Biology 30 AP- genetic inheritance

Monohybrid cross.

organisms with heterozygous traits.

Looking at one trait like for example with the peas, smooth vs wrinkled.

2 (Dominant and recessive)

A punnett sqaure representing 4 offspring. (if it has 4 boxes, it represents 4 offspring.)

Genotype=genes

Phentype=physical expression (what you see)

Ex. in Mendel's expierment, in the F2 generation, 4 flowers' genotype were PP, Pp, Pp, and pp. But, the phenotype of the 4 flowers was 3 purple and 1 white. So, the genotype ratio was 1:2:1 and the phenotype ratio was 3:1

 PP x pp (parental generation) yielded all Pp offspring (F1 generation). This means that they are all heterozygous which also means that the dominant purple trait would show.

F2 generation: Pp x Pp yielded (1:2:1) ratio. 1 is homozygous dominant meaning it will be purple, 2 are heterozygous meaning they will show the dominant purple trait, and 1 is homozygous recessive meaning it will be white. So, this results in 25% white and 75% purple with a 1:2:1 genotype ratio.

Homozygous dominant: Both of your alleles are dominant (you show dominant trait)

Heterozygous: One of your alleles is dominant and the other is recessive (you show dominant trait but carry recessive trait)

Homozygous recessive: both of your alleles are recessive (you show recessive trait).

uppercase letter= dominant allele

lowercase letter= recessive allele

To express a dominant trait you must have atleast one dominant allele. To express a recessive trait you must have two recessive alleles.

Homozygous: same alleles (ex. RR or rr) 

Heterozygous: different alleles (ex. Rr)

Segregation is Mendel's first law of heredity. In this law it is stated that,

1. Inherited factors are controlled by paired genes. During cross pollination, each parent contributes one of it's genes or alleles. Not all copies of a trait/factor from each parent are identical.

2. Gene pairs seperate during formation of sex cells (meiosis)- law of segregation (Haploid sex cells form from diploid parent cell)

3. One factor masks another (dominance). Just because a factor is masked, does not mean it is not still there. Dominant allele: upper case R- round seed. Recessive allele: lower case r- wrinkled seed

The dominant trait will over-rule the recessive trait and the dominant trait will be expressed. No intermediate or mix. This is called complete dominance.

In Mendel's experiment, he crossed two true breeding Pea plants (purple and white flower) purple was dominant and white was recessive. This was the P generation. When the F1 generation was created, all the flowers in the F1 generation were purple. These flowers were allowed to self fertilize. In the F2 generation, after the self fertilization, 75% percent of the flowers were purple and 25% of them were white (this was due to them carrying recessive traits that by chance matched with another recessive trait to produce a white flower).

The P generation is the parental generation and the F generations are the generations that follow (F1, F2 and so on)

Mendel hypothesized that there are alternative forms of genes (although he did not use that term), the units (heritable factor) that determine heredity.

A pea plant's sexual organs are enclosed in a flower. The male sexual organ is the stamen which produces pollen. The female sexual organs is the pistil which produces eggs.

Gregor Mendel used garden peas in his studies because:

1. characteristics are expressed in one of two ways, no in-between's, no more than 2. (Ex. Seed shape: round or wrinkled, Seed colour: yellow or green, Pod shape: inflated or constricted, Pod colour: green or yellow, Flower colour: purple or white, Flower position: Side of stem or end of stem, Stem length: tall or short)


2. Garden peas can self pollinate or cross pollinate (fertilize yourself or fertilize another)

3. Garden peas are small an easy to grow (short generation time)

Gregor Mendel is an Austrian monk from the mid-19th century who worked with garden peas to explain inheritance. He is often described as "the father of genetics". He explained "true breeding" which is when organisims exhibit the same characteristics generation after generation.

"Genes of shape and color are inherited independently." (This means that different genes have no affect on eachother- law of independent assortment)

You can cross them out because the ratios will remain the same whether you keep them or not.

16. This is because there are 4 gametes from both the mother and the father each with potentially a different a combination of alleles. The correct phenotype ratio in a dihybrid cross is 9:3:3:1. Pure breeding parents produce identical offspring.

