Chapter 9 Section 1 Mendel’s Legacy Objectives • Describe how Mendel was able to control how his pea plants were pollinated. • Describe the steps.
Download ReportTranscript Chapter 9 Section 1 Mendel’s Legacy Objectives • Describe how Mendel was able to control how his pea plants were pollinated. • Describe the steps.
Section 1 Mendel’s Legacy
Chapter
9
Objectives
•
Describe
how Mendel was able to control how his pea plants were pollinated.
•
Describe
the steps in Mendel’s experiments on true-breeding garden peas.
•
Distinguish
between dominant and recessive traits.
•
State
work.
two laws of heredity that were developed from Mendel’s •
Describe
how Mendel’s results can be explained by scientific knowledge of genes and chromosomes.
Section 1 Mendel’s Legacy
Chapter
9
Gregor Mendel
• The study of how characteristics are transmitted from parents to offspring is called
genetics
.
• Mendel is considered to be the
“father”
of genetics because of all of his work with
heredity
• Heredity is the passing of traits from parents to their offspring
Section 1 Mendel’s Legacy
Chapter
9
Gregor Mendel, continued
•
Mendel’s Garden Peas
– Mendel observed characteristics of pea plants. –
Traits
are genetically determined variants of a characteristic.
– Each characteristic occurred in two contrasting traits.
Section 1 Mendel’s Legacy Chapter 9
Gregor Mendel, continued
•
Mendel’s Methods
–
Self-pollination
occurs when pollen is transferred from the anthers (male) of a plant to the stigma (female) of the same plant –
Cross-pollination
occurs when pollen is transferred between flowers of two different plants • Mendel controlled his experiments by manually pollinating the other plants through cross-pollination, he removed anthers from the plants he was working with
Chapter
9 Section 1
P
Mendel’s Experiments
F1 F2 • Mendel bred plants for several generations that were true-breeding (self-pollinating) for specific traits and called these the
P generation. (parental)
– True breeding pea plants always produce offspring each of which can have only one form of a trait – Ex. True-breed pea plants with yellow pods will self pollinate and produce offspring with yellow pods • Offspring of the P generation were called the
F 1 generation.
• Offspring of the F 1
generation.
generation were called the
F 2
Section 1 Mendel’s Legacy
Chapter
9 Three Steps of Mendel’s Experiments
Pg 175 Figure 9-3 http://science.discovery.com/vide os/100-greatest-discoveries shorts-genetics.html
Section 1 Mendel’s Legacy
Chapter
9
Mendel’s Results and Conclusions
•
Recessive and Dominant Traits
– Mendel concluded that inherited characteristics are controlled by factors that occur in pairs. – In his experiments on pea plants, one factor in a pair masked the other. The trait that masked the other was called the
dominant
trait. The trait that was masked was called the
recessive
trait.
Section 1 Mendel’s Legacy
Chapter
9
Mendel’s Results and Conclusions, continued
•
The Law of Segregation
– The
law of segregation
states that a pair of factors is segregated, or separated, during the formation of gametes. • Law of segregation is used to describe how traits can disappear and reappear in a certain pattern from generation to generation
Section 1 Mendel’s Legacy Chapter 9
Mendel’s Results and Conclusions, continued
•
The Law of Independent Assortment
– The
law of independent assortment
states that factors for individual characteristics are distributed to gametes independently of one another. – The law of independent assortment is observed only for genes that are located on separate chromosomes or are far apart on the same chromosome.
Section 1 Mendel’s Legacy
Chapter
9
Support for Mendel’s Conclusions
• We now know that the factors that Mendel studied are
alleles
, or alternative forms of a gene.
• One allele for each trait is passed from each parent to the offspring.
– We can see this by looking at ourselves in comparison to our parents, we may have some of both our mother and father – We will study this further with Punnett Squares in 9-2
Homework
SECTION 9.1 REVIEW PG 178 #1-8
Section 2 Genetic Crosses
Chapter
9
•
Objectives
Differentiate
between the genotype and the phenotype of an organism.
