GENETICS NOTES

Chapters 12, 13, 14, 15 16

DNA contains the genetic code for the production of PROTEINS.

A gene is a segment of DNA, which consists of enough bases to code for many different proteins. The specific proteins produced by a gene determine the TRAITS of an organism.

The traits of that organism can then be

passed on to, or INHERITED by their

offspring.

The study of the inheritance of traits is

called GENETICS.

Who is Gregor Mendel?

Mendel can be called

the FATHER of

Genetics because he

developed the

principles of genetics

that we still use today!

Mendel’s most significant work was the research and experiments that he conducted by studying PEA PLANTS.

These experiments helped him explain how TRAITS were passed from one generation to the next.

Where are these genes?

Each gene controls something different, and it has a specific location on a DNA molecule.

A DNA molecule that is coiled up is called a CHROMOSOME, which may have more than a thousand genes on it.

Your chromosomes are in the NUCLEUS of the cell.

Each species of organism has a different

number of chromosomes. Every

chromosome carries genes for different

traits.

Humans have 46 chromosomes in a

somatic cell (body cell) and 23 in a gamete

(sex cell).

In body cells, chromosomes exist in PAIRS.

The pictures below are of a KARYOTYPE.

This is a picture of a test that shows human

chromosomes that have been cut out and

arranged in their pairs.

Who cares about the pairs?

Mendel’s research showed that there are twofactors that control a trait. He concluded that at the end of MEIOSIS, when the gametes are produced, each reproductive cell contains only one factor of each pair.

When the gametes combine during FERTILIZATION, the offspring will have the two factors controlling each specific trait. One chromosome is from the mom and the other chromosome from the dad.

Because the pair of factors is separated, or segregatedduring meiosis, Mendel named this the LAW OF SEGREGATION.

Humans have 23 pairs of chromosomes in every cell.

One piece of information that can be found by

reading a karyotype is the SEX of the baby.

The first 22 pairs of a male and a female are the same; they are called AUTOSOMES or body chromosomes.

The 23rd pair isn’t really a pair so it is labeled differently.

This last pair is considered to be the SEX CHROMOSOMES. These chromosomes determine the sex of the organism. They also carry GENES for other characteristics.

The sex chromosome of the female is X chromosome.

Most human females have two X chromosomes in every body cell.

The sex chromosome only found in males is the Y chromosome.

Most human males have one X chromosome and one Ychromosome in every body cell.

What is the sex of person A?

How do you know?

What is the sex of person B?

How do you know?

Are more chromosomes better?

It would be easy to think that having an

extra chromosome or two would make a

superhuman, but this in not the case.

Extra chromosomes, damaged

chromosomes, and missing

chromosomes almost always cause

MUTATIONS.

A karyotype can be used to detect some genetic disorders that may occur in a developing baby, or FETUS. Doctors will use cells taken from a developing baby to check that the baby has the correct number of chromosomes.

This is done during a procedure called AMNIOCENTESIS.

If there are too many, too few chromosomes, or damaged chromosomes, then that means that there must have been a mistake in MEIOSIS when the GAMETES are formed.

If the number of chromosomes is wrong then the TETRADS did not separate correctly during the phase of Meiosis called ANAPHASE I.

This mistake in tetrad separation is called NON-DISJUNCTION.

What could happen to the baby?

If an egg is fertilized under conditions like these, it is very likely that the mother will miscarry or the baby will die in the first year. If the baby is born, it will have a genetic abnormality. The number of extra chromosomes there are and the pairs effected determine what genetic disorder the baby has and how severe it is.

What is the probability of having

a boy or a girl?

Many times in genetics, we can figure out how likely it is that a parent will pass something on to their children. To do this we use a tool called a PUNNETT SQUARE.

This is a way to show what all of the possible combinations are from the egg and sperm and how LIKELY it is for those combinations to occur

The end product of meiosis produces 1

egg in a woman and 4 sperm in a man.

