Mitosis and MeiosisMitosis and Meiosis

Pure Pure BreedsBreeds

The puppies of purebred dogs will grow up to look very much like their parents.

Mixed BreedsMixed BreedsHowever when the parents are of a mixed breed, the final sizes,

markings, and builds of these puppies, as well in their behavioral traits, will be more varied.

Dog GeneticsDog Genetics

But whether dogs are purebred or mutts, we can ultimately explain their innate traits by using genetics, the science of heredity.

Because of inbreeding, purebred dogs often suffer from serious genetic defects.

For instance, a type of hereditary blindness called progressive retinal atrophy is common among Labrador retrievers, spaniels, and several other breeds.

About 60% of the genetic disorders in dogs are similar to human genetic diseases, so genetic researchers often examine the genetic problems of dogs.

Dog GeneticsDog GeneticsIn 2003, researchers completed the entire genome (genetic sequence) of dog DNA. This project is yielding a wealth of data that can be used to compare the DNA of humans and dogs.

Dog GeneticsDog Genetics

Biologists are also studying certain dog breeds to shed light on the relationship between genetic makeup and behavior.

Dogs of different breeds tend to have different temperaments. Pit bulls and Rottweilers, for instance, are more likely to be aggressive than some other breeds because they were bred as guard dogs: in generation after generation, the most aggressive dogs were selected for mating with each other.

In fact, selective breeding is the basis for many of the dog breeds that exist today.

Dogs are Dogs are descendantdescendants of wolvess of wolves

It is estimated that until about 14,000 years ago, dogs were very much like wolves, the species from which dogs evolved.

Dog GeneticsDog Genetics

It was at this time that dogs began to move with people into more permanent settlements, which were often geographically isolated.

As a result, different populations of dogs became isolated from one another and eventually became inbred.

At the same time, different groups of people selected dogs for different traits, depending on their needs.

Dog GeneticsDog Genetics

Herders selected dogs that were good at controlling flocks of animals, producing breeds such as the Border collie.

Hunters had developed breeds of dogs, such as the laboratory retriever, which are good at retrieving wounded prey.

Such dogs were bred to be less aggressive than some other breeds because hunters don't want their dogs to eat the quarry!

Dog GeneticsDog Genetics

Genetics isn't everything: a dog’s level of aggression and other behavioral characteristics are influenced not only by its genes but also by its environment and care.

The same is turning out to be true of human behavioral characteristics.

Traits such as shyness have some genetic basis but can also be amplified or reduced by upbringing.

MitosisMitosis

Before you can begin to understand the rules that govern how inherited characteristics are passed from parent to offspring, you need to understand the basic biological concept of how chromosomes behave during the fertilization of an embryo.

Therefore, we will first cover mitosis, how cells divide.

Chromosomal Chromosomal InheritanceInheritance

Mary was a very attractive young woman who liked to play ice hockey. Her high school gym teacher took an interest in her ability and gave her extra coaching. She hoped that one day Mary would play on an Olympic team. But something was wrong. Mary was sixteen and still not menstruating. Her parents decided to have her undergo a series of medical tests. Much to the surprise of everyone, Mary had an X and Y chromosome in the nucleus of her cells. She was a chromosomal male.

Chromosomal Chromosomal InheritanceInheritance The doctor explained to Mary and her parents that

Mary had testicular feminization syndrome. She has internal testes that produce testosterone

but her cells won’t respond to it. Her genitals are like those of a female and she

has well-developed breasts. However, she will never be able to have children. Mary will be able to go on and play hockey in the

Olympics but she has to always carry a letter explaining her condition. Otherwise she will be disqualified because of her sex chromosomes.

KaryotypingKaryotyping

In the nucleus of a cell there are chromosomes, arranged in pairs which are joined in the center. Each of these pairs are called a called a karyotype (type of chromosome pair). Humans have 23 pairs of chromosomes. When they are taken out of a cell for genetic testing, scientists arrange the pairs in order of their assigned name (which is a number from 1-23). This procedure is called karyotyping.

