Semester 1, Day 8

Mendelian Genetics

Agenda Review for Quiz Turn in HW Quiz on Meiosis Lecture on Mendelian Genetics Work/Reading Time

Review Purpose of Meiosis Meiosis I

How many cells do you start with? How many chromosomes do those cells have?

How many cells do you end with? How many chromosomes do those cells have?

Meiosis II How many cells do you start with? How many chromosomes do those cells

have? How many cells do you end with? How many chromosomes do those cells

have? Spermatogenesis Products and Oogenesis Products Draw crossing over. What phase does it occur in? Label a diagram of Meiosis What is a gamete? Is it haploid or diploid? What is a zygote? Is it haploid or diploid? How much DNA do you get from each parent? Describe fertilization

Review

Homework Due Cornell Notes on Section 10.2 (Meiosis) 10.2 Section Assessment:

#1-4 Chapter 10 Assessment:

#1, 4-6, 9, 10, 13, 15, 18, 25, 26-28

Quiz Meiosis

Sex Chromosomes Karyotype: Chromosomes of an organism organized into

homologous pairs from largest to smallest. In humans, first 22 pairs always have homologous pairs of

chromosomes with identical centromere position, lengths, and traits (may have different alleles).

23rd pair may or may not have two similar chromosomes Sex Chromosomes

Image Source: www.biotechnologyonline.gov.au

XX XY

Sex Chromosomes Probability that child will be male or female:

50:50 chance the child will be male:female

Mom100% chance of

passing on an X = 1.0

Dad50% chance of

passing on a Y = 0.5

50% chance ofpassing on an X = 0.5

Child Probability #1X Y

1.0 x 0.5 = 0.5 (50%)

Child Probability #2X X

1.0 x 0.5 = 0.5 (50%)

Sex Chromosomes Easier Method: Punnett Square

X X X X

X Y X Y

X X Female

X

Y

Male Child

Female: X X = 2 /4 = 50%

Male: X Y = 2 / 4 = 50%

Mendelian Genetics Gregor Mendel: Austrian monk & plant

breeder. Considered the father of genetics due to his findings in breeding pea plants in 1866.

Image Source: commons.wikimedia.org

Mendelian Genetics Inheritance / Heredity: Passing of traits to the next

generation. Genetics: Study of heredity.

Image Source: www.biologie.uni-hamburg.de

Mendelian Genetics Mendel’s Work

Mendel determined there must be 2

forms of a trait in pea plants

alleles!

Same Trait: Color

Different Alleles: Yellow or Green

Also said the trait seen in F1 =

dominant, while masked (hidden)

trait in F1 = recessive.

Dominant Allele: Yellow

Recessive Allele: Green

Dominant allele is labeled with a

capital letter and the recessive

allele is labeled with the

corresponding lower case letter.

Yellow (Dominant): Y

Green (Recessive): y

Generation

Parental (P)(Pure-Breeding)

First FilialGeneration (F1)

Second FilialGeneration (F2)

xYellow Green

All Yellow

6022 Yellow: 2001 Green= 3:1

Mendelian Genetics Genotype: the organism’s allele pair

Zygosity: the similarity of alleles for a trait

Phenotype: observable characteristic of

allele pair

Homozygous Dominant Genotype

Phenotype

Heterozygous Genotype Phenotype

Homozygous Recessive Genotype

Phenotype

ExampleY = yellow pea colory = green pea color

Genotype Zygosity Phenoty

pe

Y Y

Homozygous Dominant Yellow

Y yHeterozygous

Yellow

yy

Homozygous Recessive Green

“Same” “Dominant Alleles”

“Same” “Recessive Alleles”

“Different Alleles”

Y Y = “Dominant” “Dominant” = Yellow “Yellow” “Yellow”

Y y = “Dominant” “Recessive” = Yellow “Yellow” “Green”(Dominant allele masks recessive allele)

y y = “Recessive” “Recessive” = Green “Green” “Green”(No dominant allele to mask recessive)

Mendel’s Laws 1. Mendel’s Law of Segregation

The two alleles for each trait separate during meiosis.

Y Y

Y

Y

y yy

y

Grows to Plant GameteFormation

Yellow Pea (2n)

100% = 1.0

Gametes (n)

x 2

x 2

P (parental) Generation

Grows to Plant GameteFormation

Green Pea (2n)

100% = 1.0

Gametes (n)

x 2

x 2

Y

y

Fertilization Y y

F1 Generation

ZygoteHeterozygous Yellow

(2n)

(n)

(n)

1.0 x 1.0 = 1.0 = 100%

Mendel’s Laws 1. Mendel’s Law of Segregation (cont.)

Y y

Y

y

Y yY

y

Grows to Plant GameteFormation

Yellow Pea (2n)Gametes (n)

x 2

x 2

Grows to Plant GameteFormation

Green Pea (2n)

50% = 0.5

Gametes (n)

x 2

x 2

y

y

Fertilization y y

F2 Generation

ZygoteHomozygous Green

(2n)

(n)

(n)

F1 (1st Filial) Generation

50% = 0.5

50% = 0.5

50% = 0.5

0.5 x 0.5 = 0.25 = 25%

Monohybrid Punnett Square:

Genotype Probabilities

Y Y = 1 / 4 = 25%(homozygous dominant)

Y y = 2 / 4 = 50%(heterozygous)

y y = 1 / 4 = 25%(homozygous recessive)

Phenotype Probabilities

Yellow = 3 / 4 = 75%

Green = 1 / 4 = 25%

Y Y Y y

Y y y y

Y y Female

Y

y

Male Child

Y y

Law of Segregation!!!

Y y

Law ofSegregation!!!

Mendel’s Laws

“one trait”

Mendel’s Laws 2. Mendel’s Law of Independent Assortment

Alleles are randomly distributed during gamete formationExample

2 Traits: Color & Shape

Different Alleles for Color:

Yellow & Green

Different Alleles for Shape:

Round & Wrinkled

Yellow = Y (dom.)Green = y (rec.)

Round = R (dom.)Wrinkled = r (rec.)

Same Trait (Color)

Same Trait (Shape)

Mom’s Body Cell (2n): YyRr

YyRrHeterozygous

YellowHeterozygous

Round

YyRr

Gamete Formation (FOIL): Y y R r

YR yRYr yr

Each gamete should ALWAYShave one allele for EACH trait!

Mendel’s Laws Dihybrid Punnett Square

“two traits”

YyRr

YR yRYr yr

Mom’s Genotype

yyRR

yR

Dad’s Genotype

yR yR yR

YR Yr yR yr Mom

yR

yR

yR

yR

Dad

YyRR YyRr yyRR yyRr

Law of Independent Assortment!!! Genotype Probabilities

YyRR = 1 / 4 = 25%(heterozygous color, homozygous dominant

shape)

YyRr = 1 / 4 = 25%(heterozygous color, heterozygous shape)

yyRR = 1 / 4 = 25%(homozygous recessive color, homozygous

dominant shape)

yyRr = 1 / 4 = 25%(homozygous recessive color, heterozygous

shape)

Phenotype Probabilities

Yellow & Round = 2 / 4 = 50%

Green & Round = 2 / 4 = 50%

Yellow & Wrinkled = 0 / 4 = 0%

Green & Wrinkled = 0 / 4 = 0%

Reading/Work Time Section 10.1

Cornell Notes Section Assessment: #1-6

Chapter 10 Assessment 2, 3, 7, 8, 11, 12, 14, 16, 17, 20-24