Gametes are haploid, so they have half

the number of chromosomes that any

body cell has. Gametes only have one

of the sex chromosomes that are in any

body cell.

REMEMBER the Law of Segregation?

A parent randomly

passes on only one

gene for each trait

to each offspring.

You get one

chromosome from

mom and one from

dad randomly.

XXXY

X Y

XX

What are the possible sex chromosomes

that a woman can give?

X or X

What are the possible sex chromosomes

that a man can give?

X or Y

PUNNETT SQUARE

The sides of a Punnett Square are for what the gametes could have. In this case, we are investigating sex chromosomes. Write the sex chromosomes that the mother can give on the top and those from the father on the side.

Copy the letters from the top of the square into each of the boxes below it.

Copy the letters from the sides of the square into each of the boxes next to it.

Each of the boxes now shows a possible combination of the egg and sperm. Within all 4 boxes is every possible combination of these two parents.

What are the possible

combinations?

The baby will either get the combination XX or XY.

How many times does each occur? XX 2 out of the 4 times

XY 2 out of the 4 times

How likely is it for any woman and man to have a boy child?

50%

How likely is it for any woman and man to have a girl child?

50%

If a woman has a baby boy, what are the chances of her having another baby boy? Why?

How do certain traits get passed on?

Non-sex chromosomes are called

AUTOSOMES.

Every cell of an organism that has been

produced by sexual reproduction has two

copies of each autosome. The offspring

receives one copy of each autosome

from each PARENT.

Chromosomes come in pairs

you received one from your mother (egg cell)

you received the other from your father (sperm cell)

Pink = from mom

Blue = from dad

Chromosome

pair 1pair 2

Chromosome

pair 3

These two autosomes, carrying

information for the same trait, are called

HOMOLOGOUS chromosomes.

Homologous chromosomes are the

same size and shape and carry genes

for the same trait.

Homologous Chromosomes

Hair color = brown

Nose size = small

Height = tall

Hair color = red

Height = short

Nose size = big

This shows a pair of

chromosomes...

(chromosome #5 for

example)... one from

mom and one from dad.

Notice that each chromosome carries

genes for the same trait, but the

genes can be in different forms.

The different types of genes that are possible for a trait are called ALLELES. Every trait that an organism has is determined by at least two alleles. If a trait is controlled by more than two alleles, it is said to have MULTIPLE ALLELES.

Alleles are represented by a letter. Capital letters represent DOMINANT alleles and lower case letters represent RECESSIVE alleles. The trait for a dominant allele will show up over a trait for a RECESSIVE ALLELE.

The picture below is a pair of homologous

human autosomes.

The genes of an organism make up its GENOTYPE. To represent this, we write the alleles.

The genotype of this person (in the figure above) is BB. Both of these alleles are DOMINANT.

If both of the alleles are the same, for

example two dominant (GG) or two

recessive (gg), the genotype is called

HOMOZYGOUS.

If the alleles are different (Gg) the

genotype is said to be

HETEROZYGOUS, and the person who

has these genes is a carrier of the

recessive gene.

The picture below is a pair of homologous

human autosomes.

This person’s genotype is HOMOZYGOUS DOMINANT.

The way that an organism looks is called its PHENOTYPE.

If B represents the trait for brown eyes, and b represents the trait for blue eyes, what is the phenotype of this person?

This person has BROWN eyes.

List the genotypes:

1. TT

2. Tt

3. tt

4. RR

5. Rr

6. rr

List the phenotypes:

1. Tall

2. Tall

3. Short

4. Round

5. Round

6. Wrinkled

List the genotypes:

1. Homozygous Dominant

2. Heterozygous

3. Homozygous Recessive

4. Homozygous Dominant

5. Heterozygous

6. Homozygous Recessive

What are the possible genotypes and phenotypes of the

offspring of plants 1 and 3?

POSSIBLE OUTCOMES

Possible genotypes:

Tt (Heterozygous)

Possible phenotypes:

Tall

All of the offspring will inherit the TALL

trait, but each carries the trait for short.

