Brainscape's Knowledge GenomeTM

Browse over 1 million classes created by top students, professors, publishers, and experts.


See full index

IB HL Biology > 3.4 Inheritance > Flashcards

3.4 Inheritance Flashcards

You may prefer our related Brainscape-certified flashcards:
AP® Biology flashcards Biology 101 flashcards
1
Q

Describe how Mendel made his discoveries

A
  • Gregor Mendel was an Austrian monk who developed the principles of inheritance by performing experiments on pea plants
  • First, he crossed different varieties of purebred pea plants, then collected and grew the seeds to determine their characteristics
  • Next, he crossed the offspring with each other (self-fertilization) and grew their seeds to similarly determine their characteristics
  • These crosses were performed many times to establish reliable data trends (over 5,000 crosses were performed)
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
2
Q

What did Mendel discover as a result of his experiments?

A
  1. When he crossed two different purebred varieties together the results were not a blend – only one feature would be expressed
    - E.g. When purebred tall and short pea plants were crossed, all offspring developed into tall growing plants
  2. When Mendel self-fertilized the offspring, the resulting progeny expressed the two different traits in a ratio of ~ 3:1
    - E.g. When the tall growing progeny were crossed, tall and short pea plants were produced in a ratio of ~ 3:1
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
3
Q

What conclusions did Mendel make based on his findings?

A
  • Organisms have discrete factors that determine their features (these ‘factors’ are now recognized as genes)
  • Furthermore, organisms possess two versions of each factor (these ‘versions’ are now recognized as alleles)
  • Each gamete contains only one version of each factor (sex cells are now recognized to be haploid)
  • Parents contribute equally to the inheritance of offspring as a result of the fusion between randomly selected egg and sperm
  • For each factor, one version is dominant over another and will be completely expressed if present
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
4
Q

While there are caveats to Mendel’s conclusions, certain rules can be established. What are these?

A
  1. Law of Segregation: When gametes form, alleles are separated so that each gamete carries only one allele for each gene
  2. Law of Independent Assortment: The segregation of alleles for one gene occurs independently of that of any other gene*
  3. Principle of Dominance: Recessive alleles will be masked by dominant alleles†

*The law of independent assortment does not hold true for genes located on the same chromosome (i.e. linked genes)

† Not all genes show a complete dominance hierarchy – some genes show co-dominance or incomplete dominance

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
5
Q

Diagram showing Mendel’s garden pea plant experiment

A
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
6
Q

What are gametes and how are they produced?

A
  • Gametes are haploid sex cells formed by the process of meiosis – males produce sperm and females produce ova
  • During meiosis I, homologous chromosomes are separated into different nuclei before cell division
  • As homologous chromosomes carry the same genes, segregation of the chromosomes also separates the allele pairs
  • Consequently, as gametes contain only one copy of each chromosome they, therefore, carry only one allele of each gene
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
7
Q

Diagram showing male vs. female gametes

A
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
8
Q

What is the significance of the fact that gametes are haploid?

A
  • Gametes are haploid, meaning they only possess one allele for each gene
  • When male and female gametes fuse during fertilization, the resulting zygote will contain two alleles for each gene
  • Exception: Males have only one allele for each gene located on a sex chromosome, as these chromosomes aren’t paired (XY)
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
9
Q

How can the combination of alleles for any given gene be categorized?

A
  • If the maternal and paternal alleles are the same, the offspring is said to be homozygous for that gene
  • If the maternal and paternal alleles are different, the offspring is said to be heterozygous for that gene
  • Males only have one allele for each gene located on a sex chromosome and are said to be hemizygous for that gene
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
10
Q

Diagram showing the types of zygosity

A
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
11
Q

What is the genotype?

A
  • The gene composition (i.e. allele combination) for a specific trait
  • The genotype of a particular gene will typically be either homozygous or heterozygous
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
12
Q

What is the phenotype?

