Heredity Flashcards
Gene:
Genetic material on a chromosome that contains the instructions for creating a particular trait
Allele:
One of several variations of a gene
Locus:
• Location on a chromosome where a gene is located
Every gene has a unique locus on a particular chromosome
Homologous Chromosomes:
Pair of chromosomes that contains the same genetic information (gene for gene)
Law of Segregation:
• One chromosome from a pair of homologous chromosomes migrates to an opposite pole
Each gamete contains only one copy of each chromosome (and allele)
Law of Independent Assortment:
When homologous chromosomes separate, they do not influence which pole any other chromosome pairs go to
Incomplete Dominance:
• Both alleles expressed as an intermediate
i.e. Red + white= pink
Codominance:
• Both alleles are completely expressed
i.e. Blood type
Agglutination
Clumping of blood that results when antibodies attack antigens on foreign blood types
Epistasis:
• One gene affects the phenotypic expression of another gene
• Often seen in pigmentation
○ One gene turns the production of a pigment on or off
○ Second gene controls colour or amount of pigment produced
If first gene codes for no pigment, expression of second gene has no effect
Pleiotropy:
• Single gene has more than one phenotypic expression
Seems to be responsible for several different characteristics
i..e Gene that codes for whether a seed is round or wrinkled also affects starch metabolism
Opposite of Polygenic inheritance
Pleiotropy and Sickle Cell Disease
Allele incorrectly codes of Hb
□Causes RBC to become sickle shaped
Results in damage to heart, lugs kidneys…etc
Polygenic Inheritance:
Many traits are not just expressed in 2 or 3 varieties
i.e. Height is expressed as a continuous variation from very short to very tall
Continuous variation usually results from polygenic inheritance
○ Interaction of many genes to shape a single phenotype
Opposite of pleiotropy
Linked Genes
• Linked genes reside on the same chromosome
• Cannot segregate independently because they are physically connected
Genes that are linked are usually inherited together
Recombination Frequency:
Greater recombination frequency= greater distance between genes
The greater the distance between 2 genes on a chromosome, the more places between the genes that the chromosome can break
(More likely that the 2 genes will cross over during synapsis)
Linkage Map
○ Chromosome map created based on recombination frequencies of different genes
Determines sequence of genes on a chromosome
Cytological map
Map portraying the true relative positions of genes
Sex-Linked Inheritance:
Sex linked/X-linked genes are genes that reside on the X chromosome
Y linked genes are also possible, but rare because there are very few genes on the Y chromosome
Sex linked genetic defects are more common in males than females
X-Inactivation:
• In females, one X chromosomes in each cell does not uncoil into chromatin
Instead, forms a Barr body
• Only the allele of the gene on the active X chromosome are expressed • One random X chromosome becomes inactive, subsequent daughter cells will have the same X inactivated (not all cells in females are identical)
Barr Body
Chromosome remains as a dark, compact body
Mostly inactive X chromosomes
Genes not expressed
X Inactivation- Calico Cats
X chromosome with yellow allele inactivated
- Black allele on active chromosome is expressed
X chromosome with black allele inactivated
- Yellow allele on active chromosome expressed
Different cells with different X inactivated results in patches
Non-Disjunction
Failure of one or more chromosome pairs/chromatids to properly segregate
Non-Disjunction During Meiosis
Failure of homologous chromosomes (anaphase I) or chromatids (anaphase II) to segregate
Produced gametes with extra or missing chromosomes
Non-Disjunction During Mitosis
○ Failure of 2 chromatids (during anaphase) to segregate
○ Produces daughter cells with extra or missing chromosomes
Results in mosaicism
Polyploidy
○ All chromosomes undergo meiotic non-disjunction
○ Produces gametes with twice the number of chromosomes
○ If polyploid gamete is fertilized with a similar gamete, then a polyploidy zygote and individual and form
Common in plants
Point Mutation
Single nucleotide incorrect
• Most point mutations have deleterious effects on gene function i.e. Sickle cell anemia
Substitution
Nt substituted
Deletion
Nt missing
Insertion
Extra Nt inserted
Aneuploids
• Genome with extra or missing chromosomes
• Usually caused by non-disjunction
Most aneuploidy gametes are sterile
Those that survive has genetic defects
Down Syndrome
Aneuploidy in chromosome 21
Resulting in trisomy 21
Turner Syndrome
Aneuploid
□ Non-disjunction of sex chromosomes □ Sperm either have both sex chromosomes (XY) or no sex chromosomes (O) Individuals with Turner syndrome are physically abnormal, and sterile
Chromosome Aberrations
Chromosome segments are changed
Duplications
Chromosome segment is repeated on the same chromosome
Inversion
Chromosome segment rearranged in reverse orientation on the same chromosome
Translocation
○ Segment of a chromosome is moved to another chromosome
○ Down syndrome can also occur after translocation of a chromosome segment from chromosome 21 to chromosome 14
§ Ends up with 2 chromosome 21 and a chromosome 14 with a segment of 21
Same phenotypic effect as trisomy 21
