Mendelian Genetics Flashcards
Define Diploid
number of chromosomes in the somatic (body) cells
- in humans the diploid number is 46
Define Haploid
A single set chromosomes present in the egg & sperm of animals, egg & pollen of plants and in stable/transient life cycle forms of other organisms
Define Chromosome
self-replicating structures of cells that carry their nucleotide sequences in an literal array of genes
Define Karyotype
the entire chromosomes complement of an individual or cell as seen during the mitotic metaphase
Define Allele
1 of the different forms of a gene or DNA sequence that can exist at a single locus
Define Genotype
the actual alleles present in an indvidual
Define Phenotype
Observable characteristics of an organism
Define Trait
Any detachable phenotypic variation of particular inherited character
Define Gene
the fundamental physical and functional unit of heredity , which carrier info from 1 generation to the next, a segment of DNA, composed of a transcribed region and a regulatory sequence that makes transcription possible
Define Zygote
the single cell with 46 chromosomes resulting from the fertilisation of an egg by a sperm
Define Homozygous
Having 2 of the same alleles at a given locus on a pair of homologous chromosomes
Define Heterozygous
having 2 different alleles at a given locus on a pair of homologous chromosomes
What are the desirable characteristics of plants ?
- can be grown in large quantities
- produce a large number of offspring - seeds
- relatively short generation times
- many have male & female reproductive
- easy to control which individuals mate
Describe Mendel’s Experimental Methods
- hand-pollinated flowers using painbrush
- he could snip the stamens to prevent self-pollination
- covered each flower with a cloth bag
- he traced traits through several generations
What are the 8 pea plant traits ?
seed shape
seed colour
pod shape
pod colour
seed coat colour
flower position
plant height
flower colour
Describe Mendel’s well-ordered experimental plan
- used characters that were well-defined alternative traits –> purple/ white flowers - spherical/wrinkled peas
- were true-breeding –> only form present for many generations - parent generations
What are progeny from the cross of P parents called ?
the first filial generation (F1)
Define Monohybrid cross
cross involving a single trait –> flower colour
Define Dihybrid cross
cross involving 2 traits –> flower colour & plant height
What is Mendel’s 1st Law of Inheritance ?
- Law of unit characters
- Every trait is controlled by at least 1 pair of genes
Describe the Law of Assortment
alleles of different genes assort into gametes independently of each other
Describe the Law of Domimance
- one of the genes in the pair may be dominant over the other which is recessive
Describe the Law of Segregation
- the genes pair separate when gametes are formed
- only 1 of each gene pairs is represented in each of the gametes
Describe the F1 monohybrid cross results
- heterozygous X heterozygous
- 25% homozygous dominant RR
- 50% Heterozygous Rr
- 25% Homozygous Recessive rr
- offspring is called F2 generation
- genotypic ratio = 1:2:1
- phenotypic ratio = 3:1
Define Codominance
2 alleles are expressed in heterozygous individuals
- example = blood type
What are the 2 kinds of probability ?
- empirical probability
- theoretical probability
Define Empirical Probability
- its calculated by counting the number of times that event occurs and dividing it by the total number of times than event could have occurred
Define Theoretical Probability
- its calculated & reflects the number of times an even is expected to occur relative to the number of time it could possibly occur
Describe Pedigrees
- family trees
- show phenotype segregation in several generations of related individuals
Define Single Gene Disorders
- changes/mutations in the DNA sequence of one gene
What are some subtypes of single gene disorders ?
- autosomal dominant
- autosomal recessive
- X-linked dominant
- X-linked recessive
- Y-linked
Describe Autosomal Dominance Inheritance
- Aa & AA are affected
- all affected individual should have an affected parent
- both sexes should be equally affected
- Example = Huntington’s Disease
Describe Huntington’s Disease
- caused by a triple repeat expansion in the Huntingtin gene
- occurence = 1/100,000
- symptoms = personality change, progressive chorea, dystonia & dementia
Describe Autosomal Recessive Inheritance
- only aa are affected, Aa are carriers
- usually no previous family history
- inbreeding increases the chance of observing an autosomal recessive condition
- example = cystic fibrosis
Describe Cystic Fibrosis
- caused by a mutation in the CFTR gene
- 1/25 people are carriers
- Symptoms = chronic obstruction of the airway, shortness of breath, malnutrition & infertility
Define Wild Type Alleles
most common allele in population >99%
Define Mutant allele
may produce a phenotype different from that of the wild-type allele
Describe Incomplete Dominance
- when 2 traits ‘meet in the middle’ instead of showing a definite dominant/recessive relationship
- Red X white snapdragons = 1:2:1 ratio of Red:pink:white flowers
Define Pleotropic alleles
single alleles with more than 1 distinguishable phenotypic effect
–> colouration pattern & crossed eyes in siamese cats = caused by the same allele
Define Epistasis
- alleles of 1 gene cover up or alter expression of alleles of another gene
- example = several genes determine coat colour in Labrador retriever
Describe how coat colour is determined in dogs
- a single dominant allele at the first locus influences the expression or allele at a second gene locus
- Black Labs = BBEE, BBEem BbEe
- Chocolate Labs = bbEE, bbEe
- Yellow Labs with Dark skin = BBee or Bbee
- Yellow labs with pale skin = bbee
In what scenarios does epistasis occur ?