A
  • The observable characteristics of a specific trait (i.e. the physical expression)
  • The phenotype is determined by both the genotype and environmental influences
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
13
Q

Complete dominance

A
  • Most traits follow a classical dominant/recessive pattern of inheritance, whereby one allele is expressed over the other
  • The dominant allele will mask the recessive allele when in a heterozygous state
  • Homozygous dominant and heterozygous forms will be phenotypically indistinguishable
  • The recessive allele will only be expressed in the phenotype when in a homozygous state
  • When representing alleles, the convention is to capitalize the dominant allele and use a lowercase letter for the recessive allele
  • An example of this mode of inheritance is mouse coat color – black coats (BB or Bb) are dominant to brown coats (bb)
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
14
Q

Diagram of complete dominance (mouse coat color)

A
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
15
Q

Co-dominance

A
  • Co-dominance occurs when pairs of alleles are both expressed equally in the phenotype of a heterozygous individual
  • Heterozygotes, therefore, have an altered phenotype as the alleles have a joint effect
  • When representing alleles, the convention is to use superscripts for the different co-dominant alleles (recessive still lower case)
  • An example of co-dominance is feathering in chickens – black (C^B) and white (C^W) feathers create a speckled coat (C^BC^W)
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
16
Q

Diagram of co-dominance (chicken feathering)

A
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
17
Q

How can human red blood cells be categorized?

A
  • They can be categorized into different blood groups based on the structure of a surface glycoprotein (antigen)
  • The ABO blood groups are controlled by a single gene with multiple alleles (A, B, O)
  • The A, B, and O alleles all produce a basic antigen on the surface of red blood cells
  • The A and B alleles are co-dominant and each modifies the structure of the antigen to produce different variants
  • The O allele is recessive and does not modify the basic antigenic structure
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
18
Q

What is the letter I used for when representing blood group alleles?

A

To represent the different antigenic forms (isoantigens)

A allele = I^A ; B allele = I^B ; O allele = i (recessive)

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
19
Q

Table summarizing the genotypes for the different blood groups

A
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
20
Q

Explain why blood transfusions are not compatible between certain blood groups

A
  • As humans produce antibodies against foreign antigens, blood transfusions are not compatible between certain blood groups
  • AB blood groups can receive blood from any other type (as they already possess both antigenic variants on their cells)
  • A blood groups cannot receive B blood or AB blood (as the isoantigen produced by the B allele is foreign)
  • B blood groups cannot receive A blood or AB blood (as the isoantigen produced by the A allele is foreign)
  • O blood groups can only receive transfusions from other O blood donors (both antigenic variants are foreign)
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
21
Q

Summary table of the ABO blood groups

A
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
22
Q

Diagram showing the consequence of incompatible blood transfusion

A
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
23
Q

Steps of drawing monohybrid crosses

A
  • A monohybrid cross determines the allele combinations for potential offspring for one gene only
  • Monohybrid crosses can be calculated according to the following steps:
  • Step 1: Designate letters to represent alleles (dominant = capital letter ; recessive = lower case ; co-dominant = superscript)
  • Step 2: Write down the genotype and phenotype of the prospective parents (this is the P generation)
  • Step 3: Write down the genotype of the parental gametes (these will be haploid and thus consist of a single allele each)
  • Step 4: Draw a grid with maternal gametes along the top and paternal gametes along the left (this is a Punnett grid)
  • Step 5: Complete the Punnett grid to determine potential genotypes and phenotypes of offspring (this is the F1 generation)
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
24
Q

Diagram showing an overview of a monohybrid cross

A
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
25
Q

Comparison of predicted and actual outcomes of genetic crosses using real data

A
  • The genotypic and phenotypic ratios calculated via Punnett grids are only probabilities and may not always reflect actual trends
  • E.g. When flipping a coin there is a 50% chance of landing on heads – this doesn’t mean you will land on heads 50% of the time
  • When comparing predicted outcomes to actual data, larger data sets are more likely to yield positive correlations
  • Gregor Mendel performed over 5,000 crosses as part of his pea plant experiment
  • However, many statisticians believe Mendel’s results are too close to the exact ratios predicted to be genuine
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
26
Q

