Name_______________________
Date ___________ Class________
NOTES #
Genetics Notes
Genetics is the branch of science that studies _____________.
____________ is the passing of traits from parent to offspring.
_Gregor__ __________
-Did his research in the ___________________
-Born in 1822 in _________________
-Wanted to figure out why some _________ showed up
more often then others.
-Studied garden ________ plants.
Why Pea Plants?
_____________ _______________-has both male and female
reproductive structures on the same plant.
-Able to grow ________ _____________ plants. Plants
self pollinated therefore were exactly like the parent.
__________ ______________-pollen from one plant fertilizes
the ovule of a different plant.
-Carried by _____________ or _________________
Characteristic – a ___________ that has different
__________in a population.
-_____________are different forms of characteristic
-_______________ or ___________________
1
Dominant Trait— A trait that is always ________________ in the
organism.
Dominant alleles are symbolized with _________ letters.
Recessive Trait—is ______________ or hidden in the presence of a
dominant trait.
-Recessive alleles are symbolized with _____________letters.
___________-relationship between two different numbers that is
often expressed as a fraction
TRAITS AND INHERITANCE
_________ -Instructions for inherited traits
-One from each _________________
_________-different forms of a gene
_______________-an organism’s physical appearance
_______________-an organism’s genetic makeup
___________________-an organism that has _______ dominant or
two _____________ alleles. ( ____________ )
example: if T = tall and t = short then ____________________
_______________-an organism that has both a ______________
AND a ______________ allele. ( ____________ )
example: if T = tall and t = short then ____________________
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Heredity in Plants
If you were to plant corn seeds, you
would expect to grow corn plants. If
you planted seeds of a red poppy, you
naturally would expect the new plants
to produce red poppy flowers. Young
plants and animals, or offspring, tend
to resemble their own parents. The
passing of characteristics from parents
to offspring is known as heredity.
The scientific study of heredity is called
genetics.
For many years, we have used
genetics to try to improve the
characteristics of plants. From these
plants, the botanists select and crosspollinate only those plants that have
the certain characteristics they would
like to perfect. From these selected
plants, seeds may be taken and planted
for further selection.
After many
generations, it may be possible to bring
out the desired traits in an entire
planting.
One of the first people to study
plant heredity was Gregor Mendel.
Around 1860, he worked with pea
plants in order to observe the effects of
cross-pollination.
Mendel selected
plants that differed in contrasting
characteristics, such as short and tall
stems, red and white flowers, and
yellow and green seeds.
When a characteristic appeared in a
generation of plants more often than its
contrasting form, Mendel considered the
more frequent form to be a dominant
trait. The less frequent form was called
the recessive trait. After many tests, he
found that red dominates white flowers,
and yellow dominates in seeds. Mendel
learned that the tall-stem characteristic is
dominant, while shortness is recessive.
To observe these facts, Mendel started
with purebred plants, or plants that could
produce the same characteristics in each
generation following reproduction.
By
cross-pollinating two purebred plants
having contrasting characteristics, a
hybrid plant is produced. After several
years of work, Mendel was able to set up
several laws that hybrids seem to follow.
Mendel found that each trait in a
hybrid operates independently of any
other trait. One trait could be altered
without changing another.
Through
Mendel’s work and the work of other
scientists in the field of genetics, hybrids
are now produced that combine the most
desirable characteristics of a plant. Some
of the best corn, wheat, peaches, and
other food plants are hybrids.
ANSWER THE FOLLOWING:
1. The passing of characteristics from parents to offspring is known as
________________.
2. The scientific study of heredity is called ________________.
3. The offspring of two purebred plants with contrasting traits is called a
_______________.
4. A ____________trait will occur more often than a ___________ one.
3
More About Gregor Mendel
We owe our basic knowledge of the laws of heredity to a patient, nineteenth
century Austrian monk, Gregor Mendel. As a young monk Mendel spent many hours
working in a monastery garden. He was a keen observer of plants and noticed that
the seeds from tall plants usually produced tall plants, and the seeds from short
plants usually produced short plants, but not always. He also noted that the yellow
seed plants sometimes produced green seeds, and that round seed plants sometimes
produced plants with wrinkled seeds. Mendel believed that in these cases there
was a hidden or impure trait passed on from one of the parent plants. He called the
parent plants with the hidden traits hybrids. He called the plants which produced
the expected results, such as plants producing only tall plants, purebred.
To explain why the seeds from some tall plants did not produce the expected
results, Mendel planned an experiment which was to last seven years. He chose
simple garden peas to use in his experiment because they were easy to grow and
usually self-pollinating. Self-pollinating plants use the pollen from the stamen to
fertilize the eggs of the same flower. Nature helps this process by shaping the
flowers in such a way as to make it difficult for insects or the wind to bring pollen
from another flower in contact with the pistil of a self-pollinating flower.
