Introduction to Genetics

Introduction to Genetics

definitions in italics

Genetics· study of inheritance patterns and variations in organisms

Gregor Mendel (1822-1888)· father of genetics· an Austrian monk· studied pea plant traits

traits· characteristics· Mendel looked at a variety of pea plant traits

More Trait examples Cross Pollinating· producing seeds that are offspring of two different plants

Introduction to Genetics

Mendel Wondered What would happen if he cross Pollinated a...

Short plant (T) x Tall Plant (t)

P generation = parents

Pull

Pull

ALL TALL PLANTS!!!NOT WHAT MENDEL EXPECTED

F1 generation = first generation of offspring

Hybrid· offspring produced by crossing parents with different traits

PP

Pp

pp

ppPP

Pp Pp Pp

PpPp

Genes· factors that control traits by making certain proteins· Mendel studied genes that have contrasting forms

Tall vs. ShortPurple vs. White

Alleles· different forms of a gene (options)· expressed as letters (T or t, R or r, B or b)· ex. gene for height, but alleles can be tall or short· ex. gene for pod color, but alleles can be green or yellow· offspring get 1 allele from mom and 1 from dad

Introduction to Genetics

Dominant vs. Recessive· dominant = allele expressed even when the recessive traits are present in genetics

capital letter - A, B, R, T, D· recessive = not observed when the dominant allele is present

lower case letter - a, b, r, t, donly expressed when there are 2 recessive alleles

A a Pull

Pull

Pea Plant Dominant traits

Mendel wondered what would happen if he let the f1

generation self pollinate...

P

F1 F2

F2 = second generation of offspring (like grandkids)

Short

Short Plants Reappeared!

Mendel's Law of Segregation· Why did the short trait disappear in the F1 generation and reappear in the F2 generation???· during meiosis (gamete formation) alleles separate or segregate· during fertilization the alleles come back together again in a new combination

AA

A A

Segregation & Fertilization

Pull

Pull

Introduction to Genetics

Probability· the likelihood that a particular event will occur· written as fractions, ratios, and percents· 1/2 or 1:1 or 50%

Pull

Pull

Pull

Pull

Pull

Pull

Punnett Square· method used to determine the possible allele combinations in offspring from a particular set of parents

Homozygous vs. Heterozygous· homozygous = two identical alleles for the particular trait

homo = sameTT, BB, tt, rr, bb

· heterozygous = two different alleles for a particular trait

hetero = otherTt, Bb, Rr

Phenotype vs. Genotype· phenotype = what is expressed - or what you can physically see or observe

tall, short, purple, whiteuses words to describe an appearance

· genotype = genetic make-up...what genes are involved (allele combination)

TT, Tt, tt, PP, Pp, ppuses letters to describe combination of genes

Test Cross· a cross between an organism with an unknown genotype with an organism with a recessive phenotype

offspring may determine the genotype of the unknown plant

ex. P? x pp

Independent Assortment· genes on different chromosomes line up randomly during meiosis· increases genetic diversity· occurs during metaphase I

Introduction to Genetics

Independent Assortment using Punnett Squares