Ch.11-2 Applying Mendel’s Principles Genetics

POINT > Review Mendel’s first crosses POINT > Describe dominant and recessive alleles POINT > Describe homozygous and heterozygous genotypes POINT > Distinguish between genotype and phenotype POINT > Use Punnett Squares to predict genotypes and phenotypes

POINT > Review Mendel’s first crosses Looking back at Mendel’s pea plants… Parental plants (P) were all purebred x First generation (F1) offspring all showed dominant allele

POINT > Review Mendel’s first crosses Looking back at Mendel’s pea plants… Second generation (F2) offspring showed both dominant & recessive alleles

POINT > Review Mendel’s first crosses 6022 = 3.01 2001 Looking back at Mendel’s F2 pea plants... Trait Dominant Recessive Ratio Seed Color 6022 Yellow 2001 Green 3.01 : 1 Seed Shape 5474 Round 1850 Wrinkled 2.96 : 1 Flower Color 705 Purple 224 White 3.15 : 1 Pod Color 428 Green 152 Yellow 2.82 : 1 Plant Height 787 Tall 277 Short 2.84 : 1

POINT > Describe dominant and recessive alleles Alleles are represented by a single letter, usually the first letter of the dominant allele Dominant alleles  Uppercase letter Recessive alleles  Lowercase letter

POINT > Describe dominant and recessive alleles Example from Mendels peas: Dominant alleles  yellow seeds = Y Recessive alleles  green seeds = y

POINT > Describe homozygous and heterozygous genotypes An organism is homozygous for a trait if it has two identical alleles Ex. both alleles code for: Yellow seeds – YY (homozygous dominant) Green seeds – yy (homozygous recessive)

POINT > Describe homozygous and heterozygous genotypes An organism is heterozygous for a trait if it has two different alleles Ex. Alleles codes for: One yellow, one green – Yy

WB CHECK: In pea plants, the allele for purple flowers is dominant (P) and the allele for white flowers is recessive (p). A plant with alleles pp would be a) homozygous dominant and have purple flowers b) homozygous recessive and have purple flowers c) homozygous dominant and have white flowers d) homozygous recessive and have white flowers e) heterozygous and have purple flowers f) heterozygous and have white flowers

WB CHECK: A pea plant with alleles Pp would be a) homozygous dominant and have purple flowers b) homozygous recessive and have purple flowers c) heterozygous and have purple and white flowers d) heterozygous and have purple flowers e) heterozygous and have white flowers

POINT > Distinguish between genotype and phenotype The genotype is the genetic makeup of the alleles for a specific gene Indicated by writing both alleles: YY Yy yy

POINT > Distinguish between genotype and phenotype The phenotype is the physical expression of a trait Indicated by writing the name of expressed allele: Yellow Yellow Green

WB CHECK: A pea plant with alleles P and p would be a) genotype = Pp phenotype = white flowers b) genotype = purple flowers phenotype = Pp c) genotype = Pp phenotype = purple flowers d) genotype = white flowers phenotype = Pp

We can predict the results of a cross if we know the genotypes of the parents…

POINT > Use Punnett Squares to predict genotypes and phenotypes A Punnett Square is a diagram that shows the mathematical probability of genotypes & phenotypes

POINT > Use Punnett Squares to predict genotypes and phenotypes Parent 1 The two axes represent the two parents The boxes represent offspring Pa r en t 2

Meiosis of a plant heterozygous for seed color:

Meiosis of a plant heterozygous for seed color:

Meiosis of a plant heterozygous for seed color:

y Y 50% 50% y Y Y y

We can use meiosis & a Punnett square to show why Mendel’s first cross for pea color resulted as it did:

POINT > Use Punnett Squares to predict genotypes and phenotypes X Mendel’s first cross: Alleles Yellow (Y) Yellow (Y) Green (y) Green (y)

POINT > Use Punnett Squares to predict genotypes and phenotypes Mendel’s first cross: Yellow (Y) Yellow (Y) Y Y Green (y) Y Y Green (y)

POINT > Use Punnett Squares to predict genotypes and phenotypes Mendel’s first cross: Yellow (Y) Yellow (Y) Y y Y y Green (y) Y y Y y Green (y)

POINT > Use Punnett Squares to predict genotypes and phenotypes Mendel’s first cross: Yellow (Y) Yellow (Y) Y y Y y Green (y) Y y Y y y Green (y) Y

POINT > Use Punnett Squares to predict genotypes and phenotypes 100% Yy Yellow (Y) Yellow (Y) Ratio 4 : 0 Y y Y y Green (y) Phenotype 100% Yellow Ratio 4 : 0 Y y Y y Green (y)

What about Mendel’s second cross What about Mendel’s second cross? How would a Punnett square show the results of the self-pollinating F1 generation?

POINT > Use Punnett Squares to predict genotypes and phenotypes Mendel’s second cross Genotype: 25% YY 50% Yy 25% yy Y y Ratio 1 : 2 : 1 Y Y Y y Y Phenotype: 75% Yellow 25% Green Ratio 3 : 1 Y y y y y

WB CHECK: Determine both the genotype & phenotype ratios using a Punnett Square: A pea plant homozygous dominant for seed color is crossed with a pea plant heterozygous for seed color Yellow = dominant (Y), green = recessive (y)

WB CHECK: Determine both the genotypic & phenotypic ratios. Cross a pea plant homozygous recessive for flower color to a pea plant heterozygous for flower color Purple = dominant (P) , white = recessive (p)

WB CHECK: Determine both the genotypic & phenotypic ratios. Cross a fruit fly heterozygous for wing shape to another fruit fly heterozygous for the same trait Curly = dominant (C), Straight = recessive (c)

Homework: Read pages 313-318 Assess #1-3 page 318 Karyotype exercise pages 153-157 Workbook pages 163-4