- whenever 2 or more loci interact to create new phenotypes
- whenever an allele at 1 locus masks the effects
- whenever an allele at one locus modifies the effect of ales at 1 or more other loci
Describe how temperature effects evening primrose
- mutations affected by temp are conditional or temperature-sensitive mutations
- evening primrose produces red flowers at 23 degrees and white flowers at 18
Describe how temperature effects Himalayan Rabbit
- has black fur on its extremities due an ancestral trait
- temperature sensitive tyrosinase genes which controls fur pigmentation
- natural selection has favoured a gene that allows for a darker pigmentation which activates in low temperatures - chaining the individual rabbits phenotype to fit the climate
- black fur absorbs light & solar heat, keeping that part of the rabbit which has dark fur warmer
Define penetrance
proportion of individuals in a group with a given genotype that actually show the expected phenotype
Define Expressivity
Degree of expression of a given trait or combination of traits that is associated with a gene
- condition may have severe or mild symptoms
Define Monoecious
- example = corn & peas
- every diploid adult has both male & female reproductive structures
Define Dioecious
- example = other plant & most animals
- some individual produce only male gametes, other produce only femlae gametes
What are examples Sex Chromosomal Disorders ?
- Turner’s syndrome - XO, monosomy X
- Triple-X syndrome - XXX
- Jacob’s Syndrome - XYY
Describe Sex Determination
- some XY individuals lack a small portion of Y chromosomes are phenotypically female
- some XX individuals with a small piece of the Y chromosome are male
- fragment contains the maleness-determining gene
- SRY = Sex-determining Region on the Y chromosome
- SRY codes for a functional protein - protein present = testes develop
Describe X chromosome inactivation
- Anhidrotic ectodermal dysplasia
- EDA gene which are inherited in an X-linked recessive pattern
- Małe hemizygotes = no teeth, sparse hair & no sweat glands
- female hemizygotes = random patterns of tissue, with/without sweat glands
Describe Sex Linked Inheritance in relation to Pedigrees
- phenotype appears much more often in males than female
- male with mutation can only pass it to his daughters
- daughters who receive 1 mutant X are heterozygous carriers
Describe X-Linked Dominant Inheritance
- females and males are affected
- no cases of male to male transmission
- examples = Focal Dermal Hypoplasia & Familial Hypophosphatemic rickets
Describe X-Linked Recessive Inheritance
- affected males have normal sons & carrier daughters
- affected females will have 50% chance that their child inherits the disorder (sons) or is a carrier (daughters)
- examples = Colour blindness & Haemophilia
Describes Y-Linked Inheritance
- only males affected
- no cases of male –> female transmission
- usually results in infertility
- Y chromosome is relatively small and contains few genes so there are relatively few y-linked disorders
Describe Maternal Inheritance
- a mother with mitochondrial DNA gene mutation will pass abnormal gene to all her children
- children will all be affected with varying degrees of severity
Define Homoplasmic cells
homoplasmic cells = cells which only contain normal mtDNA
Define Heteroplasmic cells
- people with a maternally inherited disease and their maternal relatives usually have heterplasmic cells –> some of the mtDNA is normal and some aren’t - containing mutations
Describe Mosaicism
- somatic mosaicism = occurrence of 2 genetically distinct populations of cells within an individual - derived from a post zygotic mutation
- may only affects a portion of the body & isn’t transmitted to the progeny
Describe Genomic Imprinting
- for imprinted genes only 1 working copy is inherited - as opposed to 2 - 1 from each parent
- depending on the gene one gene copy is epigenetically silenced
- silencing usually happens through the addition of methyl groups during gamete formation
