Genetics
Chapter 17
Gregor Mendel
An Austrian Monk
1822 - 1844
An Austrian Monk. Spent 10 years in a monastery
experimenting with selective breeding of peas.
Experimented with traits like: seed shape,
seed colour, pod shape, pod colour, stem height
Hypotheses:
- Elements are passed from parent to offspring
- Different elements control different traits
- Elements unchanged during life of organism
passed to offspring
- Elements are passed on in the gametes of
organisms
Definitions
Characteristic- observable feature example; eye colour etc.
Trait – a variation that can exist for a characteristics
Heredity – The passing of a characteristic from parents to offspring.
Genetics – The field of science that deals with heredity.
Selective Breeding – Producing preferred types of plants and animals by controlling
how they reproduce. Has been done throughout history.
Purebred - offspring that are the result of mating between genetically similar kinds of
parents
Hybrid - result of mating between two genetically different kinds of parents-opposite
of purebred.
It was discovered that it takes at least 3 generations to determine a pattern
P generation – parents generation
F1 generation – offspring of the parents, usually hybrids
F2 generation – offspring from the offspring??? 2 individuals from the F1 is
crossed.
Handout pg 49.
Probability
–
The chances that something will happen. In genetics, the chances of
inheriting a certain trait.
If you flip a coin, there is a 50% probability it will be heads and a 50% probability
it will be tails – no matter how many times it is flipped!
Mendel perform 1000’s of experiments and his results were not an exact ratio of
3:1. But he was very close, one of his ratios were 705 to 224, which can be simplified to
3.15:1. This is VERY close to 3:1.
Mendel added details to his hypothesis:
Genes are passed on from parents to offspring.
An allele on a gene is responsible for a certain trait, ex; colour of leaves
Alleles – different forms of the same gene that produce different variations of a trait.
(eg. one allele produces a green pod, another a yellow pod)
Different alleles are located at the same point on homologous chromosomes.
Many traits have just 2 alleles.
Eg. Height of pea plants have 1 allele for Tall and 1 allele for short. One of the alleles
will be dominant and the other will be recessive.
Homozygous – Individual has both alleles the same.
Eg. TT – homozygous tall.
tt – homozygous short
Heterozygous – Has one of each allele.
Eg. Tt – heterozygous tall
Genotype – The combination of alleles that an organism possesses. Eg. (TT, Tt and tt
are different genotypes.)
Phenotype – The outward appearance of an organism
eg. The phenotype for TT would be tall
The phenotype for Tt would be tall.
The phenotype for tt would be short.
Punnett Squares and Probability
An easy way of predicting genotypes is the use a Punnett square.
 It was designed by a British Biologist R.C. Punnett.
 It shows all the possible combinations of the alleles that parents might give to
their offspring.
Here is a Punnett square for the crossing of 2 HETEROZYGOUS plants.
T = tall t = short
(T is dominant)
T
t
T
TT
Tt
t
Tt
tt
The parents genotypes are along the top and the sides, in the shaded region. The
potential combinations of the offspring are in the unshaded region.
The chance of the TT is 1 out of 4 = ¼
The chance of the Tt is 2 out of 4 = 2/4 = ½
The chance of the tt is ¼
Therefore the probability that the offspring will have a tall phenotype is the sum of the
TT and the Tt genotypes
tall = ¾ = 75%
Therefore the probability that the offspring will have a short phenotype is the sum of the
tt genotype short = ¼ = 25%
Example; R is red and is dominant, r = white
R
r
R
r
What is the probability of the flower being red? __________
What is the probability of the flower being white? __________
What is the probability of the flower being HOMOZYGOUS RECESSIVE? _________
What is the probability of the flower being HOMOZYGOUS DOMINANT? _________
What is the probability of the flower being HETEROZYGOUS? _________
Example; R is red and is dominant, r = white
r
r
R
r
What is the probability of the flower being red? __________
What is the probability of the flower being white? __________
What is the probability of the flower being HOMOZYGOUS RECESSIVE? _________
What is the probability of the flower being HOMOZYGOUS DOMINANT? _________
Example; A heterogyzous tall pea is crossed with a homozygous tall pea. Determine the
possible genotypes and phenotypes of the offspring.
