Chapter 9 - Evolution Produces Changes Across Generations

Question 1

Define the term Evolved

Answer 1

Having gone through the process of evolution

Question 2

Define evolution

Answer 2

the gradual change in the characteristics of a species

• change that occurs over a number of generations, rather than a particular individual or generation
• reflects the changes in allele frequency in populations

Question 3

Define Allele

Phenotype

Genotype

Answer 3

Allele: an alternate form of a gene

Phenotype: the observable set of characteristics in an individual due to genotype

Genotype: the combination of alleles for a gene

Question 4

Why may evolution occur?

Answer 4

1. Changes to the alleles present in a population may be due to new alleles forming as a result of mutations or being introduced to a population through migration.
2. The frequency of these alleles may alter because of selective pressure in the natural selection or by chance in genetic drift.

Question 5

Define Population

Answer 5

A group of organisms of the same species living together in a particular place at a particular time.

Question 6

Who are geneticists?

Answer 6

Scientists who specialize in the study of inheritance

Question 7

What is a Gene Pool?

Why is it significant?

Answer 7

Gene pool is the sum of all the alleles in a given population

GENETICISTS Prefer to consider the characteristics of the population as a whole and those of the individuals that make up the population.

They find it convenient to pool the genotypes of all the individuals capable of reproducing as refers to this as a GENE POOL.

Question 8

What are allele frequencies?

Why are they significant?

EXAMPLE

Answer 8

Allele frequency: how often each allele of a gene occur in a population

When studying a population, geneticists are interested in how often each allele of a gene occurs in the gene pool for that population. CALLED ALLELE FREQUENCIES

EXAMPLE:
CF on chromosome 7
if the frequency of CF allele in a given population is 5%, t
- then among population members, 5 in every 100 of chromosome 7 will carry that allele.
- 95/100 chromosome 7s will have the normal form on the gene

Question 9

Explain populations, gene pools, allele frequencies

Example

Answer 9

Populations that differ in the characteristics they possess are likely to have different frequencies of the various alleles of a gene in their irrespective gene pools.

Thus two populations having different characteristics are likely to have different gene pools.

Example: Scandinavians commonly have blue eyes, whereas black Africans have brown eyes.

• THE FREQUENCY OF THE ALLELE FOR BLUE EYES WOULD BE MUCH HIGHER IN THE SCANDIAVAIN GENE POOL THAN IN THE AFRICAN GENE POOL

Question 10

What is a mutation

Answer 10

Sudden and permanent change to an allele

• variations that do not resemble either parent and have never occurred before in the history of the family.
• DNA IS CHANGED

NOT DUE TO ALLELE BEING PASSED DOWN FROM PARENTS, BUT FROM A NEW ALLELE BEING FORMED.

Question 11

What is a mutant?

Answer 11

An organism with a characteristic resulting from a mutation.

Question 12

What are the two main types of mutations?

Define them

Answer 12

1. Gene mutations: changes in a single gene so that the traits normally produced by the gene are changed or destroyed.
   - ALTERATION TO A SINGLE GENE
2. Chromosomal mutations: all or part of the chromosome is affected
   - A CHANGE TO THE STRUCTURE AND/OR NUMBER OF CHROMOSOMES IN AN ORGANISM

Question 13

If there is a mutation what may occur?
What happens if it remains?
How many in humans?
What happens to the gamete daughter cell?

Answer 13

Humans experience relatively few mutations, considering millions of cell divisions.
- occurs sometimes to produce traits that better suit a particular environment and hence contribute to survival
(hence not all bad)

THE CHANGE MAY HAVE SIGNIFICANT EFFECTS ON THE FUNCTIONING OF THE CELL WHEN mistake may occur spontaneously when
- the DNA molecule is copied DURING MITOSIS OR MEIOSIS
- Chromosomes are separated DURING MEIOSIS
- a change in bases in the DNA could change the amino acid, hence alter the protein
- possible for a mutation to have not impact at all, or it may alter the protein or prevent it from being produced.
- THUS, IF THE DNA OF A PARTICULAR GENE IS ALTERED, THE PROTEIN FOR WHICH IT CODES MAY BE MISSING OR ABNORMAL.
JUST ONE MISSING OR ABNORMAL PROTEIN CAN HAVE AN ENORMOUS EFFECT ON THE ENTIRE BODY.

Many mutations are REPAIRED, and therefore and Don’t cause a problem
- regular and neutral mutations, easily repaired via enzymes

If they DO REMAIN when the cell divides the mutated DNA will be copied and passed onto daughter cells.

