inheritance Flashcards
(23 cards)
what is a gene
specific set of nucleotides that codes for the synthesis one one polypeptide
what is an allele
alternative form of a gene, slightly diff nucleotide sequence that is in the same gene loci on a pair of homologous chromosomes
what is a genotype
combination of alleles of genes in an organism
what is a phenotype
OBSERVABLE physical traits of an organism
result of the expression of all the genotypes in the organism + environmental factors
what is dominant
the allele of a gene that is expressed in both the homozygote and a heterozygote
what is recessive
allele of a gene only expressed in a homozygote. (masked expression my the dominant allele)
homozygous
the organism having the genotype with the same alleles at the gene loci on a pari of homologous chromosomes
heterozygous
the organism having 2 different alleles of the same gene at a particular locus on a pair of homologous chromosomes
what is a monohybrid test cross for?
determine if the organism is heterozygous or homozygous
examples of sex linked inheritance
red green colour blindness (x linked recessive)
haemophilia (x linked recessive)
describe someone with haemophilia
forming a blood clot involves many proteins. the DEFICIENCY of the proteins result in excessive bleeding
- excessive bleeding
- female will die when she reaches puberty
- linked recessive
- males have a higher probability of having it than females (if they inherit the x linked recessive gene from their mother they do not have a corresponding gene in the y chromosome to mask the recessive allele) they only need ONE copy of the defective allele
- females need TWO copies of the defective allele
characteristics of a pedigree analysis: autosomal dominant
- equal probability of being affected and unaffected
- present in every generation
- if the offspring if affected, one of its parents is affected
- (prove it isn’t sex linked): the affected father with an unaffected mother has an affected son
huddington’s disease
characteristics of pedigree analysis: autosomal recessive
- unaffected parents can have affected offspring
- lower probability of being affacted (rare)
sickle cell aneamia, albinism
characteristics of pedigree analysis: x linked recessive
- if a mother is affected, all her sone will be affected
- phenotypically normal parents have affected sons (mother is a carrier)
- more males than females affected
what are the types of mutations?
- change to nucleotide sequence
- change to structure of chromosome
- change the number of chromosomes
example of a beneficial mutation
- mutation in the immunoglobin gene allows for a ponetntial to generate antibodies of high affinity towards many antigens
- important in the rise of viruses with novel antigens like sars
what are mutagens
chemical or physical agents that cause mutations
examples of mutagens
chemical carcinogens: mustard gas, caffeine, certain constituents of tobacco drugs, formaldehyde, pesticides
particles: alpha and beta particles, neutrons, cosmis radiation
high energy radiation: x ray, gamma ray, uv light
sickle cell anaemia
Mutation of the beta globin gene
One defective copy also has the sickle cell trait
HbA is a protein and transports oxygen (normal), made up of 2 alpha and 2 beta polypeptide chains
However, HbS is formed instead due to the mutation of the Beta global gene.
Base pari substitution from thymine to adenine. Change in the mRNA codon from GAG to GUG
Hydrophilic glutamic acid becomes hydrophobic valine
Polypeptide folds DIFFERENTLY, exposing hydrophobic patch
When the HbS releases oxygen, the hydrophobic patch is exposed, polymerisation ==> rigid rod like fibres, sickle shaped
Distorts the bioncave shape
Impacts: inefficient in transporting oxygen, clump and clog small capillaries
Insufficient oxygen to organs, organ failure
They have a shorter life span, haemolyse easily, resulting in anaemia
Accumulate in the spleen for destruction, spleen enlargement
down syndrome type of mutation and how?
- chromosomal abbreviation
- addition of chromosome 21 (somatic)
what is discontinous variation and exmple
phenytypic variation with 2 or more distinct, non overlapping classes with no intermediates in between them. usually controlled by 1 gene and not affcted by environmental factors
- blood group and sex
what happens during natural selection
there are a range of phenotypes
- organisms with the phenotypes best suited to the envronment will be selected for
- increase in frequency of those alleles over generations
how to answer natural selection questions?
the phenotype before was more common as___
however after the ___
the organisms could ____
the allele frequency shifted in favour of the allele conferring rhe dark colour
