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Mendelian Genetics The Scientific study of heredity 1850’s; 21 y.o.

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Presentation on theme: "Mendelian Genetics The Scientific study of heredity 1850’s; 21 y.o."— Presentation transcript:

1 Mendelian Genetics The Scientific study of heredity 1850’s; 21 y.o.
Scientist + Mathematician Paper: 1865 “Father of Modern Genetics”

2 Mendel’s crosses and results
Easy to grow Matures quickly Produces generations quickly Large # offspring Cross and self pollination *Each trait on a separate gene

3 The Perfect Flower Self Pollination: has both male and female parts

4 Controlled Cross-Pollination
Removal of Stamens Transfer of pollen from a white flower to the purple stigma (P1- parents) Carpel/peapod/seeds Plant the seeds (F1- First Generation) First Filial

5 Mendell’s Experiments F1 x F1

6 Generations 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

7 Genetics Terminology 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 1st letter of the dominant trait)

8 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)

9 Mendel’s crosses and results
Statistics/Ratios Conclusions Dominant/Recessive 4 Principles Notesheet

10 A trait is controlled by factors (genes) that occur in pairs
1865 Paper Published by Gregor Mendel based on his research with garden peas 1. Principle of Unit Characters: A trait is controlled by factors (genes) that occur in pairs

11 2. Principle of Dominance:
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).

12 3. Principle of Segregation:
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)

13 4. Principle of Independent Assortment:
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.

14 Inherited Traits in Humans
Handout: DOMINANT vs RECESSIVE Dark Hair Nonred hair Dark Skin Skin Pigment Brown eyes Near or far sighted Astigmatism Normal Hearing

15 Cross …. Punnett Square. (TT x tt)
Cross … Punnett Square* (TT x tt) *Represents ONE offspring- 4 possible genetic outcomes… Phenotype: % Ratio: Genotype: % Hom. Dom. % Het. Dom. % Hom. Rec. *HW: Key, Cross, Punnett, Answer Genetics Online Practice Problems More Online Genetics Problems HW: #1-5,7

16 Incomplete Dominance Neither gene dominates Blending of traits
Notation: 2 different Capitol Letters Example: White Flowers x Red Flowers produce PINK flowers WW x RR = RW white red pink (HW #8-9)

17 Codominance 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)

18 Example of Codominance: ‘Pink’ Roan Horse RR= red WW =white RW= Roan (RR, R’R’,R’R)

19 Sex-linked inheritance (on X or Y)
Sex-linked inheritance (on X or Y) *We will look at only X-linked traits 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 Xc Y = Color blind male*More in males-50/50 X X = Normal vision female X Xc = Female color blind carrier Xc Xc = Color blind female (or written with hashmarks X ’ X ’)

20 Sex-Linked Recessive 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 Sex-Linked Inheritance Problem Sets (#20-24)

21 “X” linked Problem #20: or X Y x X’X’ Key: Cross: XR Y x XrXr
Answer 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. *Phenotype: “Carrier Females” are considered “Unaffected/Normal”

22 Multiple Alleles 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)

23 Blood Typing 3 different possible alleles for the blood type gene:
Co-dominant A or B, or recessive O 4 possible Phenotypes: Genotypes: Type A IAIA, IAIi (AA,AO) Type B IBIB, IBIi (BB,BO) Type AB IAIB (AB) Type O IiIi (OO) (#10-12)

24 Worksheet #11 Key Cross i i x IAIB
Answer Worksheet #11 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 (#10-12)

25 DiHybrid Cross: Independent Assortment
The factors for different traits are sorted into the gametes independent of each other. S = Smooth pea Y = Yellow Color Determine all possible combinations of alleles in the gametes for each parent. (#13-19)

26 Dihybrid crosses Involves TWO traits Ex: tall/short, green/yellow
1. To set the Crosses: The FOIL Method: First Outer, First Inner, Last Inner, Last Outer 2. Fill in, matching the traits back up again Typical Question: What is the Phenotypic Ratio? ie: Number that will be bothTall and Yellow, etc Start with the FIRST box and count (add up to 16) Marking boxes as you go, choose the NEXT Phenotype and add those that match, until all boxes accounted for; final ratio (#13-19)

27 Dihybrid Crosses

28 DiHybrid Crosses Dihybrid Cross Problem Sets

29 Genetics Probability Mendelian Cross:
PROBABILITY: Same set-up: what is the probability that the offspring will be homozygous recessive? Probability that an egg from the F1 (Pp) will receive a p allele = 1/2. Probability that a sperm from the F1 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. 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? Rules of Multiplication n and Addition 10.35


31 Pedigree Charts 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

32 Basic Symbols


34 Pedigree: Dominant Inheritance 1
Pedigree: Dominant Inheritance 1.Every affected individual has at least one affected parent 3. Two affected MAY have unaffected children

35 Pedigree: recessive disorder 1
Pedigree: recessive disorder 1. An individual who is affected may have parents who are unaffected. 2. ALL children of 2 affected parents are affected

36 Sample Pedigree: Inheritance 1
Sample Pedigree: Inheritance 1.Dominant (has the trait, one parent has the trait) or recessive trait? If Dominant….Know the FIRST allele is a Large letter, so can fill that in…. If recessive, must be two small letters

37 Dominant or recessive trait?
Autosomal Recessive (nn) *Back of Problems

38 Autosomal Dominant (D_)
Dominant or recessive trait?

39 Test Cross

40 Two- Point Test Cross *Dominant = Gray, Normal wings= Bb Vv Or
b+bvg+vg Where + is dominant


42 +

43 % Recombination 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.

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