Transcript Chapter 6 - HeredityV3x

Genetics: The Science of Heredity
Table of Contents
What Is Heredity?
Probability and Heredity
Patterns of Inheritance
Chromosomes and Inheritance
Learning Goal
Develop and use a model to describe
why asexual reproduction results in
offspring with identical genetic
information and sexual reproduction
results in offspring with genetic
variation.
Big Question
Why don’t offspring always look
like their parents?
Discuss….
Lesson 1 Vocabulary
Lesson 1
Definition
heredity
Passing of physical characteristics (traits) from parent to offspring
trait
A specific characteristic
genetics
The scientific study of heredity
fertilization
A new organism begins when an egg and a sperm join in this process
purebred
When an organism is the offspring of many generations that have the same form
of a trait.
gene
Factors to control a trait
allele
The different forms of a gene
dominant allele
One whose trait always shows up if the allele is present.
Recessive allele
This allele is hidden if the dominant allele is present.
hybrid
An organism that has two different alleles for a trait.
Almost Forgotten
Read Almost Forgotten and answer the question. (Be
prepared to share…)
Share
Read What did Mendel Observe?
As a priest in a monastery Mendel had little opportunity to
come in contact with scientists. Ironically, his work was
rediscovered by three scientists working independently in the
same year.
Why is it important for scientists to do library research before
lab research?
Family Resemblances
Have you ever wondered why some
family members look very similar while
others look very different?
Share
Lab Zone
Do the Inquiry Warm-Up
What Does the Father Look Like?
Share answer to #4.
Read Mendel’s Experiments
Why is it necessary to cut off the stamens of the pea flower?
To make sure the pollen that landed on the pistil came from the
plant Mendel wanted to use in the cross.
What Is Heredity?
Crossing Pea Plants
Mendel devised a way to cross-pollinate pea plants.
Purebred Organisms
Every living thing has traits it inherited from its
parents. Until the work of Mendel, people did not
understand how traits were passed on from parents
to offspring.
What is a purebred organism?
The offspring of many generations that have the same
form of the trait.
Read The F1 and F2 Offspring and Experiments
With Other Traits and complete the chart.
Mendel began each experiment plants that differed in one
specific trait.
What did Mendel find when he crossed purebred tall plants with
purebred short plants?
The offspring were all tall.
Was the trait for shortness lost?
No, when Mendel crossed the offspring, or F1 generation, with one another, some
of the offspring were short, so the trait wasn’t lost.
Are the plants in the F1 generation purebred plants?
No, they were not all identical to the parent plants.
Mendel did not always get exactly three-fourths and
one-fourth, but the results were close enough to
recognize a pattern.
What could be a reason why there might be a slight
variation.
Some plants might have died or seeds not germinated.
probability
Latin Origins
The terms F1 and F2 are derived from the Latin words filius
and filia. In Mendel’s time an educated person would have
studies Latin and Greek. In addition, his training as a monk
would have included studying Latin.
What other reasons might there be for using Latin terms in
science?
It could be a universal language. Other scientists probably studied
Latin in other countries.
Where else in your study of science have you seen words
that are derived from Latin?
Names of the elements.
What Is Heredity?
Results of a Cross
In Mendel’s crosses, some forms of a trait were hidden in one
generation but reappeared in the next. What was surprising about the
offspring in the F2 generation?
Read How Do Alleles Affect Inheritance?
An organism’s alleles come from it’s parents.
What are two kinds of alleles?
Dominant and Recessive
How are they different?
The dominant one is the one whose trait is always seen if the trait is
present. The recessive allele is hidden whenever the dominant is present.
Why were purebred pea plants so important for Mendel’s
experiments?
Purebred plants have two identical alleles for a gene. Therefore, in a cross,
each parent contributes a known allele, making the pattern of inheritance
easier to detect.
What Is Heredity?
Alleles in Pea Plants
Mendel studied the inheritance of seven different traits in pea plants.
Look at Figure 3
Remember that the traits that Mendel studied have two
distinct forms.
Look at the seed shape.
What are the two kinds of seed shape?
Round or Wrinkled
What trait is the dominant allele?
