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Chapter 12/13 - Mendelian Patterns of Genetics and Inheritance - Coggle…
Chapter 12/13 - Mendelian Patterns of Genetics and Inheritance
Genetics
the study of inheritance, and the variations between offspring from one generation to the next
important to medicine, but also to agriculture and animal husbandry
alleles can be
dominant
or
recessive
alleles are alternate versions of genes
Dominant = uppercase (G)
Recessive = lowercase (g)
Blending Concept of Inheritance
- because parents that looked different often produced children who looked a little like both parents, it was believed that factors contributed by each parent would "blend" in the offspring.
Gregor Mendel
developed "
Particulate Theory of Inheritance (1860s)
studied pea plants because they were easy to grow and had quick generation time
Genotype vs Phenotype
Genotype
- alleles an individual receives at fertilization, indicated with letters
Homozygous dominant (TT)
Homozygous recessive (tt)
Heterozygous (Tt)
Phenotype
- the physical appearance (trait) corresponding to the genotype
"the expression of the alleles"
Dominant alleles can mask the expression of recessive alleles
TT and Tt will both be "tall", while only tt will be "short"
Mendel's Laws
Mendel First Law
The Law of Segregation
each individual has 2 alleles for each trait
the alleles segregate during the formation of the gametes
each gametes contains only 1 allele
fertilization gives each new individual 2 alleles for each trait
Mendel's Second Law
The Law of Independent Assortment
each pair of alleles segregates independently of the other pairs
all possible combinations of alleles can occur in the gametes
probability
genotype
chance of offspring receiving A or a from each Aa parent is 50%
product rule
- multiply the chances of independent events to determine the probability the offspring will inherit two specific alleles
phenotype
albinism: phenotype only appears in homozygous recessive (aa)
the phenotype for any genotype containing A will be normal pigmentation (AA or Aa)
the sum rule
- when the same event can occur in more than one way, we can add the results
Mutations
many are autosomal (on any chromosome but X or Y
Autosomal Recessive
- normal allele (A) is dominant, so only individuals with aa show the disorder phenotype
Autosomal dominant
- normal allele (a) is recessive, so individuals that are Aa or AA show the disorder pheno
Recessive (aa) has disorder
typically the result of a loss-of-function mutation in a gene, resulting in a recessive allele
Dominant (Aa or AA) have disorder
typically result of a gain-of-function mutation in a gene, resulting in a dominant allele (only one copy of the allele is needed for the phenotype
EXCEPTION TO MENDEL LAWS
incomplete dominance
codominance
incomplete penetrance
polygenic inheritance
pleiotropy
sex linked inheritance
X-Linked Inheritance
Y chromosome carries the SRY gene, which determines sex
"X-linked" refers to the genes that have nothing to do with sex, but are carried on the X chromosome
Genes that are on the X chromosome are "X-linked"
males are "hemizygous"
only have 1 allele for X-linked traits
Color Blindness = X-linked
X-linked Recessive disorders
more males than females = affected
if women has characteristics, all sons will have it
for female to have it, her father must also have it. her mother must have it or be carrier
affected son can have parents who have the normal phenotype
characteristics often skips generations from grandfather to grandson