Download File - Ms. Richards IB Biology HL

10.3 GENE POOLS AND SPECIATION
HL Evolution
UNDERSTANDINGS
Nature of science: Looking for patterns, trends and discrepancies—patterns of
chromosome number in some genera can be explained by speciation due to
polyploidy. (3.1)
•A gene pool consists of all the genes and their different alleles, present in an
interbreeding population.
•Evolution requires that allele frequencies change with time in populations.
•Reproductive isolation of populations can be temporal, behavioral or geographic.
•Speciation due to divergence of isolated populations can be gradual.
•Speciation can occur abruptly. (IB guidance: punctuated equilibrium implies long
periods without appreciable change and short periods of rapid evolution).
APPLICATIONS AND SKILLS
•Application: Understand examples of directional, stabilizing, and
disruptive selection.
•Application: Explain speciation in the genus Allium by polyploidy.
•Skill: Comparison of allele frequencies of geographically isolated
populations.
RETRO-BIO
1. Describe the changes in beaks of finches on Daphne Major in the
Galapagos Islands.
2. Comparison of the pentadactyl limb of mammals, birds, amphibians and
reptiles with different methods of locomotion.
GALAPAGOS ISLANDS: 1000 KM OFF THE COAST OF
ECUADOR IN THE PACIFIC OCEAN. PROVINCE OF
ECUADOR.
CHARLES DARWIN VISITED THESE ISLANDS IN 1835
AND COLLECTED SPECIMENS OF SMALL BIRDS.
These birds turned out to be finches. 14 species in all.
Sizes and shapes of beaks varied as did their diet.
From the overall similarities between the birds and their distribution over the islands, he
hypothesized that they originally were one species that had been modified over time for
different ends.
Investigators, Peter and Rosemary Grant have shown that beak characters and diet are closely
related and when one changes, the other does also. (Have spent 6 months each year since 1973
capturing, tagging, taking blood samples)
Their focus has been a population of the medium ground finch, Geospiza fortis.
Almost but not quite absent at this time was the small ground finch, G. fuliginosa.
Both species feed on small seeds though G. fortis can also eat larger seeds.
SPECIES OF FINCH. 3 SEEN ON DAPHNE MAJOR
AFTER 1982.
RETRO 1: DESCRIBE THE CHANGES IN BEAKS OF FINCHES ON DAPHNE MAJOR
IN THE GALAPAGOS ISLANDS. IN 1973 2 SPECIES PRESENT: G. FORTIS AND
G. FULIGINOSA . IN 1982 A 3 RD SPECIES COLONIZED: G. MAGNIROSTRIS
IN 1977, A DROUGHT ON DAPHNE MAJOR CAUSED A SHORTAGE OF SMALL
SEEDS, SO G. FORTIS FED INSTEAD ON LARGER, HARDER SEEDS, WHICH THE
LARGER-BEAKED INDIVIDUALS WERE ABLE TO CRACK OPEN.
Most of the population of G. fortis died that year, with the highest mortality among
individuals with shorter beaks.
In 1982-3 there was a severe El Nino event, causing 8 months of heavy rain and as a
result an increased supply of small, soft seeds and fewer large, hard seeds.
G. fortis bred rapidly in response to the increase in food availability.
With a return to dry weather conditions and greatly reduced supplies of small seeds,
breeding stopped until 1987. Only 37% of 1983 population survived, but not a
random sampling: 1987 G. fortis had longer and narrower beaks correlating with
the reduction in supply of small seeds.
Let’s look at the data.
BEAKS OF FINCHES ON DAPHNE MAJOR: BEAK
SIZE IS DUE IN LARGE PART BY GENETIC FACTORS.
1982-1983 SEVERE EL NINO EVENT WITH LOTS
OF RAINFALL. FOLLOWED BY DRY CONDITIONS.
1987 birds had longer and narrower
beaks than the 1983 birds, correlating
with the reduction in supply of small
seeds.
In the case of Geospiza fortis significant
changes have occurred that are clearly
linked to natural selection.
RETRO 2: COMPARISON OF THE PENTADACTYL LIMB OF MAMMALS, BIRDS,
AMPHIBIANS AND REPTILES WITH DIFFERENT METHODS OF LOCOMOTION.
PENTADACTYL LIMB IN MAMMALS
Homologous structures in all
vertebrates.