Round
What combinations of alleles will produce round seeds?
Two dominant alleles or one dominant and one recessive.
Are you confused?
Trait refers to the general characteristic.
Example- hair color
Allele refers to the specific forms the characteristic can have.
Example – blonde or brown
“We Have It So It Must Be Dominant” Worksheet – work with a partner
Use tally marks to add your info to this chart.
Trait
Dimples
Earlobes
Mid-digit
hair
Forelock
Pinky
Thumbs
Dominant Class Total
Recessive Class Total
Assess Yourself
Rate yourself on the Learning Goal
Where do you stand?
1,2,3,4.
Be honest.
Read Allele’s in Mendel’s Crosses and
Symbols for Alleles
Look at Figure 4 – Remember that when you write alleles you
list the dominant letter first.
How would you write the alleles for a plant that is purebred
tall?
TT
How would you write the alleles for the offspring of a cross
between a purebred tall and a purebred short?
Tt
What term did Mendel use for the individual with one
dominant allele and one recessive allele?
Hybrid
What Is Heredity?
Dominant and
Recessive Alleles
What are the
symbols and
descriptions
of allele? Use the
word bank to
complete
the statements.
What are the two
possible ways the F2
offspring
could look?
Lab Zone
Inferring the Parent Generation Corn Quick
Lab –
Examine an ear of colored corn to determine the
alleles of the parent generation. Complete and
turn in lab.
Genetics Packet – Finish for Homework
No Traits Lost
Remember that Mendel was the first person to show that traits are inherited
as discrete units that do not get lost or modified as they are passed from
one generation to the next.
Why do some of the offspring of two hybrid individuals show the recessive
form of the trait?
The hybrid parents each had one of the recessive genes. If an offspring receives both
of these recessive genes, it will show the recessive form of the trait.
Predict
When you predict, you use evidence and prior
experience to make an inference about a future event.
A prediction is more than a guess.
Key Concept Summary
Key Concept Summary
Chapter 6 Lesson 2
Probability and Heredity
Read My Planet Diary p. 204 - Storm on the Way
Have you ever followed a developing storm on the
news?
Do Weather forecasters guess about the weather?
No they rely on data and past experience.
What kind of evidence do scientists studying genetics
rely on?
Experience from crosses they have done.
Vocabulary
Homozygous and Heterozygous
“Homo” means the same and “Hetero” means other or
different.
An individual who is …..
homozygous has two of the same alleles for a trait or
purebred
heterozygous has two different alleles for a trait or hybrid
Lesson 2 Vocabulary
Lesson 2
Definition
probability
A number that describes how likely an event will occur.
Punnett square
A chart that shows the possible ways alleles can combine in a genetic cross.
phenotype
Physical appearance or visible traits
genotype
An organism’s genetic makeup
homozygous
An organism with two identical alleles for a trait.
heterozygous
An organism that has two different alleles for a trait.
Probability
Have you ever used a coin toss to decide an issue?
Why did you toss a coin in this situation?
It is the fairest way to make a decision.
Why is a coin toss fair?
Each person has a 50-50 chance of winning.
Mendel used the principles of probability to explain his results.
Probability
Read p. 205
What is probability?
A number that describes how likely it is
that an event will occur.
Probability
Does probability predict what will definitely
occur?
No, it predicts what is likely to occur.
What does probability predict will happen if
you toss a coin 10 times?
The coin will land on heads 5 times and
tails 5 times.
Probability
Do the Math p. 205
Read p. 206 and 207
Probability
The alleles an offspring receives from it’s parents depends on
probability.
How is this similar to a coin toss?
The allele passed on from a parent to offspring is based on
probability and whether a coin lands on heads or tails is also
probability.
What tool can be used to predict the results of a cross?
Punnett Square
Probability
What is a punnett square?
A punnett square is a chart that shows all the possible
combinations that can result from a genetic cross.
Probability and Heredity
How to Make a Punnett Square
What are the steps in using
a Punnett Square to find the
probabilities of a genetic cross?
Probability
Draw a punnett square for a cross between a purebred pea
plant with purple flowers (PP) and a purebred pea plant with
white flowers (pp).
