Genetic Inheritance Flashcards
Genes
Segments of DNA in a chromosome
Locus (Loci)
A specific place where a gene is located
Chromatid
One of two identical copies of a chromosome
Centromere
Connects identical sister chromatids
Telomere
A region at the ed of a chromosome for stability
Typical human diploid cells have ___ pairs of chromosomes - a total of ___
22 pairs are called ____
And the 23rd pair is ___ or ___
23 , 46
Autosomal
XX or XY
Human somatic cells are _____
Diploid cells that are differentiated
What cells are haploid?
Gametes
_______ cells are cells that are undifferentiated and can divide into two _________ cells
Stem, diploid
Refer to pairs of chromosomes
Homologous chromosomes
Karyotype
Entire set of a person’s chromosomes. 46 chromosomes show in the karyotype of each of the patient’s cells
Mosaicism
A condition in which cells from a patient have different genotypes (and karyotype)
Downs Syndrome
Some 46XX, some 47XX, +21
Klinefelter Syndrome
Some 46XY, some 47XXY
Turner Syndrome
Some 46XX, some 45XO
Lionization
X inactivation - the choice of which x -chromosome to be inactivated is random
Ovaries and testes undergo ________ to produce ________ that have one of each pair of chromosomes and are called _________ cells
Meiosis ; gametes ; haploid
Interphase
Chromosome duplication
Cell division
One copy of each chromosome and 1/2 of the cytoplasm/organelles are distributed b/w the 2 daughter cells
Homologous recombination
Can produce new combos of genes in meiosis; homologous chromosomes are not identical
Non-disjunction
The failure of one or more pairs of homologous chromosomes, or SISTER CHROMATIDS to separate normally during division
Meiosis consists of __ round(s) of DNA ________ and __ round(s) of nuclear __________
1 ; replication
2 ; divisions
Autosomal
Chromosomes common in both genders, one from each parent
Sex chromosomes
X, female
Y, male
Name two ways that meiosis creates genetic diversity.
1) Random segregation of homologs
2) Cross-over exchange
Nondisjunction
When homologs fail to separate properly
Common and increases w/ advancing maternal age
Cause of spontaneous abortions and mental retardation
Aneuploid
Cells with abnormal chromosome number
Trisomy 21 (Down Syndrome): most common cause of mental retardation
In 90% of trisomy 21 patients, the additional chromosome is maternal
70% occur during MI
30% occur during MII
Euploid
Cells with a normal number of chromosomes
Genotype vs. phenotype
An individual’s genetic makeup vs. what is actually observed
Autosomal Dominant Inheritance
- Only 1 allele of a gene is needed for expression
- Affected offspring has one affected parent
- Males and females can transmit trait to both males and females
- Recurrent risk is 50%
Ex) Postaxial polydactyly
Autosomal Recessive Inheritance
2 copies of a gene is needed to influence phenotype
Recurrent risk for heterozygous parents is 25%
Ex) tyrosinase-negative albinism
X-linked Recessive
Because males have one X, disease Allen on X in males is termed “hemizygous”
No such thing as a male carrier - they have it or they don’t
Females can be heterozygous carriers though
Ex) Duchenne Muscular Dystrophy
X-Linked Dominant
Very rare, no carriers
Males with the disease
Males transmit the trait only to females - 100% transmission
Females with the disease transmit the trait to both males and females-50% of offspring
Ex) hypophophatemia
The frequency a gene manifest itself is called ________
Penetrance
Reduced Penetrance
In some cases, 100% of individuals inheriting a genetic defect show the clinical presentation (phenotype) of the disease (100?% penetrance)
In other cases penetrance is less than 100%
Ex) Retinoblastoma (autosomal dominant inheritance): phenotype occurs in 90% of individuals inheriting gene defect, so 90% penetrance
Variable Expressivity
Term used to describe the range of phenotype that vary b/w individual w/ a specific genotype
Ex) Neurofibromatosis
Pts develop tumor-like growths called neurofibromas and develope cafe-au-lait spots
Locus heterogeneity
Single disorder, trait or pattern of traits caused by mutations in genes at different chromosomes loci
Ex) Osteogenesis imperfecta
- brittle-bone disease - mutations in collagen genes
Probability
Defined as the proportion of times that a specific outcome occurs in a series of events - b/w 0 and 1
What is the probability of producing three girls? (THe probability of producing 1 girl is 1/2)
1/2 x 1/2 x 1/2 = 1/8
What is the probability of producing either three girls or three boys?
1/8 + 1/8 = 1/4
______ specify the proportions of each allele in a population
Gene frequencies
________ specify the proportions of each genotype in a population
Genotype frequencies
Hardy-Weinberg Principle
P^2 + q^2 + 2pq = 1
Specifies the relationship b/w gene frequencies and genotype frequencies
Useful in estimation genes frequencies from disease prevalence data and in estimating the incidence of heterozygous carriers of recessive disease genes
Autosomal Dominant Inheritance
Characterized by vertical transmission of the disease phenotype, lack of skipped generations, and roughly equal numbers of affected males and females
Autosomal Recessive Inheritance
Characterized by clustering of the disease phenotype among siblings,but the disease is not typically seen among parents or other ancestors. Equal numbers of males and females and consanguinity may be present
Consanguineous makings are more likely to produce offspring affected by rare __________ Disorders
Autosomal Recessive
Studies show that mortality rates among the offspring of _______ matings are up to 9% higher than those of the general population
First-cousin
Each person carries one to five ________ lethal to offspring if matched with another copy of the mutation (homozygosity)
Recessive mutations
Traits in which variation is thought to be caused by the combined effects of multiple genes are called ________
Polygenic genes
When environmental factors cause variation in the trait, the term ________ is used
Multifactorial
Liability distribution
Seen in diseases that do not follow the bell-curve distribution
For multifactorial diseases that are either present or absent, it is thought that a ____________ use be crossed before the disease is expressed
Threshold liability
Pyloric Stenosis
5x more common in _______ than ________
Muscular hypertrophy b/w stomach and duodenum leading to vomiting and obstruction
Males than females
Males need less risk genes to show disease
Least affected sex has a higher risk threshold and transmits the condition more often to the most frequently affected sex
Multifactorial disease
Caused by the simultaneous influence of multiple genetic and environmental factors