IF DAUGHTER CELLS ARE GAMETES:
the mutation may be passed on from one generation to the next.

Question 14

What causes mutations?

WHAT ARE MUTAGENIC AGENTS?

EXAMPLES?

Answer 14

Mutations occur WITHOUT ANY KNOWN CAUSE

A number of AGENTS are known to INCREASE the RATE at which they OCCUR. = MUTAGENIC AGENTS

MUTAGENIC AGENTS/ MUTAGEN = an environment agent that increases the rate of mutation

EXAMPLES = mustard gas, formaldehyde, sulfur dioxide, some antibiotics, ionising radiation: UV, X-rays, cosmic rays, radiation radioactive waste, the fallout from atomic and nuclear explosions.

Question 15

What is albinism?

SYMPTOMS

Answer 15

An inherited inability to produce pigment in hair, skin and eyes.

• RESULT OF ONE MISSING PROTEIN
• MARKED BY THE ABSENCE OF PIGMENT FROM HAIR, SKIN, AND EYES.

the hair of a person with albinism tends to be whitish blond, the skin extremely pale and the eyes pinkish.

called autosomal recessive inheritance

Question 16

How to determine the overall impact of the mutation?

Answer 16

Mutations can be classified by a number of different characteristics.

it is the sum of these characteristics that determines the overall impact the mutation will have on the individual.

Question 17

What are induced mutations?

What are spontaneous mutations?

Answer 17

Induced mutation: A mutation caused by a mutagenic agent

Spontaneous mutation: a mutation that occurs due to an error in a natural biological process

Question 18

What is a somatic mutation?

Answer 18

SOMATIC MUTATION: when the body cell/ somatic cells are involved with a mutation
- only the individual with the somatic mutation is affected

• each time the mutant body cell divides, the mutation is passed on to the daughter cells
• HOWEVER, as the REPRODUCTIVE CELLS are NOT AFFECTED, once the INDIVIDUAL DIES the Mutation is LOST.
• INVOLVED in many CANCEROUS GROWTHS that may be a RESULT OF A MUTAGENIC AGENT

Question 19

What is a GERMINAL or GERMLINE MUTATION?

example.

Answer 19

if the REPRODUCTIVE CELLS are affected, the mutation can occur in the GAMETES and may then be PASSED onto to the NEXT, and SUBSEQUENT, GENERATIONS.

• the INDIVIDUAL in whom the MUTATION occurs is NOT USUALLY AFFECTED.
• HOWEVER, that individual PRODUCES GAMETES with CHANGED DNA.
• if CONCEPTION OCCURS involving one of the AFFECTED GENES, the EMBRYO IS OFTEN NATURALLY ABORTED EARLY IN PREGNANCY.
• Diseases such as PHENYLKETONURIA (PKU) can arise through a mutation during the formation of gametes and can be passed onto offspring/.

Question 20

What is PKU?

Phenylketonuria

Answer 20

autosomal recessive pattern

A birth defect which causes an amino acid called phenylalanine to build up in the body.

a rare disorder that prevents the body from properly breaking down a substance called phenylalanine (Phe)

Diagnosis: prick of a needle in heel to get blood, tested first week of birth

Treatment: a low-protein diet that completely avoids high-protein foods (such as meat, eggs, and dairy products) and controls the intake of many other foods, such as potatoes and cereals.

Question 21

Another way that mutations can be classified is based on their effect. List them

Answer 21

Missense Mutations
Nonsense Mutations
Neutral Mutations
Silent Mutations

Question 22

What is missense mutation?

Answer 22

A mutation causes a change in amino acid, and therefore in the protein produced

Question 23

What is nonsense mutation?

Answer 23

A mutation causes the base sequence to the code to STOP.

This means that the synthesis of the protein will stop, and so a shorter protein is produced that is unlikely to be able to fulfil its function.

Question 24

What is neutral mutation?

Answer 24

A mutation causes a change in amino acid; however, the amino acid is of the same type and does not change the structure of the protein enough its function.

Question 25

What silent mutation?

Answer 25

A mutation that does not cause any change in amino acid, and therefore in the protein produced.

This is possible, as most amino acids are coded for by more than one base sequence.

Question 26

Explain the extent of a mutation.

gene mutation. vs chromosomal mutation.

Answer 26

Another characteristic that is used to classify mutations is the amount of DNA affected.

This could be RANGE from a SINGLE BASE to a WHOLE CHROMOSOME

• A gene mutation affects only a single gene,
• while a chromosomal mutation affects a number of genes.

It may change the structure of a chromosome or the number of chromosomes.

