Mendel’s work was “lost” for about Mendel’s work was “lost” for about 35 years35 years

In 1900, it was In 1900, it was rediscovered. rediscovered.

In 1902 Walter In 1902 Walter Sutton showed that Sutton showed that Mendel’sMendel’s genetics genetics work was related to work was related to chromosomeschromosomes

Sometimes Mendel’s laws Sometimes Mendel’s laws don’t seem to applydon’t seem to apply

We sometimes see We sometimes see mutationsmutations occur occur Mutation: Mutation: sudden change in DNAsudden change in DNA.. MutagenMutagen. . Something which causes Something which causes

mutation (radiation, chemicals etc.)mutation (radiation, chemicals etc.) For an example, consider those For an example, consider those

famous organisms in the history of famous organisms in the history of Biology…Biology…

How did they get to be mutants?How did they get to be mutants?

Answer: “The Ooze”Answer: “The Ooze” The ooze was a The ooze was a

chemical mutagen…it chemical mutagen…it caused these ordinary caused these ordinary turtles to mutateturtles to mutate

If you have a mutation in one of your If you have a mutation in one of your spermsperm cells or cells or eggegg cells, it is more serious cells, it is more serious for the human species than if you have it for the human species than if you have it in one of your in one of your bodybody cells. cells.

Why?Why? Answer: because you can pass it on Answer: because you can pass it on to to

your childrenyour children, they can pass it on to their , they can pass it on to their children etc.children etc.

Are mutations good or bad?Are mutations good or bad?

It dependsIt depends Mutations Mutations can becan be goodgood.. They cause They cause differencesdifferences between between

individuals.individuals. Nature selects the ones with the good Nature selects the ones with the good

differences to live, and the others to die.differences to live, and the others to die. This is called This is called natural selectionnatural selection.. Natural selection causes species to Natural selection causes species to

change. That’s called change. That’s called evolutionevolution..

Consider, the giraffeConsider, the giraffe

Its ancestors had shorter necks, but mutations Its ancestors had shorter necks, but mutations lengthened them, and the longer necks were an lengthened them, and the longer necks were an

advantage for survivaladvantage for survival

HOWEVER, HOWEVER, mostmost mutations are mutations are lethallethal (they result in death) (they result in death)

Some mutations create real Some mutations create real problemsproblems

Chromosomal mutations: 3 Chromosomal mutations: 3 typestypes

Chromosomal mutationsChromosomal mutations are those are those which involve a “chunk” or a piece of which involve a “chunk” or a piece of a chromosomea chromosome

A whole piece of a chromosome can A whole piece of a chromosome can break off and break off and go awaygo away, break off and , break off and reattachreattach on the same chromosome, on the same chromosome, or break off and reattach on a or break off and reattach on a different chromosomedifferent chromosome

Deletion mutationDeletion mutation

A piece of a A piece of a chromosome chromosome breaks off breaks off and is lostand is lost..

Inversion mutationInversion mutation

A piece of a A piece of a chromosome chromosome breaks off and breaks off and switches switches position on position on the same the same chromosome.chromosome.

Translocation mutationTranslocation mutationA piece of a A piece of a chromosome chromosome breaks off and breaks off and reattaches to a reattaches to a different different chromosomechromosome..

Sometimes the mutation is just Sometimes the mutation is just in one of the in one of the A’s, or T’s or G’s A’s, or T’s or G’s

or C’sor C’s This is called a This is called a point point mutation.mutation. How can such a simple change How can such a simple change

create problems?create problems? Consider…Consider…

Consider a simple English Consider a simple English sentencesentence

How might you How might you express the idea express the idea that “the that “the overweight overweight feline consumed feline consumed a rodent” using a rodent” using one sentence of one sentence of 3-letter words?3-letter words?

““The fat cat The fat cat ate the rat”ate the rat”

Now let’s “mutate” the Now let’s “mutate” the sentence…sentence…

Let’s Let’s substitutesubstitute a “b” at a strategic spot. a “b” at a strategic spot. ““The fat cat ate the rat”The fat cat ate the rat”

And the sentence now reads…And the sentence now reads…

““The fat The fat batbat ate the rat” ate the rat” Still an English sentence, but with a new Still an English sentence, but with a new

meaningmeaning

Substitute “b”

Let’s mutate by Let’s mutate by removingremoving a a letterletter

““The fat cat ate the rat”The fat cat ate the rat”

Here’s our new sentence…Here’s our new sentence… ““Tef atc ata tet her at_”Tef atc ata tet her at_” Doesn’t make much sense. Doesn’t make much sense.

