chapter 3 heredity heredity: passing of traits from parent to offspring

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Page 1: Chapter 3 Heredity Heredity: Passing of traits from parent to offspring

Chapter 3Heredity

Page 2: Chapter 3 Heredity Heredity: Passing of traits from parent to offspring

Heredity: Passing of traits from parent to offspring.

Page 3: Chapter 3 Heredity Heredity: Passing of traits from parent to offspring

Gregor Mendel “Father of Genetics”

Page 4: Chapter 3 Heredity Heredity: Passing of traits from parent to offspring

Gregor Mendel

Lived from July 20, 1822 – January 6, 1884)

Austrian monk Worked in monastery garden Used pea plants to show that the

inheritance of traits follows particular laws, which were later named after him

Page 5: Chapter 3 Heredity Heredity: Passing of traits from parent to offspring

Trait – a characteristics of an organism

Heredity – the study of how traits are passed

from parents to offspring

Page 6: Chapter 3 Heredity Heredity: Passing of traits from parent to offspring

Why Mendel used pea plants:

1. Quick reproduction and growth

2. Easily observed traits3. Many observable traits4. Easy cross pollination

Page 7: Chapter 3 Heredity Heredity: Passing of traits from parent to offspring

Self pollinating

Plants usually contain both male and female reproductive structures

Page 8: Chapter 3 Heredity Heredity: Passing of traits from parent to offspring

During self pollination• Pollen from anthers

(male) is transferred to the stigma (female)

• Fertilization occurs when a sperm from the pollen travels through the stigma and enters the egg in the ovule.

Page 9: Chapter 3 Heredity Heredity: Passing of traits from parent to offspring

True breeding plants – have offspring that always show the same form of the trait

Cross fertilization – a process in which one plant fertilizes the egg in a flower of a different plantPollen – tiny grains containing plant sperm cells

Page 10: Chapter 3 Heredity Heredity: Passing of traits from parent to offspring

P generation – parental

generation

F1 generation – offspring in first cross =hybrids

Page 11: Chapter 3 Heredity Heredity: Passing of traits from parent to offspring

• Offspring from first cross are known as first generation.

• Dominant: The trait observed when at least one dominant allele for a characteristic is inherited.

• Recessive: A trait that is apparent only when two recessive alleles for the same characteristic are inherited,

Page 12: Chapter 3 Heredity Heredity: Passing of traits from parent to offspring

Each parent donates one set of

instruction to an offspring known as

genes.

Page 13: Chapter 3 Heredity Heredity: Passing of traits from parent to offspring

ALLELES Two forms of

the same gene for

every characteristic

Page 14: Chapter 3 Heredity Heredity: Passing of traits from parent to offspring

Hybrids – the offspring of two different true breeding plants

Monohybrid cross – a cross between two plants that differ in only one trait

F2 generation – the offspring that result when 2 hybrid plants are crossed

Page 15: Chapter 3 Heredity Heredity: Passing of traits from parent to offspring

Mendel’s P (Parental) Cross

true breeder X true breedershort long

Resulted in all long offspring (F1)

Page 16: Chapter 3 Heredity Heredity: Passing of traits from parent to offspring

Mendel’s F1 (first filial) crossCross pollinated 2 of the long offspring

produced in the P generation

F1 long X F1 longResults:

75% long and 25% short

Page 17: Chapter 3 Heredity Heredity: Passing of traits from parent to offspring

Mendel’s conclusions:Gene – the factor that controls traits

Allele – the possibilities of a gene (e.g. A or a)

Simple dominance – one allele is dominant to a recessive allele

Page 18: Chapter 3 Heredity Heredity: Passing of traits from parent to offspring

Mendel VocabularyDominant – the allele that masks any other allele when there are 2 alleles present (A in

Aa) (symbolized by the first letter in the dominant trait’s name, always capital)

Recessive – the allele that is masked by another allele (a in Aa) (symbolized by the

first letter in the dominant trait’s name, always lower case)

Page 19: Chapter 3 Heredity Heredity: Passing of traits from parent to offspring

Homozygous – having two identical alleles for a trait (AA or aa) (Mendel called this “true-breeding”)

Homozygous dominant – having two dominant alleles for a trait (AA) (Mendel called this “true breeding dominant”)

Homozygous recessive – having two recessive alleles for a trait (aa) (Mendel called this “true breeding recessive”)

Heterozygous – having two different alleles for a trait (Aa)

More Mendel Vocabulary

Page 20: Chapter 3 Heredity Heredity: Passing of traits from parent to offspring

Phenotype – the visible traits of an organism (e.g.

long or short)

Genotype – the alleles that an organism carries (e.g. Aa

or AA or aa)

Page 21: Chapter 3 Heredity Heredity: Passing of traits from parent to offspring

Punnett square – a model used to represent crosses between

organisms

Example: What are the possible offspring of a cross between a homozygous dominant green plant (GG) and a homozygous recessive green plant (gg)?

