Download File

Intro. To Genetics
Chapter 11
You Only Write What
You Feel Necessary
This will be on my website
tonight.
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
•
1.
2.
3.
4.
Look at yourselves and classmates to
determine who has these traits:
Widows Peak vs. straight hairline
Attached vs. free earlobs
Hitch-hiker’s thumb vs. straight
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 generation called F2 (second filial)
generation – produced when tall 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
•
•
•
•
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…
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.
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?