20 Patterns of Genetic Inheritance Flashcards
Genotype
Symbols for specific gene type (TT or tt)
Phenotype
The physcial or outward expression of the genotype.
(How genes make something look)
E=dominant, unattached earlobe
e = recessive, attached earlobe
EE-unattached earlobe
Ee-unattached earlobe
ee-attached earlobe
MUST BE HOMOZYGOUS RECESSIVE (ee) FOR A RECESSIVE TRAIT TO BE SEEN IN PHENOTYPE
Alleles
Alternate forms of specific gene at the same locus (chromosome position)
Eg. allele for unattached earlobes or attached lobes.
Alleles are in pairs, one on each of the paired chromosomes - one allele comes from each parent
Gametes (sperm or eggs, being N or haploid) only carry one allele for each characteristic, so if an individual has the genotype Ww the possible gametes this inidividual can form (and therefore traits they can pass on to offspring are either a “W” or a ‘w’ - but not both
Dominant Allele
The trait coded for will always be expressed (be seen in the phenotype), and will mask a recessive allele - is usually denoted as the capital letter, eg. “T”.
Recessive Allele
Only expressed in the phenotype when a genore has two of this type of allele - is usually denoted as a lower case letter , eg. ‘t’
Homozygous dominant genotype
Both alleles of the pair are dominant (TT)
Homozygous recessive genotype
Both alleles of the pair are recessive (tt)
Heterozygous genotype
one dominant allele and one recessive allele in the pair (Tt)
Autosomal Trait or Autosomal Linked
Alternate forms of a specific gene at the same locus (position) on one of the autosomal (body or non sex) chromosomes, numbered 1 through 22
Sex Linked Trait
Alternate forms of a specific gene at the same locus on either an X or Y (sex) chromosome
Cross
When parents’ trait mix
- One trait cross - considers the inheritance of one characteristic Eg. WW x Ww
- Two trait cross - considers the inheritance of two characteristics Eg. WWTT x WwTT
Autosomal recessive disorder
- affected children can have unaffected parents
- heterozygotes (Aa) have an unaffected phenotype
- two affected parents will always have affected children
- affected individuals with homozygous unaffected mates will have unaffected children
- close relatives who reproduce are more likely to have affected children
- both males and females are affected with equal frequency
Autosomal dominant disorders
- affected children will usually have an affected parent
- heterozygotes (Aa) are affected
- two affected parents can produce an unaffected child
- Two unaffected parents will not have affected children
- both males and females are affected with equal frequency
Tay-Sachs Disease
(Autosomal/Recessive)
Seen in central and eastern European Jews - lack of the enzyme that breaks down lipids result sin excessive lysosomes in brain cells and eventually death of a baby, usually by age 5.
Cystic Fibrosis
(Autosomal/Recessive)
Seen in any ehtnicity.
Cl- does not pass normally through cell membranes resulting in thick mucus in lungs and other places, often causing infections.
Phenylketonuria (PKU)
(Autosomal/Recessive)
Lack of an enzyme needed to metabolize a certain amino acid (phenylalanine). Affects nervous system development - reponds to special diet.
Sickle-Cell Disease
(autosomal/receissive)
Mostly sub-Saharan African descent. Red blood cells are sickle shaped rather than biconcave because of abnormal hemoglobin (one amino acid in protein is wrong). Sickle cells clog blood vessels.
Heterozygotes may show sickling with hypoxia (low oxygen) or dehydration.
Hunthington disease
(Autosomal/Dominant)
Huntington protein has too many glutamine amino acids, leading to the progressive degeneration of brain cells.
Polygenic Inheritance
Two or more pairs of alleles govern one trait
- each dominant allele code for a product, so these effects are additive
- results in a continuous variation of phenotypes
- environmental effects cuase intervening phenotypes
- e.g. skin color ranges from very dark to very light
- e.g. heigh variation
MULTIFACTORIAL TRAIT: a polygenic trait that is particularly influenced by the environment, such as skin color influenced by the sun, or height can be affected by nutrition
Environmental influence on Phenotype
- Himalayan rabbit’s coat color infuenced by temperature
- An Allele responsible for melanin production appears to be active only at lower temperatures
- The extremities have a lower temperature and thus the ears, nose, paws and tail are dark in color
Incomplete Dominance
When the hetrozygote in intermediate in phenotype between the 2 homozygotes
Eg.
Curly Hair - CC x cc - Straight Hair
= Cc - Wavy Hair
Multiple Allele Inheritance
- When a gene exists in several allelic forms
- A person can only have 2 of all the different possible alleles (oe on each of their homologous chromosomes)
- A good example is the ABO blood system
- A and B are co-dominant alleles
- The O allele is recessive to both A and B, therefore to have O blood type, you must have two recessive O alleles
Co-Dominance
When both alleles are equally expressed in a heterozygote
Type A Blood-AA x BB-Type B Blood
= AB
The type AB blood has characterisitc antigens of both blood types A and B on cell surface
Sex Linked Inheritance
Traits controlled by genes on sex chromosomes (X and Y)
- X-linked inheritance: the allele is carried on the X Chromosome
- Y-linked inheritance: the allele is carried on the Y Chromosome
MOST SEX-LINKED TRAITS ARE X-LINKED.
