Introduction to Genetics Chapter 11

Genetics  The study of how traits are passed on from parents to offspring.  Trait: Physical characteristic  Ex: hair color, seed color, height

Gregor Mendel ( )  “Father of genetics”  A monk from Austria  Lived in a monastery where he was a priest and a school teacher  Experimented with pea plants in the garden

 Mendel studied 7 different pea plant traits  Pea color, plant height, flower color, etc…  He wanted to know how the traits were passed  So he crossed (bred) two different plants to see what the offspring would look like

MendelMendel believed that the characteristics of pea plants are determined by the:  a)inheritance of units or factors from both parents  b)inheritance of units or factors from one parent  c)relative health of the parent plants at the time of pollination

 Crossed a tall pea plant with a short pea plant  What did the offspring look like?

Where did the short trait go?  Then he crossed the F 1 offspring  What happened?  Short trait reappeared!

Mendel concluded:  Allele - form of a trait (written as letters)  Ex: Tall pea plant = TT or Tt  A trait has two alleles  1 from mom, 1 from dad  Some traits are dominant and others are recessive. (Why some of us look more like 1 parent than the other)

An allele is… aa)another word for a gene bb)a homozygous genotype cc)a heterozygous genotype dd)one of several possible forms of a gene

 Dominant- Capital letter allele overpowers small letter, and the dominant trait is shown.  Ex: Tt = Tall plant  Recessive- lowercase allele that is masked by dominant one, must have two recessive alleles to show the recessive trait.  Ex: tt = short plant

 Traits can be described in 2 ways:  Genotype - Genetic makeup (Tt, TT or Tt)  Phenotype - Physical appearance (Tall or short)  Homozygous - Two of the SAME alleles (both dominant OR both recessive)  TT or tt  Heterozygous - One dominant allele and one recessive allele  Tt

 Sex cells (sperm and eggs) can only carry 1 allele at a time for each trait.  If mom has a trait Gg  Her eggs can only have a G or g  If dad is GG, his sperm all have one G  Those sex cells mix to form the offspring’s genotype.  Those offspring can either be GG or Gg

When the genotype consists of a dominant and a recessive allele, the phenotype will be like _________________ allele.  a)the dominant  b)the recessive  c)neither

 Stop  Do activity

 Problem: Cross a heterozygous tall pea plant with a heterozygous tall pea plant.  Step 1 : What are the parents (P) genotypes?  Tt x Tt

 Step 2 : Set-up your Punnett square.

 Step 3 : Fill-in genotypes of offspring

 Step 4: Make table to organize data  Step 5 : Answer any questions asked of you about the results  Genotypic ratio:  Phenotypic ratio:  %chance having tall offspring:  % chance having short offspring:

 Freckles (F) is a dominant trait. Patty is homozygous for freckles while her hubby Harry is heterozygous for freckles.  What are the chances of their children having freckles ?  What is the phenotypic ratio?

Practice:  Two dogs mate and have puppies. The male dog is homozygous for black fur and the female is homozygous for yellow fur. Black is dominant and yellow is recessive. Parents: ____ x ____ How many puppies will have black fur? What percent of the offspring have yellow fur? Is it possible for these dogs to have a puppy with yellow fur? Why/Why not? Genotype # Phenotype