Practice with Punnett Squares

Review P1 generations= Parental generation F1 generation= first offspring F2 generation= second generation of offspring

Laws of Segregation Each organism contains: 2 factors for each trait ( one from both parents)

Law of independent assortment Factors for different characteristics are distributed to the gamete (egg or sperm) independently.

More REVIEW A segment of DNA on a chromosome that controls heredity is a ___________ Genes occur in pairs, WHY? Alternative forms of a gene is an________ CAPITAL letter refer to a ________________ Will be expressed Hides the recessive trait lower case letter refer to a ______________ Only is expressed in a homozygous recessive organism

Review continued… When both alleles in a pair are alike (AA or aa), the organism is ________________ When the two alleles are different, the organism is __________________

What the point? PREDICT the likely outcome of genetic crosses. What happens when you breed two organisms together? What do we get? Genetic engineering Genetic diseases/disorders

HOW DO WE PREDICT PUNNETT SQUARES- aid in predicting the probability that certain traits will be inherited TYPES: MONOhybrid-cross between individuals that involves one pair of contrasting traits= different

PRACTICE Example 1: Cats S= Dominant for spots s= Recessive no spots Homozygous X homozygous What is the probability that the offspring will have the GENOTYPE Ss?

Homozygous x homozygous SS X ss

Example 2: homozygous X heterozygous Rabbits: B= dominant black b=recessive brown Genotypes: ______ x ______ What are the predicted genotypes? What is the probability of each genotype?

Example 3: heterozygous x heterozygous Flies: L= dominant for Long wings l = recessive for short wings Genotypes: _______x________ What is the genotypic ratio? What is the phenotypic ratio

Ratios Genotypic ratio: ratio of the genotypes that appear in offspring Phenotypic ratio: ratio of the ________ that appear in offspring

Test Crosses Determines the genotype of an ____________ Cross an unknown individual with a HOMOZYGOUS RECESSIVE individual. Why? A testcross can determine the genotype of any individual with a dominant phenotype (BB or Bb)

What???? If the unknown genotype is homozygous black (BB)what will all the offspring be? If the genotype is heterozygous black (Bb) what will all the offspring be?

More confusion: Complete and incomplete dominance When one allele has complete dominance over another = ___________________ EXCEPTION- sometimes the offspring will result in a phenotype that is mixed between the dominant and recessive traits THIS IS INCOMPLETE DOMINANCE

4 O’clocks Rr x Rr In snap dragons, both the allele for red flowers (R) and the allele for white flowers ( r) will influence the phenotype Neither allele is completely dominant over the other….which one will be expressed?

Red mixed with White = ???? Rr Cross RR with rr WHAT?? ALL Rr = pink flowers Now cross Rr X Rr What happens The parent traits return! Rr

Wait….there is more What is neither allele is Domainant or Recessive, nor do the alleles blend in the phenotype? ___________________ Calico Cats, painted horses, spotted cows

Dihybrid crosses Predict the possible genotypes and phenotypes for two traits Example: R= dominant round r= recessive wrinkled Y= Dominant yellow y= recessive green

Example: Homozygous x homozygous Genotypes________x _______ Cross these individuals

Example 2 Heterozygous X heterozygous Genotypes ______x_______ Why do you pair R and Y together instead of RR and YY on the punnett square? Independent assortment

What is the genotypic and phenotypic ratios _______ with round, yellow seeds Genotypes: _______with round green seeds _______with wrinkled, yellow seeds _______ with wrinkled green seeds

What is the phenotypic ratio ____ : ____ : ____ :____

Sex Determination Sex in Humans, and other organisms is determined by X and Y CHROMOSOMES

FEMALE Have two X Chromosomes (XX)

Males Have one X and one Y (XY)

23 is the magic Number Sex of offspring is determined by chromosome pair number 23 Sex linked traits in humans are determined by genes carried ONLY on the X chromosome

Too bad boys  These rarely appear in FEMALES Because…a dominant gene mask them BUT: if there is a recessive allele, it will always show up in the male since he has only ONE X chromosome Example: Hemophilia and colorblindness

More punnett Squares… In sex linked traits: The Letters will Always be and X and Y Superscripts represent the dominant or recessive trait Capital superscript= Dominant Lowercase superscript= Recessive XBXB OR XbY

Lets Practice John and Mary have 4 Girls. John wants a 5th child to be a boy. What is the probability of John and Mary having a son? Always 1:1 or a 50% chance

More Practice Shauna is hybrid for colorblindess. She Marries Jake who is NOT colorblind. What are the chances their son will be Colorblind?

WHAT???? Shauna’s Genotype: Jake’s Genotype: There is a 50% chance * The chances of having a colorblind child is 1:4 or 25%

You TRY…Just give it a try On a separate Sheet of paper Victoria is heterozygous for hemophilia, a recessive sex-linked trait. Her husband is not a hemophiliac. What percentage of their children will have hemophilia? Describe what each child genotype. TURN IN WHEN FINISHED