Species – Genetic Species – Genetic VariationVariation

Main Points for Class Meeting:Main Points for Class Meeting:1.1. What is a Species?What is a Species?

2.2. What makes species different from What makes species different from each other?each other?

3.3. What are the sources of variation What are the sources of variation within species?within species?

SpeciesSpecies : Latin for “kind” or : Latin for “kind” or “appearance”“appearance”

Morphological differences used to Morphological differences used to distinguish species distinguish species

Differences in body function, Differences in body function, biochemistry, behavior, and genetic biochemistry, behavior, and genetic makeup also usedmakeup also used

Copyright © 2002 Pearson Education, Inc., publishing as Benjamin Cummings

1. What is a Species?

Species: Species:

A population whose members can A population whose members can interbreed under natural conditions to interbreed under natural conditions to produce healthy, fertile offspring, but produce healthy, fertile offspring, but cannotcannot produce healthy, fertile offspring produce healthy, fertile offspring with members of other species.with members of other species.

The Biological species conceptThe Biological species concept

Species are based on Species are based on infertilityinfertility, , notnot physical similarity.physical similarity.

Eastern and western meadowlarks have Eastern and western meadowlarks have similar shapes and coloration, but similar shapes and coloration, but differences in song help prevent differences in song help prevent interbreeding between the two species.interbreeding between the two species.

Copyright © 2002 Pearson Education, Inc., publishing as Benjamin Cummings

Species are based on Species are based on infertilityinfertility, , notnot physical similarity.physical similarity.

In contrast, humans haveIn contrast, humans haveconsiderable diversity,considerable diversity,but we all belong to thebut we all belong to thesame species because ofsame species because ofour capacity to our capacity to interbreed.interbreed.

Genes! Genes!

Where are genes found?Where are genes found?

On On Chromosomes!Chromosomes!

Copyright © 2002 Pearson Education, Inc., publishing as Benjamin Cummings

2. What makes species different from each other?

Chromosomes are made of condensed DNA

Here is a complete set of Human chromosomes:

Different species have Different species have different numbers of different numbers of

chromosomes:chromosomes:Species: Number of

Chromosomes:

Mosquito 6

Guinea pig 16

Yeast 32

Cat 38

Humans 46

Dog 78!

Different species have Different species have different numbers of different numbers of

chromosomes:chromosomes:Species: Number of

Chromosomes:

Mosquito 6

Guinea pig 16

Yeast 32

Cat 38

Humans 46

Dog 78!

Half of an individual’s Half of an individual’s chromosomes come from its chromosomes come from its

mother, & half from its mother, & half from its fatherfather

If the chromosomes from If the chromosomes from the 2 parents don’t the 2 parents don’t “match,” then the 2 “match,” then the 2

parents are NOT the same parents are NOT the same speciesspecies

Example?

Then what happens?• No offspring can be produced• OR the offspring are infertile

The MULE:The MULE:

Mules are a hybrid between a horse & a donkey – 2 closely related species

3. What are the sources of variation within species?

Genetic Diversity – combinations of different forms of genes!

Genes are located on Chromosomes

Some genes have 2 (or more) forms, called “alleles”

Offspring can inherit 1 form of the gene from one parent, and another form from the other parent.

Human Human GeneticsGenetics

Modified from a presentation by Timothy G. Standish,

Ph. D.http://www.grisda.org/tstandish/teachers/presentations/General%20Biology/Human%20Genetics.ppt#1

 

The Madness of King The Madness of King George IIIGeorge III Partly as a result of the erratic behavior of

King George III the American colonies decided to break away from the United Kingdom

Other members of King George’s family also exhibited strange behavior with dire consequences: Mary Queen of Scots and her son James I both of whom were beheaded.