•
Explain
how probability is used to predict the results of genetic crosses.
•
Use
a Punnett square to predict the results of monohybrid and dihybrid genetic crosses.
•
Explain
how a testcross is used to show the genotype of an individual whose phenotype expresses the dominant trait.
•
Differentiate
a monohybrid cross from a dihybrid cross.
Section 2 Genetic Crosses
Chapter
9
Genotype and Phenotype
• The
genotype
is the genetic makeup of an organism.
• EX: RR, rr, Rr, • • The
phenotype
is the appearance of an organism.
EX: The chicken is red (the allele for red feather color is dominant) • •
Homozygous
– when both alleles of a pair are alike “ R R ” or “ r r “ • •
Heterozygous
– when two alleles in a pair are different “ R r ”
Section 2 Genetic Crosses
Chapter
9
Probability
•
Probability
is the likelihood that a specific event will occur. Probability = number of times an event is expected to happen number of times an event could happen • A probability may be expressed as a decimal, a percentage, or a fraction.
Probability of drawing a red marble Probability = 2 red marbles = 2 = 1 8 marbles total 8 4
Section 2 Genetic Crosses
Chapter
9
Predicting Results of Monohybrid Crosses
• • A
Punnett square
can be used to predict the outcome of genetic crosses.
• • A cross in which one characteristic is tracked is a
monohybrid cross.
Genotypic ratio
is the ratio of genotypes that appear in offspring
Phenotypic ratio
is the ratio of offspring’s phenotypes
Section 2 Genetic Crosses
Chapter
9 Monohybrid Cross of Heterozygous Plants
Chapter
9 Section 2 Genetic Crosses
Y = Yellow y = Green (non-yellow) What is the genotypic ratio for this monohybrid cross?
What is the phenotypic ratio for this monohybrid cross?
Chapter
9
Y = Yellow y = Green (non-yellow)
Section 2 Genetic Crosses
What is the genotypic ratio for this monohybrid cross?
1:2:1
What is the phenotypic ratio for this monohybrid cross?
3 yellow : 1 green 3:1
Section 2 Genetic Crosses
Chapter
9
Predicting Results of Monohybrid Crosses, continued • A
testcross
, in which an individual of unknown genotype is crossed with a homozygous recessive individual, can be used to determine the genotype of an individual whose phenotype expresses the dominant trait.
• R ? x rr
Section 2 Genetic Crosses
Chapter
9
Predicting Results of Monohybrid Crosses, continued •
Complete dominance
occurs when heterozygous individuals and dominant homozygous individuals are indistinguishable in phenotype.
• Ex. Both pea plants PP and Pp for flower color have purple flowers PP or Pp
Section 2 Genetic Crosses Chapter 9
Predicting Results of Monohybrid Crosses, continued •
Incomplete dominance
occurs when two or more alleles influence the phenotype and results in a phenotype intermediate between the dominant trait and the recessive trait.
• In four o’clock flowers, red flowers (R) self pollinate and only produce red offspring, while white flowers (R’) self-pollinate and only produce white offspring • IF, red (R) and white (R’) are crossed they will produce 100% pink (RR’) offspring RR R’R’ RR’
Section 2 Genetic Crosses Chapter 9
Predicting Results of Monohybrid Crosses, continued •
Codominance
occurs when both alleles for a gene are expressed in a heterozygous offspring. • Four human ABO blood types, A, B, and AB and O, are determined by three alleles. The letters A and B refer to two molecules on the surface of the red blood cell. The genotype of a person with blood type AB is I A I B , and neither allele is dominant over the other type. Type AB blood cells carry both A and B-types of molecules on their surface.
Section 2 Genetic Crosses
Chapter
9
Predicting Results of Dihybrid Crosses
• A cross in which two characteristics are tracked is a
dihybrid cross.
– To create this type of cross we will use the FOIL method to be used in a 4x4 Punnett Square
Section 2 Genetic Crosses
Chapter
9 Dihybrid Crosses