Patterns Of Inheritance Flashcards

Terms Definitions
heterozygous
Bb
phenotype
offspring
incomplete dominance
homozygous
BB or bb
gamete
A sperm or an egg.
codominance
Both traits are dominant; the offspring show both traits.
allele(s)
-alternate forms of genes-for example, the gene for flower color in pea plants exists in one form for purple and in another form for white
testcross
mating of an individual of unknown genotype but dominant phenotype with a homozygous recessive individual
dihybrid cross
crossing organisms differing in two characteristics
intermediate inheritance (a.k.a. incomplete dominance)
-inheritance in which heterozygotes have a phenotype intermediate between thephenotypes of the two homozygotes
chromosome theory of inheritance
states that genes are located on chromosomes, and the behavior of chromosomes during meiosis and fertilization accounts for inheritance patterns
MITOCHONDRIAL DISORDERS
• MELAS-Mitochondrial Encephalomypathy, Lactic Acidosis, Stroke-like episodes• MERRF-Myoclonus Epilepsy with Ragged Red Fibers• Kearns-Sayre syndrome• ophthalmoplegia• retinal degeneration• heart block• Leber's hereditary optic atrophy• blindness in early adulthood
Sex specific Inheritance Patterns:
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Summary Quiz
Reduced penetrance, variable expressivity and new mutations are characteristics of ______________ conditions._____________ disorders show vertical transmission, variable phenotype and are transmitted only by females.Answer:autosomal dominant;Mitochondrial
Meiosis
two successive nuclear divisions (with corresponding cell divisions) that produce gametes (in animals) or sexual spores (in plants and fungi) that have one-half of the genetic material of the original cell
Genotype
Describes which allels are present
LYONIZATION
random inactivation of one X chromosome in the somatic cells of females in early embryonic life. This leads to mosaicism for X-linked disorders and explains variable expression in female heterozygotes
Cytoplasmic segregation
segregation in which genetically different daughter cells arise from a progenitor that is a cytohet
Heterozygote
an individual organism having a heterozygous gene pair
Pedigree
a "family tree," drawn with standard genetic symbols, showing inheritance patterns for specific phenotypic characters
Cytoplasmic segregation
segregation in which genetically different daughter cells arise from a progenitor that is a cytohet
Cytohet
a cell containing two genetically distinct types of a specific organelle
Monohybrid
a single-locus heterozygote of the type A/a
PENETRANCE
Refers to all-or-none expression of a trait• May appear as a skipped generation• May be age or sex dependent• Reduced penetrance – condition is expressed in less than 100% of persons who carry the geneMisc. Fact: In Huntington’s disease you have age dependent penetrance.
Y linkage
the inheritance pattern of genes found on the Y chromosome but not on the X chromosome (rare)
Equal segregation
equal numbers of progeny genotypes attributable to the seperation of two alleles of one gene at meiosis
Dominant allele
an allele that expresses its phenotpic effect even when heterozygous with a recessive allele; thus, if A is a dominant over a, then A/A and A/a have the same phenotype
Self
to fertilize eggs with sperms from the same individual
Gametes
Eggs and sperm, have to be haploid
Different versions of the same gene are called what?
alleles
Fragile X syndrome
• Most common inherited form of mental retardation in males• Incidence 1/3000 males• Locus at Xq27.3• Increase in CGG repeats with inactive methylation status• X-linked semi-dominant**- because women who are carriers can be clinically affected• Carrier females may be clinically affected**• Transmitting males may be clinically unaffected ** (because it’s a pre-mutation)
1) DUCHENNE MUSCULAR DYSTROPHY2) Fragile X syndrome3) Cystic fibrosis4) Hurler's Disease5) Achondroplasia6) MYOTONIC DYSTROPHY7) NEUROFIBROMATOSIS8) MELAS-Mitochondrial Encephalomypathy, Lactic Acidosis, Stroke-like episodes9) MERRF-Myoclonus Epilepsy wit
1)X-recessive. psuedohypertrophy of calves in children.2)X-semi-dominant-mutation. Affects carrier females but not necessarily male transmitters since it is a pre-mutation. Mental Retardation, big ears.3) AR. 4) AR. large head, mucopolysacharide problem.5) AD. Lots of mutations.6) AD. • Myotonia, muscle weakness and wasting, facial diplegia- looks dull/expressionless. Sustained grasping.7) AD. Complete penetrance, variable expressitivity. Lisch nodules- one of hallmarks; Optic glioma; Tibial pseudoarthrosis, sphenoid dysplasia; bowing of tibia/ skeletal abnormalities8-11) MD10) ophthalmoplegia retinal degeneration heart block
Maternal inheritance
a type of uniparental inheritance in which all progeny have the genotype and phenotype of the parent acting as the female
Autosome
any chromosome that is not a sex chromosome
Mendel's second law
the law of independent assortment; unlinked or distantly linked segregating gene pairs assort independently at meiosis
Haploid
One copy of every chromosome- half the number you need
Gene
Peice of DNA that codes for a protein
Pleiotropy
One gene with multiple effects on the phenotype. Cysstic Fibrosis because the mutated gene affects the airways, pancreas, sweat glands, and reproductive ducts, etc.
