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Principles of Heredity. What patterns of inheritance can be observed when traits are passed to the next generation?. Parental: Round seed x Wrinkled seed. F1: All round seed coats. F2: 5474 round: 1850 wrinkled (3/4 round to 1/4 wrinkled).

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principles of heredity
Principles of Heredity

What patterns of inheritance

can be observed when traits

are passed to the next generation?

mendel s experiment with peas differing in a single trait

Parental: Round seed x Wrinkled seed

F1: All round seed coats

F2: 5474 round: 1850 wrinkled (3/4 round to 1/4 wrinkled)

Mendel’s Experiment With Peas Differing in a Single Trait

F1 round plants x F1 round plants

mendel s proposal
Mendel’s Proposal
  • Each trait is governed by two factors – now called genes.
  • 2. Genes are found in alternative forms called alleles.
  • 3. Some alleles are dominant and mask alleles that are recessive.
mendel s experiment with peas differing in a single trait4

Parental: Round seed x Wrinkled seed

F1: All round seed coats

F1 round plants x F1 round plants

Rr

Rr

Heterozygous

Heterozygous

Mendel’s Experiment With Peas Differing in a Single Trait

RR

rr

HomozygousDominant

HomozygousRecessive

Rr

Heterozygous

F2

slide5

R

R

R

R

Homozygous parents can only pass one form of an allele to their offspring.

slide6

Heterozygous parents can pass either of two forms of an allele to their offspring.

R

r

R

r

Locus: Area on the chromosome where a gene is located.

For a heterozygote, homologous chromosomes will have different alleles at the same locus.

mendel s principle of genetic segregation
Mendel’s Principle of Genetic Segregation

In the formation of gametes, the members of a pair of alleles separate (or segregate) cleanly from each other so that only one member is included in each gamete.

Each gamete has an equal probability of containing either member of the allele pair.

genetic segregation

R R r r

R r R r

R

r

Genetic Segregation

Parentals:

RR x rr

F1 x F1:

Rr x Rr

r r

R r

RR

Rr

R

R

Rr

Rr

Rr

Rr

rr

Rr

100% Round seeds

75% Round seeds25% Wrinkled seeds

mendel s experiment with peas differing in two traits

Parental: Round Yellow x Wrinkled Green

F1: All round yellow seed coats

F1 plants x F1 plants

315 round, yellow

9/16

108 round, green

3/16

F2

101 wrinkled, yellow

3/16

32 wrinkled, green

1/16

Mendel’s Experiment With Peas Differing in Two Traits
mendel s principle of independent assortment
Mendel’s Principle of Independent Assortment

When gametes are formed, the alleles of one gene segregate independently of the alleles of another gene producing equal proportions of all possible gamete types.

genetic segregation independent assortment

RY RYRYRY

ry ryryry

ry

RY

Genetic Segregation + Independent Assortment

Parentals: RRYY x r r y y

F1:

RrYy

100% round, yellow

genetic segregation independent assortment13

RY RyrY ry

RY RyrYry

Genetic Segregation + Independent Assortment

F1 x F1 : R r Y y x R r Y y

Four different types of gametes are formed in equal proportions.

f1 x f1 rryy x rryy

Eggs

F1 x F1 RrYy X RrYy

14

14

14

14

RY

Ry

rY

ry

RY

14

116

116

116

116

RRYY

RRYy

RrYY

RrYy

Ry

14

116

116

116

116

RRYy

RRyy

RrYy

Rryy

Pollen

rY

14

116

116

116

116

RrYY

RrYy

rrYy

rrYY

ry

14

116

116

116

116

RrYy

Rryy

rrYy

rryy

gene products
Gene Products
  • A gene is a segment of DNA that directs the synthesis of a specific protein.
  • Alleles of the same gene direct the synthesis of different forms of the same protein.
solving genetics problems
Solving Genetics Problems
  • Convert parental phenotypes to genotypes
  • Use Punnett Square to determine genotypes of offspring
  • Convert offspring genotypes to phenotypes
lethal alleles

