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3. Genetics > Inheritance > Flashcards

Inheritance Flashcards

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Biology 101 flashcards
1
Q

What did Mendel discover in his experiments?

A
  • When two different purebred varieties are crossed together the results show one feature expressed
  • When the offspring it self-fertilized, the resulting progeny expressed the two different traits in a 3:1 ratio (co-dominance)
  • He performed experiments in which he crossed large numbers of pea plants
  • Traits are inherited in discrete units, one from each parent.
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2
Q

What are the three laws of inheritance?

A
  • The law of segregation
  • The law of independent assortment
  • The law of dominance
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3
Q

Explain the law of segregation.

A
  • When gametes form, alleles are separated so that each gamete carries only one allele of each gene
  • The inheritance of each characteristic is controlled by a pair of alleles in an individual
  • Alleles are passed on to the next generations
  • A parent has a pair of alleles for each gene, only passes on one to the offspring
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4
Q

Explain the law of independent assortment?

A
  • The distribution of alleles for one gene occurs independently to that of any other gene
  • The allele inherited for one trait does not affect which allele will be inherited for any other trait
  • The copy of genes that the gamete receives during meiosis is the result of random orientation
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5
Q

Explain the law of dominance.

A
  • Recessive alleles will be masked by dominant alleles
  • Some genes also show co-dominance or incomplete dominance
  • One allele will determine the trait, since the other is recessive
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6
Q

Are gametes haploid or diploid and why?

A
  • Gametes are haploid sex cells produced through meiosis
  • The maternal and paternal chromosomes contain one allele for each gene, during meiosis the chromosomes are segregated into haploid nuclei
  • Hence the allele pairs are separated
  • Since gametes contain only one copy of each chromosome, they only carry one allele of each gene (either maternal or paternal)
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7
Q

What results from the fusion of gametes?

A
  • When male and female gametes fuse during fertilisation, the zygote contains 2 alleles for each gene.
  • If the maternal and paternal alleles are the same, offspring homozygous
  • If maternal and paternal alleles are different, offspring heterozygous
  • Males have one allele for each gene located on a sex chromosome, called hemizygous
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8
Q

What is complete dominance?

A
  • One allele is expressed over the other
  • The dominant allele will hide the recessive allele when in heterozygous state
  • Homozygous dominant and heterozygous forms will be phenotypically indistinguishable
  • Recessive allele only expressed when in homozygous state
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9
Q

What is co-dominance?

A
  • Occurs when pairs of alleles are both expressed equally in the phenotype of a heterozygous individual
  • Altered phenotype, since alleles have a joint effect
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10
Q

What type of blood groups exist and how do they differ?

A
  • A, B, AB, O
  • Based on the ABO gene
  • Categorized based on the structure of a surface glycoprotein (antigen)
  • A and B are alleles, can appear as co-dominant if present at the same time
  • O is recessive
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11
Q

Explain the types of antigens in blood groups A and B.

A
  • In blood group A, there are Antigens A, cannot accept blood from type B or AB, since the isoantigen is foreign
  • In blood group B, there are Antigens B, cannot accept blood from type A or AB, since the isoantigen is foreign
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12
Q

Explain the types of antigens in blood groups AB and O.

A
  • In blood group AB, is contains Antigens A and B. People with this blood group can receive blood from any type, contains both antigenic variants
  • In blood group O, there are no Antigens. People can only receive blood from other blood O donors, both antigens foreign
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13
Q

Be able to construct punnet squares.

A
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14
Q

How do you compare predicated and actual outcomes of genetic crosses using data?

A
  • The genotypes and phenotypes ratios from punnet squares show the probabilities not the actual trends
  • For example there might be a 50% probability of something being round, it does not mean that it will always be round 50% of the time
    Check book for methods
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15
Q

What are genetic diseases and why do they occur?

A
  • Caused when gene mutations result in abnormal cellular function, develops of a disease phenotype
  • Genetic diseases can be caused by recessive, dominant or co-dominant alleles
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16
Q

Can genetic diseases occur through recessive genes? Give an example.

A
  • Only occur when both alleles are faulty (homozygous)
  • Autosomal recessive
  • E.g. Cystic fibrosis
17
Q

Can genetic diseases occur through dominant genes? Give an example.

A
  • One copy of faulty allele can cause the disorder
  • Homozygous and heterozygous dominant, both cases develop full range of disease symptoms
  • E.g. Huntington’s disease
18
Q

Can genetic diseases occur through co-dominant genes? Give an example.

A
  • Only one copy of the faulty allele required for a genetic disease to be caused
  • Heterozygous individuals will have milder symptoms
  • E.g. sickle cell anaemia
19
Q

What is cystic fibrosis?

