BIOL 1107 Unit 4: trait inheritance

Life Cycles Introduction

A defining characteristic of sexual reproduction is that it results in offspring that are unique but also similar to each other and to the parents. In sexually-reproducing species, not two individuals (with the exception of identical twins) have the same DNA, and as a result, each member of the population possesses somewhat different characteristics. This ability to produce unique offspring can be a tremendous advantage in a changing environment. If an individual is not doing well in a changing environment, it is possible that some of its offspring will be more successful since they have somewhat different traits from their parents and from each other. Some of these traits might make them better suited to living in the conditions of the new environment.

DQ19: If male and female Labrador retrievers with genotypes BbEe and bbEe are crossed, what phenotypes are expected for their offspring?

A. 3/8 black, 3/8 chocolate, 1/4 yellow

DQ8: Katniss and Peeta are normal, but each has a parent with Wilson's disease. This condition is autosomal recessive and caused by a mutation in the ATP7B gene, resulting in the inability to dispose of copper. What is the probability that two of their three children inherit the disease?

A. 9/64 3 combinations for 3 children

DQ17: An X-linked dominant trait is observed in a family for three generations. Based on the following pedigree of the family, what is the probable genotype of the individual marked with an asterisk?

A. XDXd

DQ24: Who can donate red blood cells to someone with type A blood in need of a transfusion?

A. type A D. type O

Life Cycles 3

Alternation of generations -2 multicellular stages (alternate) -what you think of as the plant= usually sporophyte -moss= gametophyte Sporophyte ploidy: diploid (2n) >Processes: meiosis & cytokinesis Spore ploidy: haploid (n) >Processes: mitosis & cytokinesis Gametophyte ploidy: haploid (n) >Processes: mitosis & cytokinesis (or Gamete ploidy: haploid (n)) >Processes: fertilization Zygote ploidy: diploid (2n) >Processes: mitosis & cytokinesis

Codominance

Another non-Mendelian inheritance pattern is codominance, where heterozygotes express both phenotypes of homozygous individuals. ABO blood types are an example in humans. Gene ABO is on chromosome 9 and codes for an enzyme that attaches different sugars (A, B or none) to the surfaces of red blood cells.

DQ18: An unknown trait is documented in a family for three generations, and phenotypes are shown in the pedigree below. Which inheritance patterns are possible for this trait based on the pedigree?

Autosomal dominant Autosomal recessive X-linked dominant

DQ11: Assume hair curliness is controlled by a gene that is on an autosome and has two alleles. Dominant alleles result in curly hair, recessive alleles produce straight hair, and heterozygotes have wavy hair. Han has curly hair, while Leia has wavy hair. Han and Leia are both normal, but their first child has maple syrup urine disease, which is an autosomal recessive disorder. What is the probability that their second child will be a daughter who has wavy hair and is also a carrier for maple syrup urine disease?

B. 1/8

DQ14: If any Kardashian sister expresses an unknown X-linked recessive trait, what is the probability that her son would also express the same trait?

B. 100% XY sex-linked hemizygous

DQ22: Assume pumpkin size is a quantitative trait determined by two genes, and one pumpkin variety ranges from six to ten pounds. Each dominant allele adds one pound to pumpkin size. If two plants that are heterozygous for both genes are crossed, what fraction of the offspring will have eight-pound pumpkins?

B. 3/8

DQ7: An autosomal recessive condition is caused by mutations in a gene. If Beyonce and Jay-Z are carriers, what is the probability that their child will be a son who is either affected or a carrier?

B. 3/8

DQ4: Romeo and Juliet are both carriers for cystic fibrosis. This disorder is autosomal recessive and caused by a mutation in the CFTR gene, resulting in production of thick mucus. What is the probability that their first child would be homozygous dominant or a heterozygote?

B. 75% Addition rule of probability ("or")

DQ20: If a yellow lab and a chocolate lab have several litters with 17 black and 18 chocolate offspring, what are the probable genotypes of the parents?

B. Bbee and bbEE

DQ6: Assume the number of tail fins in goldfish is determined by one gene, and double fins (F) are dominant to single fins (f). Which of the following mates should you choose for your double-finned goldfish to find its genotype?

B. single-finned Test cross= using homozygous recessive mate to test for genotype

DQ16: A type of colorblindness is observed in a family for three generations, and phenotypes are shown in the pedigree below. If the trait is X-linked recessive, which genotype cannot be determined?

C.

DQ5: Homer and Marge are carriers for Tay-Sachs disease. This condition is autosomal recessive and caused by a mutation in the HEXA gene, resulting in nerve damage and death within a few years of birth. What is the probability that all three of their children will also be carriers?

C. 1/8 Multiply for multiple events

DQ12: Ned has type A blood, which is common, while Catelyn has type AB blood, which is the rarest type in the world. What is the probability that their two children will both have type A blood?

