Genetics Introduction What is genetics Genetics the study

Genetics: Introduction

What is genetics? • Genetics – the study of inheritance or heredity • Heredity – passing of traits from parents to offspring • Gene – section of DNA that codes for proteins that determine an organism’s characteristics.

Fertilization Review • Fertilization – the process where haploid gametes (sperm and egg) come together to make a diploid zygote • Each organism inherits 2 copies of each gene -One from mom -One from dad

Meiosis Review • Law of segregation – genes for a trait segregate (separate) when gametes are formed • Law of independent assortment – alleles of different genes separate independently of one another during the formation of gametes

What are alleles? • Genes are made up of 2 or more alleles. – Allele - different versions of a gene.

Law of Dominance • Law of Dominance – alleles can be dominant or recessive. • Dominant – allele that is expressed even when another allele is present – Signified by a capital letter : R – Example: Hair color other than red • Recessive – trait that is only expressed if the dominant allele isn’t present – Signified by a lower case letter : r – Example: Red hair

Let’s See an Example! Let’s look at the gene for coat color in dogs. There are 2 alleles: B=black, b=yellow Bruce Molly

What is Bruce’s Genotype? • Genotype: Set of alleles for a trait – 2 dominant alleles= homozygous dominant – 1 dominant and 1 recessive allele= heterozygous – 2 recessive alleles= homozygous recessive Remember: B=black, b=yellow Bruce can have the genotype BB or Bb. Why?

What is Bruce’s Phenotype? • Phenotype: Physical expression of a trait. What is Bruce’s phenotype?

Now it’s your turn! What is Molly’s genotype and phenotype? Remember: B=black, b=yellow

What if Bruce and Molly had puppies? • Bruce has BB genotype. • Molly has a bb genotype. • What predictions could we make about the color of their offspring. ?

Punnett Squares • Used to calculate the probability an offspring inheriting a certain genotype and phenotype

What if Bruce and Molly had puppies? BB bb Punnett Square

So… • What is the probability of the offspring having each of the following genotypes? – BB: – Bb: – bb: • What is the probability of the offspring having each of the following phenotypes? – Black – Yellow

Problem #1 The owners of Bruce and Molly breed 2 of their offspring (Bb) to get more puppies. They want to know the predicted fraction of black puppies and yellow puppied is. Help them out!

Problem # 2 A red flower (Rr) and a white flower (rr) are bred. What is the predicted fraction of red flowers and what is the fraction of white flowers?

Problem #3 A spotted cat (Ss) breeds with a solid colored cat (ss). What is the predicted ratio of spotted to solid colored cats?

Gregor Mendel: The Man, the Myth, the Legend • Father of Genetics • Austrian Monk • Studied science & math as well as ran a garden • Experimented on garden peas • https: //www. youtube. com/watch? v=Mehz 7 t. Cxj. SE

Mendel’s Experiments • Mendel Crossed pea plants of contrasting characteristics • He did this with 7 different characteristics.

Crossed Plants First, Mendel crossed a purebreeding yellow plants with pure breeding green plants. All offspring in the F 1 generation were yellow!

Crossed Plants • Then, he let the plants in the F 1 generation selfpollinate. • The F 2 generation came out with a 3: 1 ratio of yellow to green. • This proved that alleles weren’t lost, but hidden!

Remember: If yellow peas are dominant to green peas, what is the predicted ratio yellow and green peas of a Yy plant to a yy plant.

THE DIHYBRID CROSS Studying the inheritance of two traits simultaneously (at the same time) © 2007 Paul Billiet ODWS

Mendel’s peas Character Seed shape Seed color © 2007 Paul Billiet ODWS Trait Allele Round R Wrinkled r Yellow Y Green y

Combinations Genotype RRYY RRYy Rr. YY Rr. Yy RRyy Rryy rr. YY rr. Yy rryy © 2007 Paul Billiet ODWS Phenotype Round Yellow Round Green Wrinkled Yellow Wrinkled Green

Mendel & Meiosis • The pairs of chromosomes could orientate in different ways at Anaphase 1 © 2007 Paul Billiet ODWS

Dihybrid cross genetic diagram P Phenotypes Round Yellow seed Genotypes RRYY rryy meiosis RY ry Gametes X Wrinkled Green seed fertilization F 1 Phenotypes Rr. Yy Genotypes Round Yellow Proportions 100% © 2007 Paul Billiet ODWS (Pure bred)

When working with Dihybrid Crosses we use the FOIL method to determine possible gametes. Round is dominant to wrinkled Yellow is dominant to green peas Example of a Dihybrid Genotype First RY Rr YY Outside Inside RY r. Y Last r. Y

Examples of FOIL- Use these parental genotypes to find the possible gametes: 1. 2. 3. 4. 5. Rr. Tt RRTT rr. Tt RRTt Rrtt No need to repeat gametes if they are the same…pay close attention!

In mice, running is dominant to waltzing, and black coat color is dominant to white. Use a punnet square to predict the results of a cross between a heterozygous running, white mouse and a waltzing, heterozygous black mouse. *First we need to FOIL out the genotypes ____, ____ X ____, ____ F: O: I: L:

In mice, running is dominant to waltzing, and black coat color is dominant to white. Use a Punnett square to predict the results of a cross between a heterozygous running, white mouse and a waltzing, heterozygous black mouse.

Your turn! In pea plants, yellow color is dominant to green, and smooth seeds are dominant to wrinkled seeds. If a green and wrinkled plant is crossed with a homozygous yellow wrinkled plant, what would be the phenotypic ratio for the offspring?