Introduction to Genetics Notes - HUSD



Introduction to Genetics Notes

Genetics-

The scientific study of heredity

What are Genes?

The chemical factors that determine traits

What are Alleles?

The different forms of a gene

Ex. Gene= plant height Alleles= tall plants or short plants

19th century-

People wanted to understand how inheritance is passed on from generation to generation

Gregor Mendel-

Austrian monk in charge of the monastery garden

- Worked with pea plants

Self- pollination-

The sperm cells in pollen fertilize the egg cells in the same flower

True-Breeding-

A plant is allowed to self-pollinate.

- This produces offspring identical to themselves.

Cross-pollination-

Produces seeds that had 2 different plants as parents

• Cut away the pollen-bearing male parts and dusted the pollen from another plant onto the flower

7 Traits Mendel Studied

Why these 7 traits?

Each of these 7 traits had 2 contrasting characters (alleles)

Ex. Seed green seed

Color yellow seed

Mendel’s Experiment

Mendel crossed plants with each of the 7 contrasting characters and studied their offspring.

Parental

Generation

First Filial

Generation

- To Mendel’s surprise, all of the offspring had the character of only one of the parents (the other parent seemed to disappear)

1st conclusion-

Biological inheritance is determined by factors that are passed from 1 generation to the next.

2nd conclusion-

Principle of Dominance: States that some alleles are dominant and others are recessive

Dominant-

An organism with a dominant allele for a particular from of a trait will always exhibit that form of the trait.

Recessive-

An organism with a recessive allele will exhibit that form only when the dominant allele for the trait is not present.

What happened to the recessive trait?

It was still there, but was masked by the dominant allele

Next,

Mendel crossed the F1 generation with itself and found that the traits controlled by the recessive alleles had reappeared.

- This reappearance indicated that at some point the recessive allele separated from the dominant allele.

Segregation-

The separation of alleles during gamete formation

The recessive trait did not disappear!!!

When each F1 plant flowers and produces gametes, the 2 alleles segregate from each other. So, each gamete carries only a single copy of each gene. Each F1 plant produces 2 types of gametes: a dominate allele (T) and a recessive allele (t)

• Gene combinations that might result from a genetic cross can be determined by drawing a Punnett square.

• Punnet Squares – can be used to predict and compare the genetic variations that will result from a cross

• Cannot predict the precise outcome of an individual event

Homozygous-

Organisms that have 2 identical alleles for a particular trait; a.k.a. Purebred

Ex. TT or tt

Heterozygous-

Organisms that have 2 different alleles for the same trait; a.k.a. Hybrid

Ex. Tt

Genotype-

Genetic makeup (letter combination)

Ex. TT, Tt or tt

Phenotype-

Physical characteristic (what it looks like)

Ex. Tall or Short

How do you determine the genotype and phenotype of offspring?

Punnett squares are used to predict the outcomes of genetic crosses. The genotype and phenotype are determined by looking at the result of the Punnett square.

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