Table showing Mendel’s pea plant experimental data

A
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
27
Q

Methodology of Mendel’s pea plant experiments

A
  • Mendel crossed different varieties of pea plants and recorded the characteristics of the resultant offspring
  • Initially, he crossed purebred dominant and purebred recessive plants to produce heterozygotes (F1 generation)
  • He then self-pollinated the heterozygotes to produce an F2 generation and counted the dominant and recessive phenotypes
  • The expected ratio of dominant: recessive phenotypes was 3: 1 – this ratio was supported by the experimental data
28
Q

What causes genetic diseases?

A
  • Mutations to a gene (or genes) that abrogate normal cellular function, leading to the development of a disease phenotype
  • Genetic diseases can be caused by recessive, dominant, or co-dominant alleles
29
Q

When will an autosomal recessive genetic disease only occur?

A
  • If both alleles are faulty
  • Heterozygous individuals will possess one copy of the faulty allele but not develop disease symptoms (they are carriers)
  • An example of an autosomal recessive genetic disease is cystic fibrosis
30
Q

Autosomal dominant genetic diseases

A
  • These only require one copy of a faulty allele to cause the disorder
  • Homozygous dominant and heterozygous individuals will both develop the full range of disease symptoms
  • An example of an autosomal dominant genetic disease is Huntington’s disease
31
Q

Genetic diseases caused by co-dominant alleles

A
  • If a genetic disease is caused by co-dominant alleles, it will also only require one copy of the faulty allele to occur
  • However, heterozygous individuals will have milder symptoms due to the moderating influence of a normal allele
  • An example of a genetic disease that displays co-dominance is sickle cell anemia
32
Q

Diagram showing inheritance patterns for dominant and recessive genetic disorders

A
33
Q

Cystic fibrosis

A
  • Cystic fibrosis is an autosomal recessive disorder caused by a mutation to the CFTR gene on chromosome 7
  • Individuals with cystic fibrosis produce mucus that is unusually thick and sticky
  • This mucus clogs the airways and secretory ducts of the digestive system, leading to respiratory failure and pancreatic cysts
  • Heterozygous carriers who possess one normal allele will not develop disease symptoms
34
Q

Diagram of chest X-rays for people without and with cystic fibrosis

A
35
Q

Huntington’s disease

A
  • Huntington’s disease is an autosomal dominant disorder caused by a mutation to the Huntingtin (HTT) gene on chromosome 4
  • The HTT gene possesses a repeating trinucleotide sequence (CAG) that is usually present in low amounts (10 – 25 repeats)
  • More than 28 CAG repeats are unstable and cause the sequence to amplify (produce even more repeats)
  • When the number of repeats exceeds ~40, the huntingtin protein will misfold and cause neurodegeneration
  • This usually occurs in late adulthood and so symptoms usually develop noticeably in a person’s middle age (~40 years)
  • Symptoms of Huntington’s disease include uncontrollable, spasmodic movements (chorea) and dementia
36
Q

Diagram of proteins and brains of people without and with Huntington’s disease

A
37
Q

Identification of genetic diseases in humans

A
  • There are over 4,000 identified single gene defects that lead to genetic disease, but most are very rare
  • Any allele that adversely affects survival and hence the capacity to reproduce is unlikely to be passed on to offspring
  • Recessive conditions tend to be more common, as the faulty allele can be present in carriers without causing disease
  • Dominant conditions may often have a late onset, as this does not prevent reproduction and the transfer of the faulty allele
38
Q

What is sex linkage?

A
  • When a gene controlling a characteristic is located on a sex chromosome (X or Y)
  • The Y chromosome is much shorter than the X chromosome and contains only a few genes (50 million bp; 78 genes)
  • The X chromosome is longer and contains many genes not present on the Y chromosomes (153 million bp; ~ 2,000 genes)
  • Hence, sex-linked conditions are usually X-linked - as very few genes exist on the shorter Y chromosome
39
Q

Diagram of X and Y chromosomes

A
40
Q

Why do sex-linked inheritance patterns differ from autosomal patterns?

