3.4 inheritance Flashcards
gametes: haploid or diploid?
haploid; only one allele of each gene
3 types of alleles
dominant, recessive, co-dominant
phenotype
the expression of alleles of a gene
genotype
the combination of alleles of a gene
homozygous dominant
having 2 copies of the same dominant allele
homozygous recessive
having 2 copies of the recessive allele; recessive alleles are only expressed when homozygous
codominant
pairs of alleles which are both expressed when present
heterozygous
having 2 diff alleles; the dominant allele is expressed
carrier
heterozygous carrier of a disease-causing allele
Mendel’s 3 laws
- the law of segregation
- the law of independent assortment
- the law of dominance
law of segregation
Each inherited trait is defined by a pair of alleles. Parental genes are randomly separated to the sex cells so that sex cells contain only one allele for that gene. Offspring therefore inherit one genetic allele from each parent when sex cells unite in fertilization
law of independent assortment
Genes for different traits are sorted separately from one another so that the inheritance of one trait is not dependent on the inheritance of another.
law of dominance
An organism with alternate forms of a gene (alleles) will express the form that is dominan
test cross
If an individual shows a dominant phenotype, their genotype is not always clear. They could be Yy (heterozygous) or YY (homozygous). In order to determine the genotype of the dominant individual, they are crossed with a recessive individual
3 types of dominance
- complete dominance (one allele masks the other)
- incomplete dominance (both phenotypes are blended)
- co-dominance (both alleles are expressed equally)
codominance example
chicken feathering; black chicken + white chicken -> speckled chicken
inheritance of ABO blood groups: chromosome
9
blood type alleles
A allele = Iᴬ B allele = Iᴮ O allele = i (recessive)
example of co-dominant alleles
A and B alleles (blood)
genotypes of blood type A
IᴬIᴬ or Iᴬi
genotypes of blood type B
IᴮIᴮ or Iᴮi
genotype of blood type AB
IᴬIᴮ
genotype of blood type O
ii
why do humans produce antibodies for antigens?
to protect the body from foreign antigens
antibodies
Y-shaped proteins found in the blood plasma
what do antibodies do?
target specific antigens and mark that cell for destruction by the immune system (hemolysis)
why are some blood types not compatible with each other?
Antibodies for foreign blood types exist in the plasma
blood type: universal recipient
type AB
blood type: universal donor
type O
what type of blood can type A receive or not receive?
- cannot have B or AB blood
- can have A or O blood
what type of blood can type B receive or not receive?
- cannot have A or AB blood
- can have B or O blood
what type of blood can type AB receive or not receive?
can have any type of blood
what type of blood can type O receive or not receive?
- can only have O blood
agglutination
clumping
what happens in an incompatible blood transfusion?
surface antigens + opposing antibodies -> agglutination -> haemolysis
Rhesus factor
blood types can be + or -
Rh+
have D-antigen on red blood cell but no anti-D antibodies
Rh-
have no D-antigens but do produce anti-D antibodies
chi-square test
compares two variables to see if they are independent or not. In a more general sense, it tests to see whether distributions of categorical variables differ from each other
what does a very small chi square test statistic mean?
observed data fits your expected data extremely well. In other words, there is a relationship
what does a very large chi square test statistic mean?
the data does not fit very well. In other words, there isn’t a relationship
how to draw a pedigree chart
square = male
circle = female
shaded = affected
unshaded = unaffected
how are genetic diseases caused?
Caused when an gene (or genes) mutates and alters cell function.
autosomal
a specific gene is not on a sex chromosome and is a numbered chromosome
autosomal recessive
two copies of the allele must be present (dd). Heterozygous individuals do not develop symptoms
example of autosomal recessive genetic disease
cystic fibrosis
- gene found on 7th chromosome pair
- Patients produce mucous that is unusually thick and sticky. It clogs airways and digestive secretory ducts (such as in the liver and pancreas)
autosomal dominant
one copy of the allele will result in symptoms (Dd, or DD)
example of an autosomal dominant genetic disease
Huntington’s disease
codominant genetic disease
one copy of the allele will result in symptoms. However, a heterozygous individual (cᴰ cᵈ) will have less severe symptoms than a homozygous individual (cᵈcᵈ)
example of a codominant genetic disease
sickle cell anemia
huntington’s disease
- Affects the HTT gene on chromosome 4
- The individual has a 50% chance of passing the trait to his/her children
- Symptoms include spasmodic movements, loss of coordination, and dementia
- symptoms present ~40 years old
how is the mutated gene of huntington’s diseasese
The normal HTT gene has a repeated nucleotide sequence CAG. It does not repeat frequently. The mutated gene has many CAG repeats which alters the structure of the proteins and causes it to damage cells in the brain
sex-linked genetic disease
the gene is located on a sex chromosome (X or Y). Because it is larger, it is more likely that the disease causing gene is located on the X chromosome (we call these X-linked)
examples of sex-linked genetic diseases
Haemophilia
Colour blindness
3 steps to deduce the patterns of inheritance of genetic diseases
- do unaffected parents have affected offspring? (y: recessive; n: dominant)
- are both sexes affected? (y: autosomal; n: sex-linked)
- do affected males have affected sons? (y: y-linked; n: x-linked)
what do radiation and mutagenic chemicals do?
increase the mutation rate and can cause genetic diseases and cancer
mutation
change in the sequence of DNA that may consequently alter the structure and function of a protein.
2 types of mutations
spontaneous (occur during DNA replication) or induced (caused by a mutagen)
examples of mutagens
Radiation (X-rays, UV waves, gamma radiation)
Chemical
Biological (bacteria / viruses)
effects of chronic (long-term) exposure to radiation
- Benign or malignant tumours. A strong correlation exists between exposure and the development of cancer.
- Health risks to fetuses (cancer, mental retardation, retarded growth, microcephaly, death)
- Organ damage (Cataracts, cirrhosis)
- Leukemia/Immune deficiency - reduced T-cells resulting in increased risk of infection.
