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chp 14 - Mendal and Patterns of inheritance, chp 15- Chromosomal Basis of…
chp 14 - Mendal and Patterns of inheritance
Defenitions
Testcross
determining the unknown when bicrossing with homozygous
Linked genes
close together
Dihybrids cross
Cross involving two traits
Complete dominance
Normal Mendelian genetics
Codominance
when two alleles are dominant together (Blood types) (usally in cows , ex stripped and cross black lines = both together )
Incomplete dominance
When two alleles blend together (will state “a person with straight hair and curly hair have kids and all their kids have wavy hair )
• Dominant alleles
are not necessarily more common in populations than recessive alleles
• One baby out of 400 in the United States is born with extra fingers or toes (usally cut them off when born)
This condition, polydactyly, is caused by a dominant allele, found much less frequently in the population than the recessive allele
BB- homozygous dominant
Bb- heterozygous
bb- homozygous recessive
T=tall
t=short
Phenotype
what you see
Genotype
genes that make it
Rh factor – first identified in rhesus monkeys with additional factors called h factors which since we are so close related we wanted to see if we had it and we did (negative=protein is missing
When Rh factor is negative in women , when you have your first child and its positive , nothing will happen but if the second child is also positive ( and they don’t take treatment(shot)) the body will want to reject the foreign Rh and lead to miscarriage
ex
• Tay-Sachs disease is a fatal inherited disorder; a dysfunctional enzyme causes an accumulation of lipids in the brain
Mandels laws
Law of segregation
Anaphase 1 or 2
.
• The model accounts for the 3:1 ratio observed in the F2 generation of Mendel’s crosses
• Possible combinations of sperm and egg can be shown using a Punnett square
A capital letter represents a dominant allele, and a lowercase letter represents a recessive allele
Law of indipendent assortment
Metaphase 1
, is how they line up , and it is random
Crossing-over-prophase 1, two chromosomes get so close together the DNA get passed on to the other
Mitosis Vs Meiosis
Meiosis is what goes in the sperm and egg
while mitosis is everything else
Homosygous and Heterozygous
.
• An organism with two identical alleles for a gene is called a homozygote
• It is said to be homozygous for the gene controlling that character
• An organism with two different alleles for a gene is a heterozygote and is said to be heterozygous for the gene controlling that character
Unlike homozygotes, heterozygotes are not true-breeding
• Most genes exist in populations in more than two allelic forms
• For example, the four phenotypes of the ABO blood group in humans are determined by three alleles for the enzyme that attaches A or B carbohydrates to red blood cells: IA, IB, and i
The enzyme encoded by the IA allele adds the A carbohydrate, whereas the enzyme encoded by the IB allele adds the B carbohydrate; the enzyme encoded by the i allele adds neither
epistasis
one gene affects the phenotype of another due to interaction of their gene products
• expression of a gene at one locus alters the phenotypic expression of a gene at a second locus
-example : there are genes that are responsible for pigmentation for animals. Some people pigmentation are off, that off gene , will turn off color for hair eyes, etc, will turn into a albino
One gene affects the rest
polygenic inheritance
an additive effect of two or more genes on a single phenotype
Environmental
influences are called multifactorial
-ex smoking, drinking
Pedigree
A pedigree is a family tree that describes the inheritance of a trait across generations (we can see gen disorder with pedigree/ carrier)
When you have a genetic disorder that is sex linked traits (ex color blind)
chp 15- Chromosomal Basis of Inheritance
Morgan & Fruit Flies
chose to study Drosophila melanogaster, a common species of fruit fly
• Several characteristics make fruit flies a convenient organism for genetic studies:
They produce many offspring
A generation can be bred every two weeks
They have only four pairs of chromosomes
• Morgan noted wild type, or normal, phenotypes that were common in the fly populations
Wild type
Normal traits
Mutant phenotypes
White eyes (first mutant)
Sex-linked inheritance
Eye color on X chromosome
X-Inactivation (Females)
• Inactivation of an X chromosome involves modification of the DNA and proteins bound to it called histones
• A part of the chromosome contains several genes involved in the inactivation process
• One of the genes there becomes active only on the chromosome that will be inactivated
The gene is called XIST (X-inactive specific transcript)
Sex Chromosomes
In mammals, a gene on the Y chromosome called SRY (sex-determining region on the Y) is responsible for development of the testes in an embryo
Human Y chromosome
Only 78 genes, coding for about 25 proteins
X-linked disorders
Duchenne muscular dystrophy
Hemophilia
Color blindness
.
Chromosome Structure Changes
• Deletion
• Duplication
• Inversion
• Translocation
Genetic Mapping
genetic map
an ordered list of the genetic loci along a particular chromosome
linkage map
is a genetic map of a chromosome based on recombination frequencies
Chromosomal Errors
nondisjunction
pairs of homologous chromosomes do not separate normally during meiosis
(consequences of law of segregation gone wrong)
Aneuploidy
results from the fertilization of gametes in which nondisjunction occurred
monosomic
zygote has only one copy of a particular chromosome
trisomic
zygote has three copies of a particular chromosome
Polyploidy
is a condition in which an organism has more than two complete sets of chromosomes
Linked genes
Genes that are located on the same chromosome tend to be inherited together a
• Morgan did experiments with fruit flies to see how linkage affects inheritance of two characters
• Morgan crossed flies that differed in traits of body color and wing size
• The first cross was a P generation cross to generate F1 dihybrid flies
The second was a testcross
concluded that these genes do not assort independently and reasoned that they were on the same chromosome
Human Disorders (Ex)
• Down syndrome
is an aneuploid condition that results from three copies of chromosome 21
Klinefelter syndrome
is the result of an extra chromosome in a male, producing XXY individuals
The syndrome cri du chat (“cry of the cat”),
results from a specific deletion in chromosome 5
Turner syndrome
produces X0 females, who are sterile; it is the only known viable monosomy in humans