Dihybrid cross is when you are looking at TWO seprate traits, not one like in monohybrid cross.

The tall plant on the left because each of it's offspring were also tall plants. The tall plant on the right is heterozygous/hybrid because only some of it's offspring were tall plants, others were short. This process is known as test cross.

Independent assortment. In this law, Mendel states that genes assort independently (no influence) of eachother during gamete formation (homologous pairs align themselves independently of eachother on the metaphase plate).

Ex.

testcross is the process of mixing an organism with a known (homozygous recessive) genotype with an organism that has an unknown genotype (shows dominant phenotype) and looking at the offspring's phenotypes to figure out the unknown parental genotype. (for example, if some of the offspring show the recessive trait, you know that the unknown parent is heterozygous but if the offspring all show the dominant trait, you now know that the parent is homozygous dominant)

1:2:1 (1 original trait, 2 mixes, 1 of the other original trait)

A Barr Body is a tightly condensed, inactive X chromosome in females (females are a genetic mosaic.) which can result in a mixed phenotype. 

Ex. the black and orange color mix only in female calico cats. This color mix is made by the fact that in each cell, only one of the two X-chromosomes is active (different x-chromosomes with different genes for fur color active and the other inactive in each cell resulting in these different colors.)

Due to the fact that colorblindness is determined by a recessive gene located on the X chromosome, this means that males will be more likely to become colorblind because it only takes a recessive gene on the one X chromosome they have to make them colorblind while with women it would take one recessive gene on each X chromsome to make them colorblind.

Red-green colorblindness, hemophilia, and baldness.

X-linked traits are more common in men because since the Y chromosome is missing some information so that means that whatever the X codes for certain genes will be what is expressed.

Men get X-chromosome from mom, Y from dad.

the Y chromosome. Some of the genes that X has are missing on the Y chromosome.

genes on sex chromosomes (X or Y, but especially X)

Genes that interfere with the expression of other genes (ex. pigment allele turning off an eye color allele or skin allele)

The X chromosome.

In this expirement, Thomas Hunt Morgan breeded a white-eyed male fruit fly with a red-eyed female fruit fly to produce many offspring. All of the offspring in the F1 generation had red eyes (red eyes is the dominant allele). He let the F1 generation reproduce. Most of the F2 generation had red eyes but some had white eyes. When examining this, Thomas Hunt Morgan realized that only the male fruit flies were able to have white eyes. Morgan concluded that because the X and Y (sex) chromosomes are not homologous, they must contain different genes (non-linked genes). This means that something in the male sex chromosomes must cause some of the male fruit flies to have white eyes (usually because there is nothing else to cancel out the recessive eye color allele in the X chromosome that males contain since the Y chromosome does not code for eye color). Traits on the sex chromosomes are called sex-linked traits.

Thomas Hunt Morgan is an American geneticist (1866-1945) who studied mutations and recessiveness (white eye) in fruit flies (drosophilia) to discover sex-linked traits.

Co-dominance is when both alleles are fully expressed (no blending).

Ex. Roan coat- one hair is white the other next to it may be black.


Ex. 

Normal red blood cells: have good O2 transport but malaria can reproduce very well in them

combination of normal and sickle cell RBC's: Malaria has harder time reproducing in these cells, but these cells will have some trouble with O2 transport.

Full sickle cell anemia RBC's: malaria resitant but very poor O2 transport.

normal RBC's: Hb(A) and Hb(A) (homozygous)

combination of normal and sickle cell RBC's: Hb(A) and Hb(S) (heterozygous)

sickle cell anemia: Hb(S) and Hb(S) (homozygous)

Incomplete dominance is the blend of two equally dominant traits (both expressed at the same time). This results in 3 phenotypes being produced (the two originals plus the mix)


Ex. Sickle cell anemia or flowers: 

Although both chromosomes posses two alleles that are equally dominant, one expresses itself and the other dosen't for that particular cell but may do so in other cells.

In co-dominance there is a certain trait in one spot and another in a different spot. In incomplete dominance, it is a blend of the two traits.