Sex-Linked traits
Genes found on sex chromosomes and show sex-specific patterns of inheritance
What is phenotype?
Phenotype is the physical expression of genotype. For example: If a genotype is Ww (where "w" represents widow's peak hairline) - Ww is the genotype, and widow's peak is the phenotype.
Dihybrid
a double heterozygote such as A/a ; B/b
Chi-square test
a statistical test used to determine the probability of obtaining observed proportions by chance, under a specific hypothesis
Mendel's second law
the law of independent assortment; unlinked or distantly linked segregating gene pairs assort independently at meiosis
Y linkage
the inheritance pattern of genes found on the Y chromosome but not on the X chromosome (rare)
Y choromosome
one of a pair of sex chromosomes, distinguished from the X chromosome
Reciprocal crosses
a pair of crosses of the type genotype A(female) x genotype B (male) and B (female) x A (male)
Why are gametes haploid?
Because if they weren't, the chromosome number would double each generation
What are the 5 modes of inheritance?
Autosomal recessive
Autosomal dominant
X linked
Mitochondrial inheritance
Multifactorial
X chromosome
one of a pair of sex chromosomes, distinguished from the Y chromosome
Sex linkage
the location of a gene on a sex chromosome
Mendel's two Laws of Inheritance:
1). Principal of Segregation: diploid individuals have two copies (alleles) for each gene and these alleles separate from each other such that each egg or sperm gets only one allele. 2.) Principle of Independent Assortment- Alleles of one gene assort independently of the alleles at another gene.
What does heterozygous mean?
A genotype Ww is heterozygous because the letters are different - a capital W and a small case w.
Reciprocal crosses
a pair of crosses of the type genotype A(female) x genotype B (male) and B (female) x A (male)
Hemizygous gene
a gene present in only one copy in a diploid organism - for example, an X-linked gene in a male mammal
What is a locus?
A locus (plural loci) is the specific location of a gene or DNA sequence on a chromosome.
When might a female show signs of an X-linked recessive disorder?
1.) Unfavorable lyonization. (Lyonization is the silencing of one of the female X chromosomes → a.k.a. “X-inactivation”) This is so that females have the same amount of X gene products as males. The process is random, so if by CHANCE the female is a carrier for an X-linked disorder and the bulk of the good X genes get turned off, a female could show signs of the disorder.
2.) Homozygous for the mutation → both mother and father transmit a mutated X. Especially true for common traits (ex: red-green color blindness)
3.) Uniparental Isodisomy → inherit both Xs from your mother. (Rare)
4.) Chromosomal abnormalities → i.e. 45X or 46 XY females
Human female X-Chromosome Inactivation
To compensate for the lack of 2 X chromosomes in males, one of the X chromosomes in females is inactivated and shrivels up. Heterochromatized.
How are Y-linked sex-linked traits passed from one generation to the next?
Y-linked genes are passed from fathers to sons.
What are some differences between X linked dominant and X linked recessive? What would you see on a pedigree for a LETHAL X-linked dominant condition? How does X linked dominant differ from autosomal dominant?
Heterozygous females CAN be affected in XLD. Males are often more affected, but not always. Some XLD are MALE LETHAL → so on the pedigree you’ll see no affected males, a female to male progeny ratio of 2:1 overall (i.e. there is a paucity of males), and an increased incidence of miscarriages and infertility.

Difference between X linked dominant and autosomal dominant: Still no male-to-male transmission in X linked dominant, but there is in autosomal dominant.
How is colorblindness passed from one generation to the next?
Colorblindness is a sex linked trait carried on the X chromosome.
What are the two problems with the blending inheritance Model?
1. All individuals should eventually look alike2. Some traits skip a generation and appear in the next, unblended
One which human sex chromosomes are most sex-linked traits found - and why?
female or X chromosome because it is much larger than the male Y chromosome
How can you tell if a trait is polygenic?
The phenotypes of a polygenic trait form a normal distribution (bell-shaped curve)
For what is Thomas Hunt Morgan, the American scientist, known?
The theory of the gene proposed in 1911
How is it possible for a genetic XX female to turn into a male?
There may be a portion of Y chromosome present carrying the SRY gene. This is extremely rare.
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