Page 22: Chapter 3 Heredity Heredity: Passing of traits from parent to offspring

Steps to doing a Punnett Square:

1. identify the gametes of the parents

Example: What are the possible offspring of a cross between a homozygous dominant green plant (GG) and a homozygous recessive green plant (gg)?

GG parent will produce all G gametesgg parent will produce all g gametes

Page 23: Chapter 3 Heredity Heredity: Passing of traits from parent to offspring

Steps to doing a Punnett Square:2. draw a square with 4 boxes

Example: What are the possible offspring of a cross between a homozygous dominant green plant (GG) and a homozygous recessive green plant (gg)?

GG parent will produce all G gametesgg parent will produce all g gametes

Page 24: Chapter 3 Heredity Heredity: Passing of traits from parent to offspring

Steps to doing a Punnett Square:3. put the gametes from one parent on the top of

the box and the gametes from the other parent on the side of the box

GG parent all G gametesgg parent all g gametes

G G

g

g

Page 25: Chapter 3 Heredity Heredity: Passing of traits from parent to offspring

Steps to doing a Punnett Square:4. cross multiply to find the genotypes of the children

G G

g

g

G g

Page 26: Chapter 3 Heredity Heredity: Passing of traits from parent to offspring

Steps to doing a Punnett Square:4. cross multiply to find the genotypes of the children

Gg Gg

Gg Gg

G G

g

g

Page 27: Chapter 3 Heredity Heredity: Passing of traits from parent to offspring

Steps to doing a Punnett Square:5. write the phenotypes of each child in the boxes

Gg Gg

Gg Gg

G G

g

g

Green Green

Green Green

Page 28: Chapter 3 Heredity Heredity: Passing of traits from parent to offspring

Steps to doing a Punnett Square:6. calculate genotypic and phenotypic ratios of the offspring

GgGreen

GgGreen

GgGreen

GgGreen

G G

g

g

List all possible Genotypes:GGGggg

List all possible Phenotypes:greenyellow

Page 29: Chapter 3 Heredity Heredity: Passing of traits from parent to offspring

Steps to doing a Punnett Square:6. calculate genotypic and phenotypic ratios of the offspring

GgGreen

GgGreen

GgGreen

GgGreen

G G

g

g

Count how many of each: Genotypes:

GG Gggg

Phenotypes:greenyellow

= 0/4 = 0%= 4/4 = 100%= 0/4 = 0%

= 4/4 = 100%= 0/4 = 0%

Page 30: Chapter 3 Heredity Heredity: Passing of traits from parent to offspring

Now try this one…

What are the possible offspring of a cross between a pea plant which is heterozygous for green peas and a pea plant which is homozygous recessive for green peas?

Page 31: Chapter 3 Heredity Heredity: Passing of traits from parent to offspring

Another example…

• What are the possible offspring of a cross between a mother and father who are both heterozygous for the ability to roll their tongues?

Page 32: Chapter 3 Heredity Heredity: Passing of traits from parent to offspring

Incomplete Dominance

• Sometimes, there are two dominant alleles and no recessive alleles.

• Ex: flower color

Page 33: Chapter 3 Heredity Heredity: Passing of traits from parent to offspring

In some flowers, red and white are both dominant.

A red flower has the phenotype ______ and the genotype RR.

A white flower has the phenotype ______ and the genotype WW.

RED

WHITE

Page 34: Chapter 3 Heredity Heredity: Passing of traits from parent to offspring

What if you cross a RED (RR) flower with a WHITE (WW)

flower?

R

R

W

W

RW RW

RW RW

Page 35: Chapter 3 Heredity Heredity: Passing of traits from parent to offspring

What color are the offspring?

R R

W

W

RW RW

RW RW RED

WHITE+

PINK

Page 36: Chapter 3 Heredity Heredity: Passing of traits from parent to offspring

What is the phenotype of this flower?

What is the genotype of this flower?

PINK

RW

Page 37: Chapter 3 Heredity Heredity: Passing of traits from parent to offspring

So, when a trait is inherited by incomplete dominance, there are ____ possible phenotypes

and ____ possible genotypes.

3

3

Red WhitePink

RRWWRW

Page 38: Chapter 3 Heredity Heredity: Passing of traits from parent to offspring

Multiple Alleles

In some cases, there are more than 2 possibilities.

Ex: hair color, eye color, skin color

Page 39: Chapter 3 Heredity Heredity: Passing of traits from parent to offspring

Blood Type

• 2 Dominant alleles – A and B• 1 recessive allele – O

Genotype Phenotype

AA AAO AAB ABBB BBO BOO O

Page 40: Chapter 3 Heredity Heredity: Passing of traits from parent to offspring

What if you cross a AO parent with a BO parent?

A O

B

O

AB BO

AO OO