3.4 Flashcards
What did Mendel discover and how?
Mendel discovered the principles of inheritance with experiments in which large number of pea plants were used
He used pea plants because they can be artificially cross-pollinated, breed quickly, and show many clear phenotypes
He collected lots of quantitative results:
- this is significant because he had lots of replications (pioneer in reliability)
- repeats can be compared with each other
- statistical tests can be done
He concluded that there were hereditary factors (genes) showing dominant or recessive properties and that hereditary factors don’t blend but remain unchanged from one generation to the next
Gamete Production
- gametes are produced by meiosis where the number of chromosomes is halved—> gametes are haploid cells
- Haploid cells contains one chromosome of each homologous pair and therefore only one alleles of each gene
Define homozygous
having 2 identical alleles of a gene
shown as AA, aa
define heterozygous
having 2 different alleles of a gene
shown by Aa
define dominant
an alleles which is expressed in the phenotype even if only one copy of the allele is present
shown by capitalisation A
define recessive
an allele which is only expressed in the phenotype of two copies of the allele is present
shown by small letter aa
define genotype
all the allele that a cell/organism has
define phenotype
the outward expression of a cells/organisms genotype
Construction of punnet grids for predicting outcomes of monohybrid crosses
- parental phenotype
- parental genotype
- gametes
- punnet grid
- offspring genotypes (f1)
- offspring phenotype (f1)
What is the general pattern for the ratio of offspring phenotypes from a monohybrid cross between 2 heterozygotes?
3:1
What happens if an organism shows recessive characteristics in its phenotype?
it must have homozygous recessive genotype (eg bb)
What happens if an organism shows a dominant characteristic in its phenotype?
it may either have a heterozygous genotype (eg Bb) or have a homozygous dominant genotype (eg BB)
Explain what is meant by co-dominance? And what is the general pattern for the ratio of offspring phenotypes from a monohybrid cross between 2 heterozygotes when alleles are codominant?
2 alleles which are equally expressed in the phenotype
1:2:1
2 is the codominant phenotypes
Comparison of predicted and actual outcomes of genetic crosses using real data
Why do actual outcomes of genetic crosses not always correspond to predicted ratios?
because each time an offspring is born, it is independent of the previous one. the predicted outcomes are just based on portability’s
Inheritance of ABO blood groups
- the gene for blood group has three alleles: I^A, I^B, and i
- I^A and I^B are codominant alleles
- both are dominant over i which is recessive
Blood transfusions
What is cystic fibrosis? show how two individuals who don’t suffer from CF may have a child sufferer
- cystic fibrosis is an autosomal recessive disorder caused by a mutation of the CFTR gene on chromosome 7
- it causes unusually thick and sticky mucus to be produced in lungs which leads to chest infections, shortness of breath, coughing, and may even cause intestinal blockages
What is Huntington disease? and using a genetic diagram show the probability of a person who has huntingtons disease passing it on to a child
- huntingtons is an autosomal dominant disorder caused by a mutation of the HTT gene on chromosome 4, which causes neural degeneration
- symptoms include:
difficulty focusing, memory
lapses, depression, clumsiness, muscle spasms
Sickle cell anemia
sickle cell anemia is an autosomal co-dominant disorder
What is meant by the term sex-linkage?
sex linked genes are located on either of the sex chromosomes, X or Y
If a recessive condition is caused by a gene on the X chromosome, then which sex is most likely to be affected and why?
males, because they have one copy of X chromosome they have nothing to mask the effects of a recessive allele so they only need one copy to be affected
Red-green colour blindness
Red green colourblindness is a sex linked recessive condition, where males cannot be carriers
Haemophilia
it’s a genetic disorder where blood doesn’t clot properly
it’s a sex linked recessive disorder where makes cannot be carriers because even if they have one of the recessive alleles that leads to haemophilia (X^h Y) they will have haemophilia as a carrier needs one dominant and one recessive allele
