10 1 genetics developed from curiosity about inheritance n.
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10.1 Genetics developed from curiosity about inheritance. I. The Blending Hypothesis of Inheritance. A trait is a variation of a particular characteristic such as for red flowers or yellow flowers

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i the blending hypothesis of inheritance
I. The Blending Hypothesis of Inheritance
  • A trait is a variation of a particular characteristic such as for red flowers or yellow flowers
  • In the early 1800’s many biologists believed in the blendinghypothesis, which stated that offspring would be a blend of their parents traits. A red and yellow flower would produce and orange flower
ii mendel s plant breeding experiments
II. Mendel’s Plant Breeding Experiments
  • Mendel’s work gave rise to the branch of Biology called genetics, the study of heredity
  • Mendel developed the particulate hypothesis which states that parents pass on separate and distinct factors, or genes
mendel s plant breeding experiments
Mendel’s Plant Breeding Experiments
  • To test this hypothesis, Mendel crossed true-breeding plants that had distinct and contrasting traits such as purple and white flowers
  • Mendel cross-fertilized all his pea plants by hand to control which traits he wanted to control
i mendel s principle of segregation
I. Mendel’s Principle of Segregation
  • The offspring of two different true-breeding varieties are called hybrids

B. When Mendel crossed plants that differed in only one-trait it was called a mono-hybrid cross

c from these results mendel developed the following hypothesis
C. From these results Mendel developed the following hypothesis
  • There are alternative forms of a gene called alleles.
  • For each inherited trait, an organism has two alleles for the gene controlling that character, one from each parent. If both alleles are the same the individual is homozygous, and if the alleles are different the individual is heterozygous.
mendel developed the following hypothesis
Mendel developed the following hypothesis

3. When only one of the alleles in a heterozygous individual appears to affect the trait, that allele is called the dominant trait. The allele that does not appear to have an affect on the individual is called the recessive trait

mendel developed the following hypothesis1
Mendel developed the following hypothesis

4. The two alleles for a character separate during the formation of gametes, so each gamete carries only one allele for each character. This is known as Mendel’s Principle of Segregation

ii probability and punnett squares
II. Probability and Punnett Squares
  • The inheritance of alleles follows the laws of probability
  • If you were to flip two pennies the probability of flipping a head or a tail on one does not affect the probability of the other one
  • A diagram that shows all the possible outcomes of a genetic cross is the Punnett Square
punnett square
Punnett Square

Eye color


Brown male X


Blue female

iii genotypes and phenotypes
III. Genotypes and Phenotypes
  • The way an organism looks is not the same as its genetic make-up
  • An observable trait is called a phenotype while the genetic make-up of alleles is called the genotype
iv the testcross
IV. The Testcross
  • A testcross breeds individuals of unknown genotypes, but the dominant phenotype with a homozygous recessive individual
  • Depending on the ratios of the offspring, the genotype of the unknown can be determined
v mendel s principle of independent assortment
V. Mendel’s Principle of Independent Assortment
  • Mendel also did crosses between plants that differed in two traits called a dihybrid cross
  • From this he developed his Law of Independent Assortment which states that during gamete formation the way in which one allele is inherited does not affect the way another is inherited if they are on separate chromosomes
problem monohybrid 1
Problem: Monohybrid 1
  • 1. An allele for brown eyes B is dominant over that for blue eyes b. A blue-eyed man, both of whose parents were brown-eyed, marries a woman. They have one child who is blue-eyed. What are the genotypes of all the individuals mentioned?
problem 1
Problem 1

Man’s parents: Bb

Dad: bb

Mom: Bb

Kids: Bb or bb

problem monohybrid 2
Problem: Monohybrid 2

2. The ability to taste the chemical PTC is determined by a single gene in humans with the ability to taste given by the dominant allele T and inability to taste by the recessive allele t.  Suppose two heterozygous tasters (Tt) have a large family. 

problem monohybrid 21
Problem: Monohybrid 2
  • Predict the proportion of their children who will be tasters and nontasters.  Use a Punnett square to illustrate how you make these predictions.
  • What is the likelihood that their first child will be a taster?  What is the likelihood that their fourth child will be a taster?
  • What is the likelihood that the first three children of this couple will be nontasters?
problem 2
Problem 2
  • 3:1

b. 3/4, 3/4

c. 1/64

dihybrid cross foil
Dihybrid Cross- FOIL





RrYy x RrYy

problem 3 dihybrid
Problem 3: Dihybrid

3. In pepper plants, green (G) fruit color is dominant to red (g) and round (R) fruit shape is dominant to square (r) fruit shape.  These two genes are located on different chromosomes.

3 dihybrid
3. Dihybrid

a.   What gamete types will be produced by a heterozygous green, round plant?

b. If two such heterozygous plants are crossed, what genotypes and phenotypes will be seen in the offspring and in what proportions?

