Inheritance 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.
2
Q
What are the three laws of inheritance?
A
- The law of segregation
- The law of independent assortment
- The law of dominance
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
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
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
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)
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
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
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
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
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
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
13
Q
Be able to construct punnet squares.
A
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
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
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
What is red-green colour blindness an example of?
- 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
What is haemophilia an example of?
- 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
What are gene mutations?
- 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
What agents increase the rate of genetic mutations?
- 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
What type of mutagens exists?
- 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
What two events resulted in the release of radioactive material? When did they occur?
- 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
Which of the two incidents released more radiation? What consequences are specific to the incidents?
- 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
What are long-term consequences of radiation exposure?
- Increase incidence in cancer development
- Reduced T cell counts, altered immune functions, higher rates of infections
- Wide variety of organ-specific health effects
33
How do you analyze pedigree charts? Explain how to identify dominant, recessive and sex-linked.
- 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
