1. Whom do you look like?
Why do you look more like your relatives than other people?
Where do traits, such as eye color and shape, come from?
The parts of your cells that determine these traits are called genes.
Q: What are traits?
A: The characteristics that an organism has are called traits.
Look at the photo of seal on pg. 138
Q: What traits do you feel these seals received from their parents?
A: color, size ,eyes, ears.
Q: How do you think these traits are passed from parents to offspring?
A: by fertilization of male and female cells in sexual reproduction.
2. Enquiry Activity
ALB pg 69
Materials: Coin
Purpose: In this activity, students predict whether a tossed coin
will turn up heads or tails for different number of tosses.
Students will toss the coin and record the results to determine
whether their predictions were correct.
3. Pg. 140 What is heredity?
The passing of inherited traits from parents to offspring
Q: What are the different types of traits?
Traits
Inherited Traits Acquired Traits
traits that are passed from parent to offspring traits that are influenced by experience or environment
example: example:
1. dogs pass their fur color to their puppies 1. nutrition affects how large a kitten grow
2. Inherited trait in humans include height ,eye color, 2. practice may help musician gain musical skills.
dimples, freckles
5. Q: What is Genetics?
A: Genetics is the study of heredity.
Genetics is the study of how genes and how traits are passed down from one generation to the next.
Our genes carry information that affects our health, our appearance, and even our personality!
A gene is the portion of a chromosome that controls a particular inherited trait
Genes come in pairs.
You get half of your genes from your mother
and the other half from your father.
6. Some scientists were curious about basic questions of life: Where did it come from? Why is it so varied?
Why do children look like their parents?
To answer these questions, they study a type of biology called GENetics (juh-net-icks).
"Gen" means beginning.
The science of genetics began in the 1800s when Gregor Mendel, an Austrian
monk, figured out how traits are inherited by studying peas.
7. Pg. 142 What did Mendel do?
Mendel cultivated thousands of pea plants in his garden.
He kept precise records of the pea plants.
He experimented with pea plants to study how traits are passed from parent plants to their
offspring.
Through this work Mendel revealed for himself some basic properties of heredity.
Today, many consider Mendel to be the founder of genetics.
9. Q: Why did Mendel chose pea plants for his study?
A: To study genetics, Mendel chose to work with pea plants because
1. They have identifiable traits.
example - pea plant is either tall or short which is an easy trait to observe.
2. Pea plants grow quickly
Mendel could complete many experiments in a short period of time.
3. Pea plants can either self-pollinate or cross-pollinate.
Self-pollination- the transfer of pollen from the anther of a flower to the stigma of the same flower.
Cross-pollination- the transfer of pollen from the anther of a flower to the stigma of the another flower
10. In one of his early experiments, Mendel crossed a tall pea plant and a tall pea plant.
What do you think the offspring of these plants were?
11. Next, Mendel crossed a tall pea plant and a short pea plant.
What do you think the offspring of these plants were?
Mendel observed that every one of the hybrid was tall.
Hybrid: Organisms that have inherited two different forms of the same trait, one from each parent
12. Why were the hybrids tall? What happened to the short trait?
Mendel believed that the trait of short plant was present but was hidden by the trait of tall plant.
He hypothesized that the presence of tall trait prevented the short trait from appearing.
Mendel named the tall traits as dominant trait while the short hidden trait as the recessive trait.
According to the law of dominance, one trait in a gene pair will be dominant over the other.
For example,
1. When pea plants with smooth seeds were crossed with plants with wrinkled seeds.
all seeds in first generation were found to be round.
Q: Identify the dominant and recessive trait in seeds of pea plant
A: Dominant – smooth Recessive - wrinkled
2. When pea plants with purple flowers were crossed with plants with white flowers.
all flowers in first generation were found to be purple.
Q: Identify the dominant and recessive trait in flowers of pea plant
A: Dominant – purple Recessive - white
14. Dominant Recessive
The trait that masks the other form of the trait is called
Dominant trait
The hidden form of the trait is the recessive trait..
The dominant trait is represented in capital letters.
Example : tall pea plant (T)
The recessive trait is represented in small letters.
Example: short pea plant (t)
Some of the dominant features observed in humans are:-
Right handedness
Almond- shaped eyes
Detached earlobes
Some of the recessive features observed in humans are:-
Left- handedness,
Round eyes
Attached earlobes
Q: Differentiate between Dominant trait and recessive trait.
15. Pg. 144 Why is Mendel’s work important?
Mendel’s work can be used to predict the traits of offspring from crossing two organism.
To further understand heredity, Mendel used the concept of mathematical relationship called ratios.
In 1905, English geneticist Reginald Punnett created a technique to illustrate some of
Mendel’s discoveries. His technique employs what we now call a Punnett square.
Q: What is a Punnett Square?
A: This is a simple graphical way of discovering all of the potential combinations of traits that can occur in
children, given the traits of their parents.
Punnett square predicts the possible outcomes of genetic crosses
16. Q: How is a Punnett square made?
A: To make a Punnett square:
1. First, divide a large square evenly into 4 smaller squares.
2. Next, the female’s genes are written outside down the left and the male’s genes are written outside along to top
3. The results of a cross between them is found by carrying the letters downward and across into the boxes.
g
g
17. TT = pure tall
Tt = hybrid tall
tt= pure short
18. Draw a Punnett square to determine the possible outcomes of a cross for an offspring with one parent
having brown eyes and the other blue.
Use the capital letter 'B' to represent brown color of the eye and the lowercase letter ‘b' to represent blue.
(to be done in class)
What is the probability that the offspring will have blue eyes?
a. 25% c. 75%
b. 50% d. 100%
20. Pg. 146 What is selective breeding?
Mating certain organisms in order to promote offspring with desirable trait is called selective breeding.
Q: What is a breed?
A: Members of an animal species with similar traits are part of a group called a breed.
Selective breeding is when humans choose which animals or plants breed together.
For example: Dairy farmers use selective breeding to produce cows that give large volumes of milk
and chickens that produce large eggs.
21. Discussion Questions
•Why would people use selective breeding?
•What might go wrong if a breed of animal or variety of plant is constantly used to breed others?
Q: What are the advantages and disadvantages of selective breeding?
A:
Advantages Disadvantages
Produces animals with specific desirable traits
that humans want.
Example: Small schnauzers were bred to hunt
rats.
Example: Milk cows produce more milk
Decreased variation.
Can bring out harmful recessive traits or
diseases can accumulate in the population
Example: deaf dalmatians, boxers with heart
disease, Labradors with hip problem.
Editor's Notes
Mendel selected seven characteristics to study; purple or white flower color, flowers positioned on the side or top of the stem, smooth or pinched seed pod, green or yellow pod color, round or wrinkled seeds, yellow or green seed color, and long or short stems. Mendel studied each trait and learned how they were passed down to the offspring plant.
For each inherited trait, the offspring has two genes – one from each parent. If both genes are either dominant or recessive, the trait is called a purebred trait. If only one gene is dominant, the combination is known as a hybrid trait. This Punnett square shows a cross between two hybrid tall pea plants. T represents the dominant gene for tall and t represents the recessive gene for short. When two hybrid tall pea plants are crossed, three-fourths of the plants are tall, and one-fourth are short. You can predict that there is a 75% probability the offspring will be tall and a 25% probability the offspring will be short.
