Parent generation = P Offspring of P generation = F1 Offspring of F1 generation = F2 Cross a homozygous dominant Tall flower with a homozygous recessive short flower. Give the F1 genotype and phenotype percents. Tall = TT, short = tt
Phenotype – the physical appearance of an organism. Determined by it’s alleles (maternal/paternal) “Photo” Genotype – the genetic makeup of an organism“Genes” The many different alleles that an organism can possess: BB, Bb or bb (Often use the 1 st letter of the dominant trait)
Homozygous – an individual who has the same alleles for a trait. Ex. 2 genes for cystic fibrosis (CC = homozygous dominant or cc = homozygous recessive) Heterozygous – an individual who has different alleles for a trait. Ex. One gene for cystic fibrosis, one for normal (Cc)
A trait is controlled by factors (genes) that occur in pairs
One gene in a pair can mask or hide the expression of the other gene (dominant vs recessive) Dominant allele: When only ONE of the alleles affects the trait. (Use a CAPITAL letter) Recessive allele: the allele that is NOT expressed if there is a dominant allele present. (Use a small letter).
A pair of genes (alleles) separate during the formation of sex cells (gametes) (Later learned that gametes are formed during meiosis…come together later to supply the alleles that form a trait)
The inheritance of one gene does not affect or depend on the inheritance of another gene *Mendel was looking at traits on different chromosomes….. *Modification: Linked genes are inherited together on a chromosome) **EXCEPTION: crossing over.
Handout:DOMINANT vs RECESSIVE Dark Hair Nonred hair Dark Skin Skin Pigment Brown eyes Near or far sighted Astigmatism Normal Hearing
Phenotype: % Ratio: Genotype: % Hom. Dom. % Het. Dom. % Hom. Rec. Ratio: *HW: Key, Cross, Punnett, Answer HW: #1-5,7 Genetics Online Practice Problems More Online Genetics Problems
Neither gene dominates Blending of traits Notation: 2 different Capitol Letters Example: White Flowers x Red Flowers produce PINK flowers WWx RR = RW white red pink (HW #8-9)
BOTH genes are expressed Notation: 2 different Capitol Letters Example: “ROAN” cows/horses White/Red hair dispersed evenly …looks pink P176 L1 text…(HW #7) (HW #7)
Genes on the X chromosome Usually recessive; different chances male/female Ex: Color-blindness, hemophilia NOTATION: How males and females inherit: X Y = Normal vision male X c Y = Color blind male *More in males-50/50 X X = Normal vision female X X c = Female color blind carrier X c X c = Color blind female (or written with hashmarks X ’ X ’ )
males get their X from their mother fathers pass their X to daughters only females express the trait only if they get a copy from both parents. recessive in females; females can be ‘carriers’ ALWAYS expressed in males if present; can NEVER be carriers of X-linked traits (#20-24) Sex-Linked Inheritance Problem Sets
White eyed fruit flies are the result of an X- linked recessive gene. Show the results from a cross between a red-eyed male and a white-eyed female Drosophila. Indicate the results of each sex separately for genotype and phenotype. Key: Cross: X R Y x X r X r or X Y x X ’ X ’ Answer *Phenotype: “Carrier Females” are considered “Unaffected/Normal”
There are more than 2 alleles in the gene pool BUT an individual inherits only TWO (one allele from mom, and one from dad) When there are 4 or more possible phenotypes for a particular trait. Example: Blood Typing: Inherited A,B,O Six GENOTYPE possibilities ?? = FOUR different bloodtypes: ?? (#10-12)
3 different possible alleles for the blood type gene: Co-dominant A or B, or recessive O 4 possible Phenotypes: Genotypes: Type AI A I A, I A I i (AA,AO) Type BI B I B, I B I i (BB,BO) Type AB I A I B (AB) Type O I i I i (OO) (#10-12)
If a type O person marries a type AB person, what blood type could occur in their children? Remember, type O is recessive to both A and B Key Cross i i x I A I B Answer (#10-12)
The factors for different traits are sorted into the gametes independent of each other. S = Smooth pea Y = Yellow Color 1.Determine all possible combinations of alleles in the gametes for each parent. DiHybrid Cross: Independent Assortment (#13-19)
DiHybrid Crosses Dihybrid Cross Problem Sets Dihybrid Cross Problem Sets Dihybrid Cross Problem Sets
Mendelian Cross: In Pea Plants, the flower color Purple is dominant to white. If two heterozygous plants are crossed, what % of the offspring will be white? PROBABILITY: Same set-up: what is the probability that the offspring will be homozygous recessive? Probability that an egg from the F 1 (Pp) will receive a p allele = 1/2. Probability that a sperm from the F 1 will receive a p allele = 1/2. The overall probability that two recessive alleles will unite, one from the egg and one from the sperm, simultaneously, at fertilization is: 1/2 X 1/2 = 1/4. Rules of Multiplication n and Addition 10.35
Pedigree charts follow a genetic mutation/disease through several generations of a family. You can determine what chance offspring has of having a disease based on family history and Punnett Square. The main diseases that are tracked this way are: ◦ Tay-sachs ◦ Huntingtons ◦ Colorblindness ◦ Hemophilia ◦ Cystic fibrosis
Calculating the frequency of crossing-over reveals the linear order of linked genes on a chromosome. Total Recombinant/Total # Offspring X 100 = 11% where 1% recombination = 1 map unit So the loci are 11 map units apart on the same chromosome (11 centimorgans) The closer two genes are to each other, the less likely crossing over will occur; genes are linked.