To begin his experiment, Mendel crossed tall plants with tall plants and
short plants with short plants for several generations to be certain he had all
purebred plants. Then he crossed the purebred tall plants with the purebred short
plants by transferring the pollen by hand. He called the purebred plants for his
parent of P1 generation. The seeds from the P1 generation gave rise to all tall
plants. These he called the F1 generation. Mendel was surprised that all of the
plants of the F1 generation grew tall. He knew that they all had one tall parent and
one short parent and, although tall, they were not purebred. He referred to the F1
generation as being hybrid tall. From this Mendel reasoned that the tall factor
must be stronger than the short factor. He called the stronger, tall trait
dominant, and the short weak trait recessive.
1. How long was the experiment expected to last?
2. Why use pea plants?
3. Why was the F1 generation referred to as being hybrid tall?
4
Chapter 5 Section 2
1. In _______________ reproduction, only one parent cell is
needed for reproduction.
2. In ______________ reproduction, two parent cells join
together to form a new individual.
3. Human body cells have ____ chromosomes.
4. Human ____ ______ have only ___ chromosomes – half the
usual number. Male sex cells are called ________. Female
sex cells are called _______.
5. _________ produces new sex cells with half the usual number
of chromosomes.
6. Genes are located on ________________.
7. _____ ___________________ carry genes that determine
whether the offspring is male or female.
8. Females have ___ ___ chromosomes.
9. Males have ___ ___ chromosome and ___ ___ chromosome.
10. Explain the difference between sex cells and sex
chromosomes. (Think)
5
Punnett Squares
An Englishman named Punnett figured out an easy way to predict the
possible appearance of certain hereditary traits. He used a checkerboard
square. On one side he put the genes carried in the egg, and along the top
he put the genes carried in the sperm or the pollen of plants. Capital
letters indicate genes of dominant traits and small letters indicate the
recessive traits.
Directions for drawing a Punnett Square:
1. Draw a square and divide it into four sections.
2. Write the letters that represent the alleles from one parent along
the top of the box.
3. Write the letters for the other parent along the side of the box.
4. Carry the alleles down or across into each box.
Example: Red (R) color is dominant over white (r) color. We use the same
letters in our punnett squares. In this case we choose the letter R since it
is the dominant trait.
Cross a homozygous red plant (RR) and a homozygous white plant (rr).
Note: homozygous means the same (it is purebred). In the white plant, the
only way the white color will appear is that both alleles are recessive (no
dominate trait is present to mask or hide the recessive white color)
Genotype:
Phenotype:
Now try another one:
Cross a heterozygous red plant (______) and a homozygous white plant
(_______)
Note: heterozygous means different (it is hybrid).
Genotype:
Phenotype:
6
Use the Punnett squares to predict the results of various crosses
between tall and short pea plants. Then fill in the phenotype and genotype
of each cross. The first square which corresponds to Mendel’s first cross
between tall and short plants has been done for you.
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8
Chromosomes are made of _________.
-Genes must be able to supply _____________ for cell
processes and for __________ cell structures.
- ________ and ________ build models of DNA. They
concluded that DNA resembles a twisted ladder shape known as a
________ _______.
-The structure of DNA can be compared to a _________
_________
-_____________ ______________ is when a trait appears to
blend together but each allele has his own degree of influence.
For example:
Nose size – Large nose is dominant (L) over small nose (l). When
the genotype is LL a large nose is present. When the genotype is
ll a small nose is present. When a person is heterozygous (hybrid)
for the large nose - the genotype is Ll, the phenotype
(appearance of the nose) is NOT a large nose, as you would
expect (the L dominating or hiding the recessive allele l), instead
you get a new 3rd trait: a medium size nose. This is incomplete
dominance, the dominant trait does not completely hide the
recessive trait.
- Many things in your ________________ also influence how you
grow and develop.
-Give an example.
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Chapter 6 Section 2
1. __________ act as chemical messengers. Give an example of what
they help to determine.
2. ____________ occur when there is a change in the order of bases
in an organism’s DNA.
3. The three possible consequences to changes in DNA include:
A.
B.
C.
4. A ________ is anything that can cause a mutation in DNA.
5. _______ ______ _________ is a disease that affects red
blood cells.
6. Genetic __________ provides information and counseling to
couples who wish to have children but are worried that they might
pass a disease to their ________.
7. A _________ is a diagram for tracing a trait through generations
of a family.
8. In _________ __________ organisms with certain desirable
characteristics are mated to produce a new breed.
9. This process of _______ ______________ allows scientists to
transfer genes from one organism to another.
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Bill Nye - Genes Video
1. The way you are and the way you look when you are born is determined
by your ___________ from your parents.
2. Your whole body is made of __________.
3. DNA has all the ______________ needed to determine what you are.
4. Your ____________ are strung out on a DNA molecule.
5. ____________________ are very long DNA molecules and are found
in almost every cell of every living thing.
6. We need a lot of ________________ or genes to make a person.
7. Genes are passed down from ______________ to their children.
8. Humans have______ chromosomes and about _____________genes.
9. Give some examples of what genes determine.
10. The female reproductive cell is the _______. The male reproductive
cell is the ____________.
