How Genetics Began

How Genetics Began

The passing of traits to the next generation is called inheritance, or heredity.

Mendel performed cross-pollination in pea plants.

Mendel followed various traits in the pea plants he bred.

Mendelian Genetics

Sexual Reproduction and GeneticsSection 2

How Genetics Began

Mendelian Genetics


How Genetics Began

Mendelian Genetics


Sexual Reproduction and Genetics

Mendelian Genetics

Section 2

The parent generation is also known as the P generation.

The offspring of this P cross are called the first filial (F1) generation.

The second filial (F2) generation is the offspring from the F1 cross.



Mendelian Genetics

Section 2

Genes in Pairs


Allele An alternative form of a single gene passed

from generation to generation Dominant (Purple flower color)

Expressed form of a trait represented by a capital letter and first letter of the trait (P).

Recessive (White flower color) Only appears when both alleles are

recessive. Represented by a lower case letter of the dominant trait (p)

Mendelian Genetics

Section 2

Dominance


An organism with two of the same alleles for a particular trait is homozygous. PP or pp

An organism with two different alleles for a particular trait is heterozygous. Pp

Mendelian Genetics

Section 2

Genotype and Phenotype


An organism’s allele pairs are called its genotype. Example would be Pp

The observable characteristic or outward expression of an allele pair is called the phenotype. Example would be purple flower color

Mendelian Genetics

Section 2

Mendel’s Law of Segregation


The law of segregation, states that the two alleles for a trait segregate (separate) when gametes are formed.

Two alleles for each trait separate during meiosis.

During fertilization, two alleles for that trait unite. Each offspring receives one allele from each

parent resulting in two alleles for each trait.

Mendelian Genetics

Section 2

Mendel’s Law of Segregation


Mendelian Genetics

Section 2

Mendel’s Law of Independent Assortment


Mendel found that the inheritance of one trait, such as plant height, did not influence the inheritance of any other trait, such as flower color.

The law of independent assortment states that the alleles of different genes separate independently of one another during gamete formation.

This occurs during meiosis I when the homologous chromosomes line up along the metaphase plate

Mendelian Genetics

Section 2

Mendel’s Law of Independent Assortment


Mendelian Genetics

Section 2

Mendel’s Laws


Mendelian Genetics

Section 2

Monohybrid Cross


A cross that involves hybrids for a single trait is called a monohybrid cross.

Mendelian Genetics

Section 2


Punnett Squares

Predict the possible offspring of a cross between two known genotypes

Mendelian Genetics

Section 2


Mendelian Genetics

Section 2


Mendelian Genetics

Section 2


Dihybrid Cross

The simultaneous inheritance of two or more traits in the same plant is a dihybrid cross. For example, if you crossed a yellow round

pea (YYRR) with a green wrinkled pea (yyrr) What would be the predicted offspring

genotypes and phenotypes?

Mendelian Genetics

Section 2


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.

Mendelian Genetics

Section 2

Incomplete Dominance

In some organisms, however, an individual displays a trait that is intermediate between the two parents, a condition known as incomplete dominance.

For example, when a snapdragon with red flowers is crossed with a snapdragon with white flowers, a snapdragon with pink flowers is produced.

Complex Patterns of Inheritance


Incomplete Dominance



Codominance

For some traits, two dominant alleles are expressed at the same time.

In this case, both forms of the trait are displayed, a phenomenon called codominance.

Codominance is different from incomplete dominance because both traits are displayed. Instead of pink you would get a red and white

flowerComparing Dominances



Codominance



Polygenic Inheritance

When several genes influence a trait, the trait is said to be a polygenic trait.

The genes for a polygenic trait may be scattered along the same chromosome or located on different chromosomes.

Familiar examples of polygenic traits in humans include eye color, height, weight, and hair and skin color.



Polygenic Inheritance



Multiple Alleles

Genes with three or more alleles are said to have multiple alleles. Example: Blood types A, B, AB, and O

Multiple Alleles



Multiple Alleles



Pedigree

Geneticists often prepare a pedigree, a family history that shows how a trait is inherited over several generations.

Pedigrees are particularly helpful if the trait is a genetic disorder and the family members want to know if they are carriers or if their children might get the disorder

Pedigree



Pedigree



Pedigree

Scientists can determine several pieces of genetic information from a pedigree: Autosomal or Sex-Linked? If a trait is autosomal, it will

appear in both sexes equally. If a trait is sex-linked, it is usually seen only in males. A sex-linked trait is a trait whose allele is located on the X chromosome.

Dominant or Recessive? If the trait is autosomal dominant, every individual with the trait will have a parent with the trait. If the trait is recessive, an individual with the trait can have one, two, or neither parent exhibit the trait.



Sex-linked - Hemophilia

Sex-linked traits occur on the X chromosomes Females have 2 Xs so they must have both

defective alleles to have the genetic disorder Males only have 1 X making sex-linked

disorders much more common in malesSex-linked with Flies

Hemophilia is a sex-linked trait a condition that impairs the blood’s ability to clot.

Hemophilia



Sex-linked



Sex-linked - Hemophilia



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How Genetics Began