Origin of Genetics

All of your traits come from your parents  Hair color  Eye color  Height  Weight

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

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

Alaskan Malamutes were bred to be sled dogs.

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 heredity  Austrian Monk  Born in 1822  Parents were peasants  Studied Theology and Science and Math  Learned to use Math to explain natural phenomena

Mendel used T.A. Knights previous experiments on Pea Plants Crossed a variety of Purple Pea plant with a White Pea Plant

Purple Pea plant + White Pea Plant

When the second generation were crossed with themselves…

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 flowers  1 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 apart  Easy to mate pea plants  Garden pea is small and grows quickly

Mendel’s first experiments were Monohybrid crosses  A cross that involves 1 pair of contrasting traits  Either purple or white pea plants

Mendel first formed true- breeding pea plants  PURE 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 plant  He 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 pollinate  This next generation was called F2  He 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 = We can say that this was about a 3 ratio. 1

3:1 3 purple for every 1 white

Dr. Mendel studied other pea traits as well  Flower color ---- purple or white  Seed color----- yellow or greed  Seed shape ---- round or wrinkled  Pod color----- green or yellow  Plant height----- tall or dwarf

A monohybrid cross occurs when two plants with one different trait are crossed  Example: when a plant with purple flowers are crossed with a plant with white flowers

Mendel discovered that offspring are not just a blend of traits If 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 pp  Both 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

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 Segregation  When 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 pants  Y - Yellow  y- Blue When sponge bob makes gametes, how do his alleles separate?.

SsYy  4 Possible Gametes:  1) SY  2) Sy  3) sY  4) sy  The Law of Segregation:  Cells go from 46 chromosomes to 23  Each 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  AaBb  aaBB… etc

Step 2 - Determine the possible gamete combinations for each parent

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 Recessive  In 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 DOMINANT  So 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

This is a pedigree of Color blindness, which is passed down on the X chromosome Which sex show color blindness more, male or female?

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

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 factors  People 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 Hemophilia  Notice only males have hemophilia

British Royal Family  After generations of inbreeding (royals marrying royals)  Hemophilia

Hemophilia in the British Royal Family