Genetics11.1

Learning Targets

I can explain how genes pass traits from parents to offspring

I can describe the role of chromosomes in heredity

I can identify patterns of heredity in humans

I define genetics, dominant gene, recessive gene, genotype, and phenotype

Genetics

Experiments Human Heredity Applied Genetics

Mendel

Morgan

Twins Genetic Disease

s

Environment

Selective Breeding

Genetic Engineerin

g

Genetics and Heredity

Genetics is the study of heredity

What is heredity?› The passing on of traits from parents to

offspring

› All organisms pass information (DNA) about traits to their offspring

Mendel

More than 100 years ago, a scientist named Gregor Mendel made important discoveries about heredity

He took seeds from tall pea plants and planted them.

Some plants were tall, but some were short. WHY??

Mendel’s Studies

Mendel decided to study pea plants and their seeds

He wanted to grow only tall pea plants Since the flowers of pea plants have

both male and female sex organs, Mendel tried self-pollination

Self-pollination occurred when Mendel moved pollen from the male sex organs to the female sex organs on the same plant

Mendel’s Studies (cont.)

After self-pollination occurred, each flower produced seeds

Mendel planted the seeds and then self-pollinated the plants that grew from those seeds

He did this again and again Finally, Mendel had seeds that

produced only tall pea plants (pure tall seeds)

The “P” Generation

Using the same self-pollination process, Mendel grew only short plants as well (pure short seeds)

Mendel called these plants the P Generation.

P stands for the parent generation

Cross-Pollination

Eventually, Mendel wanted to know what type of offspring two different pure parent plants would make

He used the process cross-pollination to find out.

Cross pollination is the movement of pollen from the male sex organs to the female sex organs of a different plant

The F1 Generation

So Mendel moved the pollen from pure tall pea plants to the female sex organs of pure short pea plants (and vice versa)

When the seeds produced plants, Mendel took the seeds from those flowers and planted them.

He called these plants the F1 Generation

F stands for filial (son or daughter)

Results of F1 Plants

Mendel found that all F1 Generation plants were tall

He crossed hundreds of pure short plants with pure tall plants

All the results were similar…tall plants What happened to the short trait??

Punnett Squares

Tt(tall)

Tt(tall)

Tt(tall)

Tt(tall)

t

t

T T Tall pure P generation

Short pureP generation F1 Generation

All tall

Punnett Squares

Mendel used these to explain his crosses

A gene is the information that a parent passes to its offspring for a trait

A pea plant inherits two genes for height (one gene received from each parent)

Genes

A gene that is hidden when it is combined with another gene is called a recessive gene (lower case letter)

The gene that shows up is called the dominant gene (capital letter)

All pea plants were tall, so the dominant gene is tallness

Genotypes and Phenotypes

An organism’s combination of genes for a trait is called its genotype

For example, the genotype of the F1 pea plants is Tt

What an organism looks like as a result of its genes is its phenotype

The phenotype of the F1 pea plants was tall

The F2 Generation

Mendel then self-pollinated the F1

Generation plants Mendel found that short plants started

showing up again (25% of the time) This F2 Generation always included

short plants Short plants reappeared because in the

F2 Generation, the plants inherited two recessive genes for shortness

Punnett Square

TT(tall)

Tt(tall)

Tt(tall)

tt(short)

T t

T

t

F1 Generation (Tt)

F1 Generation(Tt)

F2 Generation

¾ Tall¼ Short

Mendel’s Conclusions

Mendel concluded that there was information in a plant that caused it to have certain traits

The dominant genes hid the appearance of recessive genes

The offspring receive half their genes from one parent and half from the other

Vocabulary

Genetics Genotype Self-pollination Phenotype Cross-pollination Gene Dominant Gene Recessive Gene

Self Check questions, pg. 238 #1-5 COMPLETE SENTENCES

What are Chromosomes?11.2

What are Chromosomes?