Chromosomal mutations often cause abnormalities so severe that miscarriage often occurs early in the pregnancy.

Question 27

What are point mutations?

Answer 27

Mutations vary in the change of DNA

POINT MUTATIONS - are due to changes in a single nucleotide; therefore only one base is changed.

Question 28

What are point mutations caused by?

Answer 28

THESE MUTATIONS MAY BE DUE TO A NUCLEOTIDE BEING

1. INSERTED - a new nucleotide is added to the DNA strand
2. SUBSTITUTED - an existing nucleotide is REPLACED with another one, WITH A DIFFERENT BASE
3. DELETED - a nucleotide is REMOVED from the DNA strand
4. Frameshift - occurs when bases have been added or removed.

Question 29

Explain frameshift mutation in detail

Answer 29

Frameshift - occurs when bases have been added or removed.
- This results in the series of 3 BASES that code for an AMINO ACID starting at a different base.

• therefore, although the mutation may have only altered a single base, frameshift mutations affect the outcome for all the DNA from that point on

Frameshift mutations WILL NOT OCCUR when three bases are ADDED OR DELETED.
- in these instances, the DNA will simply code for 1 or more, or 1 less, amino acid, but the rest of the amino acids will be the same.

Therefore, it would still be a mutation but not a frameshift mutation.

Question 30

CHROMOSOMAL MUTATIONS - how they occur?

Answer 30

AFFECTS A LARGER SECTION OF THE DNA

1. DUPLICATION: (or INSERTION) - a section of the chromosome occurs twice.
2. DELETION - a piece of DNA is removed
3. INVERSION - breaks occur in a chromosome and the broken piece joins back in, but the wrong way around
   - opposite
4. TRANSLOCATION - part of a chromosome breaks off and is rejoined to the wrong chromosome
   - (4% trisomy)
5. NON-DISJUNCTION - DURING MEIOSIS, a chromosome pair does not separate and so one daughter cell has an extra chromosome, and one daughter cell has one less than the normal number
   - (95% of trisomy)
   THESE CELLS ARE SOMETIMES REFERRED TO NOT AS MUTATIONS BUT AS ANEUPLOIDY.

Question 31

DEFINE: ANEUPLOIDY

Answer 31

A change in the chromosome number

Question 32

List the conditions due to GENE MUTATIONS

Answer 32

DUCHENNE MUSCULAR DYSTROPHY

CYSTIC FIBROSIS

Question 33

list the conditions due to Chromosomal mutations

- CATEGORY AND EXAMPLES

Answer 33

1. TRISOMY
   - Down syndrome (trisomy 21)
   - Patau syndrome
   - Klinefelter syndrome
2. MONOSOMY
   - MONOSOMY VS PARTIAL MONOSOMY

• Cri-du-chat syndrome
• Turner syndrome

Question 34

Explain what is Duchenne’s muscular dystrophy

Answer 34

OCCURS THROUGH GENE MUTATION

• MAY ARISE through a mutation in MOTHER, which can be INHERITED BY HER SONS.
• also occur in MALE ZYGOTE so that the child DEVELOPS THE DISEASE

DISEASE: results in a WASTING of the LEG MUSCLES and LATER the ARMS, SHOULDERS, AND CHEST.

BECOMES APPARENT around the age of 3-5years- WHEN MUSCLE WEAKNESS BECOME APPARENT.

EVENTUALLY, death occurs DUE TO FAILURE OF THE RESPIRATORY MUSCLES.

BOYS with the forms of DMS are UNLIKELY TO LIVE FOR MORE THAN 20-25 YEARS.

Question 35

Explain what is Cystic Fibrosis

Answer 35

Mutation occurs in a huge gene on chromosome number 7
the MUTANT ALLELE IS RECESSIVE, SO A SUFFERER MUST INHERIT IT FROM BOTH PARENTS

• The gene has the code for 1480 amino acids that make up a protein that regulates the passage of chloride ions across the cell membrane

WITHOUT THE CORRECT PROTEIN, the affected person suffers from a variety of symptoms;
- SALTY-TASTING SKIN, PERSISTENT COUGHING, WHEEZING, OR PNEUMONIA; AND DIGESTIVE AND OTHER PROBLEMS.

Question 36

What is trisomy?

Answer 36

Trisomy is a result of NON-DISJUNCTION

failure of one or more chromatids to separate in the second division of meiosis.

The eggs or sperm formed when non-disjunction occurs have one chromosome too many, or one chromosome is missing.

Question 37

What is down syndrome?

