Ch. 14 Mendel and the Gene Idea
The number of_in a combination of alleles determine how many genos you will have for the diversity
heterozygous
The type O has what genotype? phenotype?
ii has non carbohydrate on the surface of the blood cells
The dominant allele is called like this because
it is seen in the phenotype
Is the dominant more likely to happen in all the case?
no it is not, It depends on the case
what was the name of Mendel's hypothesis?
particulate mechanism of inheritance
For any character, the observed dominant/recessive relationship of alleles depends on
the level at which examine phenotype
by linked or dependent assortment to happen you need
the locus close together on the same chromosome.
gene idea
the model that says that parents pass on discrete heritable unit-genes-that retain their separate identities in offspring
Mendel chose to track_
those characters that occurred in two distinct, alternative forms
Biologists recognized that offspring inherit _
traits form their parents
nature vs.nuture
genes vs. environment
A punnett square is a
graphical representation of mendelian probabilities.
The formula to determine how many genos for punnet square is:
2^n where "n" represents the number of heterozygous alleles
In the types of blood there is_phenotypes and_alleles representing_
-4 -3 -codominance and incomplete dominance
Each allele has a _% chance of ending up in an egg or sperm cell
-50
There is an equal chance (_%) for each egg and sperm to join forming a zygote. Thus producing an offspring from each trait has a _ (being in a gamete) times _ (joining with another gamete) chance = _
-50% -1/2 -1/2 -1/4
Mendel always saw_in dihybrid combinations. However there is a _phenotypic ration for_.
-9:3:3:1 -3:1 -each one of the two characters if you consider them separately
Locus
-A specific place along the length of chromosomes where a given gene is located -place where alleles are stored -character
Monohybrids
-An organism that is heterozygous with respect to a single gene of interest. -All the offspring from a cross between parents homozygous for different alleles are monohybrids. Ex. AA X aa produces Aa
Allele
-Any of the alternative versions of a gene that may produce distinguishable phenotype effects -Physical (show) -trait -They can be the same or different on the homologous pair of chromosomes
Pleiotropy :
-The ability of a single gene to have multiple effects on a phenotype (a single locus) (e.g. sickle cell can cause anemia, kidney failure, pain, organ and vessel damage, etc.)
The law of independent assortment
-The alleles for each trait assort independently of each other during gamete formation. -Similar to the law of segregation but dealing with multiple traits
dihybrids
-An organism that is heterozygous with respect to two genes of interest. -All the offspring form a cross between parents doubly homozygous for different alleles are dihybrids. -Ex. parents of genotypes AABB and aabb produce a dihybrid of genotype AaBb
Describe Mendel's experiment
- Purple x White flowers (P) produced offspring (F1) with all purple flowers (lost white trait) -Then Mendel took the offspring from the F1 generation and let them self-fertilize.These offspring made up the F2 generation. -Mendel suggested that if the white trait was "lost", then all the other flowers in subsequent generations would be purple. -By studying the F2 generation, Mendel discovered things that lead to his alternative hypothesis on inheritance.
Blending Theory of Inheritance
-Early Biologists believed that traits passed from parents blended together in their offspring -analogous to the way blue and yellow paints blend to make green.
codominance
-Expression of both alleles in the heterozygote -the two alleles each affect the phenotype in separate, distinguishable ways
The union of parental gametes produces _having a_. When the hybrid plants produce gametes. the two alleles_, which means_
-F1 hybrids -Pp Combination -segregate -half of the gametes receive the P allele and the other half receive the p allele
Heterozygous
-Having two different alleles for a given trait -e.g. one allele for white flowers and one for purple -heterozygous produces gametes with different alleles
Homozygous
-Having two identical alleles for a given trait -AKA... "true breeding"
Epistasis :
-Interaction between two genes where one modifies expression of the other -One character stands over the other -independent assorted -the phenotypic expression of a gene at one locus alters that of a gene at a second locus -Ex: B gene is epistatic to the C gene (b controls c) -Control cactus spines (long, short, none) -most common ratio is 9:3:3:1
Law of segregation
-Mendel's first law -the two alleles at a locus are separated during meiosis and only chance determines which will end in each gamete.
particulate mechanism of inheritance
-Mendel's hypothesis for inheritance -This model proposed that parents passed on discrete heritable units that retain their separate identities in offspring.
