Genetics: The Science of Heredity
Page 110
1Who was Gregor Mendel?
 a 19th century priest
 attended a garden in a European monastery
2What did Mendel study?
Experimented with pea plants
3What did Mendel’s studies lead to?
Genetics---the scientific study of heredity
4In a flower what does the pistil produce?
Female sex cells---egg or ovum
Haploid
5In a flower what does the stamen produce?
Male sex cells---sperm
Haploid
6What is pollination?
When pollen lands on the pistil
7Pollination must occur
before____Fertilization_____________.
Fertilization---joining of an egg/ovum and sperm to
produce a zygote. Two haploid cells produce a
diploid cell
8What is self pollination?
When pollen from a flower lands on the pistil of the
same flower.
9What is cross-pollination?
When pollen of a flower on one plant lands on the
pistil of a flower on a second plant.
10Purebred organism---the offspring of many generations
that have the same trait
11What do scientists call parent plants?
Parental generation or P generation
12What are offspring of the parental generation called?
The first filial or F1
13Explain the origin (where it comes from) of the word filial.
Filial come from filia and filius, the Latin words for
“daughter” and “son”
14What were the offspring of the first filial generation called?
Second filial or F2
15What did Mendel observe about the F2 plants?
Shortness trait had reappeared
16List 4 things Medel concluded from his experiments.
 Individual factors or sets of genetic
information control the inherited traits in peas
 Factors that control each trait exist in pairs
 Female parent contributes on factor, male
parent the other
 One factor can hide or mask the other factor
17What do scientists call the factors that control a trait?
Genes---make up chromosomes
18Different forms of a gene are called?
Alleles
19One allele comes from the ___egg or ovum________________
and one from the ____sperm____________
20Complete this sentence. An organism’s traits are
controlled by the alleles it inherits from its parents.
21Dominant allele---a trait that always shows up in the
organism when the allele is present
22Recessive allele---the hidden allele that does not show
up when a dominant allele is present
23When will a recessive allele show?
 Only when a dominant allele is NOT present
 Recessive alleles must pair in order to appear
24In Mendel’s crosses all purebred tall plants in the P generation
had ____2______ alleles for _____tall________________. The
purebred plants for short had _____2_____ alleles for ____Short___.
25The F1 plants each inherited and allele for ___tall____________
from_____the tall parent____ and allele for __short_______
from the ____short parent_________
26Hybrid--organism that has two different alleles for a trait
27Geneticists use ___Letters_____________ to represent alleles
28How is a dominant allele represented?
Recessive?
Capital Letter
Lower case Letter
29How would you write two dominant alleles for tall stems? TT
30tt would represent a purebred short plant
31Tt would represent a plant carrying one allele for tall
and one for short
32Before Mendel’s discoveries what did people think about
inherited traits?
An organisms traits were blends of their parent’s
characteristics
33What was unfortunate about Mendel’s discoveries?
His discoveries were not recognized during his
lifetime.
34Mendel is known as
The “Father of Genetics”
Probability and Heredity
Page 118
What is probability?
A number that describes how likely it is that
an event will occur.
Each time you toss a coin, what 2 ways can it land?
Heads up or tails up
How do you write this in mathematical terms?
1 in 2
½
or 50%
Does probability predict what will definitely occur?
Predicts what is likely to occur---more trials
The closer to actual results will be to results
predicted by probability
What do we mean by “Independence of Events?
Each event is independent of the other---the
results of the first five events does not affect
the sixth
Page 120
What is a Punnett square?
A chart or tool that shows all the possible
combinations of alleles that can result from a
genetic cross---named after Reginald C. Punnett--developed in the early 1900’s
Draw a Punnett square.
Why do geneticists use Punnett squares?
Helps you understand how the laws for
probability apply to genetics
Looking at directions at the top of pages 120 and 121 set up a
Punnett square for round and wrinkled seeds. Label each part
R is dominant allele for round
r is recessive allele for wrinkle
How can you use a Punnett square?
Use a Punnett square to calculate the
probability that offspring with a certain
combination of alleles will result.
The allele each parent will pass on to its offspring in a genetic
cross is based on ____Probability___________.
Phenotype--Physical appearance or visible traits
Genotype--Genetic makeup or allele combinations
If a smooth pea pod is represented by an “S” and a pinched pea
pod by an “s”, what is the phenotype of an “Ss” pea pod?
Smooth---“S” is dominant
Homozygous--An organism that has two identical alleles
for a trait---homo means same
Heterozygous--An organism that has two different alleles
for a trait===hetero means different
Codominance--When there is neither a dominant or
recessive allele. Both alleles are expresses
in an offspring.
How are codominant alleles written?
Capitol Letter with a
Superscript
FB for black feathers FW for white
If a black chicken and a white chicken are
crossed, color how their offspring’s phenotype will appear.
Will the offspring be heterozygous or
homozygous? Explain.