Sex ChromosomesSex Chromosomes

Males have one pair of chromosomes that are not the same length. The larger chromosome in this pair is the X chromosome and the smaller is the Y chromosome. Females have two X chromosomes. This pair is called the sex chromosomes because they contain the genes that determine the sex.

Males are called XY Males are called XY Females are called XX. Females are called XX. The male is the parent that The male is the parent that

determines the sex of the child.determines the sex of the child.

GENESGENES

Genes are the structures Genes are the structures constructed of DNA that control constructed of DNA that control the characteristics of the the characteristics of the individualindividual

Genes are like small dots on each chromosome. Each dot contains the blueprint for some aspect of the body. One gene is for eye color, one for liver function, one for right or left handedness, etc. Every aspect of the body corresponds to a gene on one of the chromosomes.

Human Cell DivisionHuman Cell Division

All cells in our body divide by a All cells in our body divide by a process called process called mitosismitosis

Mitosis produces two daughter cells Mitosis produces two daughter cells with the same number and kind of with the same number and kind of chromosomes as the parent cell. chromosomes as the parent cell.

If a parent cell has 7 If a parent cell has 7 chromosomes prior to mitosis, chromosomes prior to mitosis, how many chromosomes will the how many chromosomes will the daughter cells have? daughter cells have?

Answer = 7.Answer = 7.

Sex CellsSex Cells In addition to mitosis, the sex cells (and

only the sex cells) undergo a second process called meiosis.

Meiosis: Meiosis: each daughter cell has only half each daughter cell has only half of the chromosomes. of the chromosomes.

In males, it produces the cells that become In males, it produces the cells that become spermsperm

In females, it produces the cells that In females, it produces the cells that become eggs. become eggs.

The sperm and the egg are the sex cells, or The sperm and the egg are the sex cells, or gametes. gametes.

GAMETES contain half the number of GAMETES contain half the number of chromosomeschromosomes compared to the rest of compared to the rest of the body cells. the body cells.

Sex CellsSex Cells Therefore, meiosis requires two

nuclear divisions, resulting in four daughter cells, each with half of the parent chromosomal number

 When a sperm cell fertilizes an egg, the resulting zygote has the all of the chromosomes from each of the sex cells, for a total of 46 (or 23 pairs). Thereafter, when the cells of the zygote/embryo/fetus/infant/child/adult divide by mitosis, each cell has 23 pairs of chromosomes.

Mitosis Video ClipMitosis Video Clip

Stages of MitosisStages of Mitosis

InterphaseInterphase ProphaseProphase MetaphaseMetaphase AnaphaseAnaphase TelophaseTelophase

Mitosis Overview Mitosis Overview VideoVideo

InterphaseInterphase

The chromosomes make an The chromosomes make an identical clone of themselves identical clone of themselves within the nucleus.within the nucleus.

For a human with 46 chromosomes, For a human with 46 chromosomes, they now have 92 chromosomes (just they now have 92 chromosomes (just for a few minutes!). for a few minutes!).

The clone is joined to the original at The clone is joined to the original at the middle so they look like an “X”.the middle so they look like an “X”.

InterphaseInterphase

Interphase Video ClipInterphase Video Clip

ProphaseProphase

The nuclear envelope The nuclear envelope dissolves awaydissolves away, and the , and the chromosomes are released into chromosomes are released into the cytoplasm of the cell.the cytoplasm of the cell.

The chromosome pairs start to The chromosome pairs start to shorten and thicken as they get shorten and thicken as they get ready to separate.ready to separate.

ProphaseProphase

Prophase VideoProphase Video

MetaphaseMetaphase

During metaphase, the During metaphase, the chromosomes line up at the chromosomes line up at the center of the cell.center of the cell.

MetaphaseMetaphase

Metaphase Video ClipMetaphase Video Clip

AnaphaseAnaphase

At the start of anaphase,At the start of anaphase, the the sister chromosomes separate sister chromosomes separate and move toward opposite and move toward opposite sides of the cell.sides of the cell.

There will now be 23 There will now be 23 chromosomes on each side of the chromosomes on each side of the cell.cell.