Structures that superficially different
and perform a different function, but
which have had the same origin, from
an ancestor that had a pentadactyl
or five-digit limb, and that they have
become different because they
perform different functions. This is
called adaptive radiation.
THE PENTADACTYL LIMB CONSISTS OF THESE
STRUCTURES:
Bone structure
Forelimb
Hindlimb
Single bone in the proximal part
humerus
Femur
Two bones in the distal part
Radius and ulna
Tibia and fibula
Group of wrist/ankle bones
carpals
Tarsals
Series of bones in each of 5
digits
Metacarpals and phalanges
Metatarsals and phalanges
COMPARISON
Crocodiles (reptiles) walk or crawl on land and use their webbed hind limbs
for swimming
Penguins (birds) use their hind limbs for walking and their forelimbs as flippers
for swimming.
Echidnas (mammals) use all 4 limbs for walking and also use their forelimbs for
digging.
Frogs (amphibians) use all 4 limbs for walking and their hindlimbs for jumping.
Differences can be seen in the relative length and thicknesses of the bones.
Some metacarpals and phalanges have been lost during the evolution of the
penguin’s forelimb.
Same bones, in the same relative positions.
GENE POOLS: CONSIST OF ALL THE GENES AND THEIR
DIFFERENT ALLELES, PRESENT IN AN INTERBREEDING
POPULATION
Species: a group of potentially interbreeding populations, with a common
gene pool that is reproductively isolated from other species.
Some populations of the same species are geographically isolated so it is
possible for multiple gene pools to exist for the same species. Individuals that
reproduce contribute to the gene pool of the next generation.
Evolution is defined as the cumulative change in the heritable characteristics
of a population over time. That means that gene (or more specifically) allele
frequencies change with time in populations.
HARDY WEINBERG THEOREM: WHY THE WORLD
IS NOT SLOWLY BECOMING POLYDACTYLOUS
The frequencies of alleles
and genotypes in a
population’s gene pool
remain constant from
generation to generation,
provided that only
Mendelian segregation and
recombination of alleles are
at work.
HARDY WEINBERG MODEL
p = frequency of A
q = frequency of a
p + q = 1 so p = 1- q
If the frequency of A is p in a population that is large, randomly
mating, with no mutation, migration, or natural selection then the
chances of bumping into another A in the gene pool are A x A or
AA = p2 and Aa = 2pq and aa = q2
WE CAN USE THIS THEOREM TO MAKE
PREDICTIONS
If q2 = 0.0001, then q = .01, p = 0.99
2pq = 2(.01x.99) = 0.02 and
Let’s use the Hardy Weinberg theory to
calculate the frequency of heterozygotes
for blue eyes.
p2 = 0.99 x 0.99 = 0.98
Frequency of the tongue rolling and nonrolling gene?
If carrier detection were important than
when a test is devised, it should identify
approximately 2% of the subjects as
carriers.
What other relatively neutral trait can
we use?
MECHANISMS OF EVOLUTION OF ALLELE FREQUENCY
CHANGE: MUTATION AND MIGRATION
Mutation: creates genetic variation but
does not change gene frequencies very
fast
Mutations of a particular gene occur on
the order of 1 x 10-4 or -5
Hb C in Central Africa; lactose tolerance
in dairy herders of Northern Europe
about 7,000 years ago.
Coupled with natural selection, can
rapidly move through a population
Migration: (also called gene flow) can
cause an influx of a new gene that might
spread throughout the population
because it is novel or gives a selective
advantage. Ex. We can follow the
change in the frequency of the B blood
type from the Steppes of Asia into
Central Europe as a result of the invasion
of the Mongols under Genghis Khan.
EXAMPLE OF THE EFFECTS OF MIGRATION:
GROUP B ALLELE IN EUROPE
EFFECTS OF SMALL POPULATION SIZE, ALSO CALLED
RANDOM GENETIC DRIFT, FOUNDERS EFFECTS, OR
POPULATION BOTTLENECKS
 Random Genetic Drift: due to random
accumulation of genetic change because of
small population size, inbreeding, genetic
bottlenecks, or Founder’s Effect.
 All of these are really a function of small
population size and reduce genetic
variability in a population.
