Genetics - Stosich Science · PP pp Pp Pp Pp Pp First experimental results Mendel used symbols for...

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Genetics

Think!

Recap from what we already know:

Mitosis

Chromosomes

Diploid numbers

Haploid numbers

Meiosis

Gametes

Genes

Chromosomes contain DNA.

The DNA codes instructions for

proteins. These proteins direct

our cells to do different things.

There is an instruction for every

trait.

We call them Genes.

Gregor Mendel

Czech monk, first to study

how traits are passed on.

First to claim that there was something being physically passed on from parents to offspring.

He called them factors. We

call them genes.

Mendel’s First Experiments

Mendel worked with pea plants.

He crossed purebred (“true breeding”) plants of

opposite traits and noticed that certain traits

blocked others.

Purple flowers > white flowers

Yellow peas > green peas

All of the offspring showed one dominant trait.

Pea Traits

Mendel’s method

Hand Pollination controlled which

plants were to breed.

Parents = P1

Offspring = F1

First experimental results

Parents = P1 (purebred - their parents

also had the same trait they showed)

Offspring = F1 (hybrids - the result of

parents with different traits)

All of the F1 plants show one trait.

Mendel called this trait Dominant.

The other trait was hidden, or Recessive.

P1

PP pp

Pp Pp Pp Pp

First experimental results

Mendel used symbols for each trait.

Capital letter = dominant

Lower case = recessive

Two symbols = from two parents

Purebred = two identical symbols

Hybrid = two different symbols

Second experimental results

F1 plants were left to self-fertilize.

The recessive trait reappeared in the F2 generation.

75% dominant, 25% recessive

Or, a 3:1 Ratio of traits

Second experimental results

Genotypes & Phenotypes

Genotypes = gene combinations written in symbols.

2 identical traits = Homozygous

2 different traits = Heterozygous

Phenotypes = visible traits described by our senses.

Genotype & Phenotype Examples

Yellow Pea, YY or Yy

Green Pea, yy

GenotypesP1 Purple parent: PP Homozygous Dominant

P1 White parent: pp Homozygous Recessive

F1: all Heterozygous, Pp

F2: white offspring pp

*Recessive traits must be homozygous.

F2: Purple offspring could be PP or Pp

*Dominant traits can be either HD or HR

Predicting Genetics

Using the symbols alone,

Mendel was able to predict

how traits would be

passed on.

Law 1 of Genetics:

Genes exist in different

forms, called Alleles.

Some alleles are dominant,

others are recessive.

You inherit one allele from each parent, for every gene.

Law 2 of Genetics:

Inheritance of one allele

doesn’t influence the

inheritance of any other.*

The distribution of dominant and recessive alleles is random.

*except Linked genes

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