Chapter
10
Sexual Reproduction and Genetics
10.2 Mendelian Genetics
How Genetics Began
 Inheritance, or heredity  passing traits to the next generation
 Mendel performed cross-pollination in pea plants.
 Mendel followed various traits in the pea plants he bred.

Chapter
10
Sexual Reproduction and Genetics
10.2 Mendelian Genetics
 The parent generation is also known as the P generation .

Chapter
10
Sexual Reproduction and Genetics
10.2 Mendelian Genetics
 The offspring of this P cross are called the first filial
(F
1
) generation .
 The second filial
(F
2
) generation is the offspring from the F
1 cross.

Chapter
10
Sexual Reproduction and Genetics
10.2 Mendelian Genetics
 Mendel studied seven different traits.
 Seed or pea color
 Flower color
 Seed pod color
 Seed shape or texture
 Seed pod shape
 Stem length
 Flower position

Chapter
10
Sexual Reproduction and Genetics
10.2 Mendelian Genetics
Genes in Pairs
 Allele
 An alternative form of a trait
 Ex. Eye color

Chapter
10
Sexual Reproduction and Genetics
10.2 Mendelian Genetics
Dominance
 Homozygous  2 of the same alleles for a particular trait, also called pure bred.
 Heterozygous  2 different alleles for a particular trait, also called hybrids.
Bb bb
BB

Chapter
10
Sexual Reproduction and Genetics
10.2 Mendelian Genetics
Genotype and Phenotype
 Genotype  allele pairs (GENES)
 TT, Tt, BB, bb, Mm
 Phenotype  The observable characteristic or outward expression of an allele pair
(WHAT YOU SEE)
Bb

Dominant 
• The phenotype of the organism is determined completely by one of the alleles
• Written with at least 1 capital letter (TT or Tt)
Recessive 
• The other allele, has no big effect on the organism's phenotype
• Written with lowercase letters (bb)
Example: Brown eyes is dominant and blue eyes is recessive

Mendel’s Conclusions cont’d…
Ex. Tall plant (T) x short plant (t) = tall offspring (Tt)
What allele was dominant?

Chapter
10
Sexual Reproduction and Genetics
10.2 Mendelian Genetics
Mendel’s Law of Segregation
 Two alleles for each trait separate during meiosis.
 During fertilization, two alleles for that trait unite.

Chapter
10
Sexual Reproduction and Genetics
10.2 Mendelian Genetics
Monohybrid Cross
 A cross that involves hybrids for a single trait is called a monohybrid cross.

Chapter
10
Sexual Reproduction and Genetics
10.2 Mendelian Genetics
Dihybrid Cross
 The simultaneous inheritance of two or more traits in the same plant is a dihybrid cross.
 Dihybrids are heterozygous for both traits.

Chapter
10
Sexual Reproduction and Genetics
10.2 Mendelian Genetics
Law of Independent Assortment
 Random distribution of alleles occurs during gamete formation
 Genes on separate chromosomes sort independently during meiosis.
 Each allele combination is equally likely to occur.
Law of Segregation
 The two alleles for each trait separate during meiosis
(ex: If a parent is Tt, then either T or t can be given to the offspring)

Chapter
10
Sexual Reproduction and Genetics
10.2 Mendelian Genetics
Punnett Squares
 Predict the possible offspring of a cross between two known genotypes

Monohybrid Crosses
Go to
Section:
Do this on your paper: Tt X Tt Cross: Give the genotypes, phenotypes, & percentages

Go to
Section:
Monohybrid Cross Answer…



Chapter
10
Sexual Reproduction and Genetics
10.2 Mendelian Genetics
Punnett Square —
Dihybrid Cross
 Four types of alleles from the male gametes and four types of alleles from the female gametes can be produced.
 The resulting phenotypic ratio is 9:3:3:1.

Chapter
10
Sexual Reproduction and Genetics
10.3 Gene Linkage and Polyploidy
Genetic Recombination
 The new combination of genes produced by crossing over and independent assortment

Chapter
10
Sexual Reproduction and Genetics
10.3 Gene Linkage and Polyploidy
Gene Linkage
 The linkage of genes on a chromosome results in an exception to Mendel’s law of independent assortment because linked genes usually do not segregate independently.

Chapter
11
Complex Inheritance and Human Heredity
11.2 Complex Patterns of Inheritance
Incomplete Dominance
 The heterozygous phenotype is an intermediate phenotype between the two homozygous phenotypes.

Chapter
11
Complex Inheritance and Human Heredity
11.2 Complex Patterns of Inheritance
Codominance
 Both alleles are expressed in the heterozygous condition.