Trait
-One of two of the detectable variants in a genetic character -such as purple or white color for flowers
Failures in the Blending Theory of Inheritance
-Our everyday observation of the characteristics of the people -the results of breeding experiments with animals and plants -It did not explain other phenomena of inheritance, such as traits reappearing after skipping a generation.
what is the prediction of what will ultimately happen in the Blending Theory of Inheritance?
-Over generations, a freely mating population should give rise to a uniform population of individuals. -Eventually everyone would have the same traits
Mendel found that when he took a true breeding plant and crossed it with another true breeding plant (_generation) ... If they "blended" then they should_
-P generation -all of the offspring demonstrated a single trait of one of those plants.(F1 generation) -all be light purple
What were the advantages for using Pea plants for inheritance experiments?
-Pea plants have several advantages for genetics. -available in many varieties with distinct heritable features (characters) with different variants (traits). -Ability to self-pollinate or be manually cross-pollinated -short generation time and large number of offspring from each mating
Polygenic inheritance
-Several genes determine a single phenotypic trait (e.g. eye color -Additive effect of two or more genes on a single phenotypic character (cumulative effect) -Skin pigment in humans is controlled by at least three different genes. Also height -Incomplete dominance -More adaptive -quantitative character
Complete Dominance
-The DOMINANT phenotype is fully expressed in the heterozygote, masking the recessive trait (like Mendel's peas) -In such situations, heterozygotes and the dominant homozygotes are indistinguishable
Incomplete Dominance
-The DOMINANT phenotype is not fully expressed in the heterozygote -blend together -Each of the alleles have their own phenotype (original) -Because that heterozygotes have a separate phenotype, the genotypic and phenotypic ratios for F2 are the same, 1:2:1
Mendel's observations and results of his experiment
-The white trait was not lost, but merely masked by the purple flower factor (gene). -Mendel called the masked factor recessive and the expressed factor dominant -Always saw a 3:1 ratio in the F2 generation
Phenotype
-Traits that can be seen (e.g. purple flowers) - refers to physiological and as well appearance -Also behaviors
Character
-a heritable feature that varies among individuals -Ex. Flower color
quantitative character
-a heritable feature that varies coninuously over a range than in an either-or-fashion Ex: polygenic inheritance
The law of independent assortment applies to genes,_,located on_or_
-allele pairs -different chromosomes, whose are not homologous -very far apart on the same chromosome
Homozygous dominant
-both alleles are dominant -e.g. both alleles code for purple flowers
Homozygous recessive
-both alleles are recessive- -e.g. both alleles code for white flowers
Degrees of dominance:
-complete -incomplete -codominance
Monohybrid cross
-cross between heterozygous (monohybrids) -A cross between two organisms that are heterozygous for the character being followed (or self-pollination of a heterozygous plant)
When a dominant allele coexist with a recessive allele in a heterozygous, they_. It is the pathway from_to_that dominance and recessiveness come into play
-do not actually interact at all -genotype -Phenotype
Alleles can show different degrees of _and_in relation to each other.
-dominance -recessiveness
what else controls human color?
-exposure to sun -other traits
The gene is passed from_, and it does not_. Thus it retains its_even if is not_
-generations -change -identity -showing
types of homozygous
-homozygous recessive -homozygous dominant
Ex of codominance. Also this example is an example of_
-human type of blood -multiple alleles
The phenotype of two plants can be _, but the genotype can be very_.
-identical -different
Mendel's quantitative analysis of the F2 plants from thousands of genetic crosses allowed him to deduce two fundamental principles of heredity, which are_
-law of segregation -law of independent assortment
If hybrids must transmit their alleles in the same combinations in which the alleles where inherited form the P generation, then the F1 hybrids will produce_classes of gametes (_) This is the_assortment hypothesis, which predicts that the phenotypic ration of the F2 generation will be_, just as_
-only two -YR and yr -dependent assortment -3:1 -monohybrid cross
In genetics, it is important to be able to_by using_
-predict outcomes of inheritance for specific genotypes. -the punnet square doing a test cross
Punnet square
-predicts the results of a genetic cross between individuals of known genotype
Mendel's laws of segregation and independent assortment reflect the same laws of _ that apply to tossing coins or rolling dice.
-probability
The alternating hypothesis is that the two pairs of alleles _. In other words, genes are_
-segregate independently of each other -packaged into gametes in all possible allelic combinations, as long as each gamete has one allele for each gene.
