Download Mendelian Terminology

Complete: Word association. Use the description that best
describes the term. This is practice for your vocab quiz.
1. a
2. e
3. c
4. d
5. b
6. f
Warm Up
1. The garden pea is a good subject for genetic study because it
a. is easy to grow.
c. produces many offspring.
b. has characters in two clearly different forms.
d. All of the above
2. Mendel first allowed each variety of garden pea to self-pollinate for several generations. This produced
the
a. F generation.
c. P generation.
b. F1 generation.
d. filial generation.
3. What did Mendel find in the F1 generation?
a. a ratio of 3:1
c. 30 percent of the plants expressed the dominant trait.
b. a ratio of 3:1:3
d. 100 percent of the plants expressed the dominant trait.
4. Which ratio of plants expressing contrasting traits did Mendel find in the F2 generation?
a. 3:1
c. 3:3
b. 3:1:3
d. 1:1
5. The trait that disappeared in the F1 generation
a. reappeared in some plants in the F2 generation.
c. reappeared in some plants in the P generation.
b. reappeared in all plants in the F2 generation.
d. was lost forever.
OBJECTIVES MENDELIAN TERMS
• Describe the patterns that Mendelian theory explains.
• Define and be able to use terminology associated with
genetics; allele, gene, those below.
• Relate genotype to phenotype, using examples from
Mendel's experiments with pea plants.
• Relate the terms recessive and dominant, with respect to
Mendelian genetics.
• Relate the terms homozygous and heterozygous.
• Summarize the laws of segregation and independent
assortment.
VOCABULARY
Allele
Dominant
Recessive
Genotype
Phenotype
Homozygous
Heterozygous
EXPLAINING MENDEL’S RESULTS
Mendel developed several hypotheses/theories to
explain the results of his experiments.
These hypotheses are collectively called the
Mendelian theory of heredity, which form the
foundation of modern genetics.
Mendelian theory explains simple patterns of
inheritance.
In these patterns, two of several versions of a gene
combine and result in one of several possible traits.
MENDEL TERMS… COMMON TERMS
Mendel Used:
We Use Now:
-
Character
-
Gene
-
Factor
-
Allele
EXPLAINING MENDEL’S RESULTS/ MODERN
TERMINOLOGY
A gene is the most basic unit of heredity. It is found in DNA.
An allele is a version of a gene. These are also found on the chromosome
in DNA.
A trait is what is seen on the outside of an organism as a result of the
specific allele combination.
Gene (hair color)  allele (brown)  trait (brown hair)
To help, think of this analogy:
When explaining Gene 
Allele 
Trait
Category for unit One version of a What is
of heredity
specific gene
observed
Analogy…
Cakes: The
category of food
Or Develop Your Own!
Chocolate cake
recipe
The finished
cake
VISUAL CONCEPT: ALLELE
Click above to play the video.
GENE  ALLELE  TRAIT
For every gene we are given 2
alleles.
One allele is from mom, one is
from dad.
The way these alleles interact Trait
give us a trait, which is
observable on the outside.
Allele
ALLELES
•How do we
end up with a
trait?
•Meiosis
•How do
gametes end up
with one allele? •How do we
end up with
two alleles for
each gene?
•Fertilization
•Alleles interact to
give us our traits.
HOW ALLELES INTERACT
• For “Mendelian Traits” alleles have one of two roles.
• An allele that is fully expressed whenever it is present is
called dominant.
• This means this is the version of the gene that will show up.
• An allele that is not expressed when a dominant allele is
present is called recessive.
• This allele cannot be seen if the dominant form is also
present.
• A recessive allele is expressed only when there is no
dominant allele present.
• The trait that results will be either dominant or recessive
depending upon the combination of alleles makes it.
VISUAL CONCEPT: COMPARING DOMINANT AND
RECESSIVE TRAITS
Click above to play the video.
DEFINING ALLELES FURTHER
Scientists use a code of letters to represent the function
of alleles.
A dominant allele is shown as a capital letter.
This letter usually corresponds to the first letter of the
word for the trait.
A recessive allele is shown as a lowercase letter.
This always relates to the dominant form.
Offspring do not show a trait for every allele that they
receive. Instead, combinations of alleles determine
traits.
ALLELES
Dominant Allele
Recessive Allele
 Written as an uppercase
 Corresponds (usually) to the first
letter of the dominant allele/trait.
 Examples.
 Yellow (dominant)…Y
 Purple flower (dom)…P
 Round seed (dom)…R
 Written as a lowercase
 Corresponds to the dominant
allele
 Examples.
