genetics final

What organism did Mendel use in his genetic experiments?

Pea Plant

Why did Mendel choose the species he did?

They are easy to raise, have many offspring per mating, can fertilize themselves and have varieties in genotype and phenotype that are easily observable.

What are the assumptions of Mendelian Inheritance?

1. Each each plant must possess two genetic factor encoding characteristics

2. The two alleles in each plant separate when gametes are formed, and one allele goes into each gamete

3. If the two alleles are different, the dominant allele determines the wild type phenotype

What is the correct description of dominance and recessiveness in genetics? Use an example from Mendel's experiments to describe these concepts/

The dominant allele doesn't subdue the recessive allele, but the recessive allele doesn't produce enough protein product to produce the recessive phenotype. Mendel experienced this with his F1 generation. All of the plants exhibited the dominant trait.

What is the relationship between dominant and recessive phenotypes and the DNA sequence of the gene?

Dominance/recessive is a reflection of how much a functional gene product (RNA or protein) is made. In a dominant phenotype, the wild-type allele in the heterozygote produces sufficient amount of protein for the development of the wild-type trait. We call this haplosufficiency. If there is no any functional product, the recessive phenotype appears.

What is a monohybrid cross?

A cross that involves hybrids for a single trait

What is a dihybrid cross?

A cross that examines the inheritance of two different traits

Principle of Segregation

States that each individual diploid organism possesses two alleles for any particular characteristic, one inherited from the maternal parent and one from the paternal parent. These two alleles segregate when gametes are formed, and one allele goes into each gamete. Furthermore, the two alleles segregate into gametes in equal proportions

Allele

Different forms of a gene

How is segregation of alleles related to the behavior of chromosomes during meiosis?

Segregation of alleles in monohybrid crosses is due to the separation of homologous chromosomes during anaphase I of meiosis.

How do you decide whether the difference between observed and expected ratios is real and not due to chance?

Chi-squared test

Explain in detail the relationship between independent assortment of alleles and the behavior of chromosomes during meiosis.

Independent assortment of alleles for different characters is related to the random alignment of non-homologous chromosomes during metaphase I of meiosis. For a diploid species with 2n = 4 chromosomes, there are two independent alignments during metaphase I, producing gametes with four chromosome combinations.

In a cross between pea plants that are heterozygous for purple flower (Pp) and height (Tt), what is the probability that the offspring will be homozygous dominant for the two traits?

1/16

In a cross between pea plants that are heterozygous for purple flower (Pp) and height (Tt), what is the probability that the offspring will be homozygous dominant for the two traits?

(1/8 + 1/2)= .625

Steps determine inheritance of multiple characteristics using the multiplication rule

a. Break the parental genotypes into monohybrid crosses

b. Determine the phenotype and genotype probabilities in each monohybrid cross

c. Combine the probabilities of the offspring in the monohybrid crosses according to the rules of probability (multiplication or addition rules)

Show the phenotype and genotype ratios for the dihybrid cross RrYy x RrYy using the rules of probability

Phenotype ratio: 9:3:3:1

Genotype ratio: 1:2:1:2:4:2:1:2:1

What is a dihybrid cross?

a cross that examines the inheritance of two different traits

In one of his experiments, Mendel crossed true-breeding pea plants with purple flowers (P) and true-breeding plants with white flowers (p). Purple flower is the dominant characteristic. Mendel collected the seeds from this cross, grew F1 plants, let them self-pollinated to from the second (F2) generation, planted the F2 seeds, and analyzed flower color. What were the results that Mendel obtained in the F1 and F2 generation?

He observed a blend of the two colors which demonstrated incomplete dominance

In sheep, the allele for belly fur (A) is dominant to the allele for no belly fur (a). A mother with the genotype Aa and a father with the genotype Aa produce an offspring. What is the ratio of the offspring with no belly fur.

1:3 will have no belly fur

In horses, the allele for straight hair (H) is dominant and the allele for curly hair (h) is recessive. A breeder mates a homozygous dominant mother with a heterozygous male. What is the chance that the offspring will have straight hair?

There is a 100% chance

In mussels, brown color (B) is dominant and blue color (b) is recessive. A homozygous brown mussel crosses with a blue mussel. What is the probability of blue mussels?

The probability of blue mussels is 0

In cats, the allele for short hair (H) is dominant to the allele for long hair (h). A heterozygous short hair cat is crossed with a long hair cat. What percentage of the offspring is expected to heterozygous for hair length?

50% of the offspring will be heterozygous for hair length

In Watermelons, solid green rind color (G) is dominant to stripes (g). A farmer crosses two watermelon plants that are heterozygous for rind color. What are the chances that the offspring will have solid green rinds?

75% of the offspring will have green rinds

Many farmers prefer cattle without horns because it is safer for their herds. The allele for no horns (N) is dominant to the allele for the presence of horns (n). A farmer mates a male with horns to a heterozygous female without horns. What is the chance that the offspring will have horns?

