Download heredity

Bell Work: 2/11/14
Create the chart below and fill out as part of the Mitosis
vs. Meiosis notes (2nd page) for BW. Write “Compare &
Contrast” on your BW sheet.
Mitosis
Meiosis
Mitosis
Meiosis
•Both are processes of cell division
•Both reproduce new cells
•Both go through Interphase, Prophase, Metaphase,
Anaphase, Telophase, & Cytokinesis
•Asexual cell reproduction
(only one parent cell is
needed)
•Produces an exact copy of
itself with 46 chromosomes
•Reproduces two new cells
•Somatic cells: body cells
(skin cells, blood cells, bone
cells, muscle cells)
•Sexual cell reproduction
(two parent cells are
needed)
•Produces cells with half as
many chromosomes (23)
•Reproduces four new cells
•Sex cells (sperm & egg)
Objectives
• Describe the relationship among genes,
chromosomes, and inherited traits.
(SPI 0707.4.3)
• Interpret a Punnett square to predict possible
genetic combinations passed from parents to
offspring during sexual reproduction.
(SPI0707.4.4)
Heredity
• Why don’t you look like a rhinoceros?
• The answer to this question seems simple: Neither
of your parents is a rhinoceros.
• But there is more to this answer than meets the
eye.
• As it turns out, heredity, or the passing of traits
from parents to offspring, is more complicated than
you might think.
• For example, you may have curly hair, while both of
your parents have straight hair. You might have
blue eyes while both of your parents have brown
eyes.
• How does this happen?
Who was Gregor Mendel?
• Read pg. 100
– “Who Was Gregor Mendel?
– “Unraveling the Mystery”
• Gregor Mendel discovered the principles of heredity
while studying the characteristics and traits of pea
plants.
• A characteristic is a feature that has different forms in a
population.
– For example, hair color is a characteristic of humans.
• The different forms, such as brown or red hair is called a
trait.
With your elbow partner,
name two
characteristics in our
class and two different
traits of those
characteristics.
Mendel’s First
Experiments
• One trait was always present in
the first generation, and the
other trait seemed to disappear.
• Mendel chose to call the trait that
appeared the dominant trait.
• Because the other trait seemed
to fade into the background,
Mendel called it the recessive
trait.
• The recessive trait for the white
flower reappeared in the second
generation.
Review: Talk with your group…
1. What is heredity?
•
The passing of genetic traits from parent to
offspring
2. Who was Gregor Mendel?
•
Discovered the principles, or ideas, of heredity
3. Which trait is present in the first
generation?
•
Dominant trait
4. Which trait is present in the second
generation?
•
Recessive trait
Challenge Question
So how is it that both of my parents
are short, but I am tall?
The Family Connections
• You and your partner
will help each other
determine the
variation of each
characteristic (trait)
that each of you
possess. Record your
traits in the chart
labeled “My
Characteristics” on
the back of the sheet.
Traits and Inheritance
• Mendel knew from his experiment with pea plants
that there must be two sets of instructions for each
characteristic.
• These instructions for an inherited trait are called
genes.
• Each parent gives one set of genes to the offspring.
• The offspring then has two forms of the same gene
for every characteristic- one from each parent.
• The two forms (often dominant and recessive) of a
gene are known as alleles.
• Dominant alleles are shown with a capital letter (P
for dominant purple flowers).
• Recessive alleles are shown with a lowercase
letter (p for recessive white flowers).
Just a side note…
Bell Work: 2/12/14
Review Question:
• What is the difference between a gene and an
allele?
Challenge Question:
• Mendel calculated that ratio of dominant traits to
recessive traits. He found a ratio of 3:1. What did
this tell him about how traits are passed from
parents to offspring?
Objectives
• Describe the relationship among genes,
chromosomes, and inherited traits.
(SPI 0707.4.3)
• Interpret a Punnett square to predict possible
genetic combinations passed from parents to
offspring during sexual reproduction.
(SPI0707.4.4)
Phenotype & Genotype
• Genes affect the traits of an offspring.
• An organism’s appearance (the way they look) is
known as its phenotype.
• In pea plants, possible phenotypes for the
characteristic of flower color would be purple
flowers or white flowers.
• The genotype of an organism is the entire
genetic makeup of an organism; the
combination of genes for a specific trait.
– An organism with two dominant or two recessive
alleles is homozygous (same size letters- PP or pp).
– An organism with one of each (Pp) is heterozygous.
Inherited Disorders
• Albinism is an inherited
disorder that affects a
person’s phenotype in
many ways.
• The boy in the picture has
inherited a condition
called albinism.
• Albinism prevents hair,
skin, and eyes from
having normal coloring
because that person’s
gene for producing
melanin is mutated.
Punnett Square
• A Punnett square is used to
organize all possible
combinations of offspring from
particular parents.
• Genotype PP is a purebred.
• What is the genotype for the
offspring to the right?
• The dominant allele P ensures
that the offspring will have
purple flowers.
• The recessive allele p may get
passed to the next generation.
• Why?
Quick Lab
pg. 107
R= round seeds
r= wrinkled seeds
• Work with your
group to complete
the Punnett
square.
• What would be the
phenotypes for
these offspring?
– RR= round seeds
– Rr= round seeds
– rr= wrinkled seeds
R
r
R
r
RR
Rr
(genotype- two
dominant
alleles)
(genotype- one
dominant
allele,one
recessive allele)
Rr
rr
(genotype- one
dominant
allele,one
recessive allele)
(genotype- two
recessive alleles)
Probability
• The mathematical chance that something
will happen is known as probability.
• Genotype probability:
– Pp x Pp cross has a 50% chance of receiving
either allele from either parent.
– The probability of inheriting two p alleles is
½x½, which equals ¼, or 25%.
Monohybrid vs. Dihybrid Punnett Square
• A monohybrid Punnett
• A dihybrid Punnett
square is one where only
square is one where two
one trait is crossed.
traits are crossed.
– Example: A tall pea
• Example: a tall, green
plant TT is crosses with
flowered plant TtGg is
a short pea plant tt.
crossed with a short,
yellow flowered plant ttgg.
T
t
t
Tt
Tt
T
Tt
Tt
TG
Tg
tG
tg
tg
TtGg
Ttgg
ttGg
Ttgg
tg
TtGg
Ttgg
ttGg
Ttgg
tg
TtGg
Ttgg
ttGg
Ttgg
tg
TtGg
Ttgg
ttGg
Ttgg
R= round seeds
r= wrinkled seeds
Rr x rr
R= round seeds
r= wrinkled seeds
Y= yellow seeds
y= green seeds
RrYy x rryy
SpongeBob Genetics
• Scientists at Bikini
Bottoms have been
investigating the
genetic makeup of the
organisms in this
community.
• Use the information
provided and your
knowledge of genetics
to complete the
SpongeBob Genetics
packet.
Exit Ticket
Create your own monohybrid
Punnett Square cross.
Use the examples in your notes
for ideas.