Transcript Presentation

Heredity & Reproduction
STANDARD IV: Objective I
Recognize heritable traits that are passed from
parents to offspring.
o Identify physical traits that are passed from parents to
offspring
o Recognize how genetic traits including diseases &
disorders are passed through generations - including
family pedigrees and monohybrid Punnett squares
o Identify what happens to DNA code when a mutation
occurs and identify major causes of mutations.
o Recognize and evaluate the harms and benefits that
result when mutations occur.
STANDARD IV: Objective 2
Explain how the DNA molecule transfers genetic
information from parent to offspring.
o Describe the relationships among DNA, genes, and
chromosomes.
o Describe in basic terms the structure and function of
DNA.
o Define the genetic purpose for meiosis from generation
to generation.
o Define and distinguish between dominant and recessive
genes and know how each is expressed in parents and
offspring.
In the 1860’s, Gregor Mendel first discovered the
principles of genetics.
Genetics- the branch of biology that studies
heredity.
Heredity- the passing on of characteristics from
parents to offspring.
By observing pea plants, Mendel was able to
successfully predict what traits would be passed on
from parent to offspring.
Pollination- the transfer of the male pollen grain
to the female organ.
Fertilization- the uniting of male and female
gametes.
He also noticed that the pea plants inherited two
forms of each gene; one from each parent plant.
From his studies, Mendel derived three basic principles:
Law of Segregation: when gametes(sex cells) are formed,
the two alleles separate – one allele into
one gamete and the other allele into a
different gamete
States that during meiosis, the factors that control
each trait separate, and only one factor from each pair
is passed to the offspring.
Law of Independent Assortment: the alleles for different
traits are inherited separately or
independently of each other
States that the inheritance of alleles for one trait is
not affected by the inheritance of alleles for a different
trait if the genes for the traits are on separate
chromosomes.
How does Mendel’s Law of Independent Assortment assure genetic diversity?
Genes
Your characteristics are determined by
specific portions of DNA which are called
genes.
Genes carry traits to be passed on from one
generation to the next.
Alternate forms of genes are
called alleles.
An allele can be dominant or
recessive.
A dominant allele will mask
(or hide) recessive gene. It is
represented with a capital letter.
A recessive allele is seen only
when no dominant gene is
present. It is represented with a
lowercase letter.
Example of Alleles
An offspring has two alleles
for each trait.
A mother might pass a gene
for freckles (dominant - F)
to her offspring, and the
father might pass a gene for
no freckles (recessive - f) to
the offspring.
Ff -- gives him freckles
A pea plant has two alleles for
seed color – yellow and green.
The gene for yellow seeds is
dominant. The gene for green
seeds is recessive.
Possible allele combinations
are:
YY – yellow
Yy – yellow
yy – green
In order for the pea plant to
produce green seeds, it must
inherit two recessive alleles.
Yellow
plant
Yy
Green
plant
YY
yy
Yy
Yy
Yy
The combination of alleles
that an individual inherits is
called the
genotype.
These are the alleles
actually present – yy, Tt,
BB, etc.
The expression of the alleles
is the
phenotype.
This is how the trait is
expressed – green, tall,
hairy, etc.
• If both alleles for a
trait are identical the
individual is
Example:
•YY
•yy
• If the two alleles for a
trait are different the
individual is
Example:
•Yy
Punnett Square
• The Punnett Square is
a grid used to
determine the possible
combinations of
alleles that the parents
may pass to an
offspring.
• Predicting Genetic
Combinations
Mother1
Mother2
Father1
Mother1/ Father1
Mother2/Father1
Father2
Mother1/Father2
Mother2/Father2
Application
In certain wasps, a hairy body is dominant
over a bald body.
What would be the resulting offspring of a
cross between a wasp homozygous for hairy
body and a wasp homozygous for bald body?
List the genotype(s) and phenotype(s) of the
possible offspring.
Specify the probabilities of each resulting
genotype and each phenotypes.
B
b
b
Bb
B
Bb
RESULTS
Genotype
Bb
Bb
Bb
Phenotype
Ratio
hairy body 4:0
Probabilities
are determined by interpreting the
# of offspring with the desired trait
out of total # of offspring
¾ or 75% are
yellow
1 YY ; 2 Yy
The following is an example:
Y – yellow seeds
y – green seeds
Mother
Yy – yellow
Father
Yy - yellow
Y
y
Y
YY
Yy
y
Yy
yy
¼ or 25% are
green 1 yy
½ or 50% are
heterozygous 2 Yy
Monohybrid Cross
Practice Problem Set
www.biology.arizona.edu/mendelian_genetics/problem_sets/monohybrid_cross/01t.html
Additional Problems:
1.
2.
In humans, tongue rolling is dominant over non-tongue rolling. If a
heterozygous roller is crossed with a non-roller, what would be the
results?
Find the results of a cross between a heterozygous red tomato plant and
another heterozygous red tomato plant. Red is dominant over yellow.
• Cells containing two alleles for each trait are
described as diploid.
• A cell with one of each kind of chromosome is
called a haploid cell.
• Meiosis occurs in the specialized body cells of each
parent that produce gametes.
• How does meiosis maintain a constant number of
chromosomes in the body cell of organisms that
reproduce sexually?
– Meiosis reduces the number by half and when
fertilization occurs the number is restored.
• The gamete that contains genes contributed only by the
mother is an egg.
– Father = sperm
• Zygote- the cell produced when a male gamete fuses with a
female gamete.
• Explain how crossing over in meiosis results in genetic
variation?
– New combinations of genes leading to an increase in genetic
variation in the offspring.
• How does knowledge of the events of meiosis explain
Mendel’s Law of Segregation?
– During meiosis, the homologous chromosome pairs line up and
split; then in the second division the chromotids split. This results
in only one of the pair of chromosomes(containing the “factor”) in
a gamete.
• Know Fig 10.11
• When an area of chromatid is
exchanged with the matching area on
a chromosome, crossing over occurs.
– The exchange of genetic material between
homologous chromosomes.
– Crossing over results in genetic
recombination.
• The failure of homologous
chromosomes to separate properly
during meiosis is called
nondisjunction.
• Explain how nondisjunction can result
in an individual having an extra
chromosome.
– When this happens one gamete can
receive both homologous chromosomes.
If this gamete is fertilized by a normal
gamete the resulting zygote will have
three copies of one chromosome.