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Intro. To Genetics
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INTRODUCTION TO GENETICS
• “Genetics tell us we have an inherited biological
blueprint that includes blood type, eye color, and
height. Sometimes it’s easy to feel trapped or
restricted by our genes. But the limits of our
achievements stem less from our genes than from
ourselves. When we think of successful people, is it
because of great genes or great efforts? Without a
doubt, it is the latter. What you inherit is the
beginning of what you can be, not the end of it.”
TRAITS
•
Look at yourselves and classmates to
determine who has these traits:
1.
Widows Peak vs. straight hairline
2.
Attached vs. free earlobs
3.
Hitch-hiker’s thumb vs. straight
4.
Gapped vs. ungapped teeth
ARE THESE TRAITS
INHERITED?
• Yes
• From whom are they inherited?
• From our parents
GENETICS
•The scientific study
of heredity
MENDEL
• Important work of a monk named Gregor
Mendel helped us to understand biological
inheritance.
• He experimented with garden pea plants.
• Knew the flower part of the plant contains
male and female parts.
• Self-pollination occurs producing seeds
that produce plants identical to the parent.
• Cross-pollination
produces plants from
different parents
• Pea plants had 8
different traits to study
• Trait is a specific
characteristic such as
color, size, shape,
etc…
• Mendel is sometimes
called the “Father of
Genetics”
GENERATIONS
• Mendel called the original plants P
generation, for parental - they were pure
breeding
• Offspring were exactly like their parents
• Crossed tall pure with short pure to get
F1(first filial) hybrid generation- all were
tall.
• Next the F2 (second filial) generation –
produced when tall F1 hybrids were bred
together –some were tall, some were
short.
• Mendel concluded that
inheritance is passed from
generation to generation
• Also concluded some genes are
dominant, some are recessive.
PROBABILITY
• Likelihood that a particular event will
occur
• When you flip a coin, what is the
probability of it being heads? Tails?
• Probability can be used to predict
outcome of genetic crosses
• Genes segregate (separate)
randomly, like a coin flip
PUNNETT SQUARES
• Diagram that is used to show gene combinations that
might occur from a genetic cross
• Letters used in Punnett square represent alleles
• Important terms
• Ex.-T=tall t=short
• TT = homozygous (dominant)
• Tt = heterozygous
• tt = homozygous (recessive)
IMPORTANT TERMS!!!
• Genotype – the actual DNA genetic
makeup for a particular characteristic
– it’s at the cellular level, you CAN'T
see it!
• We use letters to describe genotype,
ex.-T,t,B,b,W,w,G,g, etc…
• Phenotype – the result of the DNA
makeup – the actual physical
characteristic that you CAN see!!!
• Ex-tall, short, black, white, green,
yellow, round, wrinkled, etc…
PRACTICE
• Draw Punnett squares:
• A Brown dog is dominant over a spotted dog.
• Use B’s for the alleles
• Cross a male homozygous brown dog with a spotted
dog.
• Cross a heterozygous brown dog with a spotted dog.
• Cross two heterozygous brown dogs.
DEFINE THESE TERMS IN YOUR NOTEBOOK
1. Allele
2. Co-dominance
3. Dominant
4. Gene
5. Genotype
6. Heredity
7. Heterozygous
8. Homozygous
9. Incomplete dominance
10. Phenotype
11. Recessive
12. Sex linked genes
13. Trait
PRINCIPLE OF INDEPENDENT
ASSORTMENT
• Genes for different traits can
segregate independently during the
formation of gametes (sex cells).
• Mendel wondered if the gene for
one trait, such as pea color, had
anything to do with another trait
such as pea shape.
NON-MENDELIAN
INHERITANCE PATTERNS
• The simple rules of Mendel’s
inheritance do not always
apply. We will more closely
examine some of these
patterns.
INCOMPLETE DOMINANCE
• Neither allele is dominant over
the other, so the heterozygous
phenotype is a blend of the two.
• Ex.- Red flower X white flower =
pink.
CODOMINANCE
• Both alleles are present in the phenotype
• For example – if the colors black and white in chickens
are codominant, and the two are crossed, the offspring
exhibits both as a speckled phenotype.
MULTIPLE ALLELES
• Sometimes a gene has more than two alleles,
so an individual can have a combination of
two from a pool of several.
POLYGENIC TRAITS
• Some traits are controlled by two or more genes.
• For example, the wide range of skin color in humans
is partly because more than 4 different genes control
this trait.
PRACTICE: TWO FACTOR
PUNNETT SQUARE
(DI-HYBRID CROSS)
Tall is dominant over short, black is dominant over white.
1. Draw a Punnett square showing a cross
between a tall, black dog, and a short,
white dog, using TTBB X ttbb.
2. Draw a Punnett square showing this cross:
TtBb X TtBb.
3. What are the genotypic and phenotypic
ratios of each cross?