Topic 3.4: Inheritance Flashcards Preview

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Flashcards in Topic 3.4: Inheritance Deck (37)
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Mendel Experiment

a) Crossed different varieties of purebred pea plants, collected and grew the seeds to determine their characteristics
b) Crossed the offspring with each other and grew their seeds to similarly determine their characteristics


Results of Mendel's experiments

a) Organisms have discrete factors that determine its features
b) Organisms possess two versions of each factor
c) Each gamete contains only one version of each factor
d) Parents contribute equally to the inheritance of offspring
e) For each factor, one version is dominant over another


Principles of Inheritance

a) Law of Segregation
b) Law of Independent Assortment
c) Principle of Dominance


Law of Segregation

When gametes form, alleles are separated so that each gamete carries only one allele for each gene


Law of Independent Assortment

a) The segregation of alleles for one gene occurs independently to that of any other gene
b) Linked genes


Mendel's Laws

a) Recessive alleles will be masked by dominant alleles
b) Co-dominance / Incomplete dominance


Diploidy of Gametes

Haploid cells formed by meiosis


What does result from the fusion of gametes?

Diploid zygotes with two alleles of each gene



Allele combination for a specific trait


Types of allele combinations

a) Homozygous – Both alleles are the same (AA)
b) Heterozygous – Alleles are different (Aa)
c) Hemizygous – Only one allele (X/Y)



Physical expression of a specific trait


How is the phenotype determined?

It is determined by genotype and environmental factors


Modes of Inheritance

a) Complete dominance
b) Codominance


Complete dominance

a) One allele is expressed over another
b) Dominant allele is expressed in heterozygote or homozygous dominant
c) Recessive allele is masked in heterozygote
d) A recessive phenotype can only be expressed in homozygotes recessive



a) Both alleles are equally expressed in the phenotype
b) Heterozygotes have a distinct phenotype (superscript letter)


Inheritance of ABO blood groups

a) The A and B alleles are co-dominant (I^A I^B)
b) The O allele is recessive (i)


Monohybrid cross

It determines the allele combinations for
potential offspring for one gene only


Steps to do a monohybrid cross

a) Designate letters to represent alleles (A, a)
b) Identify genotype / phenotype of parents (P generation)
c) Determine genotype of gametes (haploid)
d) Work out gamete combinations with a Punnett grid
e) Identify ratios of offspring (F1 generation)


How are genetic diseases caused?

When mutations to a gene abrogate normal cellular function, leading to the development of a disease phenotype


Causes of genetic diseases

a) Recessive
b) Dominant
c) Co-dominant


Autosomal recessive

a) It require both faulty alleles (7)
b) Cystic fibrosis is caused by a mutated CFTR gene
c) Produces thick mucus that clogs airways and causes respiratory issues


Autosomal Dominant

a) It requires one faulty allele
b) Huntington’s disease is caused by a mutated HTT gene (4)
c) An amplification of CAG repeats (>40) leads to neurodegeneration


Autosomal Codominant

a) Sickle cell anemia is caused by a mutated HBB gene (11)
b) Sickling of blood cells leads to anemia and other complications


Gene mutation

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


Factor that increase mutation and can cause genetic diseases and cancer

a) Radiation | UV / X-rays
b) Chemical | Reactive oxygen species
c) Biological agents | Bacteria / Viruses


Examples of radiation exposure

a) Nuclear bombing of Hiroshima (1945)
b) Accident / meltdown in Chernobyl (1986)


Long-term consequences to radiation exposure

a) An increased incidence of cancer
b) Reduced immunity (- T cell count)
c) Congenital abnormalities (Chernobyl only)
d) A variety of organ-specific health effects
(e.g. liver cirrhosis, cataract induction, etc)


Sex linkage

When a gene controlling a characteristic is located on a sex chromosome (X or Y)


Sex chromosomes (Y / X)

a) Y chromosome is short and has few genes (<100)
b) X chromosome is large with many genes (~2000)


Sex-linked traits

a) Males have a higher rate of X-linked recessive conditions as they cannot mask the recessive allele
b) Females can be carriers for X-linked recessive conditions