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Mendelian Genetics
Mendelian Genetics
How Genetics Began
Inheritance, or heredity passing traits to the next generation
10.2 Mendelian Genetics
Sexual Reproduction and Genetics
Mendel performed cross-pollination in pea plants.
Mendel followed various traits in the pea plants he bred.
Chapter 10
The parent generation is also known as the P generation.
Sexual Reproduction and Genetics
10.2 Mendelian GeneticsChapter 10
Sexual Reproduction and Genetics
The second filial (F2) generation is the offspring from the F1 cross.
10.2 Mendelian GeneticsChapter 10
The offspring of this P cross are called the first filial (F1) generation.
Mendel studied seven different traits.
Sexual Reproduction and Genetics
Seed or pea color Flower colorSeed pod colorSeed shape or textureSeed pod shapeStem lengthFlower position
10.2 Mendelian GeneticsChapter 10
Genes in Pairs
Sexual Reproduction and Genetics
Allele
An alternative form of a trait
10.2 Mendelian GeneticsChapter 10
Ex. Eye color
Dominance
Sexual Reproduction and Genetics
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.
10.2 Mendelian GeneticsChapter 10
Bb
bb
BB
Genotype and Phenotype
Sexual Reproduction and Genetics
Genotype allele pairs (GENES)TT, Tt, BB, bb, Mm
Phenotype The observable characteristic or outward expression of an allele pair (WHAT YOU SEE)
10.2 Mendelian GeneticsChapter 10
Bb
Dominant vs. Recessive
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?
Mendel’s Law of Segregation
Sexual Reproduction and Genetics
Two alleles for each trait separate during meiosis.
During fertilization, two alleles for that trait unite.
10.2 Mendelian GeneticsChapter 10
Monohybrid Cross
Sexual Reproduction and Genetics
A cross that involves hybrids for a single trait is called a monohybrid cross.
10.2 Mendelian GeneticsChapter 10
Sexual Reproduction and 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.
10.2 Mendelian GeneticsChapter 10
Sexual Reproduction and 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)
10.2 Mendelian GeneticsChapter 10
Sexual Reproduction and Genetics
Punnett Squares
Predict the possible offspring of a cross between two known genotypes
10.2 Mendelian GeneticsChapter 10
Do this on your paper: Tt X Tt Cross: Give the genotypes, phenotypes, & percentages
Go to Section:
Monohybrid Crosses
Go to Section:
Monohybrid Cross Answer…
• Probability the chance or percentage of chance of a trait being exhibited
Sexual Reproduction and 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.
10.2 Mendelian GeneticsChapter 10
Genetic Recombination
The new combination of genes produced by crossing over and independent assortment
10.3 Gene Linkage and Polyploidy
Sexual Reproduction and GeneticsChapter 10
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.
Sexual Reproduction and Genetics
10.3 Gene Linkage and PolyploidyChapter 10
11.2 Complex Patterns of Inheritance
Complex Inheritance and Human Heredity
Incomplete Dominance
The heterozygous phenotype is an intermediate phenotype between the two homozygous phenotypes.
Chapter 11
Complex Inheritance and Human Heredity
Codominance
Both alleles are expressed in the heterozygous condition.
11.2 Complex Patterns of InheritanceChapter 11
Complex Inheritance and Human Heredity
Coat Color of Rabbits
Multiple alleles can demonstrate a hierarchy of dominance.
In rabbits, four alleles code for coat color: C, cch, ch, and c.
11.2 Complex Patterns of InheritanceChapter 11
Complex Inheritance and Human Heredity
Coat Color of Rabbits
Light gray
Dark gray Himalayan
Albino
Chinchilla
11.2 Complex Patterns of InheritanceChapter 11
Complex Inheritance and Human Heredity
Multiple Alleles
Blood groups in humans
ABO blood groups have three forms of alleles.
11.2 Complex Patterns of InheritanceChapter 11
Human Blood Typing
• 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.
What about O & AB?• 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.
Describe sex-linked alleles• 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-, O-A+ A-, A+, O-, O+B- B-, O-B+ B-, B+, O-, O+AB- A-, B-, AB-, O-AB+ A-, A+, B-, B+,
AB-, AB+, O-, O+O- O-O+ O-, O+
Sexual Reproduction and Genetics
Polyploidy is the occurrence of one or more extrasets of all chromosomes in an organism.
A triploid organism, for instance, would be designated 3n,
which means that it has three complete sets of chromosomes.
10.3 Gene Linkage and PolyploidyChapter 10
Karyotype—micrograph in which the pairs of homologous chromosomes are arranged in decreasing size.
11.3 Chromosomes and Human Heredity
Complex Inheritance and Human Heredity
Karyotype Studies
Images of chromosomes stained during metaphase
Chromosomes are arranged in decreasing size to produce a micrograph.
Chapter 11
Sexual Reproduction and Genetics
Epistasis- is a gene at one location on a chromosome can affect the expression of a gene at a second location
10.3 Gene Linkage and PolyploidyChapter 10
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.
Genetics Disorders
Recessive
Cystic Fibrosis
Affects the mucus-producing glands, digestive enzymes, and sweat glands
Albinism
Caused by altered genes, resulting in the absence of the skin pigment melanin in hair and eyes White Hair Very pale skin Pink Pupils
Tay-Sachs
• Causes inflating of brain nerve cells and mental deterioration.
• Most common in Jewish descent people
Dominant
Huntington’s Disease• Decline in nervous
system functions & causes mental retardation
• Ability to move deteriorates
Achondroplasia• small body size
and limbs that are comparatively short
Sex-Linked (On X Chromosome)
Describe sex-linked alleles• 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
Hemophilia
Red-Green Color-Blindness
Co-Dominant
Sickle Cell AnemiaChanges in hemoglobin cause red blood cells to change to a sickle shape.
Non-Disjunction
Klinefelter Syndrome• Male • Extra X-chromosome• Genotype: XXY• Sterile • Often mentally
retarded • Small testes,
enlarged breasts, and reduced sperm production
Turner Syndrome• Only one
sex chromosome (an X).
• X__• Female • Short• Fails to develop
ovaries so become infertile
Down Syndrome
Complex Inheritance and Human Heredity
PedigreesA diagram that traces the inheritance of a
particular trait through several generations
11.1 Basic Patterns of Human InheritanceChapter 11
Interpret pedigrees
• 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
Pedigree Symbols
Hemophilia Pedigree
Karyotype—micrograph in which the pairs of homologous chromosomes are arranged in decreasing size.
11.3 Chromosomes and Human Heredity
Complex Inheritance and Human Heredity
Karyotype Studies
Images of chromosomes stained during metaphase
Chromosomes are arranged in decreasing size to produce a micrograph.
Chapter 11