Rod-shaped structures made of proteins and a chemical called DNA

Found in the nucleus of the cell

A chromosome can contain hundreds of genes, which determine all the traits of an organism

Mitosis Review

Basic steps to Mitosis:› Chromosomes make a copy of themselves› Nuclear membrane dissolves› The two sets of chromosomes separate› A nucleus forms around each set of

chromosomes› RESULT: Two new identical cells each with a

nucleus and set of chromosomes

Mitosis and Cell Division

Following mitosis, the entire cell divides

Each new cell gets one nucleus with a complete set of chromosomes

Each set of chromosomes is identical to the parent’s (new cell is identical to parent cell)

Sexual Reproduction

Two gametes (sex cells) join to form one complete cell

Each gamete has only half of the chromosomes of other cells in the body

When gametes join, they form a cell that has a complete set of chromosomes

How Many Chromosomes?

Most human have 46 chromosomes in their body cells

Sperm cells and egg cells only have 23 chromosomes each

Sperm and egg join to form a cell called a zygote with 46 chromosomes total

Together, the 46 human chromosomes carry 50,000-100,000 genes

Meiosis Review

Basic steps to Meiosis:› Chromosomes make a copy of themselves› The cell divides into two new cells› Each new cell then divides again› RESULT: One parent cell results in four new

sex cells

› **Each sex cell contains half the number of chromosomes of the parent cell

Sex Chromosomes

Humans have 46 chromosomes; they consist of 23 pairs

Each chromosome that makes up a pair comes from a different parent

For 22 of the pairs, the two chromosomes look alike

However, the chromosomes that make up the 23rd pair look different from each other these are sex chromosomes

Sex Chromosomes (cont.)

These two chromosomes determine a person’s sex

There are two types of sex chromosomes› X and Y

› Females have two X chromosomes› Males have one X and one Y chromosomes

How are sex chromosomes passed?

Parents pass one of their sex chromosomes on to their offspring

A male can pass an X or a Y chromosome to its offspring

A female can only pass an X chromosome to its offspring

Human offspring

Human offspring have a 50% chance of being male or female

XX(female)

XX(female)

X

XY(male)

XY(male)

X

X

Y

Male Parent

Female parent

Offspring50% chance of being female (XX)50% chance of being male (XY)

Thomas Morgan

Morgan used fruit flies rather than pea plants to learn about chromosomes and genes

Fruit flies are easy to study because:› Their cells have only 4 pairs of

chromosomes› The chromosomes are large; easy to see› Fruit flies reproduce quickly› It’s easy to tell the female fly from the

male

Sex-Linked Traits

Traits that are linked to the sex of an organism are called sex-linked traits

Fruit flies usually have red eyes

Morgan noticed one male fly with white eyes

He mated the white-eyed male with a red-eyed female

Results

This resulted in the F1 Generation and all flies had red eyes (dominant trait)

Morgan found that when he mated flies from his F1 Generation to produce an F2 Generation, some flies had white eyes and some had red

However, all white-eyed flies were male

Results (cont.)

Morgan concluded that the white eye color in fruit flies is linked to the sex of the fly

A female fruit fly has two X chromosomes

A male has one X and one Y chromosome

Morgan found that the gene for eye color in fruit flies is on the X chromosome

There is no gene for eye color on the Y chromosome

This explains why eye color in fruit flies is a sex-linked trait

Vocabulary

Sex Chromosome Sex-linked Trait Carrier

Self-Check questions, pg. 245 COMPLETE SENTETCES!!

How is Heredity studied in Humans?

11.3

Human Genetics

Human genetics is the study of how humans inherit traits

Humans have more chromosomes, do not reproduce quickly, and cannot be used in experiments

Scientists study heredity in humans by studying identical twins

Different kinds of Twins

Identical Twins› Sperm and egg join, form one zygote› Zygote divides into two cells that separate› Cells have identical genes

Fraternal Twins› Form from two different zygotes› Zygotes develop into offspring with

different sets of genes

Heredity and Environment

Your genes determine your skin color, eye color, body shape, and other characteristics

But your environment can also affect your characteristics

Scientists study identical twins who have been separated since birth

Both twins have identical genes, but grew up in different environments

The Influence of Environment

Food, sunlight, air and other parts of the environment can affect characteristics

