GENETICS
Gregor Mendel
• “FATHER OF GENETICS”
• Geneticsscientific study of heredity; how traits are inherited
• Heredity
the passing of traits
from parents to offspring
Mendel’s Pea Plant Experiments
Why Peas?
• Pea plants have many traits
(tall/short, purple flowers/white flowers)
• self-fertilized or cross-fertilized
True-Breeding Plants:
create plants that look like themselves
Hybrid Plants:
offspring of true-breeding plants
Tall x Short = Hybrid
Drill: April 2, 2012
• What is a gene? An allele?
• Define and differentiate between a
true/pure-breed and a cross-breed/hybrid?
• Self-pollination vs cross-pollination: Explain
each and how did Mendel prevent selfpollination.
Dominance
-One trait dominates & “hides” the other
Tall x Short = all tall offspring (hybrids)
*Tall is the dominant trait
* Short is recessive
Genes and Alleles
Mendel discovered that each trait is
controlled by two factors
Genes – factors that determine your
traits
Alleles-different forms of a gene
Mendel’s Experiments
Draw the crosses
Explaining the Cross
When a parent makes sperm or eggs, their
genes separate
(PRINCIPLE OF SEGREGATION)
Gametes contain either a T allele (tall) or a t
allele (short)
Let's review what you know about genetics......
GENOTYPE what genes the organism has (TT, Tt, tt)
PHENOTYPE what the organism looks like (tall or short)
Check for understanding
1. A one-eyed purple people eater is crossed with a
two eyed purple people eater. All of their offspring
have two eyes. Which trait is dominant?
2. If you use the letter E for this
gene. What is the genotype of
the offspring?
Are these offspring the F1 or
F2 generation?
4. If you crossed the offspring
with each other? How many of the new offspring
would you expect to have two eyes?
More checking
5. The passing of traits from parents to
offspring is known as _________________
6. Who was the father of genetics? _________
7. A single gene will code for a
______________, such as flower color.
8. Every gene is made of two ______________
Drill: Thursday 5, 2011
1) How did Mendel find out whether the recessive
alleles were still present in the F1 plants?
2) About one fourth of the F2 plants from Mendel’s F1
crosses showed the trait controlled ______ by the
allele.
3) The dominant allele is represented by
a recessive allele is represented by
and
.
Probability:
the likelihood that a particular event will
occur is called_______.
The probability that a single coin flip will come
up heads.
• a. 100 percent
• b. 75 percent
• c. 50 percent
• d. 25 percent
Probability
TRUE or FALSE
The past outcomes of coin flips greatly affect the
outcomes of future coin flips
Q: Why can the principles of probability be used
to predict the outcomes of genetic crosses?
A: The way in which the alleles segregate is
completely random, like a coin flip
Punnett Square
can be used to predict and compare the genetic
variations that will result from a cross.
Show possible genotypes for the F2 offspring.
Practice #1:
In seals, the gene for the length of the whiskers has two
alleles. The dominant allele (W) codes long whiskers
& the recessive allele (w) codes for short whiskers.
a) What percentage of offspring would be expected to
have short whiskers from the cross of two longwhiskered seals, one that is homozygous dominant
and one that is heterozygous?
b) If one parent seal is pure long-whiskered and the
other is short-whiskered, what percent of offspring
would have short whiskers?
Practice #2:
A green-leafed luboplant (I made this plant
up) is crossed with a luboplant with yellowstriped leaves. The cross produces 185 greenleafed luboplants.
Summarize the genotypes & phenotypes of
the offspring that would be produced by
crossing two of the green-leafed luboplants
obtained from the initial parent plants.
Allele Types
Definitions
• Organisms that have two identical alleles
• particular trait (TT or tt) Homozygous
• Organisms that have two different alleles
• same trait (Tt) Heterozygous
• Physical characteristic of an organism Phenotype
• Genetic makeup of an organism (Tt) Genotype
Independent Assortment
• In a 2-factor cross, Mendel followed 2 genes
passed from one generation to the next
• Phenotype
Genotype (true-bred)
a. round yellow peas
__RRYY_
b. wrinkled green peas __rryy_
Independent Assortment
RRYY
rryy
RrYy
F1 generation = heterozygous dominant with
round yellow peas
Independent Assortment
• Circle the letter of the phenotypes that
Mendel would expect to see if genes
segregated independently.
• a. round and yellow
• b. wrinkled and green
• c. round and green
• d. wrinkled and yellow
Overall concept:
Q: What did Mendel observe in the F2 offspring
that showed him that the alleles for seed
shape segregate independently of those for
seed color?
A: He observed F2 offspring that had
combinations of phenotypes—and therefore
combinations of alleles—not found in either
parent.
2-Factors:Sample Problem
• Dihybrid Cross
Dihybrid Cross Problem #1:
In the breeding season, male Anole lizards court females by
bobbing their heads up and down while displaying a colorful
throat patch. Assume for this question that both males and
females bob their heads and have throat patches. Assume also,
that both traits are controlled by single locus genes on separate
chromosomes. Now, suppose that anoles prefer to mate with
lizards who bob their heads fast (F) and have red throat patches
(R) and that these two alleles are dominant to their
counterparts, slow bobbing and yellow throats. A male lizard
heterozygous for head bobbing and homozygous dominant for
the red throat patch mates with a female that is also
heterozygous for head bobbing but is homozygous recessive for
yellow throat patches
a) How many of the F1 offspring have the preferred
fast bobbing / red throat phenotype (assume 16
young)?
b) What percentage of the offspring will lack mates
because they have both slow head bobbing and
yellow throats?
c) What percentage of the offspring will have
trouble finding mates because because they lack
one of the dominant traits?
a) 12 b) 0% c) 25%