The Work of Gregor Mendel

Essential Question:  Describe Mendel’s studies and conclusions about inheritance. 

Gregor Mendel = Father of Genetics Worked with garden pea plant 1857

Mendel’s Experiments Peas are a “model system.” Started with “true breeding” plants Trait: specific characteristic (e.g., seed color, plant height) of an individual Hybrid: created from cross of true-breeding individuals Small, easy to grow. Makes them convenient to study. Help explain how organisms inherit traits

Pollination and Fertilization in Plants Male part Female part Plants have the ability to self-pollinate (self-fertilize) because they have both reproductive parts.

Cross-Pollination Pollen Taking pollen from one plant and using it to fertilize the eggs of another plant

Pea Characteristics of Mendel’s peas Mendel studied these characteristics to observe patterns in traits across generations.

Mendel’s Crosses When Mendel crossed plants with contrasting traits, the hybrid offspring showed traits of only one parent.

Dominant and Recessive Traits Yellow seed color is to green seed color. Green seed color is to yellow seed color. dominant recessive When a yellow pea plant is crossed with a green pea plant, the resulting offspring are yellow.

Principle of Dominance Some alleles are dominant, some recessive. An organism with at least one dominant allele will exhibit that trait. An organism with a recessive allele will exhibit the trait only in the absence of a dominant allele. dominantrecessivedominant

Genes and Alleles Traits (seed shape, seed color) are determined by genes. Genes: passed from one generation to the next; genetic code that determines an individual’s characteristics Forms of traits (yellow/green, round/wrinkled) are called alleles. Alleles: the different forms of a gene. Characteristics such as pod color are determined by. Yellow and green pod colors are determined by. The allele for green pods is to the allele for yellow. genes alleles recessive

The P 1 and F 1 Generation P 1 generation F 1 generation True-breeding Hybrids Let’s figure out how we can predict the F 1 gen from the P 1 gen.

Monohybrid Cross = One Trait “Height” “True Breeding” = Homozygous Tall Pea x Short Pea TT x tt T = Dominant t = Recessive X “Homozygous Dominant” “Homozygous Recessive”

Heterozygous and Homozygous Homozygous: has two identical alleles for a gene Heterozygous: has two different alleles for a gene Which are: homozygous? heterozygous? , 4 2, 3 4

1 st LAW OF HEREDITY “Law of Segregation” = –The 2 alleles for each trait must separate when gametes (sperm/egg) are formed. - A parent passes on, at random, only one allele for each trait to each offspring A  a

Segregation Segregation: separation of alleles during gamete formation

Segregation Random Fertilization

The Formation of Gametes Eggs and sperm Fertilization

Making a Punnett Square Combine gamete genotypes Gametes for a parent along one side Possible gametes A cross of birds: Beak size (B, b)

Generations P1 = Parent Plants -True breed Tall x True breed Short = First Generation (children) F1 TT x tt What’s the probability that the offspring will be tall? ________ Short? _______ Genotype of offspring? ______________ Genotype=genetic makeup of organism Phenotype of offspring? _____________ Phenotype=physical characteristics

Law of Probability “Rules of Chance” “Odds” 20:1 5% 10:1 10% 2:1 50% Numerator = winner Denominator = # horses 1/12 1:12 “odd” 8% “chance”

Probability? “Chance” of getting a tail? “Chance” of getting snake eyes on two dice?

Male: Female XYXX ½ 1:2 odd Boy 1:2 odd Girl 50% chance Survey Large Number 1:1 “Chance” of getting a boy?

Dominant = Trait Observed Recessive = Trait that disappeared Tall = Dominant (T) Short = Recessive (t) Alleles: TT = Tall Tt = Tall tt = Short PhenotypeGenotype Can’t always know an organisms genotype by looking at its phenotype?

TT tt T t TtTt Homozygous Dominant Homozygous Recessive Heterozygous

Tt x Tt 3 Tall and 1 Short T t F1 F2 TtTt Combination of Letters/Alleles? TtTt Change of colors to follow the parental alleles:

The F 2 Generation – created from a cross of two F 1 generation offspring. What proportion of F 2 offspring were short? What proportion of F 2 offspring were tall? 1/4 3/4

Dihybrid Crosses: Crossing for 2 characteristics/ traits

2 TRAITS: Seed Shape and Seed Color Shape =Round (R) was dominant to Wrinkled (R) Color = Yellow (Y) was dominant to Green (y) EXAMPLE

Making a Punnett Square: Two Factors Combine gamete genotypes A cross of pea plants: size (T, t) and pod color (G, g) All possible gametes All gametes for a parent along one side

Round Yellow SeedsWrinkled Green Seeds Homozygous dominant for both traits Homozygous recessive for both traits x _RRYY_ ___rryy____ (Genotype) 1. We need to first find all the possible gamete combinations of each parent (Genotype) Use FOIL to help you figure out the combinations (RR)(YY) F(irst)RY O(uter)RY I(nner)RY L(ast)RY Use FOIL to help you figure out the combinations (rr)(yy) F(irst)ry O(uter)ry I(nner)ry L(ast)ry gametes 2. Place your gametes in a Punnett square. RY RY RYRY ry

RrYy RY RY RYRY ry 3. Fill in the Punnett square. So the P1 cross of true breeding plants: Round Yellow SeedsWrinkled Green Seeds RRYY rryy produced RrYy P1P1 F1F1 All plants Round Yellow Seeds

1. We need to first find all the possible gamete combinations of each parent Now let’s cross two F 1 generation plants. RrYy Use FOIL! RY Ry rY ry RY Ry rY ry

RrYy RY Ry rY ry The two pairs of alleles segregate independently of each other. The presence of one specific allele for one trait has no impact on the presence of a specific allele for the second trait. Four classes of gametes (RY, Ry, rY, and ry) would be produced in equal amounts.

2. Place your gametes in a Punnett square. RY Ry rY ry RY Ry rY ry RY Ry rY ry RY Ry rY ry

RrYy Round Yellow Round GreenWrinkled Yellow Wrinkled Green

2 ND LAW OF HEREDITY Law of Independent Assortment = genes for different traits are inherited “independently” of each other. RrYy = the R and r will separate as well as the Y and y. Alleles can recombine in 4 different ways.