3.4 Inheritance Flashcards
What was Gregor Mendel experiment with pea plants? (3)
- first, 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-fertilisation) and grow their seeds to similarity determine their characteristics
- these crosses were performed many times to establish reliable data trends (5000 crosses were performed)
What did Mendel discover from these experiments? (2)
- when he crossed 2 different purebred varieties together the results were not a blend (only one features would be expressed)
(Purebred tall and short pea plants crossed, all offspring developed into tall growing plants) - when Mendel self-fertilised the offspring, the resulting progeny expressed the 2 different traits in a ration of -3:1
(When tall growing progeny were crosses, tall and short pea plants were produced in a ration - 3:1)
What conclusions did Mendel draw from the results of his experiment? (5)
- organisms have discrete factors which determine features (genes)
- organisms possess 2 versions of each factor (alleles)
- each gamete contains 1 version of each factor (sex cells are haploid)
- parent contribute equally to the inheritance of offspring as a result of fission between randomly selected egg and sperm
- for each factor, one version is dominant over another and will be completely expressed if present
What are Mendels laws? (3)
- law segregation: when gametes form, alleles are separated os each gamete carries only 1 alleles for each gene
- Law of independent assortment: the segregation of alleles for one gene occur independent to that of any other gene
- Principle of dominance: recessive alleles will be masked by dominant alleles
What are caveats to Mendels? (2)
- law of independent assortment does not hold true for genes located on same chromosome
- not all genes show a complete dominance hierarchy - some genes show co-dominance or incomplete dominance
What are gametes?
Haploid sex cells formed by process of meiosis
Describe why haploid sex cells are haploid (3)
- during MI, homologous chromosomes are separated into different nuclei prior to cell division
- as homologous chromosomes carry the same gene, segregation of the chromosome also separate allele pairs
- as ganteries contain only 1 copy of each chromosome they carry only 1 allele for each gene
What does it mean if gametes are haploid?
The only possess 1 allele for each gene
- male and female gametes fuse during fertilisation the zygote will contain 2 alleles for each gene
How many alleles for each gene are located on a sex chromosome?
Males have only 1 allele for each gene on the sex chromosome as the chromosomes aren’t paired
How can combinations of alleles be categorised? (3)
- if the maternal and paternal alleles are the same, the offspring is homozygous for the gene
- if the maternal and paternal alleles are different, the offspring is heterozygous for the gene
- males only have 2 allele for each gene located on a sex chromosome and are hemizygous for that gene
What the gene composition for a specific trait called?
Genotype
(Either heterozygous or homozygous)
What is there observable characteristics of a specific trait called?
Phenotype
What is the phenotype determined by?
- genotype and environmental influences
What will the dominant allele do? (3)
- 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
What is co-dominance?
Occurs when pairs of alleles are both expressed equally in the phenotype of a heterozygous individual
What kind of allele dominance do blood type A and B have?
Co-dominant
How do genetic diseases occur?
When mutations to a gene abrogate normal cellular function leading to the development of a disease phenotype
Only what kinds of alleles will result in an autosomal genetic diseases to occur?
Homozygous (both alleles are faulty)
What will occur to a heterozygous person with an recessive disease carrying allele?
They will not develop the disease
They will be carriers
What is an example of an autosomal recessive disease?
Cystic fibrosis
What is the type of allel which only requires one allele to cause a genetic disease?
Dominant alleles
What is an example of an autosomal dominant genetic disease?
Huntington’s disease
What occurs is a genetic disease is co-dominant alleles?
Only requires one copy of the faulty for the disease to occur
What kind of disease result will heterozygous individuals with co-dominant allele diseases have?
Milder symptoms due to the moderating influence of a normal allele
What is an example of a co-dominant genetic disease?
Sickle cell anemia
What is cystic fibrosis? (3)
- autosomal recessive disease caused by mutation of the CFTR gene on chromosome 7
- produce more mucus which is unusually thick and sticky
- heterozygous carriers will not develop disease symptoms
What are the symptoms of cyctic fibrosis?
Muscus clogs airways and secretory ducts of the digestive system leading to respiratoyy failure and pancreatic cysts
What is Huntington’s disease? (3)
- autosomal dominant disorder caused to (HTT) Huntington gene on chromosome 4
- HTT possess a repeating tri nucleotide sequence (CAG), over 28 repeats is unstable and causes sequence to amplify
- usually occurs in late adulthood
Why may recessive be more common?
Faulty alleles can be present in carriers without causing disease
What does sex-linkage mean?
Gene controlling characteristic found on a sex chromosome
Why do Y chromosomes have only a few genes compared to X?
Shorter than X
Why are sex-linked genes more likely to be X-linked?
X is much longer with more genes (which may not be found on Y)
Why are sex-linked inheritance patterns different from autosomal patterns?
Chromosomes aren’t paired in males (XY)
Why are sex-linked dominant traits more common in females?
Females have 2 X chromosomes which can be homozygous or heterozygous
What are kind of X-linked traits do males have and why? (2)
Hemi yogis X-linked trait
- have only one X chromosome
Why are X-linked recessive traits more common in males?
The condition cannot be linked by a second allel
Why at are the trends for X linked conditions? (3)
- openly females can be carries, males cannot be heterozygous carriers
- males will always inherit an X-linked trait from their mother (get Y from father)
- females cannot inherit an X-linked recessive contusion from an unaffected father (receive dominant allele)
What are examples of X-linked recessive conditions?
Red-green colour blindness
Haemophilia
What is haemophilia? (3)
- genetic disorder where the body’s ability to control blood clotting
- blood clotting is controlled by coagulation factors on the X chromosome
- one of the factors becomes defective
what is red-green colour blindness? (2)
- Genetic order where people can’t tell between green and red hues
- caused by mutation to the red-green retinal photoreceptors on X chromosome
(Diagnosed using Ishihara test)
what is a gene mutation?
change to the base sequence of the gene that can affect the structure and function of the protein it encodes
what are 3 examples of factors which can induce mutations?
- Radiation - eg.UV radiation from sun, gamma
- Chemical - eg. reactive oxygen species, alylating agents (cigarettes)
- Biological Agents - eg. bacteria
what is the name of agents that increase the rate of genetic mutations called?
- mutagens
what are 2 examples which led to the catastrophic release of radioactive material?
Hiroshima nuclear bomb
Chernobyl accident
what are long term consequences of radiation? (3)
- increased incidence in cancer development
- reduced T cell counts and altered immune functions leading to higher rates of infection
- organ-specific health effects
what are the consequences of radiation exposure at Chernobyl and Hiroshima?
Chernobyl- thyroid disease was a common consequence of the accident due to the release of radioactive iodine
- there was no significant increase in birth defects following the Hiroshima bombing
