Thursday, May 28th p. 296, 297

Thursday, May 28th

2965/28/15 Thurs.L.T.: I can use Punnett Squares, rules for reproduction, and genotypes and phenotypes to determine what % chances there are of passing a trait down from parents to offspring.DO NOW: There are definitely some rules with heredity (passing on traits) and sexual and asexual reproduction. Try making at least 3 rules from your understanding of yesterday’s class.………………………..Reflection: What is the highest % chance of 2 brown eyed parents having a blue eyed baby? Show your Punnett Square for evidence.

297Title: Punnett SquaresPhenotype:Genotype:…………………………………Rules for Gene Expression:

…………………………………..Punnett Squares:

DNAGeneChromosomeAlleles InheritanceHeredityTraitDominantRecessivePhenotypeGenotype

Reproduction Rules

• Sexual: • All organisms have a set # of chromosomes. (Humans =

46, 2 sets of 23)• Offspring will receive 50% of chromosomes from dad,

and 50% from mom. (SO, that means 1 chromosome our of the set is from one parent.)

• Asexual:• Daughters are genetic clones of mother

First, a short quiz…

• Select True or False (back up with evidence):

• 1. Genes are located on chromosomes.• 2. Traits are all linked to genes.• 3. You only have 1 gene for each trait.• 4. It is possible for you to receive more DNA from 1

parent than the other.• 5. Asexually reproducing organisms will have different

DNA from mother to daughter.

• How do we determine what traits the offspring will have?

• Things we need to know:• Rules for reproduction (both sexually and asexually)• Rules for gene expression (genotype/phenotype;

dominant/recessive)• How to use PUNNETT SQUARES

Genes and Gene Expression

• Phenotype: the result of your body doing what the gene says to do. In other words, your traits!

• Example: brown eyes, curly hair, tall height

• Genotype: the actual genes you have; your alleles

• Example: for eye color- the allele B and the allele b (Bb)

• Eye Color Genotype Possibilities:

• BB, Bb, bb

• What do they mean?

• With your partner, see if you can come up with a rule as to WHY these genotypes result in these phenotypes.

Genotype BB Bb bb

Phenotype brown brown blue

Dominant and Recessive Genes

• Rules:

• Dominant: dominant alleles will BLOCK the expression of recessive genes• BB = brown• Bb = brown

• Recessive: recessive alleles will be expressed ONLY in the absence of dominant alleles• bb = blue

Quiz• 1. A kid’s phenotype is brown eyes. What’s his genotype?

• 2. Both parents have blue eyes. What are their genotypes?

• 3. ChunDoong’s genotype is Bb for eye color. What color eyes does he have? (phenotype)

Punnett Squares

• Punnett Squares are about figuring out the % of all the possible combination of alleles parents can pass on to their children.

• Example:• Dad’s genotype: BB• Mom’s genotype: Bb

• Dad’s sperm no matter what has to contain the B allele. (Why?)• Mom’s eggs are either going to contain the B allele or the b allele.

(What % of her eggs will have the B? Why?)

• Now we use our understanding of sexual reproduction rules…