Biology Ch. 12: Mendel and Heredity

“What are the chances?”

12.1 Origins of Hereditary ScienceResults of breeding crops and

livestock is some of the first recorded information

Heredity the study of the passing of traits from generation to generation.

Genetics the study of genes and genetic information.

Gregor Mendel: The Father of Modern Genetics

Austrian monk1800’sUniversity of Vienna; math and biologyStatisticsPea plants

“Cross”, pollinate, self-pollinating

Contrasting traits, “characters”….a trait is one of the possible forms…allele (form)

HybridsMonohybrid crossesGeneration

Mendel’s First Experiments

Cross purple flower with purple flower; all offspring have purple flowers

Cross white flower with white flower; all offspring have white

Cross purple flower with white; all purple – the purple allele seems to be the ‘dominant’ trait.

Punnett Square Vocabulary

Trait/character = genetic traits; something like height, color,etc

Allele = forms/versions that genes can be expressed in; color can be green or yellow

Dominant allele = form that is always expressed; both GG and Gg are green peas

Recessive allele = this form recedes (hides) into the background, only expressed if it’s the only choice; only gg is yellow pea (‘not green’ or yellow)

Vocab. continuedMonohybrid cross = only looking at one trait

with contrasting allelesEach parent gives each offspring one gene,

offspring then contain pairs of genes (meiosis)

Punnett square shows statistical chances of inheriting certain traits.

Genotype – what genes are inheritedGenotypic ratio – number of offspring

inheriting that gene combinationPhenotype – what is physically expressed as a

result of the alleles inheritedPhenotypic ratio – number of offspring that

express each characteristic

Mom; Gg; gives either G or g

Dad;

Gg;

giv

es

eit

her

G o

r g

Genotypic ratio

1GG: 2Gg: 1gg

Phenotypic ratio

3 green: 1 not green

(yellow)

Zygote = fertilized egg with pairs of chromosomes

Homozygous = cell has same information from mom and dad (DD or dd)

Heterozygous= cell has different information from mom and dad (Dd)

Cross a heterozygous green pod pea with a heterozygous green pod pea (Gg x Gg)