Genetics and Heredity

• Genetics is the study of heredity

• Heredity is how different genes are passed down from parents to children

Genes • Your GENES,

not your JEANS.

• A gene is a segment of DNA that codes for a certain trait

Genetics Terminology: Genome, Chromosomes & Genes

• ________ -Complete complement of an organism’s DNA.

• Cellular DNA is organized in ___________.

• ______ have specific places on chromosomes.

From the Virtual Cell Biology Classroom on ScienceProfOnline.com

Gregor Mendel (lived in 1800s)

- Austrian monk who taught natural science

- Interested in how traits are passed on

- Crossbred snow pea plants to figure it out

- Is known as “The father of Genetics”

- Genetics- the study of heredity

The work of Gregor Mendel

Earlier Notions of Inheritance– Blending– Spermists– Ovists

Mendel was first to show both parents contribute equally

“Father of Genetics”

• Mendel performed breeding experiments with garden peas

• Found mathematical patterns of inheritance

• His work was not appreciated until 1900, 16 years after his death

Mendel’s work

• Why breed peas?• They were available in many varieties,

inexpensive, short life cycle, simple procedures, easy to grow.

• The use of plants also allowed strict control over the mating.

• He chose to study only characters that varied in an ‘either-or’ rather than a ‘more-or-less’ manner.

Why peas?-not too many traits to keep track of

-Pea traits-pea color, pea shape, plant height, pod shape, pod color, flower color, flower position

Mendel crossed purple flowers with white flowers. (Purebreds)

- all of the resulting flowers were purple

Then he let the F1s self-fertilize.

Result in F2 generation:

-  75% of the flowers purple

- 25% of the flowers white Explain!

F1

Interpreting Mendel’s DataParent Cross

F1 generation

F2 generation

Actual Ratio

Probability Ratio

Round x wrinkled

100% round 5,474 round 1,850 wrink.

2.96:1 3:1

Yellow x green pea

100% yellow

6,022 yell

2,001 green

3.01:1 3:1

Long x short stem

100% long stem

787 long

277 short

2.84:1 3:1

Mendel’s Observations

• “dominant” vs “recessive”

• Before “genes” and “meiosis” were known, Mendel theorized “inheritance factors”…– are in the pollen and ova of peas as alternate

forms for different traits.– occur in pairs, (equal contribution from both

parents)– separate during gamete formation and pair up

again at fertilization

Mendel's Laws

1. Law of Dominance

2. Law of Segregation

3. Law of Independent Assortment

Image: Gregor Mendel, Mendel's Principles of Heredity: A Defense by Bateson, William.

From the Virtual Cell Biology Classroom on ScienceProfOnline.com

• In a cross of parents that are pure for contrasting traits, only one form of the trait will appear in the next generation. 

• Offspring that are hybrid for a trait will have only the dominant trait in the phenotype.

1. Mendel’s Law of _________

Mendel’s Law of Segregation

• Each hereditary characteristic is controlled by two factors (alleles) that separate and pass into reproductive cells (gametes).

2. Mendel’s Law of ________Table showing how the

genes exchange according to

segregation or independent

assortment during meiosis and how this

translates into Mendel's laws.

• Alternative versions of genes (alleles) result in variations in inherited characteristics.

• For each character, an organism inherits 2 alleles (one from each parent).

• The alleles for each character segregate (separate) during gamete production (_______).

• Alleles for a trait are recombined at fertilization, becoming genotype for the traits of the offspring.

Mendel’s Law of Independent Assortment

• Pairs of inheritance factors (alleles) segregate independently of each other when sex cells (gametes) are formed.

3. Mendel’s Law of _____ ______

Image: Independent assortment and segregation diagram, Mariana Ruiz.

Diagram of how the genes exchange

according to segregation or independent

assortment during meiosis and how this

translates into Mendel's laws.

Alleles for different traits are distributed to sex cells (&

offspring) independently of one another.

Show me a video!

Remember…Mendel came up with this stuff BEFORE we know about the existence of DNA, genes, chromosomes!

From the Virtual Cell Biology Classroom on ScienceProfOnline.com

1. Law of Dominance: - In a cross of parents that are pure for contrasting traits, only one form of the trait will appear in the next generation.

  - Offspring that are hybrid for a trait will have only the dominant trait in the phenotype.

2. Law of Segregations: - During the formation of gametes (eggs or sperm), the two alleles (hereditary units) responsible for a trait separate from each other. 

- Alleles for a trait are then "recombined" at fertilization, producing the genotype for the traits of the offspring.

3. Law of Independent Assortment:- Alleles for different traits are distributed to sex cells (& offspring) independently of one another.

Mendel’s Laws:

Image: Gregor Mendel, Mendel's Principles of Heredity: A Defense by Bateson, WilliamFrom the Virtual Cell Biology Classroom on

ScienceProfOnline.com

Mendelian Inheritance in Humansdominant recessive

• Tongue Roller (T)• Free Earlobes (F)• Dimples (D)• Widow’s Peak (P)

• Can’t roll tongue (t)• Attached lobes (f)• No dimples (d)• Straight hairline (w)

Genetics and Probability

Discuss… Coin flipping Card picking Punnett Square probability vs actuality

Some Vital Vocab.

• Genetics

• Gene vs Chromosome

• Alleles

• Dominant vs Recessive

Some Vital Vocab.

• Genotype vs Phenotype

• Homozygous vs Heterozygous

• Diploid vs Haploid

• Mitosis vs Meiosis

• Zygote

Problem Solving from Mendelian Genetics

• Consider inheritance patterns for – Cystic Fibrosis– Sickle Cell Anemia– Huntington’s disease– Hemophelia– Colorblindness pedigree

Exceptions to Complete Dominance

• Polygenic Traits

• Intermediate Expression (aka incomplete dominance)

• Multiple Alleles

• Several described at this link!