Class Notes 4 - Genetics and Inheritance 2 Flashcards
what is a gene?
a specific region of a chromosome/DNA that is capable of determining the development of a specific trait through the coding for a regulation of a polypeptide or RNA product.
what is an allele?
a particular variation of a gene e.g., gene for flower colour in pea plants : F= purple flowers and f= white flowers. F/f represents flower colour.
what is a dominant trait/ allele?
an allele or trait that is expressed over its recessive form. E.g., Purple flowers expressed over white.
what is a recessive allele/trait?
an allele or trait that is only expressed in the absence of a dominant allele. E.g., white flowers only if ‘ff’.
what is a phenotype?
the trait/characteristic that is expressed (or often visible). E.g., purple flowers vs. white flowers
what is a genotype?
the combination of alleles that gives rise to the phenotype. E.g., ‘FF’ or ‘Ff’ = purple flowers vs. ‘ff’ = white flowers.
what is homozygous?
having the same alleles, e.g., ‘FF’ or ‘ff’
what is heterozygous?
having diferent alleles, e.g., ‘Ff’.
what is the parent generation?
homozygous individuals that produce the F1 generation
what is the F1 generation?
heterozygous offspring arising from two homozygous individuals.
what is the F2 generation?
offspring arising from two heterozygous (F1) individuals
what are the three basic patterns of inheritance being studied?
complete dominance
co-dominance and incomplete dominance
epistasis
what is complete dominance? give example
one allele completely masks the presence of the other. E.g., flower colour in pea plants.
what is a monohybrid cross?
crosses involving only one trait.
what is a dihybrid cross?
crosses involving two traits.
what do you have to assume in dihybrid crosses?
non-linkage. E.g., Flower colour and seed shape are found on diferent chromosomes, i.e., not linked on the same chromosomes.
what is the null hypothesis?
any deviation from the expected outcome is probably due to chance.
what is the discussion ?
the null hypothesis is Accepted/supported OR rejected. the chi square value of ____ is less/more than the critical value of ____ at 5% probability level. therefore, the deviation from the expected outcome seen in these results has at least a 5% probability of being due to chance/ not due to chance. Therefore, the deviation between the observed and expected results is not significant/ is significant.
what is a test cross?
when an individual expressing the dominant phenotype (e.g., F-R-) is crossed with a recessive individual in order to determine whether, or not, the dominant individual is homozygous or heterozygous for the traits.
what is linkage?
linkage is when genes for different traits are formed on the same chromosome.
what happens when cross over occurs?
the majority of the gametes in a AaBb meiosis with the linkage pattern A to B and a to b are AB and ab. however, when cross over occurs, some of the gametes will have the recombinant chromatids, with Ab and aB.
what is the name of the point of cross-over?
chiasma
what happens when you cross a normal linkage parent with a normal linkage parent where some recombinant linkage has occurred?
The ratio of dominant both traits to recessive both traits is 3:1, however, a small number will produce offspring showing one dominant trait and one recessive trait. these, however, make up a very small number of the offspring as they result from the recombinant linkage.
what is sex linkage?
sex linkage refers to genes that are located on (or linked to) the sex chromosomes. Typically this involves the X chromosome.
what is an example of a sex linkage disorder?
haemophilia - a condition where a person’s blood does not go through normal clotting processes.
what is the genotype for a carrier female?
xNxn
what is the genotype for a normal male?
xNy
what is the genotype for an affected male?
xny
what is codominance?
with codominance, the two parental phenotypes are both expressed or represented in the phenotype of the heterozygous individual. with codominant traits we typically see a case there are more than two alleles (e.g., one dominant one recessive). this gives rise to the term ‘multiple alleles’.
what is an example of multiple alleles?
Blood type, A,B and O
Know the blood type diagram.
see book
what is the RH factor?
> blood types are denoted in terms of ‘positive or negative’.
the RH factor includes 50 different antigen groups.
the antigen typically considered when regarding blood transfusions (and blood genetics) is the D antigen.
therefore, we say that a person is either O+ or O-, we are only considering the D antigen.
What is an antigen?
an antigen results in an immune response - in this case unwanted blood clotting when a person receives the wrong blood type in a transfusion.
how is the RH factor inherited?
the RH factor is inherited separatly from the ABO alleles. The Rh factor has two alleles: Rh+ and Rh-. Rh+ is dominant to Rh-.
what is another example of codominance?
flower colour, such as FwFw x FrFr = FrFw (showing both red and white petals)
what is incomplete dominance?
with incomplete dominance, the heterozygous individual (e.g., offspring) shows a phenotype that is intermediate to the parental homozygous phenotypes. i.e., a ‘blending effect’. In other words, a new phenotype is produced.
what is an example of incomplete dominance?
flower colour in snapdragons
what is epistasis?
epistasis is a type of gene interaction where the phenotype expression of one gene alters the expression of another independently inherited gene.
what is an example and explanation of epistasis?
coat colour in dogs.
>there is a gene that denotes coat colour - black coats are dominant over brown (B/b)
>however, there is also a second gene that determines whether or not black or brown pigment will be deposited into the hair.
>the dominant allele (E) determines that pigment will be deposited, whereas the recessive allele (e) determines that neither that neither black or brown pigment will be deposited. So if a lab is ‘ee’ their coat colour will be yellow. >So the gene that determines whether or not pigment will be deposited, i.e., E/e is said to be epistatic to the gene that determines black or brown pigment, i.e., B/b
what is the ratio in the lab coat colour?
9:3:4
Black:brown:yellow
