What are we going to talk about today?

GENETICS!!!

Objectives

Predict possible outcomes of various genetic combinations such as monohybrid crosses, dihybrid crosses and non-Mendelian inheritance (TEKS 6F)

• Describe how Mendel studied inheritance in peas

• Summarize Mendel’s conclusion about inheritance

• Explain the principle of dominance

• Describe what happens during segregation

Mendel and Genetics

What is genetics?

Genetics is the scientific study of heredity.

Heredity is the passing of traits from parents to offspring

Who is Mendel?

• Gregor Mendel was an Austrian monk. His work was important to the understanding of heredity.

• Mendel carried out his work with ordinary garden peas.

• Mendel is often referred to as the “Father of Modern Genetics”

Mendel’s Experiment

Mendel knew that • the male part of each flower produces

pollen, (containing sperm). • the female part of the flower produces

egg cells.

During sexual reproduction, sperm and egg cells join in a process called fertilization. Fertilization produces a new cell.

Pea flowers are self-pollinating. • This means the pea plants Mendel used

were true-breeding.• They pollinate themselves producing

identical offspring to themselves.

Types of Plants

1. True-Breeding - these plants always create plants that look like themselves

2. Hybrids – offspring of true-breeding plants

Tall x Tall = True-breeding

Tall x Short = Hybrid

Mendel’s Experiment

Mendel decided to study seven pea plant traits, each with two contrasting characteristics (i.e. Tall vs short).

A trait is a specific characteristic that varies from one individual to another.

Mendel cross-pollinated a true-breeding plant with one trait to another true-breeding plant with a contrasting trait.

The offspring produced was a monohybrid, which he then studied

mono = one

Mendel’s Experiment

• Each original pair of plants is the P (parental) generation. • The offspring are called the F1, or “first filial,” generation.

Objectives

Predict possible outcomes of various genetic combinations such as monohybrid crosses, dihybrid crosses and non-Mendelian inheritance (TEKS 6F)

• Describe how Mendel studied inheritance in peas

• Summarize Mendel’s conclusion about inheritance

• Explain the principle of dominance

• Describe what happens during segregation

Mendel’s Conclusions

Mendel's first conclusion :biological inheritance is determined by factors that are passed from one generation to the next.

Today, scientists call the factors that determine traits genes.

Each of the traits (genes) Mendel studied was controlled by one gene that occurred in two contrasting forms that produced different characteristics for each trait (i.e. Tall vs short).

The different forms of a gene are called alleles.

For example: The gene for “purple flowers” has two alleles. One allele from the father and one allele from the mother: PP or Pp would be the alleles for a purple flower

Therefore, a gene (or trait) is made up of at least two alleles. One allele from each parent.

Objectives

Predict possible outcomes of various genetic combinations such as monohybrid crosses, dihybrid crosses and non-Mendelian inheritance (TEKS 6F)

• Describe how Mendel studied inheritance in peas

• Summarize Mendel’s conclusion about inheritance

• Explain the principle of dominance

• Describe what happens during segregation

Mendel’s Conclusions

Mendel’s second conclusion:The principle of dominance

The principle of dominance states that some alleles are dominant and others are recessive..

Round is dominant because it is the only trait that showed up in the F1 generation

What other traits are dominant?Which are recessive?

Objectives

Predict possible outcomes of various genetic combinations such as monohybrid crosses, dihybrid crosses and non-Mendelian inheritance (TEKS 6F)

• Describe how Mendel studied inheritance in peas

• Summarize Mendel’s conclusion about inheritance

• Explain the principle of dominance

• Describe what happens during segregation

Segregation

Mendel wanted the answer to another question: Had the recessive alleles disappeared, or were they still present in the F1plants?

• To answer this question, he allowed all seven kinds of F1

hybrid plants to produce an F2 (second filial) generation by self-pollination.

• Basically, he crossed the F1 generation with itself to produce the F2 offspring

Example:

Copyright Pearson Prentice Hall

Mendel's F2 Generation

P GenerationF1 Generation

Tall Tall Tall Tall Tall TallShort Short

F2 Generation

Segregation

Segregation

The reappearance of the trait controlled by the recessive allele indicated that at some point the recessive allele (shortness) had been separated, or segregated, from the dominant allele (tallness).

Mendel suggested that the dominant and recessive alleles (tallness and shortness) in the F1 plants segregated from each other during the formation of the sex cells, or gametes.

Segregation

When a parent makes sperm or eggs, their genes separate        (PRINCIPLE OF SEGREGATION)

In the F1 generation, the gametes (egg or sperm) contain either a T allele (tall) or a t allele (short)

SegregationAlleles separate during gamete formation.

One last thing…

GENOTYPE  -  what genes (alleles) the organism has (TT, Tt, tt)

PHENOTYPE   - what it looks like (tall or short)