 Bottlenecks: Great cats being reduced to a
very small number; Founder’s Effect: Dunker
population in Pennsylvania with high
frequency of dwarfish; South African
Afrikaners: Porphyria. French Canadian:
hereditary tyrosinemia
DIAGRAMS ILLUSTRATING THE EFFECTS OF SMALL
POPULATION SIZE: BOTTLENECKS AND DRIFT
MECHANISMS OF EVOLUTION: NATURAL SELECTION.
CAN CHANGE GENE FREQUENCIES RAPIDLY
Differential reproduction +/or survival
of genotypes (i.e. natural selection as
opposed to artificial selection practiced
by plant breeders)
Some genotypes cause individuals to die
prior to reproduction or not produce
viable offspring (Muscular dystrophy,
Tay Sachs)
Other genotypes might cause an
individual to withstand an infection
better, survive, & reproduce (Sickle cell
disorder in malarial infested areas)
3 PATTERNS OF NATURAL SELECTION BASED ON
THE FITNESS OF GENOTYPE/PHENOTYPE
Selection pressures are environmental factors
that act selectively on certain phenotypes
resulting in natural selection.
Stabilizing selection: selection pressures act to
remove extreme phenotypes. Average birth
weights of human babies are favored over low
birth weight or high birth weight.
Disruptive selection: selection pressures act to
remove intermediate varieties, favoring
extremes. Dark and light banding patterns in
snails
Directional Selection: the population changes as
one extreme of a range of variation is better
adapted. Big horn sheep horn length.
STABILIZING SELECTION AND DIRECTIONAL SELECTION TOWARD
SMALLER HORNS IN BIG HORN SHEEP DUE TO TROPHY HUNTING
(KILLING OF SHEEP WITH LARGER HORNS)
EXAMPLE OF DISRUPTIVE SELECTION
OTHER EXAMPLES GIVEN BY YOUR REVIEW GUIDE
(PAGE 127)
Directional Selection: Parus major
(Great tit), breeding success has been
greater with birds that breed early than
with those that breed later because the
peak availability of prey is earlier.
Selection pressure to breed early.
Stabilizing selection: Parus major,
breeding success is greatest with
intermediate clutch sizes (# of eggs)
because in large clutches offspring have
lower survival rates and in small clutches,
fewer offspring with no greater chance
of survival than in intermediate clutches.
Disruptive selection: bird Passerina
amoena (lazuli bunting). Year-old
males with the dullest and brightest
plumage are more successful than
males with intermediate plumage at
obtaining high-quality territories,
pairing with females and siring
offspring.
DIFFERENT POPULATIONS HAVE DIFFERENT
ALLELE FREQUENCIES: PAN I GENE IN COD FISH
Pantophysin found in membranes of small cytoplasmic
vesicles
Light grey: frequency of Pan IA
Black sectors: frequency of Pan IB
1.
State the 2 populations with the highest Pan IB allele
frequencies.
2.
Deduce the allele frequencies of a population in
which half of the cod fish had the genotype PanIA
PanIA, and half had the genotype PanIA PanIB.
3.
Suggest two populations that are geographically
isolated.
4.
Suggest 2 possible reasons why the PanIB allele is
more common in population 14 than population 21.
EXAMPLE OF POPULATIONS WITH DIFFERENT
ALLELE FREQUENCIES PAGE 127
Frequency of gene delta F508 (one of the alleles that causes cystic fibrosis) is
0.04 in the Faroe Islands but only 0.03 in northern Europe and below 0.01 in
most other parts of the world.
SPECIATION THROUGH REPRODUCTIVE ISOLATION:
GEOGRAPHIC, TEMPORAL, BEHAVIORAL
Speciation is the formation of a new species by the splitting of an existing population.
Gene pools can become isolated by various barriers and speciation can occur when
this happens.
If the isolation occurs because of geographic separation of populations, this is termed
allopatric speciation.
HOW DO THEY GET ISOLATED?
ALLOPATRIC SPECIATION
THROUGH GEOGRAPHIC
ISOLATION
Antelope squirrels on
opposite rims of the
grand canyon.
WHAT COULD HAPPEN
WHEN GENE POOLS
BECOME ISOLATED?
While allopatric: Could
have a new mutation
that changes a trait such
as smell or behavior
BEHAVIORAL ISOLATION
Eastern meadowlark and the
western meadowlark have
similar body shape and
coloration. They are distinct
species because their songs and
other behaviors are different
enough to prevent
interbreeding.
