BIO110- Genetics

BIO110- Genetics

Chapter 5 Part II

Mendelian Genetics

Chapter 5- Part 2

Heredity

• Heredity is the transmission of traits from one generation to the next.

• Genetics is the study of heredity.

• Gregor Mendel was the first to deduce the basic principles of inheritance

Traits , Characters, Genes, and Alleles!

• Characters are inherited features that vary among individuals. (ex. eye color)

• Each possible variation of a character is a trait

• Traits derive from genes

• Alternate forms of a particular gene are called alleles

Multiple Choice

Each possible variation of a character is a

• Allele

• Gene

• Trait

• Character

Multiple Choice

Traits derive from

• Alleles

• Genes

• Traits

• Characters

Multiple Choice

Alternate forms of a particular gene are called

• Alleles

• Traits

• Genes

• Characters

Genotype vs Phenotype

• An organism’s phenotype is its observable traits.

• An organism’s genotype is its underlying genetic makeup, the alleles it is carrying.

Dominant vs Recessive Alleles

• In pea plants, purple (P) is the dominant trait for flower color. White (p) is the recessive trait.

• The dominant allele will usually overtake the recessive allele in a heterozygous individual (Pp= Purple plant)

• PP= Homozygous dominant; pp= homozygous recessive; Pp=Heterozygous

Multiple Choice

Hair color is a

• Character

• Genotype

• Phenotype

Multiple Choice

Red hair is a

• Character

• Genotype

• Phenotype

Multiple Choice

FF is a

• Character

• Genotype

• Phenotype

Punnett Squares

• A Punnett square can be used to predict the results of a genetic cross

• •In a genetic cross, two parents (P generation) are crossed to produce offspring (F1 generation).

The Law of Segregation of Alleles

• Alleles separate during meiosis

• The law of segregation states that the two alleles for a character separate during gamete formation.

Multiple Choice

The law of segregation states that the two _______ for a character separate during gamete formation

• Genes

• Traits

• Alleles

• DNA

Test Cross Punnett Squares

• We can use a testcross to determine an individual’s genotype

Multiple Choice

According to this testcross, what is the genotype of the mother?

• BB

• Bb

• bb

The Law of Independent Assortment

• The law of independent assortment states that the inheritance of one character has no effect on the inheritance of another.

• Traits for coat color and hearing are an example of independent assortment

Multiple Choice

According to the law of independent assortment, traits (_______) inherited together

• are

• are not

Dihybrid Crosses

• Independent assortment can be observed during a dihybrid cross

• A dihybrid cross one parents that are each heterozygous for two characters

• The gamete possibilities for the father are BD, Bd, bD, and bd. The mothers gamete possibilities are also BD, Bd, bD, and bd.

Make sure you know how this is filled out and how the gamete possibilities are found.

Genetic Conditions

• Many conditions are on the recessive allele.

• This means that a heterozygous individual can be a carrier for a genetic disorder and bear no side effects.

• Carriers can, however, pass on the genetic disorder to their offspring in some cases.

Pedigrees

• Pedigrees are genetic maps that can be used to track genetic traits in a family

• Circles represent females, squares represent males. Filled in shapes means the individual is affected with the disorder being tracked.

• The horizontal groups represent generations- connected lines mean relationships resulting in children. Practice counting how many children couples had.

Multiple Choice

How many children did the first generation of parents have?

• 1

• 2

• 3

• 0

Non-Mendelian Genetics

Chapter 5- Part 2

Incomplete Dominance

• Neither allele is COMPLETELY dominant (like Mendelian genetics suggested). Instead, they combine a new phenotype in heterozygotes.

• Individuals that are heterozygous will have a phenotype intermediate in appearance.

Multiple Alleles

• Classic Mendelian genetics only uses two allele copies (such as R and r).

• Most genes actually have multiple alleles.

• Blood types in humans are the result of multiple alleles

• Human blood types are determined by a gene with three alleles: i, I^A, and I^B

• These three alleles can be combined in six ways

Blood Types

• In addition to Blood Types following the multiple allele pattern, Alleles for blood type are also codominant, which means both are expressed

• Example, individuals with genotype I^AI^B blood exhibit both alleles in their phenotype (AB Blood)

Pleiotropy

• In some cases, one gene influences many characters, a situation called pleiotropy

• Example: The sickle-cell mutation can cause many physical changes

Polygenic Inheritance

• Many phenotypic characters are the result of many genes

• Polygenic inheritance is the effect of many genes on a single character

• In humans, height and skin color are each affected by several genes

Multiple Select

Which of the following inheritance patterns are shown in blood types? Hint: there were 2

• Multiple alleles

• Codominance

• Incomplete dominance

• Polygenic inheritance

Linked Genes

• Some genes do not follow Mendel's Law of Independent Assortment

• Linked genes are located close together on the same chromosome and tend to be inherited together

• Linked Genes are also not even affected by crossing over if they are close enough together on the chromosome.

Multiple Choice

Which Mendelian Law is not followed by linked genes?

• Law of Segregation of Alleles

• Dominance vs Recessiveness

• Law of Independent Assortment

Sex Chromosomes and Sex-linked Genes

• A human female has two X sex chromosomes; males have one X and one Y

• The Y chromosome is very small and carries virtually no genes other than the ones that confer maleness.

• However, several other human characters are controlled by single genes located on the X chromosome. Such genes are called sex-linked genes.

Sex linked genes can be predicted with Punnett Squares as well. They are done like this

Multiple Choice

How many pairs of autosomes do humans have? How many pairs of sex chromosomes?

• 1; 22

• 22; 1

• 44; 2

• 2; 44

Summary/ What to Study

Mendelian Genetics- Topics: Dominant vs Recessive, Character/Trait/Allele, Law of Segregation of Alleles, Law of Independent Assortment.

Non Mendelian Genetics- Incomplete Dominance, Codominance, Multiple alleles, Pleiotropy, Polygenic Inheritance, Linked Genes, Sex-linked genes