Download Reproduction and variation

Reproduction and variation
D.S.Q.
• 1. How often do hens (female chickens) lay
eggs?
• 2. Can these eggs hatch into a chick?
• 3. Do hens lay eggs without the presence of a
rooster (male chicken)?
• 4. How are chicken eggs fertilized?
• 5. What happens to the unfertilized eggs?
Activity Time
Discussion
• 1. Is a chicken egg an organism, organ, or cell?
• 2. What function do you think the yolk serves?
• 3. Do chickens reproduce sexually (DNA is
received from both parents) or asexually (only
one parent is involved, and the offspring is
genetically identical to the parent)?
Heredity
• The passing of traits from parents to offspring
• For example: You have blue eyes because your
mom does.
• However, what if you have blue eyes but both
your parents have brown eyes? How does this
happen?
Gregor Mendel
• He performed experiments that helped
answer these questions and how inheritance
happens.
• Mendel is known as the father of genetics
• Genetics is the study of how traits are passed
from parents to offspring
Mendel’s Experiment
• His experiment was tested on a pea plant.
• http://study.com/academy/lesson/gregormendel-genetics-experiments-lawsdiscovery.html
True Breeding PLants
• When a true-breeding plant self pollinates, it
always produces offsprings with traits that
match the parent
• Ex. If a pea plant is wrinkled and selfpollinates, then it will only produce wrinkled
seeds
Mendel’s Results
• Purple x Purple
White x White
All Purple Flowers
(True-breeding)
All white flowers
Mendel’s Result
• Purple x White
All purple flowers
(hybrids)
After doing his experiment, he was wondering why
when he mixed purple and white seeds that all of
them came out purple flowers.
Second Generation (Hybrid) Crosses
• A hybrid plant is when a plant is produced
from two true breeding plants with different
forms of the same trait.
Mendel’s Conclusion
• There are two genetic factors control each
inherited trait
• When organisms reproduce, each
reproductive cell—sperm or egg—contributes
one factor for each trait
Dominant & Recessive Traits
• Purple x White
All purple flowers
(hybrids)
Why didn’t the flowers turn white?
Mendel believed that the purple color is the only
factor seen or expressed because it blocks the white
factor
Dominant and Recessive Traits
• A genetic factor that blocks another genetic
factor is called the dominant trait
• A dominant trait is observed when offspring have
either one or two dominant factors
• A genetic factor that is blocked by the presence
of a dominant factor is called a recessive trait
• A recessive trait is observed ONLY when two
recessive genetic factors are present in the
offspring
What is inheritance?
• Who do you look like? Your mom, dad,
grandma, grandpa?
• What features do you have that are similar to
them?
• A trait is a distinguishing characteristic of an
organism
• During reproduction, traits are passed from
one generation to another
What is inheritance?
• Inheritance is the passing of traits from one
generation to another
Inheritance and DNA
• Organisms pass inherited traits to their
offspring in one of two ways:
• Either asexually or sexually
• Asexual reproduction pass traits to their
offspring by cell division and mitosis and are
identical to their parents
• Sexual reproduction, produce offspring's that
are similar to their parents
DNA & Genes
• Sexual reproduction requires DNA from a
sperm cell and egg cell
• DNA is a molecule inside a cell’s nucleus.
DNA and Genes
• Gene: is a section of DNA that has genetic
information for one trait
• Genes carry the information in the DNA
• IF you were to stretch out the DNA it would be
2 METERS LONG!
• Alleles are the different forms
Of a gene
DNA and genes
• DNA fits in the nucleus because it is tightly
coiled with proteins to form chromosomes
• A chromosome is a structure made of long
chains of DNA
Chromosomes
• The number of chromosomes differ between
every species.
• Humans have 23 paired chromosomes.
• We get 23 from the sperm cell (males) and 23
from egg cells (females)
Genotype and Phenotype
What human trait can you
observe?
Genotype and Phenotype
• Phenotypes are known as how a trait appears,
or is expressed
• Genotype is when the two alleles that control
the phenotype of a trait
• For example, the white plant in our previous
example has two recessive alleles. The two
alleles are its genotype and the WHITE flower
is its phenotype
Symbols for Genotypes
• Uppercase letters represent dominant alleles
• Lowercase letters represent recessive alleles
Homozygous and Heterozygous
• When 2 alleles are the same, its genotype is
HOMOZYGOUS.
• For example, AA or aa
• If two alleles of a gene are different, its
genotype is heterozygous
• For example, Aa
2 ways of modeling inheritance
• Punnett Squares and pedigree can be used to
predict the identify traits among genetically
related individuals
Punnett Squares
• If the genotypes of the parents are known,
then the different genotypes and phenotypes
of the offspring can be predicted
• Punnett Square is a model used to predict
possible outcomes for the offspring
Punnett Squares