A person who doesn’t have good nutrition may not grow tall, even though they have the gene for tallness

X-rays and some types of chemicals cause changes in genes, called mutations

DNA

DNA in chromosomes is the material that contains an organism’s genes

DNA passes the genes from one cell to another during cell division

DNA is a large molecule shaped like a twisted ladder

The rungs of the ladder are made of four different kinds of molecules called bases

Bases

The order of the bases in the DNA of a cell provides a code for all the information that the cell needs to live

Different organisms have different orders of bases

The greater the difference between organisms, the greater the difference in order of bases

The four bases are abbreviated as:› T, A, C, and G

Difference of Bases

The order of bases in a frog’s DNA is very different from the order of bases in human DNA

But, the difference in the order of bases between your DNA and your friend’s DNA is not as great

The order of bases in a gene for hair color, for example, determines whether the hair will be black, red, brown, or blonde

DNA Replication

DNA can replicate, or copy, itself DNA molecules are held together at the

rungs of the ladder The bases pair up in certain ways When DNA replicates, it first splits

down the middle of its rungs The paired bases separate, then new

bases pair with the separated bases

The result is two identical copies of the original DNA molecule

DNA replication occurs every time a cell divides normally

Pairing of Bases:› Base A pairs with Base T› Base C pairs with Base G

Mutations

Sometimes there is a change in the order of bases in a DNA molecule

Parts of the environment and chemicals can cause mutations

Mutations cause changes in genes

Genes determine traits, so any mutation can affect the traits of an organism

Genetic Diseases

Mutations can be harmful, helpful, or have no effect to the organism

A genetic disease is a disease that results from the genes a person inherits

Recessive genes cause most genetic diseases

That means a person must inherit the recessive gene from both parents in order to have the disease

Inbreeding

A gene pool is all the genes that are found within the population

The larger the population, the larger the gene pool

People living in a small population, often mate others who may have the same or similar genes

Sexual reproduction among people in a small gene pool is called inbreeding

Diseases

Inbreeding can cause a disease called hemophilia

This disease causes the blood to not have a certain protein that it needs to clot or clump

People who have hemophilia bleed excessively when slightly injured

Hemophilia was known as the “Royal Disease” WHY??

Human Sex-linked Traits

A number of human traits are sex-linked

The gene for color blindness in sex-linked

Color blindness is more common in males because the recessive gene is found on the X chromosome

Hemophilia and muscular dystrophy are also sex-linked

Both are found on the X chromosome, so they are both more common in males

Vocabulary

Mutation Replicate Base Gene Pool Genetic Disease Inbreeding

Self-Check Questions, pg. 251 COMPLETE SENTENCES!!

What is Applied Genetics?11.4

Applied Genetics

Farmers use breeding techniques to grow hardier and better-tasting crops

Animal breeders use breeding techniques to make prizewinning horses

These are examples of people affecting the traits that organisms inherit

Useful Mutations

A mutation that results in an animal with white fur would be helpful to that animal in a snowy region

Over long periods of time, mutations may lead to changes in population

This is one way that new species are formed

Selective Breeding

Farmers and scientists use their knowledge of genetics to produce new varieties of plants and animals

Selective breeding is selecting useful mutations and breeding organisms so the mutation shows up again

Examples: Short legged sheep, cows that produce large amounts of milk, pink grapefruits and navel oranges

Breeding Racehorses

Selective breeding is used to produce great race horses

The breeder will select two parents with desirable genes

The will also select parents that have good temperaments

An animal’s genes also affect its behavior

Genetic Engineering

The process of introducing new genes into an organism is genetic engineering

Began in the 1970’s when scientists transferred genes from one species of bacteria to another species of bacteria

Today, scientists transfer genes between entirely different organisms

Used to treat certain diseases or conditions of plants and animals

Vocabulary

Applied Genetics Selective Breeding Genetic Engineering

Self-Check questions, pg. 256 COMPLETE SENTENCES!!