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Transcript
Genetics and Heredity
• Genetics is the study of heredity
• Heredity is how different genes are passed
down from parents to children
Genes
• Your GENES,
not your JEANS.
• A gene is a segment of DNA that
codes for a certain trait
Genetics Terminology:
Genome, Chromosomes & Genes
• ________ -Complete
complement of an
organism’s DNA.
• Cellular DNA is
organized in
___________.
• ______ have specific
places on chromosomes.
From the Virtual Cell Biology Classroom on ScienceProfOnline.com
Gregor Mendel (lived in 1800s)
-
Austrian monk who taught natural science
Interested in how traits are passed on
Crossbred snow pea plants to figure it out
Is known as “The father of Genetics”
Genetics- the study of heredity
The work of Gregor Mendel
Earlier Notions of
Inheritance
– Blending
– Spermists
– Ovists
Mendel was first to
show both parents
contribute equally
“Father of Genetics”
• Mendel performed
breeding experiments
with garden peas
• Found mathematical
patterns of inheritance
• His work was not
appreciated until
1900, 16 years after
his death
Mendel’s work
• Why breed peas?
• They were available in many varieties,
inexpensive, short life cycle, simple
procedures, easy to grow.
• The use of plants also allowed strict control
over the mating.
• He chose to study only characters that
varied in an ‘either-or’ rather than a
‘more-or-less’ manner.
Why peas?
-not too many traits to keep track of
-Pea traits-pea color, pea shape, plant height, pod
shape, pod color, flower color, flower position
Mendel crossed purple
flowers with white
flowers. (Purebreds)
- all of the resulting
flowers were purple
Then he let the F1s
self-fertilize.
Result in F2 generation:
- 75% of the flowers
purple
- 25% of the flowers
white
Explain!
F1
Interpreting Mendel’s Data
Parent
Cross
F1
generation
F2
Actual Probability
generation Ratio
Ratio
Round x 100% round 5,474 round 2.96:1
wrinkled
1,850 wrink.
3:1
Yellow x
green pea
100%
yellow
6,022 yell
2,001 green
3.01:1
3:1
Long x
short
stem
100% long
stem
787 long
277 short
2.84:1
3:1
Mendel’s Observations
• “dominant” vs “recessive”
• Before “genes” and “meiosis” were
known, Mendel theorized “inheritance
factors”…
– are in the pollen and ova of peas as alternate
forms for different traits.
– occur in pairs, (equal contribution from both
parents)
– separate during gamete formation and pair up
again at fertilization
Mendel's Laws
1. Law of Dominance
2. Law of Segregation
3. Law of Independent Assortment
Image: Gregor Mendel, Mendel's Principles
of Heredity: A Defense by Bateson, William.
From the Virtual Cell Biology Classroom on ScienceProfOnline.com
1. Mendel’s Law of _________
• In a cross of parents
that are pure for
contrasting traits, only
one form of the trait will
appear in the next
generation.
• Offspring that are
hybrid for a trait will
have only the dominant
trait in the phenotype.
Mendel’s Law of Segregation
• Each hereditary characteristic is
controlled by two factors (alleles) that
separate and pass into reproductive cells
(gametes).
2. Mendel’s Law of ________
•
Alternative versions of genes
(alleles) result in variations in
inherited characteristics.
•
For each character, an
organism inherits 2 alleles
(one from each parent).
•
The alleles for each
character segregate
(separate) during gamete
production (_______).
•
Alleles for a trait are
recombined at fertilization,
becoming genotype for the
traits of the offspring.
Table showing how
the genes exchange
according to
segregation or
independent
assortment during
meiosis and how this
translates into
Mendel's laws.
Mendel’s Law of Independent
Assortment
• Pairs of inheritance factors (alleles)
segregate independently of each other
when sex cells (gametes) are formed.
3. Mendel’s Law of _____ ______
Alleles for
different traits
are distributed
to sex cells (&
Diagram of how the
genes exchange
according to
segregation or
independent
assortment during
meiosis and how this
translates into
Mendel's laws.
offspring)
independently of
one another.
Show me a video!
Remember…Mendel came
up with this stuff
BEFORE we know about
the existence of DNA,
genes, chromosomes!
Image: Independent assortment and
segregation diagram, Mariana Ruiz.
From the Virtual Cell Biology Classroom on ScienceProfOnline.com
Mendel’s Laws:
1. Law of Dominance:
- In a cross of parents that are pure for
contrasting traits, only one form of the
trait will appear in the next generation.
- Offspring that are hybrid for a trait will
have only the dominant trait in the phenotype.
2. Law of Segregations:
- During the formation of gametes (eggs or sperm), the two alleles
(hereditary units) responsible for a trait separate from each other.
- Alleles for a trait are then "recombined" at fertilization, producing
the genotype for the traits of the offspring.
3. Law of Independent Assortment:
- Alleles for different traits are distributed to sex cells (& offspring)
independently of one another.
From the Virtual Cell Biology Classroom on ScienceProfOnline.com
Image: Gregor Mendel, Mendel's Principles of
Heredity: A Defense by Bateson, William
Mendelian Inheritance in Humans
dominant
recessive
•
•
•
•
Tongue Roller (T)
Free Earlobes (F)
Dimples (D)
Widow’s Peak (P)
•
•
•
•
Can’t roll tongue (t)
Attached lobes (f)
No dimples (d)
Straight hairline (w)
Genetics and Probability
 Discuss…
 Coin flipping
 Card picking
 Punnett Square probability vs actuality
Some Vital Vocab.
•
•
•
•
Genetics
Gene vs Chromosome
Alleles
Dominant vs Recessive
Some Vital Vocab.
•
•
•
•
•
Genotype vs Phenotype
Homozygous vs Heterozygous
Diploid vs Haploid
Mitosis vs Meiosis
Zygote
Problem Solving from Mendelian Genetics
• Consider inheritance patterns for
–
–
–
–
–
Cystic Fibrosis
Sickle Cell Anemia
Huntington’s disease
Hemophelia
Colorblindness pedigree
Exceptions to Complete Dominance
• Polygenic Traits
• Intermediate Expression (aka incomplete
dominance)
• Multiple Alleles
• Several described at this link!