GeneticsThe study of heredity

http://cc040.k12.sd.us/PPTS/Intro%20to%20Genetics%20(2003).ppt#266,11,Mendel’s second cross

Gregor Mendel

• Born in 1822 in Czechoslovakia.

• Became a monk at a monastery in 1843.

• Taught biology and had interests in statistics.

• Also studied at the University of Vienna.

http://kentsimmons.uwinnipeg.ca/cm1504/mendel.htm

Mendel (continued)

• Upon return to the monastery, he continued to teach and work in the garden.

• Between 1856 – 1863 he grew and tested over 28,000 pea plants.

http://www.dnalc.org/view/16160-Gallery-2-Gregor-Mendel-s-Garden-Plot.html

Mendel’s Peas

• Easy to grow.

• Easily identifiable traits.

• Can work with large numbers of samples.

http://www.anselm.edu/homepage/jpitocch/genbio/geneticsnot.html

Trait Dominant Recessive

Mendel’s Experiments

• He first created “pure” generations.• Trait = a characteristic• Mendel studied 7 traits. • He crossed plants of contrasting traits

– Ex: Green pea plants + Yellow pea plants

• The offspring (new plants) were called the F1 generation.

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What happens when pure yellow peas are crossed with pure green peas

• All of the offspring were yellow.

• Hybrids = the offspring from crossing parents with contrasting traits.

All offspring are yellow hybrids (Yy)

Observations

Pure Yellow Pure Green

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Y Y y y

Y y Y y Y y Y y

F1 Generation

P Generation

What did Mendel Find?

A. Inheritance is determined by factors passed on from one generation to another.

• Mendel knew nothing about chromosomes, genes, or DNA. Why?– These terms hadn’t been defined yet ---

or seen!!

What were Mendel’s “factors?”

B. The “factors” are now called GENES.C. Each gene has different forms called

ALLELES.1. With the gene coding for pea color, yellow is

one form or allele of the gene – and green is another allele of the gene.

2. Some alleles are DOMINANT and others are RECESSIVE.

a. In the case of the peas, which color is Dominant & which is Recessive???

Another way to show the breeding of a pea plant with yellow seeds and a pea

plant with green seeds

y y

Y Yy Yy

Y Yy Yy

Yellow Pea ‘father’

Green Pea ‘mother’ Green seed color is a recessive allele, represented with a ‘y’

Yellow seed color is a dominant allele, represented with a ‘Y’

In all possible combos of alleles, the offspring will be yellow hybrids (Yy)

PUNNETT PUNNETT SQUARESQUARE

Mendel’s 2nd CrossHe allowed the F1 generation to self-pollinate (breed with each other) to produce the F2 generation.

Observations

Hybrid Yellow Hybrid Yellow

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Y y Y y

Y Y Y y y Y y yF2

Generation

F1 Generation

Results: ¾ chance of having yellow offspring, ¼ chance of having green offspringAlso, ¼ chance purebred Yellow, ½ chance

Hybrid Yellow, ¼ chance purebred Green

Another way to show the 2nd crossing

Y Y Y y

y Y y y

F1 Hybrid ‘father’

F1 Hybrid ‘mother’

Y y

Y

y

F2 Generation:Y Y = purebred yellowY y = hybrid yellowy y = purebred green - OR -

75% yellow 25% green

Purebred = HOMOZYGOUS; Hybrid = HETEROZYGOUS