A
  • Autosomal recessive disorder caused by a mutation to the CFTR gene (chromosome 7)
  • Increased mucus production, very thick and sticky
  • Mucus clogs the airways leading to respiratory failure and pancreatic cysts
  • Heterozygous, only carriers, will not develop disease
20
Q

What is Huntington’s disease?

A
  • Autosomal dominant disorder, mutation to the HTT gene (chromosome 4)
  • Neurodegenerative disorder
  • Loss of muscle coordination, cognitive decline and psychiatric problems
  • Develop age 30-50
  • If present in parent, high chance offspring will have it too
21
Q

Why are many genetic diseases rare?

A
  • There are 4,000 single gene defects that lead to genetic diseases
  • Any allele that negatively affects survival, is unlikely to be passed on to the offspring
  • Recessive conditions are more common, since the faulty allele can be present in carriers without showing any symptoms
  • Effects of dominant conditions are usually seen late, don’t prevent reproduction
22
Q

What are sex-linked genetic diseases?

A
  • Gene controlling a characteristic is located in a sex chromosome (X or Y)
  • Alleles can be dominant, recessive or co-dominant
  • Most sex chromosome genes found on X chromosome, since Y is smaller, less genes found
  • Y-linked genes are passed from the father only to sons only
23
Q

How do autosomal genetic diseases differ to sex-linked diseases?

A
  • The chromosomes in males are not paired (XY)
  • Sex-linked traits predominantly associated with a particular gender
  • X-linked dominant traits more common in females (either allele can be dominant and cause disease)
  • X-linked recessive traits more common in males, don’t have a second allele
24
Q

What trends only apply to X-linked conditions?

A
  • In X-linked genes, females can be unaffected carriers of recessive alleles, males only have one copy, hence cannot be carriers
  • Males always inherit X-linked trait from mother (blame mother)
  • Females cannot inherit X-linked recessive conditions from an unaffected father, father is healthy, not a carrier
25
Q

What is red-green colour blindness an example of?

A
  • Sex-linked inheritance
  • More common in males than in females
  • Individual fails to discriminate between red and green
  • Mutation to the red or green retinal photoreceptors (located on X-chromosome)
26
Q

What is haemophilia an example of?

A
  • Sex-linked inheritance
  • The body’s ability to control blood clotting is impaired
  • Gene for clotting factor 8, is located on the X chromosome
  • The fibrin formation is prevented, bleeding continues for a long time
27
Q

What are gene mutations?

A
  • A change to the base sequence of a gene that can affect the structure and function of the protein it encodes
  • They can be spontaneous (copying errors in DNA replication) or induced by exposure to external elements
28
Q

What agents increase the rate of genetic mutations?

A
  • Mutagens can increase the rate of genetic mutations and the formation of genetic diseases
  • Mutagens lead to the formation of cancer are called carcinogens
29
Q

What type of mutagens exists?

A
  • Radiation: UV radiation from the sun, gamma radiation from radioisotopes, X-rays
  • Chemical: reactive oxygen species (pollutants), alkylating agents (cigarettes)
  • Infectious agents: bacteria, viruses
  • These factors increase the mutation rate and can cause genetic diseases and cancer
30
Q

What two events resulted in the release of radioactive material? When did they occur?

A
  • Hiroshima and Chernobyl
  • Hiroshima (Japan): nuclear bomb in August 1845, end of WWII
  • Chernobyl (Ukraine): accident in April 1986, explosion at the reactor core
31
Q

Which of the two incidents released more radiation? What consequences are specific to the incidents?

A
  • In Chernobyl, far more radioactivity than in Hiroshima. Thyroid cancer was a common consequence due to the release of radioactive iodine-131. Concrete cover built to limit contamination.
  • In Hiroshima, radiation was dispersed and caused far more deaths. Significant increase in birth defects. 250% in congenital abnormalities. Still habitable.
32
Q

What are long-term consequences of radiation exposure?

A
  • Increase incidence in cancer development
  • Reduced T cell counts, altered immune functions, higher rates of infections
  • Wide variety of organ-specific health effects
33
Q

How do you analyze pedigree charts? Explain how to identify dominant, recessive and sex-linked.

A
  • Show the genetic history of a family over several generations
  • Males (squares), females (circles), shaded (affected), unshaded (unaffected)
  • Focus on heterozygous and homozygous
  • Identify autosomal dominant: every affected individual has at least one effected parent, males and females affected, same generation
  • Identify autosomal recessive: males and females affected, two unaffected parents can have affected child, skip generation
  • Identify sex-linked: only males affected, females only affected when father too

3. Genetics (5 decks)

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