topic 3.4- inheritance Flashcards
how did Mendel discover the principles of inheritance?
with experiments in which large numbers of pea plants were crossed
what did Mendel discover?
When he crossed two different purebred varieties together the results were not a blend – only one feature would be expressed
E.g. When purebred tall and short pea plants were crossed, all offspring developed into tall growing plants
When Mendel self-fertilised the offspring, the resulting progeny expressed the two different traits in a ratio of ~ 3:1
E.g. When the tall growing progeny were crossed, tall and short pea plants were produced in a ratio of ~ 3:1
gametes are haploid so…
contain one allele of each gene, and one chromosome of each type
what is the name of the single cell produced when two gametes fuse?
a zygote
define segregation of alleles
the separation of alleles into different nuclei
define a dominant allele
an allele that masks the effects of a recessive allele
define co-dominant alleles
alleles that have joint effects
what is the usual reason for dominance of one allele?
this allele codes for a protein that is active and carries out a function, whereas the recessive allele codes for a non-functional protein
what is a genetic disease and what is it caused by?
a genetic disease is an illness that is caused by a gene, and many genetic diseases in humans are due to recessive alleles of autosomal genes
what is a carrier of a genetic disease?
an individual that only has one recessive allele for a genetic disease and one dominant allele, who therefore does not shows symptoms of the disease but can pass on the recessive allele to their offspring.
give 2 causes of genetic diseases other than by recessive alleles
- dominant/co-dominant alleles
- sex-linked diseases
give an example of a disease caused by co-dominant alleles
sickle cell anaemia
define sex linkage
an inheritance pattern where the ratios are different in males and females
many genetic diseases have been identified in humans but most are ———-
very rare
what do radiation and mutagenic chemicals do?
they increase the mutation rate and can cause genetic disease and cancer
define a mutation
a random change to the base sequence of a gene
give two types of factors that will increase the mutation rate
- radiation (if it has enough energy to cause chemical changes in DNA) eg radioactive isotopes such as gamma rays and alpha particles, UV radiation and X rays
- chemical substances
what is the origin of genetic diseases?
mutations in body cells are eliminated when the individual dies but mutations in cells that develop into gametes can be passed onto offspring.
blood group A
IAIA or IAi
blood group B
IBIB or IBi
blood group AB
IAIB
blood group O
ii
describe how alleles of blood group will affect red blood cells
all 3 alleles cause the production of a glycoprotein in the membrane of RBCs:
IA:
- alters the glycoprotein by addition of acetyl-galactosamine.
- people with IA blood have anti-B antibodies in their plasma
IB:
- alters the glycoprotein by addition of galactose
- people with IB blood have anti-A antibodies in their plasma
IAIB:
- alters glycoprotein by addition of acetyl-galactosamine AND galactose
- neither anti-A nor anti-B antibodies will be produced by people with THIS genotype
ii:
- glycoprotein not altered
- both anti-A and anti-B antibodies in blood plasma
what blood group is a universal donor?
O (because its glycoprotein is unaltered)
what blood group is a universal recipient?
AB (because it does not have any antibodies in its plasma)
what 2 things will happen if blood of the wrong group is given to someone?
- agglutination, causing RBCs to clump together to facilitate phagocytosis
- white blood cells will perforate RBC’s membrane, causing toxins/toxic substances to come out and causing the person to feel unwell
describe cystic fibrosis
- due to recessive allele of the CFTR gene, located on chromosome 7
- gene product is a chloride ion channel that is involved in the secretion of sweat, mucus and digestive juices
- recessive alleles= channel does not function properly
- sweat produced contains excessive amounts of NaCl, but digestive juices and mucus w insufficient NaCl produced
- not enough water moves by osmosis into secretions making them viscous
- sticky mucus builds up in lungs causing infections
- pancreatic duct blocked so digestive enzymes do not reach small intestine
describe Huntington’s disease
- due to dominant allele of the HTT gene, located on chromosome 4
- gene product is a protein called huntingtin (function unknown)
- allele results in degenerative changes in the brain
- symptoms start between 30 and 50, people have already started having kids by then
- causes changes in behaviour, thinking and emotions
describe red-green colour blindness
- caused by a recessive allele of a gene for of the photoreceptor proteins, which are made by cone cells in the retina of the eye and detect specific wavelength ranges of visible light
- males; if their X chromosome carries the allele then it will be expressed in the phenotype
- females; both X chromosomes must carry the allele in order for it to be expressed
describe haemophilia
- inability to make Factor VIII, one of the proteins involved in the clotting of blood
- recessive allele located on the X chromosome
give an example of the consequences of nuclear bombing and accidents at nuclear power stations
- hiroshima and nagaasaki
- nuclear accidents at Three Mile island and Chernobyl
