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Why are sperm (pollen) and eggs so
important to sexual reproduction?
How are sperm and egg (gametes)
produced?
Why do you only get half of your genes from
one parent?
Where are genes located?
Why are sperm (pollen) and eggs so important to sexual
reproduction?
• hold genes that control traits (proteins)
• A sexually reproducing organism gets ½ of its genes from
Dad and ½ from Mom
How are sperm and egg (gametes) produced?
• Meiosis
Why do you only get half of your genes from one parent?
• Meiosis
Where are genes located?
• In the cells within the nucleus. Inside the nucleus the DNA
is organized on structures called chromosomes. Sections of
the chromosome or DNA that encode for proteins are known
as genes.
1. Which part of the lab simulated fertilization?
2. Why are sperm (pollen) and eggs so important to sexual
reproduction?
3. How are sperm and egg (gametes) produced?
4. Why do you only get half of your nuclear genes from one
parent?
5. Where are genes located and how do they control traits?
How do genes (alleles) control traits?
Remember: A gene is a segment of DNA that encodes for a
particular protein.
• The gene may not produce a protein.
• The protein may be dysfunctional.
• The protein may have a different
structure.
Where are the genes?
Chromatid
Somatic cell
Centromeres
Centrioles
Kinetochores
Chromatin
Nucleus
23 pairs of chromosomes
Nuclear membrane
DNA
on Histones
Telomeres
Genes (Alleles) on a Homologous Pair of
Chromosomes
Combinations of Alleles for a trait (Genotype)
Homozygous Dominant
Homozygous Recessive
Heterozygous
4 Sperm cells (in pollen)
4 Eggs (oocytes)
Haploid or N number of chromosomes
Haploid or N number of chromosomes
Polar
Bodies
Sex cells (gametes): sperm and egg from a
heterozygous individual that has undergone Meiosis
Fertilization
Sperm (pollen)
+
Egg (oocyte)
=
Zygote
Modeling Fertilization Using Punnett Squares
Parent Gametes
F1 Genotype ratio
1 : 2 : 1
F1 Phenotype ratio
3 : 1
Dominant : Recessive
F1 Zygotes
How many Black Lab Puppies?
How many Black Lab Puppies?
A Biologist’s Mother’s Day
Song
• http://www.youtube.com/watch?v=osWuWj
beO-Y
You should be able to…
1.Name and identify the phases
of Mitosis and Meiosis. Give
correct order: Prophase,
Metaphase, Anaphase,
Telophase
2.Describe what is occurring in
each phase of Mitosis and
Meiosis using appropriate
terminology.
MEIOSIS (PMAT I)
Prophase 1
Anaphase 1
Metaphase 1
Telophase 1
MEIOSIS (PMAT II)
Prophase 2
Metaphase 2
Anaphase 2
Telophase 2
Interphase and chromosome formation
produces an exact
copy of the original
chromatid.
The
Law of Segregation
1. In each organism, a trait (for example pigment/color)
is composed of two alternative states (for example,
yellow or green). These alternative states are called
alleles.
2. Only one of the alleles is passed on to the offspring.
Since an offspring gets an allele from each parent, it
Gregor Mendel
also has two alleles for each trait.
The Father of Genetics
3. Each allele has an equal chance of being passed on
to the offspring.
4. The two alleles do not blend, but remain distinct.
5. There is a dominant/recessive relationship
between the alleles. that is, if the two alleles are
different, the dominant one will be expressed
and the other will not.
Modeling Fertilization Using Punnett Squares
Parent Gametes
F1 Genotype ratio
1 : 2 : 1
F1 Phenotype ratio
3 : 1
Dominant : Recessive
F1 Zygotes
Practice Problems Using Punnett Squares
Name________________Date______Per___
Gregor Mendel worked with pea plants and discovered
basic genetic principles. In pea plants, the gene for seed
color has two alleles: ‘A’ for yellow and ‘a’ for green. If I
cross a pea plant heterozygous for seed color with itself…
• What are the different gametes produced?
• What will the phenotypic ratio be for the F1 offspring
(seeds)?
• What will the genotypic ratio be for the F1 offspring
(seeds)?
• What is the probability that you will have yellow F1
offspring (seeds)?
• If I cross this same plant with a homozygous recessive
plant (a testcross individual) what will be the probability
of getting heterozygous offspring? Yellow offspring?
Practice Problems Using Punnett Squares
Cystic Fibrosis
Inheritance
Autosomal recessive
Occurrence
1 in 3,300 Caucasians; 1 in 9,500 in Hispanics; frequency varies with ethnic
group
Description
A disease caused by defective chloride transport that leads to high levels of
mucus in the lungs and pancreas, high sweat chloride levels, and other
digestive and respiratory problems.
Gene and
Location
The gene is known as CFTR and is found on chromosome 7. Carrier testing is
available.
Two normal parents who are carriers (heterozygous) of the cystic
fibrosis gene are planning to have another child. Of their 2 current children,
one has cystic fibrosis and one does not. What is the probability that their next
child will have cystic fibrosis?
If the normal child is a carrier and someday marries a normal person
who is not a carrier, what is the chance that one of their children will have
cystic fibrosis? What is the chance that their first child will be a carrier?
Mitosis occurring in C. elegans
In Mendel's second experiment, he studied the effect
of inheritance one trait has on another. Mendel
concluded that the alleles of one gene segregated
independently from another. That is, one trait does not
affect the inheritance of another. He called this:
The Law of Independent
Assortment
Types of Gametes
Produced?
In pea plants, the genes for seed color and seed texture have two
alleles: ‘A’ for yellow and ‘a’ for green and ‘B’ for smooth and ‘b’ for
wrinkled. If I cross a pea plant heterozygous for seed color and
texture with itself…
• What are the different gametes produced? (F.O.I.L.)
• What will the phenotypic ratio be for the F1 offspring (seeds)?
• What will the genotypic ratio be for the F1 offspring (seeds)?
• What is the probability that you will have yellow F1 offspring
(seeds)?
• If I cross this same plant with a homozygous recessive plant
(a testcross individual) what will be the probability of getting
heterozygous offspring? Yellow offspring?
• Incomplete
Dominance
• Codominance
• Sex-linked Traits
Two pink flowers are crossed.
What proportion of their progeny
would you predict would be pink?
The gene for colorblindness is
carried on the X chromosome and
is recessive. A man, whose father
was colorblind, has a colorblind
daughter.
a) Is this man colorblind? How do you
know?
b) Where did he get his gene for
colorblindness?
c) Must the fathers of all colorblind girls
be colorblind? Why?
If a husband and wife have a
heterozygous girl for
colorblindness, a normal boy, a
colorblind girl, and a
colorblind boy, what would be the
genotypes of the parents?
XB = No baldness (dominant)
Xb = Male-pattern baldness (recessive)
If a Male with XbY genotype mated with a
Female with XB Xb genotype.
1. What percent of male children will have male-pattern
baldness?
a. 25% c. 75%
e. 0%
b. 50% d. 100%
2. If a male WITHOUT male-pattern baldness is mated to a
female WITH male-pattern baldness, what is the
probability that they will produce a male child WITH malepattern baldness?
a. 25% c. 75%
e. 0%
b. 50% d. 100%