• Mendel’s Laws

• Beyond Mendel’s Laws

• Sex-Linked Inheritance

• Inheritance of Linked Genes

Genetics – Part I Spring 2013 - Althoff Reference: Mader & Windelspecht Ch. 11)

Lec15

• _______— the unit of heredity…passed on to offspring. 1) Each gene has a specific location on a

chromosome. 2) Each gene contains the code for specific traits to be

expressed3) Genes come in “pairs”…each pair is known as an

allele

• _______— an allele is alternative form of a gene at a particular location

• ______________— contains genes…rod-like structures in the nucleus observed

during cell division

3 Basic Terms…for starters

ALLELES of a

GENE ata genelocus

SISTER CHROMATIDS

CHROMOSOMES

DU

PLIC

ATE

D C

HR

OM

OSO

MES

SIST

ER C

HR

OM

ATI

DS

HA

VEID

ENTI

CA

L A

LLES

The Pea Picker… _____________

• Stem length• Pod shape• Seed shape• Seed Color• Flower position• Flower color• Pod color

• Tall• Inflated• Round• Yellow• Axial• Purple• Green

Pea Traits Dominant

An Austrian monk who developed the ___________________________

• Short• Constricted• Wrinkled• Green• Terminal• White• Yellow

Recessive

Mendel in his garden…..

• Stem length• Pod shape• Seed shape• Seed Color• Flower position• Flower color• Pod color

Pea Traits Dominant Recessive

_____ Mendel

• Most animal and plant breeders agreed that both sexes contributed equally to a new individual

• Same folks had not been able to account for the presence of definite ___________ (i.e., differences) among members of a family…generation after generation.

• Mendel’s MODEL OF HEREDITY does account for such ___________

Model of Heredity….consider this!• This model is compatible with the THEORY OF

EVOLUTION which states that various combinations of traits are __________ by the environment, and those combinations that lead to _________________ are the ones passed on.

or….”all living things have a __________ ancestor, but each is adapted to a particular way of life”.

• For the record, the ________________ was formulated by Charles Darwin in the 1830s but not published until 1844 and 1859, so his perspectives did not influence Mendel (remember: no internet, little publishing, long-turn around time on exchange of information).

Some key terms….• __________ – some expressed “quality” or

“structure”

• __________ trait – exerts “quality/structure” in heterozygous allele pairing

• __________ trait – exerts “quality/structure” only in homozygous allele pairing

Some more key terms….• __ generation: original parents• __ generation: first generation offspring• __ generation: second generation offspring

• _______: haploid sex cell (____________)• ________ –exact combination of alleles• ________—exact ___________ (i.e,

physical appearance)

One-trait Inheritance…and the Punnett Square

F1 gametes

ALLELES: T = tall plant t = short plant

♂♀ T t

Eggs

T

t

Spe

rm

Results from this Punnett Square

F2 ____________________

3 Tall (T) : 1 Short (t)

Translation: with this combination of alleles, There is a ____ chance of the F2 generation individual being tall and ____ chance it will be short.

The One-Trait Testcross lead to:______________________

• Each individual has __________ (alleles) for each _______

• The factors (alleles) segregate during the formation of gametes

• Each gamete contains only one factor (allele) from each pair of factors (alleles)

• ______________ gives each new individual two factors (alleles) for each trait

Mendel’s _______ law of inheritance

Genotype vs. Phenotypeusing the One-trait Inheritance

for pea plant height

Genotype(alleles)

Genotype description Phenotype

TT Homozygous dominant Tall

Tt Heterozygous Tall

tt Homozygous recessive short

Another One-Trait TestcrossF1

gametes

ALLELES: R = round seed r= wrinkled seed

♂♀ Eggs

Spe

rm

R r

R

r

TTRR

A Two-Trait TestcrossF1

gametes

ALLELES: R = round seed r= wrinkled seed

♂♀

ALLELES: T = tall plant t = short plant

PhenotypicRatio

Tall, round (TTRR, TTRr, TtRr)Tall wrinkled (TTrr, Ttrr)Short, round (ttRR, tt,Rr)Short, wrinkled (ttrr)

Spe

rm

Eggs

TR Tr tR tr

TR

Tr

tR

tr

TTRr TtRR TtRr

TTRr TTrr TtRr Ttrr

TtRR TtRr ttRR ttRr

TtRr Ttrr ttRr ttrr

The Two-Trait Testcross lead to:_________________________

__________________

• Each pair of factors (traits) ________________ independently of the other pairs

• All possible combinations can occur in the gametes

Mendel’s ____________ law of inheritance

A few things to consider…

Remember PHENOTYPE refers to _____________ “trait”…not the ______________ unless…..

A recessive trait is expressed—because a recessive trait will only appear (i.e., be expressed) if ______ ________ are recessive.ex.

AA and Aa genotypes result in same PHENOTYPE…as long as one dominant (A) allele is present

aa –then recessive trait expressed and therefore wealso know the genotype.

vs

Examples: Dominant – Recessive

• Earlobes

• Widow’s Peak

• Straight/Bent Thumb

• Cheek dimplesPRESENT ABSENT

EEor Ee

ee

WWor

Ww

SSorSs

ss

DD or Dd dd

Beyond Mendel’s Laws• Incomplete Dominance

“intermediate” phenotype possible”

Beyond Mendel’s Laws

• ____________________ “more than 2 alleles involved”

• ABO Blood Types: 3 alleles __________

Mader, p197, Fig. 11.16

Beyond Mendel’s Laws

• __________________ “trait governed by two or more sets of alleles”

• In this example, trait is controlled by 3 genes (i.e., Aa, Ba, Cc). Only those combinations represented by capital letters contribute to the ________________

______________ & Phenotype• Ex. Temperature impact on phenotype for the

Himalayan rabbit….homozygous for allele ch, which is involved in ____________ production. Encoded (gene) enzyme is active only at low temperatures….when activated it results in _______ hair (and, yes…hare!) being produced

What are the advantages to the individual for such a trait?

Snowshoe hare

winter summer-fall