BB Bb bbbb BbBB

B B

B B

B b

b b

b b

B B B b b b

B

B

B

B

B

B

B

b

B

b

b

b

T t

T TT Tt

T TT Tt

POSSIBLE GENOTYPES:

TT- Homozygous Dominant- 2/4- 50%

Tt- Heterozygous- 2/4- 50%

Are all genes either dominant or

recessive to determine traits?

Certain traits like freckles or dimples are

caused by dominant alleles. Only one parent

has to have the dominant allele, because there

only needs to be ONE dominant gene for the

trait to show. Five digits per hand is a

recessive trait.

In your Punnett square each parent MUST be

a carrier or have the trait in order for a child to

have 2 recessive genes.

Some traits are neither totally DOMINANT nor totally RECESSIVE. In this case, we cannot tell which gene is dominant over the other. This situation is called INCOMPLETE DOMINANCE.

If there is one dominant and one recessive gene, then only the DOMINANT gene is seen. Incomplete dominance will not show either trait. In incomplete dominance, the phenotype of the organism is a mixture of both of the genes.

In this case, because both of the traits are dominant, both alleles are written as capital letters.

R R

R’ RR’ RR’

R’ RR’ RR’

R R’

R RR RR’

R’ RR’ R’R’

4/4 RR’ (100% heterozygous)

100% Pink Flowers

A heterozygous phenotype does NOT show one or the other trait. It shows a combination of the two alleles.

¼ 25% Red

½ 50% Pink

¼ 25% White

B B

W BW BW

W BW BWAll offspring are checkered

When there are two dominant genes,

and neither trait is shown because the

phenotype is a mixture of the two

dominant traits, this is called

INCOMPLETE DOMINANCE.

There are other cases, in which both

traits show when they are both

dominant. This is called

CODOMINANCE.

What’s the Difference??

COMPLETE dominance: heterozygous

individual shows the DOMINANT

phenotype

(B = brown, b = blue Bb = brown eyes)

INCOMPLETE dominance:

heterozygous individual shows

MIXTURE of both traits

(RR = red, R’R’ = white RR’ = pink)

What’s the Difference?

CODOMINANCE: heterozygous

individual shows BOTH TRAITS

EQUALLY

(BB = black, WW = white

BW = checkered)

Sickle Cell Anemia

Sickle-cell anemia is a dangerous, usually fatal genetic disorder.

Red blood cells carry OXYGEN through your body. The shape of sickle red blood cells is different from the disk-like shape of normal red blood cells. The sickle cells are unable to carry enough oxygen to body parts. Their shape also makes it difficult for them to move through blood vessels, which causes BLOOD CLOTS.

R is the gene for round cell shape and S is the gene for

sickle cell shape.

What are the genotypes from the chart above?

1. RR

2. SR

3. SS

FIX YOUR CHART.

Put checkmarks in the table to show the shape of cells for persons with the

genes listed.

What are the phenotypes shown in the chart above?1. Healthy patient- ROUND red blood cells

2. Healthy patient- ROUND AND SICKLED red blood cells

3. Anemic patient- SICKLED red blood cells

SS

SR

RR

When genes are codominant, what do you notice about

the phenotype of the heterozygous organism?

A heterozygous organism SHOWS

BOTH TRAITS.

Incomplete Dominance Vs Codominance

A YELLOW flower and a BLUE flower are crossed to produce a

YELLOW & BLUE SPOTTED FLOWERthis is an example of

CODOMINANCE

GREEN FLOWER- this is an example of

INCOMPLETE DOMINANCE

Can you explain why?

What about my BLOOD TYPE?

When a disease, or ANTIGEN enters your body, your blood cells try to learn the shape of that antigen.

Your blood cells will then make ANTIBODIESto fight the antigen in your body.

Once your body has destroyed an antigen, it will remember the shape.

If you are ever exposed to that antigen again, your blood will remember the antibodies that it made to fight the invader off last time and it will be able to make more.