TEMPORAL ISOLATION: CAN OCCUR TO
POPULATIONS IN THE SAME AREA
3 tropical orchid species of the genus
Dendrobium each flower for a single day
Flowering occurs in response to sudden drops in
temperature in all three species.
The lapse between the stimulus and flowering is
8 days in one species, 9 days in another species
and 10-11 in the third. Isolation of the gene
pools occurs, because at the time the flowers of
one species are open, those of the other species
have already withered or have not yet matured.
Some cicada species only breed every 13th
year. If some breed with each other in a
different year from the rest of the species, they
will be isolated.
SYMPATRIC SPECIATION
Mechanisms include:
Chromosomal changes
(polyploidy in plants) and
Non-random mating that
reduces gene flow. (e.g.
mate selection based on
coloration in animals).
A POLYPLOID ORGANISM IS ONE THAT HAS MORE
THAN 2 SETS OF HOMOLOGOUS CHROMOSOMES
1. Can result from hybridization events between different species.
2. Polyploids whose chromosomes originate from the same ancestral species. This can occur when
chromosomes duplicate in preparation for meiosis but then meiosis does not occur. The result is a
diploid gamete that when fused with a haploid gamete produces a fertile offspring (3n). The 3n
offspring will not be capable of mating with the 2n or 4n individual so has become it’s own species.
As a result the polyploid has become reproductively isolated from the rest of the population. A
polyploid plant may self-fertilize or combine with other polyploids.
Estimates of the number of species of angiosperms that have experienced a polyploidy event range
from 50-70%
The Allium genus includes onions, leeks, garlic, and chives (important foods in many cultures).
Polyploidy events are common in this genus.
SPECIATION IN THE ALLIUM FAMILY (GARLIC) BY
POLYPLOIDY
MANY SPECIES OF ALLIUM REPRODUCE ASEXUALLY
AND POLYPLOIDY MAY CONFER AN ADVANTAGE OVER
DIPLOIDY.
Wild onion is a native of North America. 2n = 14. Variants exist
that have 2n = 28
Two species that occur in Lithuania. One of them has a 2n = 16.
The other has one with 2n = 32.
SO…HOW FAST DOES SPECIATION OCCUR?
Two theories about the pace of
evolutionary change:
A. Gradualism: theory that species
slowly change through a series of
intermediate forms….think evolution
of the horse or cranial capacity in
humans. Dominant framework in
paleontology. However there are gaps in
the fossil record i.e. absence of
intermediate forms.
B. PUNCTUATED EQUILIBRIUM: LONG PERIODS OF
RELATIVE STABILITY IN A SPECIES PUNCTUATED BY
PERIODS OF RAPID EVOLUTION.
Gaps in the fossil record
might not be gaps.
Rapid change is much
more common in
organisms with short
generation times like
prokaryotes and insect.
10.3.1 DEFINE GENE POOL, EVOLUTION,
SPECIATION
Gene Pool: all the genes and their different alleles, present in an interbreeding
population.
Evolution: Cumulative change in the heritable characteristics of a population over
time or the changes in the allele frequencies of a gene in a population over time.
Speciation: formation of a new species by the splitting of an existing population.
10.3.2 DEFINE THE FOLLOWING PATTERNS OF NATURAL
SELECTION: STABILIZING, DISRUPTIVE AND DIRECTIONAL (USE
GRAPHS WITH GENE FREQUENCY ON X AND FREQUENCY OF
Selection pressures are environmental factors
INDIVIDUALS ON Y AXES)
that act selectively on certain phenotypes
resulting in natural selection.
Stabilizing selection: selection pressures act
to remove extreme phenotypes. EG average
birth weights of human babies are favored
over low birth weight or high birth weight.
Disruptive selection: selection pressures act to
remove intermediate varieties, favoring
extremes. EG Dark and light banding
patterns in snails
Directional Selection: the population changes
as one extreme of a range of variation is
better adapted. EG Big horn sheep horn
length.
10.3.3 IDENTIFY EXAMPLES OF EACH OF THE
PATTERNS OF NATURAL SELECTION LISTED IN 10.3.2
DISRUPTIVE SELECTION: BIRD PASSERINA AMOENA (LAZULI BUNTING). YEAR-OLD
MALES WITH THE DULLEST AND BRIGHTEST PLUMAGE ARE MORE SUCCESSFUL THAN
MALES WITH INTERMEDIATE PLUMAGE AT OBTAINING HIGH-QUALITY TERRITORIES,
PAIRING WITH FEMALES AND SIRING OFFSPRING.