Where do you write the alleles of the parents?
Outside the boxes.
What are the alleles for the offspring?
All Pp
What color flowers will the offspring have?
Purple
Fertilization
The punnett square represents the process of reproduction.
What is fertilization?
The joining of two sex cells.
The letters we write outside the box represent the parents sex
cells.
The letters inside the boxes represent the joining of the two
sex cells during fertilization.
Punnett Squares
Punnett Square Practice – use worksheet
to complete punnett squares.
Phenotypes and Genotypes
Read p. 208
What is an organism’s phenotype?
It’s physical appearance – what it looks like.
What is an organism’s genotype?
It’s genetic makeup or alleles.
Phenotype and Genotype
Review.
What is the term used to describe an organism whose
genotype consists of two identical alleles for a trait?
Homozygous
What is the term used to describe and organism whose
genotype consists of two different alleles for a trait?
Heretozygous
Homozygous or Heterozygous
What are the two ways and organism can be homozygous for
a trait?
Homozygous dominant or homozygous recessive.
What term did Mendel use to describe an organism that is
heterozygous?
Hybrid
Why can you be certain of the genotype of an organism that
shows a recessive trait?
It must be homozygous recessive because the recessive
allele is not hidden by a dominant allele.
Probability and Heredity
Describing Inheritance
An organism’s phenotype is its physical appearance. Its genotype is its
genetic makeup. Complete the missing information in the table.
Probability and Heredity
How do the smooth pods differ?
Can you tell the genotype of the parents that produced these
pods?
No
Why can you be certain of the plant that produced the pinched
pod?
The pinched pod is recessive so the the plant that produced
this pod must be ss for this trait.
Probability and Heredity
This graph shows the
phenotypes of guinea
pig pups. What would
be a good title for the
graph?
Chapter 6 Lesson 3
Patterns of Inheritance
Read p. 210 My Planet Diary (Cold, With a Chance of Males)
The laws of probability apply to situations that are not affected
by anything other than chance.
In most animal species the probability of being a male or
female is 50 percent.
But…in turtles and some other reptiles the environment is a
deciding factor.
Patterns of Inheritance
Complete Inquiry Warm-Up as a group and report your tally
on the chart.
Patterns of Inheritance
Incomplete Dominance and Codominance
The traits we have seen so far have all been traits that involve
two possible alleles.
There are patterns of inheritance that are more complex and
most traits are the result of these more complex patterns.
Read p. 211
What are two of the patterns of inheritance?
Incomplete dominance and codominance
Incomplete Dominance and Codominance
Which alleles are expressed in these offspring? both
Which organism shows incomplete dominance?
Which organism shows codominance?
Lesson 3 Vocabulary
Lesson 3
Definition
Incomplete
dominance
When one allele is only partially dominant
Codominance
When both alleles are expressed equally
Multiple
alleles
Polygenic
inheritance
There are three or more possible alleles for the trait
Occurs when more than one gene affects a trait.
Multiple Alleles
Read p. 212
In multiple alleles each individual has only two alleles for each
trait.
Each of the rabbits shown has two alleles for coat color.
The brown is the wild type or agouti
The gray is called chinchilla
The white is an albino
The albino genotype is cc.
Is cc homozygous dominant, homozygous recessive or
heterozygous recessive?
Homozygous recessive
Patterns of Inheritance
Blingwings
An imaginary insect called
the blingwing has three
alleles for wing color: R
(red), B (blue), and Y
(yellow). What are the
possible allele pairs for wing
color in the blingwings?
RY, RR, BB, BY, YY
Polygenic Inheritance
One gene with two possible alleles can produce three
genotypes. Ex. AA, Aa,aa
Two genes with two possible alleles can produce nine
genotypes.
Can we figure out the possible genotypes using the letters
A,a,B,b?
AABB, AABb, AAbb, AaBb, AaBB, Aabb, aaBB, aaBb, aabb
How Genes and the Environment Interact
Read p. 213 and 214 and 215 Complete bookwork.
No one is born knowing how to do everything!
As we live and learn we acquire traits and skills.
How Genes and the Environment Interact
Patterns of Inheritance
An individual’s phenotype is the result of the interaction of
genes and the environment.
