Download Chapter 11 Introduction to genetics

CHAPTER 10: MENDEL AND
MEIOSIS
Mrs. Geist, Swansboro HS, Biology, Spring 20102011
Standard

SCOS 3.03: Interpret and predict patterns of
inheritance.
 Dominant,
recessive and intermediate traits.
 Multiple alleles.
 Polygenic traits.
 Sex-linked traits.
 Independent assortment.
 Test cross.
 Pedigrees.
 Punnett squares.
Objectives



Introduce basic principles of probability.
Summarize the three major steps of Gregor
Mendel’s garden pea experiments.
Describe the principle of dominance.
Warm-up 02/21/2010

Genetics Facts and Fallacies Quiz
 Answer
the questions to the best of your ability.
 This is not a true quiz. Your answers will not be graded.
Think-Pair-Share



If I flip a coin, what is the chance that it will land on
heads? (Include fractions and percentages).
What is the chance that it will land on tails? (Include
fractions and percentages).
Distinguish between recessive and dominant alleles.
Provide an example of each.
Introduction to Genetics


Genetics- the scientific
study of heredity.
Fertilization- process in
sexual reproduction in
which male and female
reproductive cells join to
form a new cell.
Pollen- contains the male
reproductive cells, or sperm.
 Carpel- the female part that
produces eggs.

Cross-pollination produces
seeds that had two different
plants as parents.
Blending Hypothesis



1800’s- Red-flowered plants and yellow-flowered
plants blend to produce orange-flowered plants
 Similar to blending red and yellow paint to make
orange paint
Based on this hypothesis, all offspring of orangeflowered plants would also have orange-flowered
plants.
Eventually rejected because it could not explain
how traits that disappear in one generation could
reappear in later generations
10-1 Gregor Mendel

“Father of genetics”
 Austrian
monk.
 His work was important
to the understanding
of heredity.
 Mendel carried out his
studies on ordinary
garden peas.
Garden Peas

Pea flowers are self-pollinating.
 Sperm
cells in pollen fertilize the egg cells in the same
flower.

True-breeding
 if
allowed to self-pollinate, would produce offspring
identical to themselves.
Genes and Dominance


Trait- a specific
characteristic that varies
from 1 individual to
another
 Mendel studied 7 pea
plant traits, each with
two contrasting
characters.
Cross Pollinationjoining male and female
reproductive cells from
two different plants
Genes and Dominance



Each original pair of plants is the P1 (parental)
generation.
The offspring are called the F1, or “first filial,”
generation.
Hybrids- The offspring of crosses between parents
with different traits.
 The F1 hybrid plants all had the character of only
one of the parents
•When Mendel crossed plants with contrasting characters for the
same trait, the resulting offspring only had one of the characters.
•Mendel concluded that some alleles are dominant and others
are recessive.
Mendel’s Seven F1 Crosses on Pea Plants
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Genes

Mendel's first conclusion was that biological
inheritance is determined by factors that are
passed from one generation to the next.
 Genes-

factors that determine traits
Each of the traits Mendel studied was controlled by
one gene that occurred in two contrasting forms that
produced different characters for each trait.
 Alleles-
the different forms of a gene
Principle of Dominance

Mendel’s second conclusion is called the principle of
dominance.
 The
principle of dominance states that some alleles are
dominant and others are recessive.


An organism with a dominant allele for a trait will
always exhibit that form of the trait.
An organism with the recessive allele for a trait will
exhibit that form only when the dominant allele for
that trait is not present.
Gametes are also known as





genes.
sex cells.
alleles.
hybrids.
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 The
offspring of crosses between parents with different
traits are called
 alleles.
 hybrids.
 gametes.
 dominant.
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 In
Mendel’s pea experiments, the male gametes are the
 eggs.
 seeds.
 pollen.
 sperm.
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 In
a cross of a true-breeding tall pea plant with a truebreeding short pea plant, the F1 generation consists of
 all
short plants.
 all tall plants.
 half tall plants and half short plants.
 all plants of intermediate height.
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 If
a particular form of a trait is always present when
the allele controlling it is present, then the allele must
be
 mixed.
 recessive.
 hybrid.
 dominant.
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Segregation


When Mendel crossed pea plants differing in one
trait, one form of the trait disappeared until the
second generation of offspring.
Law of segregation- every individual has 2 alleles
of each gene and when gametes are produced,
each gamete receives 1 of these alleles
Alleles separate during gamete formation.
Basic Probability

Probability- the likelihood that a particular event
will occur.
 Coin
flip: The probability that a single coin flip will
come up heads is 1 chance in 2.
 This
is ½, or 50%.
 If
you flip a coin 3 times in a row, what is the
probability that it will land heads up every time?
½

x ½ x ½ = 1/8
The principles of probability can be used to predict
the outcomes of genetic crosses.
Punnett Squares



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
Punnett Squares can be used to
determine the gene combinations
that might result from a genetic
cross.
A capital letter, T, represents the
dominant allele for tall.
A lowercase letter, t, represents
the recessive allele for short.
Gametes produced by each F1
parent are shown along the top
and left side.
Possible gene combinations for
the F2 offspring appear in the
four boxes.
Homozygous vs. Heterozygous

Organisms that have two identical alleles for a
particular trait are said to be homozygous.
 A.k.a.

“true-breeding”
Organisms that have two different alleles for the
same trait are heterozygous.
 A.k.a.
“hybrid”
Phenotype & Genotype



All of the tall plants have
the same phenotype, or
physical characteristics.
The tall plants do not have
the same genotype, or
genetic makeup.
One third of the tall plants
are TT, while two thirds of
the tall plants are Tt.
Probability



One fourth (1/4) of the
F2 plants have two
alleles for tallness (TT).
2/4 or 1/2 have one
allele for tall (T), and
one for short (t).
One fourth (1/4) of the
F2
have two alleles for
short (tt).
Probabilities Predict Averages


Because the allele for tallness (T) is dominant over
the allele for shortness (t), 3/4 of the F2 plants
should be tall.
The ratio of tall plants (TT or Tt) to short (tt) plants
is 3:1.
Probability can be used to predict





average outcome of many events.
precise outcome of any event.
how many offspring a cross will produce.
which organisms will mate with each other.
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 Compared
to 4 flips of a coin, 400 flips of the coin is
 more
likely to produce about 50% heads and 50% tails.
 less likely to produce about 50% heads and 50% tails.
 guaranteed to produce exactly 50% heads and 50% tails.
 equally likely to produce about 50% heads and 50% tails.
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 Organisms
that have two different alleles for a
particular trait are said to be
 hybrid.
 heterozygous.
 homozygous.
 recessive.
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 Two
F1 plants that are homozygous for shortness are
crossed. What percentage of the offspring will be tall?
 100%
 50%
 0%
 25%
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The Punnett square allows you to predict

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only the phenotypes of the offspring from a cross.
only the genotypes of the offspring from a cross.
both the genotypes and the phenotypes from a cross.
neither the genotypes nor the phenotypes from a cross.
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