Pattern of inheritance Flashcards
What is mendels Principle of dominance?
n a heterozygote, one dominant allele completely masks the effects of a
the presence of recessive allele
What is mendels principle of segregation?
Each diploid organism possess 2 alleles for each trait; the alleles segregate
(separate) from each other during the formation of gametes.
What is Mendels principle of independent assortment?
The alleles on different chromosomes are distributed randomly (OR
independently assorted) of each other to individual gametes.
Give 2 examples of autosomal dominant diseases
Hypercholesterolemia
(chromosome 19): Missing protein that removes
cholesterol from the blood; heart attack by age 50
Huntington disease
(chromosome 4): Progressive mental and neurological damage; neurologic
disorders by ages 40 - 70
Give 2 examples of Autosomal Recessive Diseases
Phenylketonuria (PKU)
(chromosome 12): Missing enzyme; mental deficiency
Thalassemia (chromosome 16 or 11): Reduced amounts of hemoglobin; anemia, bone, and spleen enlargement
Sickle-cell anemia (chromosome 11): Abnormal hemoglobin; sickle-shaped
red cells, anemia, blocked circulation;
increased resistance to malaria
Cystic fibrosis
(chromosome 7): Defective cell membrane protein;
excessive mucus production; digestive
and respiratory failure
Tay-Sachs disease
(chromosome 15): Missing enzyme; buildup of fatty
deposit in brain; buildup disrupts
mental development
Who discovered Sex linked inheritence?
Thomas Hunt Morgan (1910)
What is the product rule?
The probability of simultaneous independent events equals the product of the
probabilities of the individual events.
What is the sum rule?
The probability of either of two mutually exclusive events occurring is the
sum of their individual probabilities.
What are lethal Alleles?
Allele(s) that causes an organism to die or to have reduced life expectancy before the individual can reproduce.
What happens if 2 lethal alleles are present?
Lethal allele combinations remove an expected progeny class from the population, leaving the heterozygous and either homozygous dominant or recessive.
What is Incomplete dominance?
a form of Gene interaction in which both alleles of a gene at a locus are partially expressed, often resulting in an intermediate or different phenotype. It is also known as partial dominance.
What is codominance?
This is when neither allele is dominant and both are expressed in a heterozygous individual
How does Familial hypercholesterolemia show incomplete dominance?
Heterozygote (with 1 LDL-R mutant allele) has only ~50% the normal
number of receptors in the liver for LDL cholesterol, thus showing
moderate increase in plasma cholesterol level.
Homozygous for the mutant alleles totally lacks the receptor, resulting
in very high plasma cholesterol level.
How does huntington disease show penetrance?
The defective gene causes increased number of CAG repeat (number of CAG repeats ↑; severity of symptoms ↑) but the age of onset cannot be predicted (varies from teens to late 60s)
HD gene with > 40 repeat counts has a lifetime penetrance of 100% for HD
a.k.a ________ % of individuals with the genotype (>40 repeat counts) will develop the HD
in their lifetime
but HD has an age-related penetrance incidence increase by age, and the
age of onset for the disease cannot be predicted
How does Familial hypercholesterolemia show incomplete dominance?
Heterozygote (with 1 LDL-R mutant allele) has only ~50% the normal
number of receptors in the liver for LDL cholesterol, thus showing
moderate increase in plasma cholesterol level.
Homozygous for the mutant alleles totally lacks the receptor, resulting
in very high plasma cholesterol level.
What is epistasis?
This is when a gene at one locus affects the expression of a gene in a different locus and 2 or more pairs of alleles affect a single trait. It is common during zygote development. Example includes inheritence of coat colour in dogs
What is penetrance?
the proportion of individuals carrying a particular variant of a gene that also express an associated trait
What is expressivity?
expressivity is the degree to which a phenotype is expressed by individuals having a particular genotype. Expressivity is related to the intensity of a given phenotype; it differs from penetrance, which refers to the proportion of individuals with a particular genotype that actually express the phenotype
Define gene
A segment of the DNA that codes for a protein that is used to express a trait
What is pleiotropy?
the phenomenon in which a single locus affects two or more apparently unrelated phenotypic traits and is often identified as a single mutation that affects two or more wild-type traits
What is a phenotype?
This describes the physical appearance of an individual
What is genotype?
This is the genetic makeup of an individual and the type of genes found on them
What are sex influenced traits?
Sex-influenced traits are autosomal traits that are influenced by sex. If a male has one recessive allele, he will show that trait, but it will take two recessive for the female to show that same trait. One such gene is baldness.
What are sex limited traits?
Sex-limited traits are determined by genes located on autosomes and express only in one sex. While these traits are responsible considerably for sexual dimorphism, sex-influenced traits do not show distinctive expression between women and men.
