Transcript Chapter 9 Patterns of Inheritance

Gregor Mendel 1822-1884
9.1-9.9.10
 Genetics- the scientific study of
heredity
 Mendel was an Austrian monk who
wanted to understand genetics.
 Mendel studied pea plants to improve his
understanding of how traits are passed
from parents to offspring.
Mendel Video
 Self-Pollinating-Sperm cells in pollen fertilize
the egg cells in the same flower
 Pea flowers are self-pollinating
 The seeds that are produced by self-pollination
inherit all of their characteristics from the single
plant that bore them.
The Experiment:
 True-Breeding- occurs when plants produce
offspring identical to themselves after selfpollination
 Mendel’s pea plants were true-breeding as a
result of self-pollination.
 Cross-Pollination- when pollen from one
flower is delivered to a flower from a different
plant.
 Mendel used cross-pollination to produce seeds
that had two different parents.
He cut away the pollen-bearing male
parts of the plant and dusted the plant’s
flower with pollen from another plant.
 The original parents are represented by P
(parental)
 The offspring of the original parents are called
the F1 generation (1st filial)
 The offspring of the F1 generation are called F2
generation (2nd filial)
 Hybrid- The offspring of crosses between parents
with different traits
 Ex: the offspring of a cross b/w a red rose & white rose.
 The term “crossing” means mating
 Punnett Square- A tool used to determine
the gene combinations that might result
from a genetic cross
 A capital letter is used to represent the
dominant allele
 A lower case letter is used to represent the
recessive allele
 Allele- alternative forms of genes
 Ex: Gene for flower color; the alleles are red,
purple, and yellow color.
Mendel’s Hypotheses
 If there are two or more alleles for a gene,
some of the alleles may be dominant and
others may be recessive
 A sperm cell has only one allele for each trait
 An egg cell has only one allele for each trait
 Dominant allele- always expressed
 Recessive allele- only expressed in the
absence of the dominant allele
 Homozygous- Organisms that have two
identical alleles for a particular trait
 organisms are true-breeding for a particular
trait.
 Two alleles for black fur
 Heterozygous- Organisms that have two
different alleles for the same trait
 organisms are hybrid for a particular trait.
 One allele for black fur and one allele for
white fur
 Genotype- genetic make up of the
organism
 Ex: genes for black fur and white fur
 Ex: Tall (T) allele and short (t) allele
 Phenotype- the physical characteristics or
what the organisms looks like.
 Ex: the mouse has black fur.
 Ex: all plants appear tall
 After Mendel’s experiments he formulated the
principle of segregation
 Principle of Segregation- Pairs of genes separate
(segregate) when gametes are formed.
 Alleles for a gene are at the same locus (location) on
homologous chromosomes
 Independent Assortment- Genes that segregate
(separately) independently do not influence each
other's inheritance.
 The principle of independent assortment states that
genes for different traits can segregate independently
during the formation of gametes
 Mendel did a dihybrid (two trait) cross to
see if the separation of one pair of alleles
affects the separation of another pair of
alleles.
 Instead of crossing a yellow seed with a
green seed; he observed seed color and
seed shape together
 Seeds that are round (R) and yellow (Y) are
dominant to seeds that are wrinkled (r) &
green (y)
 True-breeding round & yellow (RRYY)seeds were
crossed with true breeding wrinkled and green seeds
(rryy)
 The result: All individuals in the F1 generation were
round & yellow
Dihybrid Cross: F2
 Heterozygous F1 plants (RrYy) were
crossed with each other to determine if
the alleles would segregate from each
other in the F2 generation.
RrYy × RrYy
 The Punnett square predicts a 9 : 3 : 3 :1 ratio
in the F2 generation
 9 round & yellow: 3 round & green: 3
wrinkled & yellow: 1 wrinkled & green
 The results of the experiment:
 some seeds were round and yellow
 some seeds were wrinkled and green
 some seeds were round and green
 some seeds were wrinkled and yellow
 Mendel had discovered the principle of
independent assortment
 Independent Assortment explains the
variation observed in plants, animals, and
other organisms
 Probability can be used to predict the results
of genetic crosses.
 Probability- the likelihood that something
is going to happen.
 In genetics expressed as a ratio or
percentage.
 Ex: the probability that it will snow in
March is 50:50
Probability of Blue vs. Green Beetle
 Probabilities predict the average outcome of
a large number of events.
 Probability cannot predict the exact
outcome of an individual event
 In genetics, the larger the number of
offspring, the closer the resulting numbers
will get to the expected values.
 Geneticis who study humans triats study matings that
have already occurred.
 Pedigree charts- shows relationships w/i a family of
traits controlled by a single gene and not by
environmental influences.
 Ex: ability to taste PTC (a bitter taste)
 Colorblindness
 Albinism (lack of pigment in skin, hair, & eyes)
 People who are heterozygous for a trait are called
carriers
 Ex: DD (normal hearing)
 Dd (carrier/heterozygous)
 dd (deaf)
 There are two types of inherited disorders in
humans; recessive & dominant
 Recessive Disorders
 Most human disorders are recessive
 Cystic Fibrosis is common in the U.S.
 Excessive mucus secretion clogs the lungs
Few black people
have the disease (1/17,000)
 More white people
have the disease (1/1,800)

 Dominant Disorders
 Only copy of allele needs to present for the disordered to
have the disease
 Most genetic disorders can be detected
before the birth
 Test done between weeks 14 and 20 of the
pregnancy can determine genetic disorders
 Amniocentesis- taking a sample of the
amniotic fluid and testing it
 Chorionic villus sampling (CVS)-small
amount of fetal tissue is suctioned from the
placenta; karyotyping is performed & chemical
analysis
 Ultrasound Imaging- an image of the fetus is
used to determine anatomical deformities