 Green (recessive)…y
 White flower (rec)…p
 Wrinkled seed (rec)…r
PRACTICE ALLELES
Black hair is dominant over red hair
Brown eyes are dominant over green eyes
Left thumb on top in hand clasping is dominant over
right thumb on top. (Clasp you hands together. Which
way does it feel natural?)
Having a bent little finger is dominant over a straight
little finger. (Put your hands on the table, relax you
muscles and see if the last joint bends in towards your
ring finger)
Take 2 minutes and write a symbol for both the dominant
and recessive alleles.
As a follow up, if you show recessive for any of these traits examine
your parents to see if they both show these came characteristics.
(BTW…who should show them?)
POSSIBILITIES…THERE’S NO RIGHT OR WRONG
ANSWERS HERE, JUST USE SOLID JUDGMENT.
Dominant Trait Dominant
Allele
Black
B
Recessive trait Recessive
Allele
Red
b
Brown Eyes
B
Green
b
Left Thumb on
Top
L, T
Right Thumb
on Top
l, t
Bent Little
Finger
B, L, or F
Straight Little
Finger
b, l, or f
MODERN GENETICS TERMS
The set of specific combinations of alleles that an individual
has for a character is called the genotype.
These are given as a combination of letters that represent
the allele.
Alleles are on the chromosome so the genotype can only be
determined by examining the combination of alleles.
The observable trait that results from the genotype’s set of
alleles is called the phenotype.
This is observable. Your phenotype for your hair color is the
color your hair is, based upon the alleles you were given.
Thus, genotype determines phenotype.
But phenotype is the thing that’s measurable.
VISUAL CONCEPT: GENOTYPE
Click above to play the video.
MODERN GENETICS TERMS
If an individual has two identical alleles of a certain gene, the individual is
homozygous for the related character.
 Homozygous means that the letters are the same!
 They could be both the dominant or recessive allele!
 Examples:
 YY = two yellow alleles (both dominant)
 yy = two green alleles (both recessive)
 PP = two purple alleles (both dominant)
 pp = two white alleles (both recessive)
 Homozygous means purebred.
If an individual has two different alleles of a certain gene, the individual is
heterozygous for the related character.
 Yy = one yellow and one green allele (1 dominant/1 recessive)
 Pp = one purple and one white allele (1 dominant/1 recessive)
 Heterozygous means hybrid.
1
2
3
4
5
6
Genotype Phenotype Genotype Phenotype Genotype Phenotype
PP
Pp
pp
YY
Yy
yy
RR
Rr
rr
GG
Gg
gg
Which columns are:
• Homozygous?
• Heterozygous?
WHAT MENDEL DISCOVERED
Mendel was able to establish three things based upon the
evidence gathered from the pea plants.
First thing was dominance and recessiveness.
The second thing was that alleles end up in gametes according
to the law of segregation.
The law of segregation holds that when an organism produces
gametes, each pair of alleles is separated and each gamete
has an equal chance of receiving either one of the alleles.
The 3rd thing the law of independent assortment, that genes on
different chromosomes end up in gametes independently from
genes on other chromosomes.
Since there are two for each gene, the chance is 50/50 on
which allele ends up in any gamete. These alleles don’t
affect the inheritance of alleles for other genes.
MEIOSIS
MEIOSIS
GAMETES
• The law of segregation states that each allele is separated
giving each gamete an equal chance of receiving either
allele. This gives multiple possibilities for offspring.
OFFSPRING
• There are 16 different possibilities with just these 4 alleles!
RECALL THAT A DIPLOID
ORGANISM HAS 2 SETS OF
CHROMOSOMES
In these sets there
are 2 chromosomes
that carry the same
genes, just different
copies (sometimes)
The different
versions (the
alleles) of each
gene work together
to give each trait
seen on the
outside.
From
Mom
From
Dad
b
B
From
Mom
From
Dad
M
m
•TRAIT1
•TRAIT2
SUMMARY
Mendelian theory explains simple patterns of inheritance. In
these patterns, two of several versions of a gene combine
and result in one of several possible traits.
Genotype determines phenotype.
In modern terms, the law of segregation holds that when an
organism produces gametes, each pair of alleles is
separated and each gamete has an equal chance of
receiving either one of the alleles.
In modern terms, the law of independent assortment holds
that during gamete formation, the alleles of each gene
segregate independently.
INDEPENDENT PRACTICE
Complete the worksheet, front and
back, practicing with Mendelian
Genetics Terms.
END OF SECTION QUIZ
In addition to the 10 multiple choice questions that are being handed
out to you, answer these 5 questions in short answer form.
1. Describe the patterns that Mendelian theory explains.
2. Summarize the law of segregation.
3. Summarize the law of independent assortment.
4. Could a trait be heterozygous recessive?
5. What is the major flaw in Mendel’s independent
assortment law?
Homework follows…