Ch. 8: Heredity Flashcards
Gene
genetic material on chromosome that carries instructions for creating a specific trait
Allele
several varieties of a gene
Locus
location on chromosome where gene is located
Homologous chromosomes
pair of chromosomes that contains same genetic info. gene for gene
at any particular locus, two genes might represent two different alleles bc came from two dif. parents
Law of segregation
separation of alleles (and their chromosomes) to individual gametes
Law of independent assortment
independent assortment of alleles
independent bc migration of homologues within one pair of homologous chromosomes to opposite poles does not influence other homologues
Generations
P –> F1 –> F2
Monohybrid vs. Dihybrid cross
monohybrid: one trait
dihybrid: two traits are involved
Complete dominance (monohybrid cross)
one allele completely dominant to other allele so if Tt, T is expressed
Complete dominance (monohybrid cross)
one allele completely dominant to other allele so if Tt, T is expressed
heterozygous: Tt x Tt –> 3:1 phenotypic ratio
Complete dominance (dihybrid cross)
two different traits are observed at the same time
Yellow (Y) dominant to green (g) and Round (R) dominant to wrinkled (w)
heterozygous: YyRr x YyRr (F1) from P being YYRR x yyrr will have 9:3:3:1 phenotypic ratio Mendel saw
Test cross
mating of individual whose genotype you know (recessive bc has to be like tt), with one whose you do not know (dominant, bc can be like Tt or TT) to find the unknown
T__ x tt bc can be TT x tt or Tt x tt
perform both crosses and see if all will be tall (Tt) then is first one or if half tall (Tt) and half short (tt) then is second one
Incomplete dominance
combined expression of two different alleles in the heterozygous condition, blend
Ex. snapdragons: Rr (red and white) produce pink
Codominance
both inherited alleles in the heterozygous are completely expressed, mix
Ex. M and N blood type, M produces one molecule on red blood cells and N produces another so MN ppl produce both molecules
Multiple alleles (blood type)
IA, IB, or i blood, A and B dominant if paired w/ I but codominant if paired w/ each other, IAIB is AB blood type while ii is O
AB can accept anything and O is universal donor
Polygenic inheritance
many genes for a single phenotype
Ex. skin color, height
Linked genes
genes that reside on the same chromosome and thus cannot segregate independently bc are physically connected, do not obey law of independent assortment and are inherited together
heterozygous dihybrid cross has 41:41:9:9 phenotypic ratio bc linked genes recombine in prophase I at an 18% crossover rate
Linkage map
portrayal of sequence of genes on a chromosome
the greater distance between two genes on a chromosome, the more chance they will cross over so higher Rf means farther apart, use this to order the linkage map
Sex linked (X-linked) genes
genes that reside on the X, not really on Y bc Y is small (boys r useless)
X-linked genes are more likely expressed in males bc they don’t have another X to cover anything up
written as superscripts
females can be carriers and their sons will express it
Ex. color blindness, hemophelia
X-inactivation, Barr body
during embryonic development in females, one of two X chromosomes doesn’t uncoil into chromatin, but instead remains coiled as a Barr body: region of inactive X chromosomes
only the alleles on the one X are expressed by the cell
random and independent process, adult females will have some cells w/ one X active and others w/ the other X active
Ex. color of Calico cat & the orange/ white/ black patches
Alleles that genotype Tt can make
T or t
Nondisjunction, Mosaicism, Polyploidy
failure of 1+ chromosome pairs or chromatids of a single chromosomes to properly move to opposite poles during mitosis/ meiosis
- Meiosis: anaphase I or anaphase II messes up and gametes have extra/ less chromosomes
- Mitosis: two chromatids of single chromosome don’t separate right and some body cells will have extra/ missing chromosome (mosaicism)
- Polyploidy: all chromosomes undergo meiotic nondisjunction and produce gametes w/ twice the # of chromosomes, common in plants
Sickle-cell disease
caused by nucleotide substitution
results in production of defective hemoglobin (carry oxygen to cells), red blood cells do not flow through capillaries freely and oxygen not delivered through body, homozygous usually OK
malaria connection so more popular in malaria ridden countries
Tay-Sachs disease
caused by nucleotide insertion
lysosomes lack functional enzyme to break down certain fats, when these fats accumulate in nerve cells in brain, brain cells die and ppl usually die in childhood :(
Aneuploidy
genome w/ extra or missing chromosome, often caused by nondisjunction
most do not produce viable offspring, but some survive
Ex. Down syndrome, Turner syndrome, Klinefelter syndrome
Down syndrome
Trisomy 21, extra chromosome 21 for total of 3
example of aneuploidy
Turner syndrome
nondisjunction of sex chromosomes, aneuploidy
XO karyotype, sterile females w/ only one X
Klinefelter syndrome
XXY karyotype
male but express variety of female characteristics like reduced facial hair and breast development
Environmental influences on phenotypic expression (4)
Nutrition like dietary deficiencies can influence phenotype/ expression of genetic disorders
Temperature influences sex determination in various reptiles (females are hot)
Temperature often influences color of animal fur (arctic fox)… adaptation!
Soil pH influences flower color in Hydrangeas… blue when acidic and pink when basic
Maternal inheritance
mitochondrial DNA (and chloroplasts) have their own DNA and are inherited through mother only, w/ boys giving just some cytoplasm (again, boys r useless) can be used to trace progeny back through multiple generations