Ex. (incomplete dominance= black + white horse make grey offspring. Co-dominance= black + white horse make horse with some cells making black fur and others making white fur.)

It means that the organsim is co-dominant in that trait.

Walnut (1st one)= atleast one dominant allele in both genes. 

rose (2nd)=Atleast on dominant R

pea (3rd)= At least one dominant P

single (4th)= all recessive

Atleast one dominant in both genes= black

Atleast one dominant C= brown

Atleast one dominant B=white

Presence of dominant A and B= purple

if theres no dominant from each trait, then its white.

Pleiotropic genes are genes that affect many characteristics.

Ex. 

2 different genes that interact to produce a phenotype that neither is able to produce by itself.

quantitative characters are those that vary in the population along a continuum. They usually indicate polygenic inheritance. 

Ex. skin color is a quantitative character.

These are traits that are made up of groups of genes that all contribute to that trait. These traits generally have phenotypes that vary gradually from one extreme to another (along a scale/continuum). These traits are controlled by more than one gene (Ex. human height, skin and eye color, corn ear length). # of dominant traits produces different results.

When there are multiple alleles, they dominate each other in a specific order. 

Ex. drosophilia (fruit flies) has 4 different eye color types that are sex linked. Wild (red) eye color, apricot eye color, honey eye color, and white eye color. The order of dominance in eye color for drosophilia is: Er>Ea>Eh>e

(>= more dominant)

A: Ia Ia or Ia i

B: Ib Ib or Ib i

AB: Ia Ib

O i i

For blood types there are A,B, and O alleles. These alleles can produce 4 different phenotypes. A, B, AB, and O blood type.

Yes.

Ex. clover leaf patterns

freckles (sun exposure), fish vertebrae number (water temp), Primrose flower color (temp), Himalayan rabbit coat (temp), water buttercup leaves (water), Obesity genes (diet), muscle mass (diet, lifestyle)

recombinants.

recombinants are offspring that show unexpected phenotype from a crossover (parents meiosis). the number of recombinants is used to determine the distance between genes (recombination frequency).

Parental types are organisms that are identical to the parents in certain traits phenotypically and genotypically.

A chromosome map summarizes the distance between genes located on the same chromosome. The farther apart the physical location, locus, of two genes on a chromosome, the higher the % recombiation between those two genes.

A map unit is the distance between two genes that produces a 1% higher chance for recombination per map unit.

Genes that are further apart on a chromosome experience the most crossing over, genes that are closer together do not experience as much crossing over.

Ex. If crossing over were to happen on trait A, C would be most likely to experience corssing over next, not B.

the process of homologous chromosomes exhanging genes.

The enviornment.

Sex-linked traits: If there is more males affected than females 

incomplete dominance/polygenic: If there is a third phenotype present

If there is an affected indivdiual in every generation it is most likely autosomal dominant. If it is not present in every generation, it is most likely autosomal recessive.

Yes. These traits are linked to the x chromosome because Y is missing information.

Hemophilia, colour blindness, and muscular dystrophy.

An autosomal recessive trait. This is clear because affected children have unaffected parents meaning their parents are carriers. Additioanlly, heterozygous individuals are not affected by the trait.

An autosomal dominant trait. this is clear because heterozygous indiviudals are affected by the trait. An affected child must have aleast one affected parent, showing this trait is autosomal dominant.

Birth order, within each group of offspring, is drawn left to right, oldest to youngest (most left= oldest, most right= youngest)

males=square

females=circles

Roman numerals represent the generation while arabic numbers represent the individuals within a given generation.

Ex. individual I1 is the first individual listed in the first generation.

A pedigree chart is a flowchart of matings, offspring, and traits produced over many generations.

Using a pedigree chart.

genetic counselors estimate the genetic risks of passing on a disorder, they recommend possible treatments, and they give emotional support

Genetic screening is the process of seeing if you are at risk at passing on disorders based on your family's genetic past.

genetic screening

Selective breeding is the process of choosing parents with desirable traits (physcial, behavioural, mental...) and have them produce offspring.