Basic Mendelism Flashcards
(32 cards)
What is Pellagra?
This disease causes blindness and the three Ds (Dermatitis, Diarrhea and Dementia) and in the 20s was thought to be genetic - turns out to be a vitamin B3 deficiency. Hartnup disease, which IS genetic, affects tryptophan uptake in the SI and causes Pellagra. All treated with dietary changes.
What is Mendel’s first law?
The law of segregation: Two alleles at a locus segregate into separate equally into the gametes; half carrying one allele and the other half the other.
What is Mendel’s second law?
The law of independent assortment: During the formation of gametes, the
segregation of alleles at one locus is independent of that of the segregation of alleles at any other locus.
What were early ideas on Inheritance like?
Lamarckism or acquired characteristics. A blacksmith will develop large muscles which he would pass on to his offspring. Darwin believed in blending inheritance but noted problems with this theory
Define Atavism
The recurrence of an ancestor’s trait in a subsequent generation, especially a trait that has been absent for a generation or more.
Why was the pea a good model organism for Mendel?
Pisum Sativum has Hermaphrodite flowers with male and female sexual organs - can be self-fertilised over and over to produce inbred lines with very consistent traits.
What was Mendel’s first experiment and what was its significance?
P1: Homozygous Yellow x Homozygous Green -> F1 All yellow. Heterozygous F1 Selfed -> F2 ~25% green, rest yellow. Shows that Yellow is dominant and green recessive - more generally shows alleles particle rather than fluid behaviour.
What 7 Characters did Mendel investigate?
- Ripe seeds round or wrinkled 2. Seed interiors yellow or green 3. Petals purple or white 4. ripe pods inflated or pinched 5. Unripe pods green or yellow 6. Flowers axial or terminal 7. Long or short stems
What is a gamete?
Sperm or egg; a single set of genetic instructions; a haploid cell
What is a zygote?
The fertilised egg and all body cells; a double set of genetic instructions in a diploid cell
What is a locus?
The chromosomal location of a genetic instruction e.g. the locus for the ABO blood group
e.g. the locus for the ABO blood group
What is an allele?
Alternative forms at a particular locus – the allele for A, B, or O blood group
What is a homozygote?
Two identical copies of an allele – an AA, BB or OO
What is a heterozygote?
Non-identical copies of an allele – an AB, AO or BO
What is a phenotype?
Physical appearance of an individual with a particular genotype – blood group O
What is a genotype?
Genetic constitution that underlies the phenotype – AA, BB, OO, AB, AO or BO
What is a dominant allele?
An allele that in a heterozygote masks the effects of the other allele – A and B alleles
What is a recessive allele?
An allele that in a heterozygote has its effects masked by the other allele and is only expressed in the homozygote – O allele
Give examples of dominant inheritance
Brachydactyly, Hapsburg Lip, and Huntington’s with nuances described later
Describe Brachydactyly
Autosomal dominant genetic disorder that causes short hands and stubby fingers. Homozygotes die early in childhood.
Describe cystic fibrosis
Autosomal recessive genetic disorder causes by CFTR gene mutations coding for a transport protein that moves salt and water in and out of cells. Causes thick, sticky mucous that can clog organs like the lungs and pancreas. (can also causes digit clubbing and infertility in males) 1/25 Europeans carriers.
What is assumed in Pedigrees of Autosomal recessive disorders?
That people marrying into the family are homozygous dominant (unless Hardy Weinberg frequencies can be used)
Describe Achondroplasia
Achondroplasia is the most common form of skeletal dysplasia (Dwarfism) - prevents cartilage conversion into bone particularly in the proximal limbs. This autosomal dominant disorder usually arises from de novo mutations. Homozygosity leads to stillbirth or very short life expectancy.
What are the maths rules for independent assortment and no. possible genotypes?
If no. heterozygous loci is n, no. possible gametes is 2^n, and number possible genotypes is 3^n