Remember, we read 3 letters at a timeRemember, we read 3 letters at a time

Remove the “h”

Finally, let’s Finally, let’s addadd a letter a letter

““The fat cat ate the rat”The fat cat ate the rat”

Our new sentence starts out OK, but Our new sentence starts out OK, but then runs into trouble…then runs into trouble…

““The fat cat mat eth era t_ _”The fat cat mat eth era t_ _”

Add “m”

And one final mix-up that can occurAnd one final mix-up that can occur

Nondisjunction:Nondisjunction: Chromosomes Chromosomes don’t don’t split up and sort during split up and sort during meiosis.meiosis.

The result…?The result…?

Eggs or sperm with Eggs or sperm with too many or too many or too few chromosomestoo few chromosomes..

This is a This is a karyotypekaryotype. It is an actual picture . It is an actual picture

of chromosomes. First a human female…of chromosomes. First a human female…

2 “X” chromosomes

And a human male…And a human male…

1 “X” and 1 “Y” chromosome

But here you can see the result of But here you can see the result of nondisjunction…nondisjunction…

This personhas Down’sSyndrome.Notice the extra copy ofchromosome#21

Sex determinationSex determination

Humans have 46 chromosomes (normally) Humans have 46 chromosomes (normally) and the members of a pair look like each and the members of a pair look like each other, with the exception of the other, with the exception of the “X”“X” and the and the “Y”“Y” chromosome. chromosome.

The X and Y chromosomes are called the The X and Y chromosomes are called the sex sex chromosomeschromosomes

All other chromosomes as a group are All other chromosomes as a group are referred to as referred to as autosomesautosomes..

Individuals who receive the combination XY Individuals who receive the combination XY from their parents are from their parents are malemale

Individuals who receive the combination XX Individuals who receive the combination XX from their parents are from their parents are femalefemale

Sex determinationSex determination

So if a female is “XX”, So if a female is “XX”, what sex what sex chromosome will she chromosome will she have in all of the ova have in all of the ova she produces?she produces?

How about the sperm How about the sperm of a male?of a male?

So how is the gender So how is the gender of the baby of the baby determined?determined?

Always an XAlways an X

½ will carry an X, the ½ will carry an X, the other ½ will carry a Yother ½ will carry a Y

By the type of By the type of spermsperm which fertilizes the which fertilizes the egg (by the man).egg (by the man).

You can show this as a Punnett You can show this as a Punnett SquareSquare

XX YY

X

X

XX XY

XX XY

FEMALE

FEMALE

MALE

MALE

The Y chromosome is like an X The Y chromosome is like an X chromosome, with a lot missingchromosome, with a lot missing

X

Y

Indeed, research suggests that the Y may have developed as a mutated X

As a result…As a result…

Many genes carried on the X Many genes carried on the X chromosome, are completely chromosome, are completely missingmissing on on the Y.the Y.

It was thought that this was the only It was thought that this was the only difference between them.difference between them.

It is now known that the Y carries genes It is now known that the Y carries genes associated with “associated with “malenessmaleness”, with no ”, with no counterpart on the Xcounterpart on the X

Ear hairEar hair is one of the fun examples is one of the fun examples

Thomas Hunt MorganThomas Hunt Morgan

In 1910, Morgan In 1910, Morgan was doing genetics was doing genetics research with research with fruit fruit flies.flies.

He noticed He noticed different eye-color different eye-color phenotypes, red phenotypes, red and whiteand white

When he crossed hybrid red-eyed When he crossed hybrid red-eyed females with red-eyed males, Morgan females with red-eyed males, Morgan

noticed something startlingnoticed something startling

ALL of the white-eyedoffspring were MALE

Why was this so?Why was this so?

Morgan figured out that the gene for Morgan figured out that the gene for eye color was carried on the eye color was carried on the XX chromosome and was chromosome and was missing on missing on the Ythe Y..

We can use a Punnett Square to We can use a Punnett Square to show why that would explain the show why that would explain the results Morgan observedresults Morgan observed

First, how do we represent the First, how do we represent the various possibilitiesvarious possibilities

XXRRXXRR = = XXRRXXrr = = XXrrXXrr = =

XXRRYY-- = = XXrrYY-- = =

a red-eyed a red-eyed femalefemale

a red-eyed a red-eyed femalefemale

a white-eyed a white-eyed femalefemale

a red-eyed malea red-eyed male a white-eyed a white-eyed

malemale

XR Y-

XR

Xr

XRXR

Red-eyed ♀

XRY-

Red-eyed ♂

XrXR

Red-eyed ♀

XrY-

White-eyed ♂

¼ of the offspring have white eyes, but theyare all male.