A Punnett square can be used to determine an unknown genotype by doing a_by determining the_
-test cross -appearance of the offspring Ex: purple plants that could have either homozygous dominant alleles or heterozygous alleles
norm of reaction
-the range of phenotypes produced by a single genotype, due to environmental influences. -Ex: color of flowers depending acidity and aluminum content of the soil, and persons' blood count depending on such factors as altitude, customary level of of physical activity, and the presence of infectious agents.
While creating the second law, Mendel reasoned that if all the traits in the pea plants were joined together, then when he crossed_. Instead he obtained_.This means_
-two different traits (called a di-hybrid cross) he would get the same ratio as if it were a single trait (mono-hybrid cross = one trait) 3:1 -a ratio of 9:3:3:1 -traits (alleles) were independent of each other
Mendel's 4 hypothesis consisted of:
1) Alternative forms of genes are responsible for variations in inherited characters (called alleles). -These alleles occur at the same position (locus) on the chromosome 2) For each character an organism inherits two alleles (one from each parent) On homologous chromosomes 3) If the two alleles (traits) are different, one is fully expressed (dominant) and the other is completely masked (recessive) 4) The two alleles for each character segregate during gamete production (meiosis), ending in different gametes (sperm or egg) -If different alleles are present in the parent, then: -There is a 50% chance that a gamete will receive the Dominant Allele -There is a 50% chance that a gamete will receive the Recessive Allele -This is Mendel's first law, the law of segregation.
Mendel identifies his second law of inheritance by following _
2 characters at the same time.
How large a punnet square would you need to draw to predict the oofsprings of a self-pollination of trihybrid (YyRrLl)?
8X8= 64 possible offspring
Who disputed the idea of Blending Theory of Inheritance?
A monk called Gregor Mendel
The type A blood has what genotype? phenotype?
AA or Ai has the type A carbohydrate on the surface of the blood cells
What type of blood is the universal recipient?
AB
The type AB blood has what genotype? phenotype?
AB has both type A and B carbohydrates on the surface of the blood cell
Genotype
An organisms genetic make-up (e.g. alleles (PP))
the type B blood has what genotype? phenotype?
BB or Bi has the type B carbohydrate on the surface of the blood cells
How did Mendel studied inheritance?
By breeding garden peas
How can scientist study patterns of inheritance?
By crossing two true-breeding varieties of an organism
All alleles are _ when examined at the DNA level.
CODOMINANT
Then he crossed the F1 generation between each other to obtain _generation
F2
hybridization
In genetics, the mating, or crossing, of two true-breeding varieties.
Multiple alleles :
It is possible to have more than two forms of an allele
Because incomplete dominance is blending, does it provide evidence for the blending hypothesis?
No, the reason is that the blending hypothesis states that the red or white trait (in this case) would never be retrieved from the pink hybrids. In fact, interbreeding F1 hybrids produces F2 offspring with a phenotypic ratio of 1 red: 2 pink: 1 white.
what type of blood is universal donor?
O
When do alleles independently assort during meiosis?
Prophase in meiosis I by crossing over process
true breeding plant
a plant that always produced the same plant when self-fertilized
how AB blood shows codominance?
both type A and B carbohydrate, fully equally expressed on the surface
dihybrid cross
cross between two organisms that are each heterozygous (dihybrids) for both of the characters being followed (or self-pollination of a plant that is heterozygous for both characters)
gene
discrete heritable unit of inheritance
The capital letter in the punnet square represents
dominant allele
The characters of Mendel's pea plants were simple because
each character is determined by one gene, for which there are only two alleles, one completely dominant and the other completely recessive.
Another departure from simple Mendelian genetics arises when the phenotype for a character depends on _ as well as genotype.
environment
Mendelian genetics (mendelism), its basic principles of segregation and independent assortment apply_
even to more complex patterns of inheritance.
cross-pollination
fertilization between different plants
Alleles are variations in_
gene's nucleotide sequences
Phenotype
physical manifestation of the genotype
what is the contrary of pleiotropy?
polygenic inheritance
According to Mendel's idea, during self-pollination of plants, gametes of each class unite
randomly
The lower case letter in the punnet square represents
recessive allele
gamete
sperm or egg
The explanation of heredity most famous during 1800s was
the blending hypothesis
what is the alternative to the blending model?
the gene idea