A
  • Because chromosomes aren’t paired in males (XY)
  • This leads to the expression of sex-linked traits being predominantly associated with a particular gender
41
Q

Why are X-linked dominant traits more common in females?

A
  • As human females have two X chromosomes (and therefore two alleles), they can be either homozygous or heterozygous
  • Hence, X-linked dominant traits are more common in females (as either allele may be dominant and cause disease)
42
Q

Why are X-linked recessive traits more common in males?

A
  • Human males have only one X chromosome (and therefore only one allele) and are hemizygous for X-linked traits
  • X-linked recessive traits are more common in males, as the condition cannot be masked by a second allele
43
Q

What trends hold true for X-linked conditions?

A
  • Only females can be carriers (a heterozygote for a recessive disease condition), males cannot be heterozygous carriers
  • Males will always inherit an X-linked trait from their mother (they inherit a Y chromosome from their father)
  • Females cannot inherit an X-linked recessive condition from an unaffected father (must receive his dominant allele)
44
Q

Diagram showing inheritance of an X-linked recessive disease condition

A
45
Q

What are red-green color-blindness and hemophilia examples of?

A
  • Sex-linked inheritance/ X-linked recessive inheritance
  • Consequently, they are both far more common in males than in females (males cannot mask the trait as a carrier)
46
Q

Conventions for assigning alleles for a sex-linked trait

A
  • The convention is to write the allele as a superscript to the sex chromosome (X)
  • Haemophilia: X^H = unaffected (normal blood clotting) ; X^h = affected (haemophilia)
  • Colour blindness: X^A = unaffected (normal vision) ; X^a = affected (colour blindness)
47
Q

Hemophilia

A
  • Haemophilia is a genetic disorder whereby the body’s ability to control blood clotting (and hence stop bleeding) is impaired
  • The formation of a blood clot is controlled by a cascade of coagulation factors whose genes are located on the X chromosome
  • When one of these factors becomes defective, fibrin formation is prevented - meaning bleeding continues for a long time
  • Different forms of haemophilia can occur, based on which specific coagulation factor is mutated (e.g. haemophilia A = factor VIII)
48
Q

Red-green color blindness

A
  • Red-green colour blindness is a genetic disorder whereby an individual fails to discriminate between red and green hues
  • This condition is caused by a mutation to the red or green retinal photoreceptors, which are located on the X chromosome
  • Red-green colour blindness can be diagnosed using the Ishihara colour test
49
Q

What is a gene mutation?

A

A change to the base sequence of a gene that can affect the structure and function of the protein it encodes

50
Q

How can mutations arise?

A

They can be spontaneous (caused by copying errors during DNA replication) or induced by exposure to external elements

51
Q

Examples of factors that induce mutations

A
  • Radiation – e.g. UV radiation from the sun, gamma radiation from radioisotopes, X-rays from medical equipment
  • Chemical – e.g. reactive oxygen species (found in pollutants), alkylating agents (found in cigarettes)
  • Biological Agents – e.g. bacteria (such as Helicobacter pylori), viruses (such as human papilloma virus)
52
Q

What are mutagens?

A
  • Agents that increase the rate of genetic mutations
  • They can lead to the formation of genetic diseases
53
Q

What are carcinogens?

A

Mutagens that lead to the formation of cancer

54
Q

Diagram showing types of mutagens

A
55
Q

Nuclear bombings of Hiroshima and the accident at Chernobyl

A
  • These are two examples of a catastrophic release of radioactive material
  • The nuclear bombing of Hiroshima (and Nagasaki) occurred in August 1945, during the final stages of World War II
  • The Chernobyl accident occurred in April 1986, when an explosion at the reactor core caused the release of radioactive material
  • Of the two incidents, more people died from the nuclear bombing, but the meltdown released far more radiation (~400×)
  • The Chernobyl meltdown involved far more fissionable material and produced different isotopes with much longer half-lives
  • The Hiroshima nuclear bomb was detonated above ground and radiation was dispersed, resulting in less irradiation of the soil
56
Q