Your blood type tells doctors what kind of antibodies your blood has. If you were in need of a blood transfusion and doctors put the wrong type of blood in your body, your blood cells would attack the new blood as if it were an ANTIGEN.

Some blood types will accept a few different blood types; others will reject all blood types except for a perfect match.

Human blood type genes have multiple alleles that can show regular dominance and recessiveness or codominance. Complete the chart with the possible genes that a person with each of the following blood types could have.

REMEMBER: Chromosomes work in pairs, so the person must have TWO alleles to code for a trait.

Blood Type Possible alleles

A AA or AO

B BB or BO

O OO

AB AB

Blood Type Possible alleles

A AA or AO

B BB or BO

O OO

AB AB

Which blood types

show complete

dominance? How do

you know?

Which blood types

show codominance?

How do you know?

What possible blood types could a child have if the

parents’ blood types were A and B?

For blood type A, the parent could have

the genes AA or AO.

For blood type B, the parent could have

the genes BB or BO.

Draw the 4 Punnett Squares to show

ALL of the possibilities.

BABY MIX UP

Four newborn babies are born in the hospital at the same time. Clumsy Clara the nurse ran in to attach a wristband with each child’s name on it, but she dropped the wristbands and they got out of order. Before she alerts the parents, Clara is going to try to figure this out on her own. The only thing she has to help her are the charts with the blood types of all four babies and their parents. Please help her figure out which baby belongs to which family.

Luckily, the baby’s blood types are all different.

Baby A = blood type A

Baby B = blood type B

Baby C = blood type AB

Baby D = blood type O

The parents blood types are as follows:

The Gonzalez = blood types O and O

The Johnsons = blood types O and A

The Rogers = blood types AB and B

The Smiths = blood types O and AB

Write your Punnett Squares on a separate sheet of paper.

The Gonzalez family can only have a baby with blood type O.

The Johnsons can have a baby with the blood type A or O. Since Baby D is Baby Gonzalez, the Johnson baby is blood type A.

The Rogers can have a baby with blood type A, B or AB. Baby B or Baby C can be theirs.

The Smiths can have a baby with the blood type A or B. Baby B is a Smith and Baby C is a Roger.

Are some traits more common in

boys than girls?

Like autosomes, the sex chromosomes also carry genes for certain traits. The figure below shows some of the traits that are controlled by the GENES on the sex chromosomes. Label the sex chromosomes either male or female.

Female Male

How many genes determine whether or not a

female has dry skin?

How many genes determine whether or not a

male has dry skin?

The Y chromosome does not have ALL

of the same traits that the X

chromosome has. In autosomes, TWO

recessive genes must be present for the

recessive trait to show. This is different

in sex chromosomes.

Sex-Linked Traits

Hairy ears in humans:

The gene for hairy ears is found only on the Y chromosome (Y-linked). Therefore, males are the only ones to have this sex-linked gene.

Sex-Linked Traits cont.

Hemophilia in humans:

Babies born with hemophilia are missing or have a low level of a protein needed for normal blood clotting or blood coagulation. The protein is called a clotting factor.

Like color-blindness, the gene for hemophilia is recessive and located on the X chromosome (X-linked). This means that males are more likely to be affected than females as explained above.

Sex-Linked Traits cont.

Muscular dystrophy: Characterized by

progressive weakness and degeneration

of the skeletal and voluntary muscles

with control movement

MD is usually a recessive X-linked

disorder, but there are forms that are

autosomal.

COLOR BLINDNESS

One X-linked is color blindness.

Because this trait is on an X-

Chromosome, we write Xc for recessive

or XC for dominant.

The dominant trait is normal color vision

and the recessive trait is red-green color

blindness.

Which are red-green colorblind? D and E

Which have normal color vision? A, B and C

Which has normal color vision even with the gene for color blindness? B

In order for a female to have the disease, she must have the genotype Xc Xc.

In order for a male to have this disease, he must have the genotype Xc Y.

female female male male female