Directional Selection: Parus major (Great tit),
breeding success has been greater with birds
that breed early than with those that breed
later because of the peak availability of
prey is not earlier. Selection pressure to
breed early.
Stabilizing selection: Parus major, breeding
success is greatest with intermediate clutch
sizes (# of eggs) because in large clutches
offspring have lower survival rates and in
small clutches, fewer offspring with no
greater chance of survival than in
intermediate clutches.
10.3.4 CALCULATE ALLELE FREQUENCIES IN A
POPULATION OF RANDOMLY MATING INDIVIDUALS
If you are given q2, you can find q, p and all
of the other genotypic frequencies.
1. If, in a sampling of 1000 people, 810
had no dimples (dimples is a dominant trait),
then what is the frequency of the D allele?
What is the frequency of d?
q=0.9 p=0.1
2. If there exist a population of mice, 108
of which were BB (for long bristles), 269
were Bb (medium) and 163 were bb (short
bristles). Calculate the genotypic frequencies
and the 2 allele frequencies.
BB = 0.2, Bb 0.5, bb =0.3
B = (108 x2 +269)/1080 = 0.45
b = (163 x2 +269)/1080 = 0.55
10.3.5 COMPARE ALLOPATRIC AND SYMPATRIC
SPECIATION
Allopatric: Speciation event
that occurs with geographic
isolation of populations.
Sympatric: Speciation even
that occurs while populations
are in same geographic area
10.3.5 (I MISNUMBERED SOME OF THESE): OUTLINE VARIOUS FORMS
OF REPRODUCTIVE ISOLATION USING ONE EXAMPLE
OF EACH (TEMPORAL, BEHAVIORAL, GEOGRAPHIC).
3 tropical orchid species of the genus
Dendrobium each flower for a single day
Flowering occurs in response to sudden drops
in temperature in all three species.
The lapse between the stimulus and flowering
is 8 days in one species, 9 days in another
species and 10-11 in the third. Isolation of
the gene pools occurs, because at the time
the flowers of one species are open, those of
the other species have already withered or
have not yet matured.
Some cicada species only breed every 13th
year. If some breed with each other in a
different year from the rest of the species,
they will be isolated.
Eastern meadowlark and the western
meadowlark have similar body shape
and coloration. They are distinct species
because their songs and other behaviors
are different enough to prevent
interbreeding.
EG Antelope squirrels on opposite rims
of the grand canyon (geographic).
Species have accumulated genetic
differences as a result of geographic
isolation (barrier is the grand canyon).
10.3.6 OUTLINE 2 THEORIES ABOUT THE PACE OF
theories about the pace of
EVOLUTIONARY CHANGE. Two
evolutionary change:
A. Gradualism: theory that species
slowly change through a series of
intermediate forms….think evolution of
the horse or cranial capacity in humans.
Dominant framework in paleontology.
However there are gaps in the fossil record i.e.
absence of intermediate forms.
B. Punctuated Equilibrium: long periods of
relative stability in a species punctuated by
periods of rapid evolution
Gaps in the fossil record might not be gaps.
Rapid change is much more common in
organisms with short generation times like
prokaryotes and insect.
10.3.7 DESCRIBE HOW POLYPLOIDY CAN LEAD TO
SPECIATION WITH RESPECT TO THE GENUS ALLIUM
SYMPATRIC SPECIATION
Mechanisms include:
Chromosomal changes
(polyploidy in plants) and
Non-random mating that
reduces gene flow. (e.g.
mate selection based on
coloration).
A POLYPLOID ORGANISM IS ONE THAT HAS MORE
THAN 2 SETS OF HOMOLOGOUS CHROMOSOMES
1. Can result from hybridization events between different species.
2. Polyploids whose chromosomes originate from the same ancestral species. This can occur when
chromosomes duplicate in preparation for meiosis but then meiosis does not occur. The result is a
diploid gamete that when fused with a haploid gamete produces a fertile offspring (3n).
As a result the polyploid has become reproductively isolated from the rest of the population. A
polyploid plant may self-fertilize or combine with other polyploids.
Estimates of the number of species of angiosperms that have experienced a polyploidy event range
from 50-70%
The Allium genus includes onions, leeks, garlic and chives (important foods in many cultures).
Polyploidy events are common in this genus.