2/3 tailless + 1/3 tails

Lethal Alleles

Example: Manx cat

ML = tailless, lethal in homozygote

M = tail

Tailless male x Tailless female

ML M

MLM x MLM

X

MLML

MLM

ML

M

dies

tailless

MM

MLM

tailless

tail

multiple alleles
Multiple Alleles
  • Multiple Alleles: three or more alleles exist for one trait

(Note: A diploid individual can only carry two alleles at once.)

codominance
Codominance
  • Codominance: Neither allele masks the other so that effects of both alleles are observed in heterozygote without blending

IA =IB > i

IA and IB are codominant.

IA and IB are completely dominant over i.

codominance22

Type A

Type B

Type O

Type AB

Codominance

Effects of both alleles observed in phenotype

inheritance of rh factor another gene with multiple alleles
Inheritance of Rh Factor(another gene with multiple alleles)

*Although there are multiple R alleles, R1, R2, R3, etc. all are

completely dominant over all of the r alleles, r1, r2, r3, etc.

ABO Blood Type and Rh Factor are controlled by separate genes. They are inherited independently.

example of multiple alleles and codominance

ir

ir

IBr

ir

IAIBrr = 1/8

Momiirr

Dad

iirr

Example of Multiple Alleles and Codominance

Type A, Rh positive x Type B, Rh negative

(mother is Type O, Rh-)

(father is Type O, Rh-)

IAiRr

x IBirr

IAR IAriRir

IAIBrr

IBiRr

IBirr

IAIBRr

IAirr

iiRr

iirr

IAiRr

Child with Type AB, Rh negative blood

incomplete dominance

Red x White RR R’R’

Four o’clock flowers

R = red, R’ = white

Pink RR’

Incomplete Dominance

Neither allele masks the other and both are observed as a blending in the heterozygote

incomplete dominance26
Incomplete Dominance

½ R ½ R’

F1 x F1Pink x Pink

RR’ x RR’

¼ RR

¼ RR’

½ R

½ R’

¼ RR’

¼ R’R’

Genotypic Ratio: ¼ RR + ½ RR’ + ¼ R’R’

Phenotypic Ratio: ¼ red + ½ pink + ¼ white

epistasis

Type A

A

A

A

A

A

A

A

A

A

A

A

A

IA__H__

Type O

H

H

H

H

H

H

H

H

H

H

H

H

ii__ __ or IA__hh or IB__hh

Epistasis
  • An allele of one gene masks the expression of alleles of another gene and expresses its own phenotype instead.
  • Example of Epistasis H = enzyme that attaches antigen H

to protein on red blood cells

h= no enzyme to attach antigen H

  • Antigens A and B of ABO blood typing

(from alleles IA and IB) are attached to antigen H. Someone with the genotype hh will have Type O blood irrespectiveof their genotype for the I allele

example of epistasis

IBH

IBh

ih

iH

IAH

IAh

iH

ih

Example of Epistasis

IAiHh x IBiHh

IAIBHH

IAiHH

IAIBHh

IAiHh

Type A = 3/16

Type B = 3/16

Type AB = 3/16

*Type O = 7/16

IAIBhh*

IAihh*

IAIBHh

IAiHh

iiHh*

IBiHH

IBiHh

iiHH*

IBihh*

iiHh*

IBiHh

iihh*

pleiotropic effects
Pleiotropic Effects

One gene affects many phenotypic characteristics

polygenic inheritance many genes affect one trait
Polygenic Inheritance: Many genes affect one trait

Example: Skin color

*Based on a study conducted in Jamaica.

example of polygenic inheritance

ab

Grandma aabb

Example of Polygenic Inheritance

Medium Black Woman X Darkest Black Man

(her mother is white)

AABB

AaBb

AB AbaBab

AABb

AaBB

AaBb

AB

AABB

Dark

Black

Dark

Black

DarkestBlack

Medium

Black

¼ Darkest Black; ½ Dark Black; ¼ Medium Black