50% chance the offspring will have horns

Mendel's First Law (Law of Segregation)

Refers to the segregation of alleles of the same gene due to the separation of homologous chromosomes during anaphase I of meiosis

Mendel's Second Law (Law of Independent Assortment)

Tells us that alleles for different traits (genes) assort independently from each other during gamete formation. This is possible because non homologous chromosomes line up randomly at the metaphase plate and each chromosome assorts or mixes independently and randomly from each other.

How many different gametes can individuals with the following genotypes produce: RrYy

4 different gametes

-RY

-Ry

-rY

-ry

How many different gametes can individuals with the following genotypes produce: RRYY

1 kind of gamete

-RY

A tall pea plant with terminal flowers is crossed with a short plant with axial flowers. All offspring were tall with axial flowers.

a). Give the genotype of the parents and the offspring

b). Predict the phenotype ratio of the F2 offspring when tall plants with axial flowers are allowed to self pollinate

a). Parents were TTff and ttFF

Offspring were TtFf

b). Phenotype ratio of F2 offspring would be 9:3:3:1

A white haired guinea pig mates with a brown, curly haired animal. All five babies in the first litter have brown fur but three are curly and two have straight hair. The second litter consists of six more brown offspring, where two are curly and four have straight hair. (a) Assuming curly is dominant to straight, what are the genotypes of . the parents and offspring. (b) What is the probability of getting two female guinea pigs with straight hair in a row?

a). Parents are cchh and CCHh

Offspring are CcHh and Cchh

b). Ask Abebe: .0625

For 70% of Americans, the substance called phenylthiocarbamide (PTC), tastes bitter. It is tasteless to the rest. The taster allele is dominant to the non-taster. In addition, normal skin pigmentation is dominant to albino. A normally pigmented woman who is taste-blind for PTC has an albino father. She marries an albino man who is a taster, though the man's mother is a non-taster. Show the expected offspring for this couple

-25% will be albino tasters

-25% will be albino non-tasters

-25% will be normal tasters

-25% will be normal non-tasters

A pea plant with purple flowers and yellow, round seeds (PpYyRr) is crossed with another plant with purple flower and green, wrinkled seeds (Ppyyrr). Use the rule of probability and determine the fraction of offspring with the recessive phenotype for at least two characters

-ppyyRr (1/16)

-ppYyrr (1/16)

-Ppyyrr (2/16)

-PPyyrr (1/16)

-ppyyrr (1/16)

-Total probability is 6/16 or 3/8

Menelian Phenotype and Genotype Ratios

Monohybrid

-Phenotype: 3:1

-Genotype: 1:2:1

Dihybrid

-Phenotype: 9:3:3:1

-Genotype: 1:2:1:2:4:2:1:2:1

Trihybrid

-Phenotype: 27:9:9:9:3:3:3:1

-Genotype:1:2:1:2:4:2:1:2:1:2:4:2:2:8:2:1:2:1:1:2:2:2:4:2:1:2:1

H0 (null hypothesis)

The trait follows Mendelian inheritance. The difference between the observed and the expected numbers is small (large p-value) and it is due to chance

H1 (alternative hypothesis)

The trait does not obey Mendelian inheritance. The difference between the observed and the expected values is too big (small p-value) and cannot be attributed to chance. We need another explanation. For example, the trait does not follow Mendelian inheritance because it is sex-linked or the environment modifies its expression.

Describe the differences between sex-linked and autosomal traits. Give one example of each

Sex linked means that the allele is located on one of the sex chromosomes, either X or Y, whereas autosomal means that it is on one of the non-sex related chromosomes that everyone has. Down Syndrome is an autosomal disorder, while Klinefelter's Syndrome is a sex-linked disorder

The terminal regions of the sex chromosomes in humans have regions known as pseudoautosomal regions. What is the function of these regions?

Although the X and Y chromosomes are no generally homologous, they do pair and segregate into different cells in meiosis. They can pair because these chromosomes are homologous at small regions called the pseudoautosomal regions in which they carry the same genes. In humans, these regions are at both tips of the X and Y chromosomes.

Penetrance

The percentage of individuals with a particular genotype that actually displays the phenotype associated with the genotype.

Expressivity

the degree to which a trait is expressed

Haploinsufficiency

When one copy is not sufficient for organism to survive

Haplosufficiency

One copy of dominant allele produces enough protein to generate dominant phenotype

Complete Dominance

a relationship in which one allele is completely dominant over another

Incomplete Dominance

Situation in which one allele is not completely dominant over another allele

Co-Dominance

A condition in which both alleles for a gene are fully expressed. MN blood types are an example of this

Lethal Alleles

Cause death at an early stage of development often before birth so that some genotypes do not appear among the progeny. An example includes yellow coat color in mice. Homozygous YY mice die early in development and do not appear among the progeny, resulting in a 2:1 ratio of Yy to yy in the offspring. It can be said that for these alleles, survival is recessive

Recessive Co-Dominance

This occurs with cystic fibrosis. Those who are heterozygous for this allele produce both mutated and functional CFTR protein, but the one functional allele produces enough functional CFTR protein to allow normal chloride ion transport. While technically, this gene is co-dominant, it doesn't produce a difference in phenotype from the homozygous dominant

