not show up

Purple flower color is said to be Dominant

White flower color is said to be recessive

So any plant with a Purple allele will be purple

Dominant

The trait that is expressed

Recessive

The trait that is present but is not expressed

An organism that has two of the same allele is called Homozygous

So purple flower PP or white flowers ppBoth would be considered homozygous

An organism that has two different alleles is called Heterozygous

Because Purple is dominant, all

heterozygous plants for plant color are purple

Genotype

The actual alleles that an organism has PP, Pp or pp - these are genotypes

Phenotype

What trait is expressed So, what the plant looks like Example - purple or white = phenotype

What is the result if a pp flower is crossed with a pp flower?

What is the result if a PP flower is crossed with a PP flower?

What happens if a pp flower is crossed with a

PP flower?

What happens if a Pp flower is crossed with a

Pp flower?

What happens if a PP flower is crossed with a

Pp flower?

Probability

The likelihood that a specific event will occur

can be decimals, percentages or fractions

If an event will definitely occur…

The probablity is … 4/4 purple ; 0/4 white

100% purple offspring

Probablity = # of an outcome total number of outcomes

What if a person wanted to cross a

plant with two traits that are different?

A tall plant with purple flowers is

crossed with a short plant white flowers

How do the different alleles get split up?

Alleles from one plant are not linked to each

other

Crosses that involve two traits

Called a dihybrid cross

Mendel’s Ideas

Called Laws of Heredity

The Law of Segregation

Two Alleles for a trait separate when the gametes are formed during meiosis

A person Heterozygous for Trait G = Gg

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Mendel’s 2nd Law

Mendel wanted to know if crossing a plant with two different alleles affects the outcome of the offspring

The Law of Independent Assortment

Mendel determined that different genes separate independantly from each other

I.e. the gene that codes for eye color separates separately from the gene that codes for dimples

Mendel’s first Law

The Law of SegregationWhen daughter cells divide in Meiosis,

each daughter cell gets a separate Allele

Mendel wanted to know if the inheritance of one trait affected the inheritance of another

trait

Did flower color influence Plant height

If Sponge Bob is heterozygous for two

traits, Pant shape and color

His GENOTYPE is: SsYy

S - square pants s- round pantsY - Yellow y- Blue

When sponge bob makes gametes, how do his alleles separate?

.

SsYy

4 Possible Gametes:1) SY2) Sy3) sY4) sy

The Law of Segregation: Cells go from 46 chromosomes to 23Each daughter cell made in Meiosis will get 1

Allele instead of two for each trait

The Law of Independent Assortment

SsYs

When Sponge Bob makes gametes, the S’s and the Y’s separate independantly -

What is the probability that

Sponge Bob will pass on a Dominant gene for

Square pants?

His genotype is SsYy

If Sponge Bob is going to marry Rosie

Roundpants…(ssYY)

What is the probability that Rosie will pass on an allele for round pants?

How do we solve Dihybrid word problems

Step 1 - What are the genotypes of the parents

AaBbaaBB… etc

Step 2 - Determine the possible gamete

combinations for each parent

Mom is AABb

1) AB

2) Ab

3) AB3) AB

4) Ab4) Ab

Step 3 - Make your Punnet Square

Put your Possible Gamete combinations on top or on the side to determine your offspring

Not all traits are simply Dominant or

RecessiveIn humans many traits are controlled by

more than 1 gene Height Eye Color Hair color Weight

Polygenic Trait

A trait controlled by more than one gene

Factors that affect polygenic traits

Genes for a trait may not be located on the same chromosome Independent assortment Crossing over

There are many ways to make combinations of genes… that is why you are such a good combination of your mom and your dad

Mendel’s peas

In a pea plant, one plant was completely dominant over another

This is called Complete Dominance

Incomplete Dominance

Occurs in individuals when they display a trait that is a mixture of their two parents

Red snapdragons and White Snapdragons will

produce Pink snap dragons

=

In Caucasians, Curly and Strait hair are both

DOMINANTSo wavy hair is the result

Codominance

Occurs when BOTH traits are expressed at the same time

When a red horse and a white horse are crossed… a Roan horse results

Sex Linked Traits

Some traits are passed down on the sex chromosomes

X or Y

If a trait is passed down on any other chromosome it is

called “Autosomal”All people receive two allele’s for

autosomal traits

If a trait is passed down on the X chromosome…

Then any male who inherits that Chromosome will express that trait

Males have only 1 X chromosome

So if they receive a recessive trait (I.e. color blindness) then they will express that trait

Pedigree

A family history that shows how a trait is inherited over generations

Squares are Male ; Circles are Female

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This is a pedigree of Color blindness, which is passed down on the

X chromosomeWhich sex show color blindness more,

male or female?

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A carrier is a person who does not exhibit a trait, but has that

alleleCarriers are heterozygous

If a person is heterozygous for color blindness Rr They will not be colorblind, but they will

potentially pass the trait on to their children

Color blindness is carried on the X

chromosome If a mother who is Rr passes the

recessive allele ‘r’ down to her son - he will be color blind.

Color blindness is carried on the X

chromosome If a mother who is Rr passes the

recessive allele ‘r’ down to her son - he will be color blind.

If the same mother passes down the

recessive allele ‘r’ to her daughter

Her daughter will ONLY be color blind if she also receives a recessive allele ‘r’ from her father to make her “rr”

If she receives a dominant allele R from her father, she will be a carrier - Rr

Males have a much higher chance of

inheriting a sex - linked trait

Male pattern balding

Male - pattern baldness is X -linked

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Male pattern baldness is passed down on the

X chromosome

Men get this trait from their mothers

Hemophilia

Rare bleeding disorder People cannot produce Platelets or

clotting factorsPeople with Hemophilia cannot form

clots, they could bleed to death if they are cut.

Because Hemophilia is recessive, it occurs

almost always in Males

This is a pedigree of a family that carries the recessive gene for

HemophiliaNotice only males have hemophilia

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British Royal Family

After generations of inbreeding (royals marrying royals)

Hemophilia

Hemophilia in the British Royal Family

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