11. Every living thing is made of __________ and four chemicals called:
12. The two types of genes are ______________ and _____________.
13. _______________ are caused by jumbled up information. They can
be harmful or helpful.
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Test Cross - __________________________________________
_________________________________________________________
When an organism has a trait controlled by a dominant allele, it can
either be a hybrid or purebred. To find out which, geneticists can use a test
cross. In a test cross, the organism with the trait controlled by a dominant
allele is crossed with an organism with a trait controlled by a recessive
allele. If all offspring have the trait controlled by the dominant allele, then
the parent is a purebred. If any offspring has the recessive trait, then the
dominant parent is a hybrid. Study the test cross below, then answer the
questions.
1. Is the long-haired cat in the P generation a hybrid or a purebred?
2. Is the short-haired cat in the P generation a hybrid or a purebred?
3. If the short-haired cat in the P generation were purebred, what would
you expect the offspring to look like?
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4. In horses, the allele for a black coat (B) is dominant over the allele for a
brown coat (b). A cross between a black horse and a brown horse
produces a brown foal. Is the black horse a hybrid or a purebred?
Explain.
5. In guinea pigs, the allele for a smooth coat (S) is dominant over the allele
for a rough coat (s). Explain how you could find out whether a guinea pig
with a smooth coat is a hybrid or a purebred.
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-______________________________
______________________________________
Pedigree
A pedigree usually starts with a married couple in the
first generation, and then shows their children in the second
generation, their grandchildren in the third generation, and so
on. Standard symbols are used to represent males, females,
and the relationships among individuals, as shown in the figure
below.
Study the sample pedigree, and then answer the
questions that follow.
1. What is the name(s) of Irene’s and Leo’s son(s)? What is the name(s) of their
son(s)-in-law?
_________________________________________________________
2. How many grandchildren do Irene and Leo have? How many of their
grandchildren girls?
_________________________________________________________
3. What is the name of Ralph’s father? What is the name of Ashley’s mother?
_________________________________________________________
4. What is the name of Emily’s son? What is the name of Tim’s son?
_________________________________________________________
5. After the pedigree was made, Richard and Emily had another son, whom they
named Roger. Juliet married a man named Robert and had a daughter named
Elizabeth. Zack married a woman named Jean and had a son named Craig. Add
all of these individuals to the pedigree.
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Pedigrees of the Rich and Famous
The pedigree of Queen Victoria of England shown below is often used as an
example of sex-linked inheritance. Victoria was a carrier of hemophilia, a sexlinked disorder that is controlled by a recessive allele. The blood of a person with
hemophilia clots very slowly or not at all because the person does not produce one
of the proteins needed for blood clotting. Victoria passed the hemophilia allele on
to her son Leopold, who had the disease, and to two of her daughters, who were
carriers. The allele then passed through successive generations of Victoria’s
family, as the pedigree below shows.
1. Which of Victoria’s children were carries of the hemophilia allele?
2. Which of Victoria’s children passed the hemophilia allele on to Empress
Alexandra of Russia?
3. Which of Victoria’s children passed the hemophilia allele on to Queen Victoria of
Spain?
4. Assume that a direct descendant of Maria Cristina, daughter of Queen Victoria
Eugenie of Spain, has just been found to have had hemophilia. How would this
change Maria Christina’s status?
5. Explain why males are more likely than females to have hemophilia
15
CHROMOSOMAL NUMBERS
A normal set of human chromosomes contain twenty-three pairs.
Strictly speaking the twenty-third pair in males is not really a pair. In
normal human males the twenty-third chromosomes are shaped like XY
and in females like XX. They are usually referred to as XY
chromosomes and the XX.
People sometimes think that having an extra chromosome or two would
result in a superhuman. This is not the case. Extra chromosomes,
damaged chromosomes and missing chromosomes almost always cause
severe abnormalities.
Studies of chromosomes are made by enlarging photographs of an
individual’s chromosomes. The chromosomes are cut out of the picture
and one by one they are matched in pairs and glued into place by an
expert. This is called a karyotype. Drawn on the next page are four
karyotypes of chromosomes from four different individuals. Match
each karyotype to the description below.
*Down’s syndrome results in mental retardation. It is determined in a
karyotype with an extra twenty-first chromosome.
*Normal chromosomes show up as twenty-three pairs. The twentythird pair can be either XX for females or XY for males.
*Turner’s syndrome is the result of only one X chromosome for the
twenty-third pair. It occurs when an egg cell does not contain a
sex chromosome. Its karyotype will have only one X chromosome
which came from the male parent’s sperm. Turner’s syndrome
occurs only in females.
*Cri du chat syndrome results in severe mental and physical
retardation. The affected individuals make catlike cries, hence
the name cri du chat which is French for cry of the cat. It is
determined on a karyotype by a missing portion of chromosome
five.
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