SPECIATION IN THE ALLIUM FAMILY (GARLIC) BY
POLYPLOIDY
MANY SPECIES OF ALLIUM REPRODUCE ASEXUALLY
AND POLYPLOIDY MAY CONFER AN ADVANTAGE OVER
DIPLOIDY.
Wild onion is a native of North America. 2n = 14. Variants exist
that have 2n = 28
Two species that occur in Lithuania. One of them has a 2n = 16.
The other has one with 2n = 32.
S1 INTERPRETING ALLELE FREQUENCIES: SOME
PRACTICE
1.G ALLELE: BLUE EYE A ALLELE: BROWN EYE
2.A ALLELE: DRY EARWAX G ALLELE: WET, STICKY
HUMAN GENOME DIVERSITY PROJECT ALLELE FREQUENCIES FOR
ALLELES THAT AFFECT A) HANDLING UV LIGHT AND B) SKIN
PIGMENTATION (ANCESTRAL YELLOW, DERIVED ALLELE IS DARK
BLUE)
RETRO 1: DESCRIBE THE CHANGES IN BEAKS OF FINCHES ON DAPHNE MAJ OR IN THE GALAPAGOS
SPECIES OF FINCH. 3 SEEN ON DAPHNE MAJOR AFTER 1982.
Peter and Rosemary Grant have
shown that beak characters and diet
are closely related and when one
changes, the other does also.
Their focus has been a population of
the medium ground finch, Geospiza
fortis.
This species prefers small seeds.
IN 1977, A DROUGHT ON DAPHNE MAJOR CAUSED A SHORTAGE OF SMALL
SEEDS, SO G. FORTIS FED INSTEAD ON LARGER, HARDER SEEDS, WHICH THE
LARGER-BEAKED INDIVIDUALS ARE ABLE TO CRACK OPEN.
Most of the population of G. fortis died that
year, with the highest mortality among
individuals with shorter beaks.
In 1982-3 there was a severe El Nino event,
causing 8 months of heavy rain and as a result
an increased supply of small, soft seeds and
fewer large, hard seeds.
G. fortis bred rapidly in response to the
increase in food availability.
With a return to dry weather conditions and
greatly reduced supplies of small seeds,
breeding stopped until 1987. Only 37% of
1983 population survived, but not a random
sampling: 1987 G. fortis had longer and
narrower beaks correlating with the reduction
in supply of small seeds.
1982-1983 SEVERE EL NINO EVENT WITH LOTS
OF RAINFALL. FOLLOWED BY DRY CONDITIONS
1987 birds had longer and narrower
beaks than the 1983 birds, correlating
with the reduction in supply of small
seeds.
In the case of Geospiza fortis significant
changes have occurred that are clearly
linked to natural selection.
R2 COMPARISON OF THE PENTADACTYL LIMB OF
MAMMALS, BIRDS, AMPHIBIANS AND REPTILES WITH
DIFFERENT METHODS OF LOCOMOTION
Homologous structures in all
vertebrates.
Structures that superficially different
and perform a different function, but
which have had the same origin, from
an ancestor that had a pentadactyl
or five-digit limb, and that they have
become different because they
perform different functions. This is
called adaptive radiation.
THE PENTADACTYL LIMB CONSISTS OF THESE
STRUCTURES:
Bone structure
Forelimb
Hindlimb
Single bone in the proximal part
humerus
Femur
Two bones in the distal part
Radius and ulna
Tibia and fibula
Group of wrist/ankle bones
carpals
Tarsals
Series of bones in each of 5
digits
Metacarpals and phalanges
Metatarsals and phalanges
RETRO 2: COMPARISON OF THE PENTADACTYL LIMB OF MAMMALS, BIRDS,
AMPHIBIANS AND REPTILES WITH DIFFERENT METHODS OF LOCOMOTION.
COMPARISON
Crocodiles (reptiles) walk or crawl on land and use their webbed hind limbs
for swimming
Penguins (birds) use their hind limbs for walking and their forelimbs as flippers
for swimming.
Echidnas (mammals) use all 4 limbs for walking and also use their forelimbs for
digging.
Frogs (amphibians) use all 4 limbs for walking and their hindlimbs for jumping.
Differences can be seen in the relative length and thicknesses of the bones.
Some metacarpals and phalanges have been lost during the evolution of the
penguin’s forelimb.
Same bones, in the same relative positions.