Answer 37

TRISOMY 21 IN AUTOSOME
- CHILD HAS 3 CHROMOSOME 21s instead of normal 2

— MANY SYMPTOMS OF DOWN SYNDROME CAN
ALSO, OCCUR WHEN PART OF AN EXTRA COPY OF CHROMOSOME 21 IS ATTACHED TYO ONE OF THE OTHER CHROMOSOMES.
= CALLED PARTIAL TRISOMY

• Chromosomal mutation that occurs frequently, ESPECIALLY IN CHILDREN WITH OLDER MOTHERS

SYMPTOMS
A flattened face, especially the bridge of the nose.
Almond-shaped eyes that slant up.
A short neck.
Small ears.
A tongue that tends to stick out of the mouth.
Tiny white spots on the iris (colored part) of the eye.
Small hands and feet.
Some birth defects such as HEART DEFECTS OR DIGESTIVE ABNORMALITIES

Question 38

Patau syndrome

Answer 38

Chromosomal mutation in autosome where TRISOMY OCCURS

The extra chromosome 13 can come from either the mother’s egg cell or the father’s sperm cell.

1 IN 5000 BIRTHS, more than 80% of children with trisomy 13 die within the first month

THE FEATURES OF TRISOMY 13 RESULT FROM HAVING THIS EXTRA CHROMOSOME IN EACH OF THE BODY CELLS.

Extra chromosome 13 produces individuals with

• INTELLECTUAL DISABILITY,
• MICROCEPHALY,
• AN EXTRA FINGER ON EACH HAND,
• CLEFT PALATE AND/OR CLEFT LIP
• MALFORMATIONS OF THE EARS AND EYES.

Question 39

Klinefelter syndrome

Answer 39

TRISOMY IN THE SEX CHROMOSOMES (XXY)

NORMAL BOYS BUT DVELEOP KLINEFELTER SYNDROME.

CAUSES: In males, DUE TO NON-DISJUNCTION EITHER IN THE FIRST OR 2ND MEIOTIC DIVISION, PRODUCING INDIVIDUALS WITH EITHER AN EXTRA X CHROMOSOME (XXY) OR AN EXTRA (XYY)

CHARACTERISTICS

• small testes that do not produce sperm,
• breasts are enlarged
• body hair is sparse
• occasionally the individual has an intellectual ability

Question 40

What is monosomy?

What is partial monosomy?

Answer 40

MONOSOMY: an individual is missing a chromosome.
-if an autosome is completely missing, monosomy usually results in severe malformations and miscarriage

PARTIAL MONOSOMY: if only part of a chromosome is missing.
Part of the chromosome has 2 copies, but part has only one copy

Question 41

Cri-du-chat syndrome

Answer 41

Example of PARTIAL MONOSOMY
“CRY OF THE CAT”

DUE TO DELETION

RARE GENETIC DISORDER DUE TO MISSING PORTION OF CHROMOSOME 5

Characteristic cry of infants with the disorder.
- sounds like a meowing kitten,. DUE TO PROBLEMS IN THE LARYNX AND NERVOUS SYSTEM.

low birth weight.
a small head.
a rounded face.
a broad, flattened bridge of the nose.
eyes spaced wide apart.
folds of skin over the eyelids.
abnormalities of the palate, such as an unusually narrow and high palate.

Question 42

TURNER SYNDROME

Answer 42

MONOSOMY IN SEX CHROMOSOMES

ONLY ONE X CHROMOSOME (MONOSOMY X) suffers from Turner syndrome.

THESE FEMALES ARE short in stature, lack secondary characteristics of females, and are infertile.

Turner syndrome, a condition that affects only females, results when one of the X chromosomes (sex chromosomes) is missing or partially missing. Turner syndrome can cause a variety of medical and developmental problems, including short height, failure of the ovaries to develop, and heart defects

Question 43

Why are many gene mutations recessive?
What are the implications of this?
What happens if reproduction occurs?
EXAMPLE?

Answer 43

Most gene mutations produce a RECESSIVE ALLELE because they prevent the gene from producing a PROTEIN THAT WILL BE ABLE TO FUNCTION IN THE BODY.

A person could therefore have large numbers of mutations in the genes and be totally unaware of them.

If the person reproduces with a partner who has the same recessive mutation, the recessive condition COULD appear in offspring.

this what happens when couples unexpectedly have a child with cystic fibrosis.

Question 44

What are lethal recessives?

Answer 44

Some recessive mutations are lethal if they are not masked by DOMINANT ALLELE.

These LETHAL RECESSIVES cause the death of the embryo/foetus by MISCARRIAGE OR SPONTANEOUS ABORTION OR EARLY DEATH OF THE CHILD.