AnaphaseAnaphase

Anaphase Video ClipAnaphase Video Clip

TelophaseTelophase

Telophase begins when the Telophase begins when the chromosomes arrive at the poles. chromosomes arrive at the poles.

A nuclear envelop now forms around A nuclear envelop now forms around each set of chromosomes, so at this each set of chromosomes, so at this phase, the parent cell has two nuclei, phase, the parent cell has two nuclei, each with a complete set of each with a complete set of chromosomes. chromosomes.

Telophase is characterized by the Telophase is characterized by the formation of two daughter nuclei.formation of two daughter nuclei.

At the very end of telophase, the cell At the very end of telophase, the cell membrane pinches in two (cytokinesis) membrane pinches in two (cytokinesis) so that there are two new cells.so that there are two new cells.

TelophaseTelophase

Telophase Video ClipTelophase Video Clip

Cytokinesis Video ClipCytokinesis Video Clip

Video Clip of Animal Video Clip of Animal MitosisMitosis

MEIOSISMEIOSIS

Meiosis only occurs in the testes Meiosis only occurs in the testes and ovaries when they are ready to and ovaries when they are ready to make an egg cell or a sperm cell. make an egg cell or a sperm cell.

First, mitosis occurs as normal. First, mitosis occurs as normal. But right after that, the two But right after that, the two

daughter cells divide again, but daughter cells divide again, but this time there is no prophase, so this time there is no prophase, so the chromosomes have not made a the chromosomes have not made a clone of themselves. clone of themselves.

Crossing OverCrossing Over

When the second cell division is at the When the second cell division is at the metaphase stage, the chromosomes metaphase stage, the chromosomes touch each other and exchange a few touch each other and exchange a few genes. genes.

The exchange of genetic material The exchange of genetic material between chromatids is calledbetween chromatids is called crossing-over.crossing-over.

That is what allows for genetic That is what allows for genetic variation.variation.

Crossing OverCrossing Over

Crossing Over Video Crossing Over Video ClipClip

MEIOSISMEIOSIS

Meiosis results in four daughter cells, Meiosis results in four daughter cells, each having half the number of each having half the number of chromosomes as the parent cell. chromosomes as the parent cell.

The daughter cells are not genetically The daughter cells are not genetically identical, and neither is identical to the identical, and neither is identical to the parent cell. parent cell.

For example, For example, in MEIOSIS, if the in MEIOSIS, if the parent cell has 14 chromosomes, parent cell has 14 chromosomes, the GAMETE will have 7.the GAMETE will have 7.

Gametes to ZygoteGametes to Zygote

When a sperm and egg (gametes) When a sperm and egg (gametes) combine and contribute their combine and contribute their chromosomes, the fertilized egg chromosomes, the fertilized egg (called a zygote) will now have 23 (called a zygote) will now have 23 pairs of chromosomes.pairs of chromosomes.

NondisjunctionNondisjunction

Chromosomes can become Chromosomes can become abnormal if the sister abnormal if the sister chromosomes do not separate chromosomes do not separate properly during meiosisproperly during meiosis..

Video Clip of BlastulaVideo Clip of Blastula

Video Clip of Neural Video Clip of Neural TubeTube

BiotechnologyBiotechnology

Dog GeneticsDog Genetics

http://www.youtube.com/watch?v=K4LtTSBHjk4 (90 mins, start at 15) (90 mins, start at 15) Plants that fight air pollutionPlants that fight air pollution http://www.youtube.com/watch?v=xZ9Xp-ozZzc (23 mins) (23 mins)

Biotechnology ProductsBiotechnology Products http://www.euronews.com/2013/06/03/biotechnology-to-fight-air-pollution/ (4 mins) (4 mins)

Biotechnology TechniquesBiotechnology Techniques http://www.youtube.com/watch?v=A9mqwVZFCRk (14 minutes) (14 minutes)

Preventing Birth Preventing Birth Defects:Defects:Discussion Discussion

Maternal Health Maternal Health Habits: Discussion Habits: Discussion

Fertilization with 20 Fertilization with 20 year old sperm: year old sperm: DiscussionDiscussion