What are some traits that people inherit?
Hair color, height, eye color
What inheritance pattern does height show?
Polygenic inheritance
How might the environment affect how the genotype is
expressed?
A person on a poor diet may not grow to his/her full height.
Genes and the Environment
How do people change the phenotype of their
hair?
Straighten, color, curl
Do these changes affect a person’s genotype?
No
How do you know?
The body still produces the hair according to the
genotype.
Lesson 4 Chromosomes and Inheritance
Read My Planet Diary p. 216
Genetic research has yielded information about many genetic
disorders. By studying how genes are related to an inherited
disorder, scientists can learn to diagnose the condition early
and help the patient reduce its effects.
Inquiry Warm-Up
Read and complete inquiry Warm-Up
What is the genotype of the offspring?
Gg
What is the phenotype of the offspring?
Green
Lesson 4 Chromosomes and Inheritance
Read p. 217
What was Sutton trying to understand?
How sex cells form
What aspect of sex cell formation was he studying?
How chromosomes move
What was his hypothesis?
Chromosomes are involved in how traits are passed from
parents to offspring
Lesson 4 Chromosomes and Inheritance
Apply It!
Humans have 46 chromosomes.
Skunks have 50
Shrimp have 90
A netted adder's-tongue fern has more than 1200
??????
Lesson 4 Chromosomes and Inheritance
Read and Complete p. 218
Genes are carried on the chromosomes.
What did Sutton observe about the relative number of
chromosomes in the body cells and sex cells of
grasshoppers.
The sex cells have half the number of chromosomes as body
cells.
How are genes passed from parent to offspring?
Sex cells contain half of each parent’s chromosomes, which
include the parent’s genes. When sex cells join during
fertilization, the offspring receive a full set of chromosomes.
Lesson 4 Chromosomes and Inheritance
What is the chromosome theory of inheritance?
Genes are carried from parent to offspring on chromosomes.
If human body cells have 46 chromosomes, how many
chromosomes do human sex cells have?
23
Chromosomes and Inheritance
Paired Up
Sutton studied
grasshopper
cells through a
microscope. He
concluded that genes are
carried on
chromosomes.
Lesson 4 Chromosomes and Inheritance
Look at figure 1.
How many chromosomes are in the body cells of a
grasshopper?
24
How many chromosomes are in a grasshopper egg cell?
12
How many chromosomes are in a grasshopper sperm
cell?
12
How is the chromosome number returned to normal?
When a sperm and egg join together in fertilization , their
individual 12 chromosomes add up to 24 chromosomes.
Lesson 4 Chromosomes and Inheritance
Key Concept
According to the chromosome theory of inheritance, genes
pass from parents to their offspring on chromosomes.
A Line Up of Genes
Read p. 219
Look at Figure 2
Heterozygous and homozygous apply to the individual pairs of
genes not the chromosomes.
Individuals can be homozygous for one trait and heterozygous
for another. This leads to variety in offspring.
Write the genotype for this individual
AabbCcDdEEFFGg
Chromosomes and Inheritance
A Pair of Chromosomes
Chromosomes in a pair
may have different alleles
for some genes and the
same alleles
for others. Is the organism
homozygous or
heterozygous?
Lesson 4 Vocabulary
Lesson 4
Meiosis
Definition
Is the process by which the number of chromosomes is reduced by
half as sex cells form.
What Happens During Meiosis
Read p. 220
What kind of cells are produced in meiosis?
Sex cells
How many divisions take place during meiosis?
Two
What happens in the first division?
Chromosome pairs line up together and then move apart
What happens in the second division?
Chromosomes split into identical halves, which move to new
cells
In which division is the number of chromosomes reduced
by half?
In the first division
What Happens During Meiosis?
Look at Figure 3
How would you describe the shape of a chromosome?
Like an X
What are the two sides of the X?
The chromatids
What holds the chromatids together?
Centromere
How do the chromatids of a chromosome compare?
They are identical
When do the chromatids separate?
During the second division
Chromosomes and Inheritance
Meiosis
During meiosis, a cell produces sex
cells with half the number of
chromosomes.