Because madness seems to have run in the family, it is thought to have a genetic basis (“acute intermittent porphyria”)

Human Heredity Is Not Human Heredity Is Not UniqueUnique

The genes of humans behave in the same way as genes of other organisms

Of the estimated 100,000 human genes, most are identical in all humans

The relatively small number of “polymorphic” genes in humans account for only part of the variability that we see between humans

While each human (except for identical twins) has a unique set of genetic information, variation between humans also results from differences in the environment

Politics and GeneticsPolitics and Genetics Human genetics: how humans are - can lead

to controversy when traits seen as relating to race, gender or other sensitive issues

This is particularly true when we start to talk about the genetics of behavior

Nazis and other extreme right wing politicians see human worth and behavior being based on genetics

Communists and other extreme leftwing politicians see humans as infinitely pliable and molded by their environment not genetics

Simple Dominant/Recessive Simple Dominant/Recessive TraitsTraits

Many human genes are inherited as dominant or recessive traits (just like the traits Mendel studied in peas)

Ear lobes provide an example of this:

Attached ear lobes are inherited as a recessive trait.

Unattached ear lobes are inherited as a dominant trait.

Simple Dominant/Recessive Simple Dominant/Recessive TraitsTraits

Having a bent little finger is a dominant trait

Dominant/Recessive Dominant/Recessive Human TraitsHuman Traits

Cleft chin - A noticeable indentation at the center of the chin. For examples think of Kirk Douglas and Michael Jackson (after plastic surgery). Having a cleft chin is dominant to a smooth chin.

Double-jointed thumbs - This is commonly called a hitchhiker's thumb. The thumb can bend back at almost 90 degrees. Hitchhiker's thumb is a recessive trait, but it may vary in its expression.

Dominant/Recessive Dominant/Recessive Human TraitsHuman Traits

Hand folding - When the hands are folded either the left or right thumb will be on top. Left thumb on top is dominant.

Mid-digital hair - Hair growing from the middle section of each finger. Hair presence is dominant.

Dominant/Recessive Dominant/Recessive Human TraitsHuman Traits

Tongue rolling - Tongue rolling is the ability to form a tube with your tongue. Rolling is dominant.

Widow's peak - A sharp point in the hairline that points toward the nose. Having a widow's peak is dominant to a smooth hairline.

Sex Influenced Human Sex Influenced Human TraitsTraits

Baldness - Loss of hair from the scalp following puberty. A sex influenced trait that is most commonly fully expressed (as a dominant trait) in males

Index finger shorter than ring finger - The index finger (next to your thumb) is longer than the ring finger (next to your little finger). Check the class data to see if the frequency is different for the different sexes.

Sex Linked Human Sex Linked Human TraitsTraits

Color blindness - Inability to distinguish between colors of the same intensity. There are two types: red-green color blindness, and complete color blindness. Both types of colorblindness are sex linked traits.

Freckles - Small patches of darker pigmented skin on various parts of the body and most visible in those areas commonly exposed to the sun. These may be present on both dark and light skinned individuals.

Polydactyly - Having more than five digits on each hand and foot.

Specific Human TraitsSpecific Human Traits

S-methyl thioester smeller - S-methyl thioesters are produced in the urine after consumption of asparagus. Some individuals cannot smell this substance. If you smell a strong odor on urination after eating at least 5 asparagas spears, you are an S-methyl thioester smeller.

Specific Human TraitsSpecific Human Traits

Multiple Multiple AllelesAlleles

Eye color varies on an almost continuous scale from brown to green to gray to blue

Eye color determined by two genes: one controls texture of

the iris which refracts light to make blue;

second determines relative abundance of melanin: small amount of melanin = green eyes, increasing amounts of melanin = brown and black eyes

Multiple Multiple AllelesAlleles Hair color is determined

by more than one gene Thus hair color appears to

vary on an almost continuous scale from black to brown to blond to red

The brown and black pigment is melanin

The red pigment is an iron containing molecule

Genetic DiversityGenetic Diversity

Key Questions:Key Questions:1.1. Relationship between Relationship between speciesspecies diversity & diversity &

geneticgenetic diversity diversity

2.2. What is the hierarchy of concepts that What is the hierarchy of concepts that connect species to genes (& DNA)?connect species to genes (& DNA)?

3.3. What is the importance of genetic variation?What is the importance of genetic variation?