This kind of inheritance is This kind of inheritance is common, and important.common, and important.

This is called a This is called a sex-linked trait.sex-linked trait. Sex-linked traitsSex-linked traits are those where the are those where the

gene is gene is carried on the X carried on the X chromosomechromosome

Sex-linked traits are common in many Sex-linked traits are common in many species, including humansspecies, including humans

They are seen more often in They are seen more often in malesmales than in than in femalesfemales. Some examples are…. Some examples are…

HemophiliaHemophilia

Color blindnessColor blindness

Other genetics issuesOther genetics issues

Multiple allelesMultiple alleles: A condition where : A condition where more than two more than two alleles for a given alleles for a given trait exist trait exist in a population (or in a population (or species).species).

An example from the cat lab was striping vs. blotched vs. Abyssinian..

Human Example: blood typeHuman Example: blood type

The alleles in The alleles in Homo sapiensHomo sapiens areare

AABBOO As a result, the possible allele As a result, the possible allele

combinations are…combinations are…

AAAA && AOAOBBBB & BO& BOABABOOOO

Which both result in Which both result in type A bloodtype A blood

Which both result in Which both result in type B bloodtype B blood

Which results in type Which results in type AB bloodAB blood

Which results in type Which results in type OO

Notice how the different genes Notice how the different genes act in those examplesact in those examples

What kind of What kind of relationship do the relationship do the A and B genes A and B genes have with the O have with the O gene?gene?

How about the How about the relationship of A to relationship of A to B?B?

A and B are both A and B are both dominant to the dominant to the recessive Orecessive O

They are They are codominantcodominant

Other methods of Other methods of inheritanceinheritance

Polygenic traits: Many genes affect a Polygenic traits: Many genes affect a trait. There aren’t just pairstrait. There aren’t just pairs

Usually, we see a big variety in how Usually, we see a big variety in how they are expressedthey are expressed

Human examples would Human examples would include include skin complexionskin complexion, and…, and…

Height (in this case, 5’7”) Eye color (in this case, green)

Sex-influenced traitsSex-influenced traits

The The hybrid hybrid condition is expressed condition is expressed differently in the male and differently in the male and femalefemale

Example: Example: early pattern baldnessearly pattern baldness

If B is the allele for bald, and b is the If B is the allele for bald, and b is the allele for not bald, what phenotype will allele for not bald, what phenotype will result from the following genotypes?result from the following genotypes?

BBBB

bbbb

BbBb

Not baldNot bald

BaldBald

It depends: a male It depends: a male will be bald, a will be bald, a female will notfemale will not

Can you guess why there is a Can you guess why there is a phenotypic difference in the same phenotypic difference in the same

genotype between male and female?genotype between male and female? It’s because It’s because male hormonesmale hormones work work

together with the genotype to result together with the genotype to result in the traitin the trait

Ever notice boys beginning to go Ever notice boys beginning to go bald in high school.bald in high school.

What did they go through (hormone What did they go through (hormone change) in junior high or early high change) in junior high or early high school?school?

Some human gene examples: Some human gene examples: Dominant GenesDominant Genes

DimplesDimples

FrecklesFreckles

Pigmented (non-blue) eyesPigmented (non-blue) eyes

Some recessive human Some recessive human allelesalleles

Red hair

Blue eyesBlue eyes

Genetic testsGenetic tests

AmniocentesisAmniocentesis: Fluid is removed from : Fluid is removed from around the baby while a woman is pregnant. around the baby while a woman is pregnant. Cells from the baby are in the fluid. Cells from the baby are in the fluid. Chromosomes can be checked for mistakes.Chromosomes can be checked for mistakes.

FetoscopyFetoscopy

Taking pictures of a Taking pictures of a developing baby.developing baby.

UltrasoundUltrasound

Creating a picture Creating a picture of an unborn baby of an unborn baby using sound wavesusing sound waves

Genetic counselingGenetic counseling

If you have If you have experience, expect, or experience, expect, or are worried about are worried about genetic problems, genetic problems, genetic counseling is genetic counseling is offered by many offered by many medical institutionsmedical institutions

It involves It involves the use of the use of genetics to predict genetics to predict and explain traits in and explain traits in children.children.