Question 45

What happens to lethal recessives in the gene pool?

Answer 45

LR Causes changes in the composition of a gene pool

People who inherit 2 alleles would die before their alleles could be passed on to the next generation, so the PROPORTION OF LETHAL RECESSIVES ALLELES IN THE GENE POOL WOULD GRADUALLY REDUCE.

Question 46

TAY SACHS DISEASE

Answer 46

TSD IS AN EXAMPLE OF LETHAL RECESSIVES
IN SOMATIC CELLS

Disorder of lipid metabolism that is inherited in an autosomal recessive pattern.

A lethal recessive condition caused by a mutation in the HEXA GENE that codes for the ENZYME BETA-HEXOSAMINIDASE.
- enzyme is responsible for BREAKING DOWN TOXIC SUBSTANCES including a fatty substance called GM2 GANGLIOSIDE, IN THE BRAIN.

The missing enzyme results in the ACCUMULATION OF GM2 ganglioside in the nervous system, which destroys the neurons.

A baby with 2 recessive alleles of TSD develops ABNORMALLY FOR FIRST FEW MONTHS, AND THEN DETERIORATION THAT CAUSES INTELLECTUAL AND PHYSICAL DISABILITIES BEGIN/

DEATH USUALLY OCCURS IN EARLY CHILDHOOD = APPROX 5YRS

FREQUENCY = 1 IN 500 000
EASTERN EUROPEAN JEWISH PPL 
- Ashkenazi Jewish heritage (of central and eastern European descent)
= 1 IN 2500
DUE TO GENETIC DRIFT, SMALL COMMUNITIES

Question 47

What changes the frequencies of the gene pool?

WHAT IS GENE FLOW? HOW?

Answer 47

Changes in alleles frequencies in a gene pool can also be due to GENE FLOW BROUGH BY MIGRATION.

GENE FLOW IS THE MOVEMENT OF GENETIC MATERIAL FROM ONE POPULATION TO ANOTHER.

When individuals move between populations, they enable gene flow.

Question 48

What is MIGRATION.

Answer 48

When individuals move between populations - FROM BIRTHPLACE TO ANOTHER REGION

Human migration involves the movement of people from one place to another with intentions of settling, permanently or temporarily, at a new location.

Question 49

Example of gene flow affected - china

Answer 49

In the past, Chinese populations all had Rh-positive blood groups.

The Rh, or rhesus factor, is an antigen found on the surface of RBCs.

When European countries began trading with China in the 16th century, European immigrants and sailors INTRODUCED Rh -negative allele to the Chinese population.

HOWEVER, the FREQUENCY OF THE Rh- allele is very low in China compared to other countries.

Question 50

AN example of how DISTRIBUTION OF ABO BLOOD GROUPS HAVE BEEN INFLUNECEC BY MIGARTYION.

Answer 50

AN example of how DISTRIBUTION OF ABO BLOOD GROUPS HAVE BEEN influenced BY migration is the change in frequency of the I^B allele across Asia and Europe.

The inhabitants of Esat Asia, the MONGOLS, have a proportional higher frequency of the allele than those living to their est in Europe,

in fact, it is thought, that western Europeans did not have the I^B allele.

in the 12th and 13th centuries, the MONGOLS invaded Europe on a number of occasions, spreading not only their culture but genes as well.

Today, there is a steady decrease in the allele from central Asia to western Europe.

INteretsky, the lowest concentrations of the I^B allele is now in Pyrenees mountainsnad a few isolated locations in SCANDINAVIA.

Question 51

Explain barriers to gene flow?

How to classify them?

List the two

Answer 51

Populations are often kept apart by barriers that inhibit the amount of interbreeding between them.

The isolation leads to separate gene pools forming.

Barriers to gene flows can be classified based on their cause.

1. Geographical barriers
2. Sociocultural barriers

Question 52

Explain with examples the two different BARRIERS to gene flow

Answer 52

1. Geographical barriers - include oceans, large lake systems, mountain ranges, deserts, and expansive ice sheets.

For example, the original inhabitants of Australia were isolated for 1000s of years by ocean barriers that formed as sea levels rose.

2. Sociocultural barriers - such as economic status, educational background, and social position are barriers to interbreeding

For example, statistics indicate Australians tend to marry people with similar educational background, members of particular religions favour partners who have the same faith.

RELIGION AND LANGUAGE CAN ALSO BE BARRIERS TO GENE FLOW.

Some religions do not allow marriages outside the religion,
it is unlikely that people who cannot communicate with one another will marry.