6. Heredity + Flashcards
1
Q
Gene
A
- genetic material on a chromosome for a trait
2
Q
Locus
A
- location on chromosome where gene is located
3
Q
Allele
A
- variance of genes such as different color
4
Q
Homologous Chromosomes
A
- a pair of chromosomes that contain same genetic material (gene for gene).
- each parent contributed 1 of the chromosome pair and thus different alleles might exist
5
Q
Law of Segregation
A
- one member of each chromosome pair migrates to opposite pole so that each gamete is haploid
- occurs in anaphase I
6
Q
Law of Independent Assortment
A
- migration of homologues within one pair of chromosomes doesn’t influence migration of other homologous pairs.
7
Q
Test Crosses
A
- monohybrid: test one gene
- dihybrid: test two genes (on different chromosomes)
- unknown dominant genotype x homozygous recc to determine if hetero or homo dominant
8
Q
Incomplete Dominance
A
- blending of expressions of alleles
- unique hetero phenotype
- R = red, r = white, Rr= pink
9
Q
Codominance
A
- both inherited alleles are expressed
- ex. blood type. blood type AB is codominance of A and B
10
Q
Multiple Alleles
A
- blood groups have three alleles, A, B, O, 6 genotypes
- AO or AA -> A type
- BO or BB -> B type
- AB -> codominant AB type
- OO -> O type
11
Q
Epistasis
A
- one gene affects phenotypic expression of second gene
- ex. pigmentation. one gene turns on production of pigment, another gene controls color or amount. if first gene is turned off, then no pigment is produced. ex. fur color in mice
12
Q
Pleitropy
A
- single gene has more than 1 phenotypic expression
- ex. gene in pea plants that codes for seed texture also influences starch metabolism and water uptake
- ex. sickle cell anemia leads to diff health conditions
13
Q
Polygenic Inheritance
A
- interaction of many genes to shape a single phenotype w/ continuous variation (height, skin color)
- opposite of pleitropy
14
Q
Linked Genes
A
- two or more genes that reside on same chromosome and cannot separate independently because they are physically connected (inherited together)
- linked genes exhibit recombination about 18 % of time
- greater recomb. freq. (above 18%) means farther distance of genes on same chromosome
15
Q
Linkage Map
A
B-V is 18% A-V is 12%, and B-A is 6%
B—–A————-V
16
Q
Sex-Linked
A
- single gene resides on sex chromosome
- when male (XY) receives an X from mother, whether it is dominant or recessive, it will be expressed bec there is no copy on Y chromosome
17
Q
Sex-influenced
A
- can be influenced by sex of individual carrying trait
- ex. Bb female not bald, Bb male is bald
18
Q
Sex Chromosomes v. Autosomes
A
- sex chromosomes: pair of homologous chromosomes that doesn’t have exactly the same genes, X, Y
- autosomes: all other chromosomes
19
Q
Hemophilia
A
- sex-linked recessive
- hemophiliacs cannot properly form blood clots and in worst cases can die from minor injuries by bleeding to death
- in order for female to be a hemophiliac, she must have two copies of the defective allele, a male needs only one defective copy -> as a result, hemophilia and other sex-linked genetic defects are much more common in males.
- heterozygous females have normal clotting abilities but are said to be carriers
20
Q
Penetrance
A
- probability an organism w/ a specific genotype will express a particular phenotype
21
Q
Expressivity
A
- term describing variation of phenotype for a specific genotype
22
Q
X-inactivation
A
- during embryonic development in female mammals, one of two x chromosomes does not uncoil into chromatin -> dark and coiled compact body chromosome (barr body) -> can’t be expressed
- either chromosome can be inactivated -> genes in female will not be expressed similarly, so all cells in a female mammal are not necessarily functionally identical (some have one x inactivated, others have the other x inactivated) (calico cats)
- what does this mean for sex-linked defects such as hemophilia? carrier female (Hh) is usually normal but it is possible that all cells producing the clotting factor H are inactivated -> smae symptoms of hemophilia as a male
23
Q
Nondisjunction
A
- failure of chromosme separation
- failure of sister chromatids to separate during anaphase of mitosis
- failure of homologous chromosmes to separate during anaphase I of meiosis
- failure of sister chromatids to separate during anaphase II of meiosis
24
Q
Mosaicism
A
- nondisjunction in mitosis during embryonic development
- fraction of body cells, those descendent of a cell where nondisjunction occurs, have an extra or missing chromosome
25
Polyploidy
- all chromosomes undergo meiotic nondisjunction and produce gametes w/ twice the number of chromosomes.
- common in plants
26
Point Mutation
- single nucleotide changes causing substitution, insertion, or deletion (latter 2 could cause frameshift)
- transition mutation: purine to purine or pyrim to pyrim
- transversion mutation: purine to pyrim or pyrim to purine
27
Aneuploidy
- genome w/ extra/missing chromosome
- often caused by nondisjunction
- down syndrome (trisomy 21)
- turner syndrome: nondisjunction in sex-chromosome. resulting in abnormal gametes: XX, XY, O. zygote XO -> sterile, physically abnormal
- Klinefelter: XXY
28
Chromosomal Aberrations
- duplications: chromsome segment repeated on same chromosome
- inversion: chromosome segment rearranged in reverse on same chromosome
- translocation: segment of chromosome moved to another chromosme. sometimes can result in down syndrome. ex. translocation of segment from 21 to 14 - > individual would inherit three copies of a segment of chromsome 21 (two chromsomes 21 and 14/21 chromosome) -> same phenotypic effect as trisomy 21
29
Mutagenic Agents
- include cosmic rays, xrays, uv rays, radioactiity, chemical compounds (cholchicine -> inhibit spindle formation), mustard gas.
- mutagenic agents are generally also carcinogenic
- proto-oncogenes stimulate normal growth, if mutated become oncogenes -> cancer
30
Genetic Disorders
- Autosomal recessive:
a. PKU - inability to produce proper enzyme for phenylalanine breakdown
b. cystic fibrosis - fluid buildup in tracts
c. Tay-sachs -lysosome defect, can't breakdown lipids for normal brain function
d. sickle cell - defective hemoglobin do to subst mutation
- Autosomal dominant
a. Huntington's - degenerate nervous system disease
- Sex-linkd recessive
a. hemophilia - abnormal blood clotting
b. color blindness
c. duchenne - muscular dystrophy
- Chromosomal
a. down syndrome
b. turner - XO
c. klinefelter - XXY
d. Cri Du Chat - deletion on chromosome 5
- turner's doesn't usually cause mental retardation, but downs, kline, and cri du chat do.
31
Forward vs. Backward Mutations
- forward: already mutated organism mutates again
| - backward: already mutated goes back to original
32
Extranuclear Inheritance
- extranuclear genes found in mitochondria and chloroplasts.
- defects in mitochondria's DNA can reduce ATP production
- mitochondria all come from mother, so all related diseases are inherited from mother.
- mitochondria have their own ~ 70S ribosomes that make mitochondrial proteins w/in mitochondrial matrix
33
Homozygous
- two copies of same allele
| - AA or aa
34
Heterozygous
- different alleles of same gene
| - Aa
35
Hemizygous
- one single copy of a gene instead of two
| - male has XY sex chromosome -> hemizygous
36
Genetic Family Pedigree
- if phenotype "skips" generations -> be suspicious of an autosomal recessive disorder
- if no "skip" then most likely autosomal dominant.
- be suspicious for x-linked recessive - > if a father doesn't have the phenotype then none of his daughters display it