Chapter
11
Complex Inheritance and Human Heredity
11.2 Complex Patterns of Inheritance
Coat Color of Rabbits
 Multiple alleles can demonstrate a hierarchy of dominance.
 In rabbits, four alleles code for coat color:
C , c ch
, c h
, and c .

Chapter
11
Complex Inheritance and Human Heredity
11.2 Complex Patterns of Inheritance
Coat Color of Rabbits
Chinchilla
Light gray
Albino
Dark gray Himalayan

Chapter
11
Complex Inheritance and Human Heredity
11.2 Complex Patterns of Inheritance
Multiple Alleles
 Blood groups in humans
 ABO blood groups have three forms of alleles.

• Human blood is classified according to the presence or absence of certain markers called antigens that are located on the surface of red blood cells.
• If you have the A antigen , you have type A blood and antibodies against B blood .
• If you have the B antigen , you have type B blood and antibodies against A blood .

• If you don’t have either the A or B antigen, you have type O blood .
• In the US, O is the most common blood type.
• You have antibodies against A and B .
• You are also a universal donor. (You can give blood to anyone)
• If you have both the A and B antigens, you have type AB blood and this is the rarest form of blood. No antibodies against either A or B .

• Sex-linked alleles: controlled by genes located on sex chromosomes
• Usually carried on X chromosome
• Since females are XX, they are usually carriers of the trait
• Since males are XY, they have a higher tendency for inheritance of trait

Recipient’s blood type Compatible donor’s blood type
A-
A+
A-, O-
A-, A+, O-, O+
B-
B+
B-, O-
B-, B+, O-, O+
AB-
AB+
O-
O+
A-, B-, AB-, O-
A-, A+, B-, B+,
AB-, AB+, O-, O+
O-
O-, O+

Chapter
10
Sexual Reproduction and Genetics
10.3 Gene Linkage and Polyploidy
 Polyploidy is the occurrence of one or more extra sets of all chromosomes in an organism.
 A triploid organism, for instance, would be designated 3 n , which means that it has three complete sets of chromosomes.

Chapter
11
Complex Inheritance and Human Heredity
11.3 Chromosomes and Human Heredity
Karyotype Studies
 Karyotype —micrograph in which the pairs of homologous chromosomes are arranged in decreasing size.
 Images of chromosomes stained during metaphase
 Chromosomes are arranged in decreasing size to produce a micrograph.

Chapter
10
Sexual Reproduction and Genetics
10.3 Gene Linkage and Polyploidy
 Epistasisis a gene at one location on a chromosome can affect the expression of a gene at a second location
A good example of epistasis is the genetic interactions that produce coat color in horses and other mammals. In horses, brown coat color ( B ) is dominant over tan ( b ).
Gene expression is dependent on a second gene that controls the deposition of pigment in hair.

 Affects the mucusproducing glands, digestive enzymes, and sweat glands

 Caused by altered genes, resulting in the absence of the skin pigment melanin in hair and eyes
 White Hair
 Very pale skin
 Pink Pupils

• Causes inflating of brain nerve cells and mental deterioration.
• Most common in
Jewish descent people

•Decline in nervous system functions & causes mental retardation
•Ability to move deteriorates

• small body size and limbs that are comparatively short

• Sex-linked alleles: controlled by genes located on sex chromosomes
• Usually carried on X chromosome
• Since females are XX, they are usually carriers of the trait
• Since males are XY, they have a higher tendency for inheritance of trait

Changes in hemoglobin cause red blood cells to change to a sickle shape.

• Male
• Extra X-chromosome
• Genotype: XXY
• Sterile
• Often mentally retarded
• Small testes, enlarged breasts, and reduced sperm production

• Only one sex chromosome (an X).
• X__
• Female
• Short
• Fails to develop ovaries so become infertile

Chapter
11
Complex Inheritance and Human Heredity
11.1 Basic Patterns of Human Inheritance
Pedigrees
 A diagram that traces the inheritance of a particular trait through several generations

• Pedigrees: graphic representation of family tree
• Symbols identify sex, if they are carriers, if they have a certain trait, etc.
• Follows one trait
• May be used if testcross cannot be made

Chapter
11
Complex Inheritance and Human Heredity
11.3 Chromosomes and Human Heredity
Karyotype Studies
 Karyotype —micrograph in which the pairs of homologous chromosomes are arranged in decreasing size.
 Images of chromosomes stained during metaphase
 Chromosomes are arranged in decreasing size to produce a micrograph.