The genotypes would be:
What fraction would be tall? (phenotype) ____
What fraction would be short? ____
Handout pg 56/57
Genetics
Chapter 17
Gregor Mendel
An Austrian Monk
1822 - 1844
An Austrian Monk. Spent 10 years in a monastery
experimenting with selective breeding of peas.
Experimented with traits like: seed shape,
seed colour, pod shape, pod colour, stem height
Hypotheses:
- Elements are passed from parent to offspring
- Different elements control different traits
- Elements unchanged during life of organism
passed to offspring
- Elements are passed on in the gametes of
organisms
Definitions
______________ - observable feature example; eye colour etc.
______________ – a variation that can exist for a characteristics
______________ – The passing of a characteristic from parents to offspring.
______________ – The field of science that deals with heredity.
______________ – Producing preferred types of plants and animals by controlling
how they reproduce. Has been done throughout history.
______________ - offspring that are the result of mating between genetically
similar kinds of parents
______________ - result of mating between two genetically different kinds of
parents-opposite of purebred.
It was discovered that it takes at least 3 generations to determine a pattern
______________– parents generation
______________– offspring of the parents, usually hybrids
______________– offspring from the offspring??? 2 individuals from the F1
is crossed.
Handout pg 49.
Probability
–
The chances that something will happen. In genetics, the chances of
inheriting a certain trait.
If you flip a coin, there is a 50% probability it will be heads and a 50% probability
it will be tails – no matter how many times it is flipped!
Mendel perform 1000’s of experiments and his results were not an exact ratio of
3:1. But he was very close, one of his ratios were 705 to 224, which can be simplified to
3.15:1. This is VERY close to 3:1.
Mendel added details to his hypothesis:
_______ are passed on from parents to offspring.
An _______on a gene is responsible for a certain _______, ex; colour of
leaves
_______ – different forms of the same gene that produce different variations of a
trait. (eg. one allele produces a green pod, another a yellow pod)
Different alleles are located at the same point on homologous chromosomes.
Many traits have just 2 alleles.
Eg. Height of pea plants have 1 allele for Tall and 1 allele for short. One of the alleles
will be dominant and the other will be recessive.
_____________________ – Individual has both alleles the same.
Eg. TT – homozygous tall.
tt – homozygous short
_____________________ – Has one of each allele.
Eg. Tt – heterozygous tall
______________ – The combination of alleles that an organism posseses. Eg. (TT,
Tt and tt are different genotypes.)
______________ – The outward appearance of an organism
eg. The phenotype for TT would be tall
The phenotype for Tt would be tall.
The phenotype for tt would be short.
Punnett Squares and Probability
An easy way of predicting genotypes is the use a Punnett square.
 It was designed by a British Biologist R.C. Punnett.
 It shows all the possible combinations of the alleles that parents might give to
their offspring.
Here is a Punnett square for the crossing of 2 HETEROZYGOUS plants.
T = tall t = short
(T is dominant)
T
t
T
TT
Tt
t
Tt
tt
The parents genotypes are along the top and the sides, in the shaded region. The
potential combinations of the offspring are in the unshaded region.
The chance of the TT is 1 out of 4 = ¼ = 25%
The chance of the Tt is 2 out of 4 = 2/4 = ½ = 50%
The chance of the tt is ¼ = 25%
Therefore the probability that the offspring will have a tall phenotype is the sum of the
TT and the Tt genotypes
tall = ¾ = 75%
Therefore the probability that the offspring will have a short phenotype is the sum of the
tt genotype short = ¼ = 25%
Example; R is red and is dominant, r = white
R
r
R
r
What is the probability of the flower being red? __________
What is the probability of the flower being white? __________
What is the probability of the flower being HOMOZYGOUS RECESSIVE? _________
What is the probability of the flower being HOMOZYGOUS DOMINANT? _________
What is the probability of the flower being HETEROZYGOUS? _________
Example; R is red and is dominant, r = white
r
r
R
r
What is the probability of the flower being red? __________
What is the probability of the flower being white? __________
What is the probability of the flower being HOMOZYGOUS RECESSIVE? _________
What is the probability of the flower being HOMOZYGOUS DOMINANT? _________
Example; A heterogyzous tall pea is crossed with a homozygous tall pea. Determine the
possible genotypes and phenotypes of the offspring.
The genotypes would be:
What fraction would be tall? (phenotype) ____
What fraction would be short? ____
Handout pg 56/57