Long-term consequences of radiation exposure following Hiroshima and Chernobyl

A
  • An increased incidence of cancer development (with a strong correlation between the dose of radiation and the frequency of cancer)
  • Reduced T cell counts and altered immune functions, leading to higher rates of infection
  • A wide variety of organ-specific health effects (e.g. liver cirrhosis, cataract induction, etc.)
  • Some of the consequences of radiation exposure are specific to the incident due to the types and amounts of radiation released
  • Thyroid disease was a common consequence of the Chernobyl accident due to the release of radioactive iodine
  • There was no significant increase in birth defects following the Hiroshima bombing, but an estimated 250% increase in congenital abnormalities following the Chernobyl meltdown
57
Q

Are Hiroshima and Chernobyl still habitable?

A
  • While Hiroshima is still habitable and well populated, certain regions of Chernobyl remain unsafe for human habitation
  • There is anecdotal evidence to suggest that radiation levels around Chernobyl have caused variation to local flora and fauna
  • The presence of residual radiation in the environment can become concentrated in organisms via bioaccumulation
58
Q

What is a pedigree?

A

A chart of the genetic history of a family over several generations

59
Q

Describe how pedigree charts are drawn

A
  • Males are represented as squares, while females are represented as circles
  • Shaded symbols mean an individual is affected by a condition, while an unshaded symbol means they are unaffected
  • A horizontal line between man and woman represents mating and resulting children are shown as offshoots to this line
  • Generations are labeled with roman numerals and individuals are numbered according to age (oldest on the left)
60
Q

Determining autosomal inheritance

A

Dominant and recessive disease conditions may be identified only if certain patterns occur (otherwise it cannot be confirmed)

61
Q

Determining autosomal inheritance- autosomal dominant

A
  • If both parents are affected and an offspring is unaffected, the trait must be dominant (parents are both heterozygous)
  • All affected individuals must have at least one affected parent
  • If both parents are unaffected, all offspring must be unaffected (homozygous recessive)
62
Q

Determining autosomal inheritance- autosomal recessive

A
  • If both parents are unaffected and an offspring is affected, the trait must be recessive (parents are heterozygous carriers)
  • If both parents show a trait, all offspring must also exhibit the trait (homozygous recessive)
63
Q

Determining X-Linked inheritance

A
  • It is not possible to confirm sex linkage from pedigree charts, as autosomal traits could potentially generate the same results
  • However, certain trends can be used to confirm that a trait is not X-linked dominant or recessive
64
Q

Determining X-Linked inheritance- X-linked dominant

A
  • If a male shows a trait, so too must all daughters as well as his mother
  • An unaffected mother cannot have affected sons (or an affected father)
  • X-linked dominant traits tend to be more common in females (this is not sufficient evidence though)
65
Q

Determining X-Linked inheritance- X-linked recessive

A
  • If a female shows a trait, so too must all sons as well as her father
  • An unaffected mother can have affected sons if she is a carrier (heterozygous)
  • X-linked recessive traits tend to be more common in males (this is not sufficient evidence though)
66
Q

Incomplete dominance

A
  • Sometimes, when two alleles are present in an individual, the phenotype is different than in either homozygous state.
  • This is incomplete dominance, where neither of the two alleles is dominant, and both impact the phenotype.
  • The notation for co-dominant alleles is a capital letter (indicating the trait) with a capital superscript (indicating the allele).
  • For example, snapdragons show incomplete dominance for flower color.
  • C^R is the allele for red flowers while C^W is the allele for white.
  • A plant will have red flowers if it has the genotype C^RC^R and white flowers if the genotype is C^WC^W.
  • However, if its genotype is C^RC^W, it will have pink flowers (a blend of red and white).

IB HL Biology (68 decks)

Brainscape helps you reach your goals faster, through stronger study habits.
© 2024 Bold Learning Solutions. Terms and Conditions