Intro to Genetics

Mendel

What is genetics?• the study of how traits

and diseases are inherited from one generation to the next

through genes.

• Every living thing including plants, animals, microbes, etc., has a set of characteristics inherited from its parent(s).

Mendel (Father of Genetics)Studied the inheritance of traits in pea plantsDeveloped the laws of inheritanceMendel's work was not recognized until the turn of the 20th century

Gregor Gregor MendelMendel

(1822-1884)(1822-1884)

• Mendel notices that there were tall plants and short plants.

-Tall parents produced tall offspring

-Short produced short offspring.

• He decided to cross pollinate, meaning the pollen from one flower fertilized the egg of another. This way they would get different traits from each parent.

• A A traittrait is a specific characteristic such as height is a specific characteristic such as height or eye color that makes organisms or eye color that makes organisms vary from one vary from one anotheranother. .

• Mendel called the parents the P (parental) Mendel called the parents the P (parental) generation.generation.

• The offspring were called F1 or first filial. The offspring were called F1 or first filial. FiliusFilius is is the Latin word for son. the Latin word for son.

• The offspring F1 generation are now called The offspring F1 generation are now called hybridshybrids since since they are a cross of parents with they are a cross of parents with different traitsdifferent traits. .

• Mendel crossed the tall plant with the short plant. Mendel crossed the tall plant with the short plant.

What do you think happened?What do you think happened?

• All offspring were tall in the F1 generation. 1. Biological inheritance is determined by factors

passed from one generation (parents) to the next (babies).

Today, these factors are called genes. Different genes of the same trait are called alleles. Ex. Tall and shorts are alleles for height. (T t)

• 2. Mendel discovered the Law of Dominance - some genes can overpower other genes, these genes are called the dominant genes. The "weaker genes" are called recessive genes.

• Any time a dominant gene is present the dominant trait will be expressed.

• Parents (tall and Parents (tall and short)short)

• F1 generation: F1 generation: all tallall tall

• F2 generation: 3 tall, F2 generation: 3 tall, one shortone short

InheritanceInheritance

Mendel stated that physical traits are inherited as “particles”Mendel did not know that the “particles” were actually Chromosomes & DNA

Vocabulary

Trait:- any characteristic that can be passed from parent to offspring

Heredity: - passing of traits from parent to offspring

Genetics: - study of heredity Purebred: one that always

produces offspring with the same form of a trait as the parent. (homozygous)

• Hybrid: has both forms of a trait (heterozygous)

• Gamete: - A sex cell, either and egg or a sperm.

More Vocabulary

Alleles - two forms of a gene (dominant & recessive)

Dominant - stronger of two genes expressed in the hybrid; represented by a capital letter (R)

• Recessive - gene that shows up less often in a cross; represented by a lowercase letter (r)

• Homozygous and purebred = BB• Heterozygous and hybrid= Bb

Eight Pea Plant Traits

• Seed shape --- Round (R) or Wrinkled (r)

• Seed Color ---- Yellow (Y) or  Green (y)• Pod Shape --- Smooth (S) or wrinkled

(s)• Pod Color ---  Green (G) or Yellow (g)• Seed Coat Color ---Gray (G) or White

(g)• Flower position---Axial (A) or Terminal

(a)• Plant Height --- Tall (T) or Short (t)• Flower color --- Purple (P) or white (p)

Generations

P-Generation (Parents)

F1 Generation (1st Generation of Offspring)

F2 Generation (2nd Generation of Offspring)

Probability

• The likelihood that a The likelihood that a particular even will occur particular even will occur is call is call probabilityprobability. .

• For example: toss a coin For example: toss a coin and it will either land on and it will either land on heads or tails. The heads or tails. The probability that the coin probability that the coin will land on heads is will land on heads is ½½. .

• The probability that it will The probability that it will land on tails is also ½. land on tails is also ½.

• If you flip a coin three times, If you flip a coin three times, what is the probability that what is the probability that all three will be heads?all three will be heads?

• ½ x ½ x ½ = ½ x ½ x ½ = 1/81/8

• The principles of probability The principles of probability can be used to predict the can be used to predict the outcomes outcomes of genetic crosses of genetic crosses as well. as well.

• A A Punnett squarePunnett square is used to is used to do this.do this.

Punnett Squares

• The gene combinations that might result from a genetic cross can be determined by drawing a diagram known as the punnett square.

Pare

nt

2

Parent 1

Try these: Tt x TT, Bb x bb, TT x tt , and Bb x Bb

Genotype and Phenotype• Genotype is an organisms genetic

makeup. For example Bb or BB or bb

• Phenotype is the physical characteristics or what they look like. For example if we were talking about eye color, the phenotype would be blue or brown eyes.

• If B =brown eyes and b= blue eyes– Bb=would have brown eyes– BB= brown eyes– bb = blue eyes

Let’s PracticeGenotype or phenotype

• BB• Brown• Blonde• Bb• bb

• Blue• Tt• Tall• Tt• Short

Beyond Dominant and Recessive Alleles

• Some alleles are neither dominant or recessive, and many traits are controlled by multiple alleles or multiple genes.

• Incomplete dominance: one allele is not completely dominant over another. A red flower crossed with a white flower, produce pink flowers. (blending)

• Codominance: Both alleles contribute to the phenotype of the organism. Black chicken crossed to a white chicken produce a black and white chicken

Incomplete Dominance

Polygenic traitsPolygenic traits

• Unfortunately, not all traits are as Unfortunately, not all traits are as easily predicted as plant height. easily predicted as plant height.

• Many traits living organisms have Many traits living organisms have are polygenic traits.are polygenic traits.

• Polygenic traitsPolygenic traits are traits that are are traits that are controlled by two or more genes. controlled by two or more genes. Poly means many. Genic refers to Poly means many. Genic refers to genes. Polygenic means many genes. Polygenic means many genes.genes.

For example

• There are at least three genes involved There are at least three genes involved in the reddish brown pigments in the in the reddish brown pigments in the eyes or fruit flies. eyes or fruit flies.

• Also, skin color in humans is controlled Also, skin color in humans is controlled by at least four different genes. by at least four different genes.

• Mendel’s principals of probability could Mendel’s principals of probability could not be used to predict these traits. not be used to predict these traits.

• However they can be used in some However they can be used in some human and fruit fly traits. human and fruit fly traits.