3 types of gametes
#3 Types of gametes


First- GR

Outside- Gr

Inside- gR

Last- gr

pepper plants
Pepper Plants

9 Green, round

3 Green, square

3 Red, round

1 Red, square

i intermediate inheritance
I. Intermediate Inheritance
  • When an organism has two alleles and neither is dominant the phenotype is intermediate between the two alleles
  • This pattern of inheritance is called intermediate inheritance
problem intermediate inheritance
Problem: Intermediate Inheritance

4. A hybrid pink CRCW snapdragon was crossed with a pure white one CWCW. Red flower color is incompletely dominant.

  • Make a diagram and list the genotypic and phenotypic ratios of the F1 generation
problem 4
Problem 4




ii multiple alleles
II. Multiple Alleles
  • Many genes have several alleles for each trait which expands the number of genotypes and phenotypes
  • Codominance is when a heterozygous individual expresses both traits equally.
problem multiple alleles
Problem: Multiple Alleles

5. Paul is blood type O. His father was blood type A and his mother was blood type B. What were the genotypes of his parents and what are the possible blood types and ratios expected for crosses involving these parental genotypes?

problem 5
Problem 5

IAi and IBi



iii polygenic inheritance
III. Polygenic Inheritance
  • When multiple genes affect a character the variation in phenotypes can become even greater.
  • When two or more genes affect a single character, it is called polygenic inheritance
  • Examples of polygenic inheritance would include skin color, and height
problem polygenic
Problem: Polygenic
  • 6. Melanin is coded for when the gene L, M, or N is present. The more of these genes are present, then the darker the skin the individual. Number the following genotypes in order of the darkest to lightest skin color phenotypes.
problem 6
Problem 6

1= Darkest 6=Lightest

iv the importance of environment
IV. The Importance of Environment
  • An individuals phenotype depends on environment as well as on gene
  • In humans, nutrition influences height, exercise affects build, and exposure to sunlight darkens the skin
i chromosome theory of inheritance
I. Chromosome Theory of Inheritance

A. Biologists worked out the processes of mitosis and meiosis in the late 1800s and observed the parallels between the behavior of chromosomes and the behavior of Mendel’s heritable factors

chromosome theory
Chromosome Theory

B. The chromosome theory of inheritance states that genes are located on chromosomes, and the behavior of chromosomes during meiosis and fertilization accounts for inheritance patterns

C. The alleles for a gene reside at the same location or gene locus

ii genetic linkage and crossing over
II. Genetic Linkage and Crossing Over
  • Mendel’s principles only work when for genes that are located on separate chromosomes
  • The tendency for the alleles on one chromosome to be inherited together is called genetic linkage

C. The closer the two genes are on a chromosome, the greater the genetic linkage

i sex linked genes
I. Sex-linked Genes

A. Many species have sex chromosomes, designated X and Y that are associated with determining an individual’s sex XX= Female, while XY= Male

sex linked genes
Sex-linked genes

B. Any gene located on a sex chromosome is called a sex-linked gene

C. Sex-linked genes were discovered by Thomas Hunt Morgan while studying fruit flies

ii sex linked disorders
II. Sex-Linked Disorders

A. A number of human conditions, including red-green color blindness and hemophilia are inherited as sex linked recessive traits

B. It takes two copies of the allele to be present in females for them to show signs of the disorder while it only takes one in males

problem sex linked
Problem: Sex-linked

7. A color blind father and a mother who carries the color blind trait (b) have a boy and a girl. What are the percent chances of the children being color blind? A carrier for color blindness?

color blindness sex linked
Color blindness: Sex-linked

50% color blind


25% carrier

i down syndrome
I. Down Syndrome

A. Trisomy 21 results in having three number 21 chromosomes

B. In most cases, a human embryo with an abnormal number of chromosomes results in a miscarriage

C. People with trisomy 21 have Down syndrome, named after John Langdon Down

ii nonseparation of chromosomes
II. Nonseparation of Chromosomes

A. Nondisjunction is when homologous fail to separate

B. A woman’s age will have an effect on the possibility of nondisjunction occurring

C. This is due to the time line of egg cell development

iii damaged chromosomes
III. Damaged Chromosomes

A. Duplication is when part of a chromosome is repeated

B. Deletion is when a fragment of a chromosome is lost

C. Inversion involves reversing a fragment of the original chromosome

D. Translocation occurs when a fragment of one chromosome attaches to a non-homologous chromosome

iv jumping genes
IV. Jumping Genes

A. Single genes may move from one location to another in a chromosome or to a different chromosome

B. This was discovered by Barbara McClintock in the 1940’s

C. These genes can land in the middle of other genes and disrupt them

D. These genes are called transposons

i working with human pedigrees
I. Working With Human Pedigrees
  • A. Human geneticists cannot control matings, but must analyze the patterns of existing families
  • B. A pedigree is a family tree that records and traces traits
ii disorders inherited as recessive traits
II. Disorders Inherited as Recessive Traits

A. There are over one thousand genetic disorders that are inherited as a dominant or recessive trait controlled by a single gene

B. Most human genetic disorders are recessive

C. A carrier is an individual who has a copy of the recessive disorder but does not show symptoms

pedigree 9
Pedigree #9
  • Is the attached ear lobe trait a dominant or recessive trait? How do you know?

Recesssive, only those ff colored.

  • What two terms could be used to describe the Ff genotype?

Heterozygous, or carrier

problem 9 pedigree
Problem 9: Pedigree

What are the percent chances?

25% FF 50% Ff

25% ff

75% Unattached

25% attached

iii disorders inherited as dominant traits
III. Disorders inherited as Dominant Traits

A. Dominant alleles that are lethal are more common than lethal recessives

B. Usually, the person with the dominant disorder dies before the allele can be passed on

iv sex linked disorders
IV. Sex-Linked Disorders

A. Sex-Linked alleles are usually located on the X Chromosome in humans

B. A male only needs to inherit one copy of the allele to exhibit the trait

C. A female must inherit two copies of the allele to exhibit the trait

deaf pedigree
Deaf Pedigree

Draw a pedigree for the punnett square. Children: 2 older boys are deaf. 2 younger girls are carriers.

v predicting and treating genetic disorders
V. Predicting and Treating Genetic Disorders

A. A genetic counselor is trained to collect and analyze data about inheritance patterns

B. This information is used by couples to determine the risks of passing on genetic disorders to their children

C. Genetic tests are done before and after the baby is born