Multiple Alleles

Some genes have more than tow alleles in the population. An example of this are the three alleles for the ABO blood group in humans: IA,IB, and i

Pleiotropy

A single gene produces multiple phenotypes. Sickle-cell confers resistance to malaria, causes anemia, muscle damage, etc. Cystic fibrosis affects lungs, pancreas, and sweat glands

What is the mechanism of lethal yellow color in mice

The A^Y allele contains a deletion between the coding region of Raly and the 5' UTR of A (agouti). This brings the coding region of A under the control of the Raly promoter. Raly codes for RNA binding protein that is required for embryo development. Deletion of both alleles of this gene is lethal

Why do we call individuals with blood type O universal donors and individuals with blood type AB universal recipients

People with blood type O don't have any antigens so their blood can be given to anyone. People with blood type AB have both A and B antigens so they can receive any blood type

Epistasis

One gene masks (suppresses) the expression of another gene at a different locus but this interaction does not produce a new phenotype

Epistatic Gene

The gene that does the masking

Hypostatic Gene

The gene whose effect is maked

Recessive Epistasis

when the recessive allele of one gene masks the effects of either allele of the second gene. This happens in Labrador coat color.

1. B stabilizes tyrosinase (for melanin)

2. E controls the type of melanin deposited in the hair

-To be black, B and E must be functional

-A mutation in B produces brown pigment

-A mutation in E produces no pigment (yellow)

-This produces a 9:3:4 ratio in the F2 generation because yellow dogs can carry alleles for black or brown hair, but these alleles are not expressed when the E locus is homozygous recessive (ee). ee is epistatic to B

Dominant Epistasis

Only a single copy of an allele is required to inhibit the expression of an allele at a different locus. This is seen in the interaction of two loci that determine fruit color in summer squash, which is commonly found in one of three colors: yellow, white, or green. The allele W determines if the squash produces any pigment. The Y allele determines which color the squash will be

How do silver labradors occur?

Silver color in Labs is due to the dilution of the chocolate color by another gene known as D (for dilute). D codes for MLPH (melanophilin), which controls the intensity of eumelanin and pheomelanin

Polygenic Trait

Traits that are additive. Skin, hair, and eye color and stature and shape of humans are controlled by these traits. Three separate genes affect human skin color. Heterozygous individuals (AaBbBb) carry three dark-skin alleles and three light skin alleles. These traits are called continuous because if these traits were graphed you would notice a bell curve for the values of phenotypes. They have a continuous distribution

Why do people have different skin color?

Human skin color evolved as a way to find balance between the benefits and the dangers of ultraviolet radiation from the sun. Solar radiation is stronger in the tropics and decreases as we go to the northern and southern hemisphere. UV radiation can damage DNA and cause skin cancer. Dark skin in the tropics evolved to protect the body from the damaging solar radiation. Dark skin contains a type of melanin called eumelanin. Which absorbs most of the radiation. Light skin on the other hand contains more pheomelanin (reddish yellow melanin). This type of melanin is non effective against UV radiation thus people with lighter skin evolved in forested areas further from the equator where the sun light is weaker. Blocking UV radiation completely is not optional because this wavelength is needed for the synthesis of vitamin D. Lack of vitamin D can cause many diseases, including rickets and osteoporosis. In the tropics, enough UVB penetrates the outer layer of the dark skin and triggers the synthesis of vitamin D. People with light complexion in the northern latitude can still absorb enough UVB in the summer time and synthesize vitamin D.

Sex-Influenced Traits

Traits determined by autosomal genes and are inherited according to Mendel's principles, but they are expressed differently in males and females. A particular trait is more readily expressed in one sex; in other words, the trait has higher penetrance in one of the sexes. For example, the presence of a beard on some goats is determined by an autosomal gene (Bb) that is dominant in males and recessive in females. In males, a single bearded allele is required for the expression of this trait: both the homozygote and heterozygote have beards, whereas the B+B+ male is beardless. Females require two bearded alleles in order for this trait to be expressed.

Sex-Limited Traits

An extreme form of sex-influenced characteristic that is encoded by autosomal genes that are expressed in only one sex; the trait has zero penetrance in the other sex. In domestic chickens, a plumage pattern known as cock-feathering, is a recessive sex-limited characteristic encoded by autosomal genes. Other males and females display a pattern called hen-feathering.

Genetic Maternal Effects

The phenotype of the offspring is determined by the genotype of the mother. The genes are inherited from both parents, but the offspring's phenotype is determined not by its own genotype, but by the genotype of its mother. This occurs with the shape of snail shells (dextral or sinistral)

Cytoplasmic Inheritance

Inheritance of characteristics encoded by genes located in the cytoplasm. Because the cytoplasm is usually contributed entirely by only one parent, most cytoplasmically inherited characteristics are inherited from a single parent. This was seen in the inheritance of leaf color of Four-O'-Clocks. This is different from nuclear inheritance in that nuclear genetic material is inherited from both parents. In addition, cytoplasmically inherited characteristics frequently exhibit extensive phenotypic variation because no mechanism analogous to mitosis or meiosis ensures that cytoplasmic genes are evenly distributed during cell division.