C. 25%

Principle of Segregation 2

Cross between two homozygotes -homozygous father (RR) x homozygous mother (rr) -offspring genotypes: all Rr (heterozygous) -offspring phenotypes: all round seeds Cross between two heterozygotes -heterozygous mother (Rr) x heterozygous father (Rr) -offspring genotypes: 1/4 RR, 1/2 Rr, 1/4 rr -offspring phenotypes: 3/4 round, 1/4 wrinkled

DQ13: Rh factor is a protein found on red blood cells that is inherited in a Mendelian pattern (+ is dominant to -) and independently of ABO. Buttercup is type A- with parents who were both type AB+, and Westley is type B+ with parents who were type AB- and O+. What is the probability that Westley and Buttercup will defeat Prince Humperdinck and have a child with A- blood?

D. 25%

DQ15: One of the genes that controls color vision is on the X chromosome in humans. Dominant alleles result in normal color vision, and the recessive allele causes colorblindness. Ginny has normal color vision and is heterozygous, but Harry is colorblind. If Ginny and Harry have three children, what is the probability that at least one of them is a colorblind son?

D. 37/64

DQ10: If a diploid organism is heterozygous for two genes (Gg and Hh) on different chromosomes, which of the following alleles would be found on a single pair of homologous chromosomes inside a nucleus at the beginning of meiosis I?

D. G, G, g, g

DQ2: Which of the following statements are true? A. Dominant traits are always beneficial in comparison to recessive traits B. Recessive traits are always less common than dominant traits

D. Neither statement is true Huntington's disease= dominant allele

Principle of Segregation

DNA and meiosis were not discovered yet. Mendel proposed that a parent carries two of each hereditary factor (gene), and those factors separate (during meiosis) such that a gamete will carry only one of the factors. Uppercase and lowercase letters were used to represent dominance and recessiveness. RR is homozygous dominant (round seeds), and individuals make gametes with R allele. rr is homozygous recessive (wrinkled seeds), and individuals make gametes with r allele. Rr is a heterozygote (round seeds due to the dominance of R alleles), and individuals can produce gametes that carry the R or r allele.

Principle of Independent Assortment 2

Data are consistent with the predictions of independent assortment. Phenotypes: -9/16 yellow round (RX, YX) -3/16 green round (RX, yy) -3/16 yellow wrinkled (rr, YX) -1/16 green wrinkled (rryy) [Dependent assortment= Phenotypes: -3/4 yellow round (1/4 RRYY and 1/2 RrYy) -1/4 green wrinkled (rryy)] Principle of independent assortment proposes that genes affecting different traits are passed down to offspring independently of each other. Does this principle hold true in all situations? No, not when genes are located near each other on the same chromosome (linkage). Traits like hair color and eye color. The farther apart the genes are, the more likely recombination will occur.

Life Cycles

Diploid Dominance (majority of life cycle is diploid) Adult ploidy: diploid (2n) >Processes: meiosis & cytokinesis Gamete ploidy: haploid (n) >Processes: fertilization Zygote (fertilized egg) ploidy: diploid (2n) >Processes: mitosis & cytokinesis

DQ21: A tomato plant with the genotype AabbCcDd for a quantitative trait self-fertilizes. What is the probability that an offspring of the plant will inherit a completely recessive genotype?

E. 1/64

DQ3: Assume earlobe shape is controlled by a single gene that has two alleles. Dominant alleles will produce free earlobes, while the recessive allele generates attached earlobes. Leonard has free earlobes, while Penny and their first child both have attached earlobes. What is the probability that their second child will have free earlobes?

E. 50%

DQ9: Assume earlobe shape is determined by a single gene with two alleles. Dominant alleles will generate free earlobes, while the recessive allele produces attached earlobes. A second gene on a different chromosome controls earwax consistency, where wet is dominant and dry is recessive. Bella has free earlobes with wet earwax and is heterozygous for both traits. Edward has attached earlobes with dry earwax. What is the probability that their child will have both dominant or both recessive traits?

E. 50%

DQ1: If a person goes outside without sunscreen and UV radiation from the sun mutates the DNA in their skin cells, who will inherit the mutations?

E. no children

Epistasis

Epistasis is an interaction in which one gene can influence how another gene is expressed. Example is the color of Labrador retrievers. One gene codes for a protein that is needed to produce the pigment, and black pigment (B) is dominant to the chocolate brown (b). Another gene encodes a protein involved in depositing the pigment in hair follicles, and pigment (E) is dominant to no pigment (e). Yellow xxee Chocolate bbEx Black BXEX

Life Cycles 2

Fungi (haploid dominant) Nuclear fusion: 2 haploid nuclei fuse Zygospore >Diploid 2n Meiosis Spores >Haploid 1n Mitosis Hyphae + mating type & - mating type

Blood types

Group A: AA or AO -Red blood cell type= A -Antibodies in Plasma= Anti-B -Antigens in Red Blood Cell= A antigen Group B: BB or BO -Red blood cell type= B -Antibodies in Plasma= Anti-A -Antigens in Red Blood Cell= B antigen Group AB: AB -Red blood cell type= AB -Antibodies in Plasma= None -Antigens in Red Blood Cell= A and B antigens Group O: OO -Red blood cell type= O -Antibodies in Plasma= Anti-A and Anti-B -Antigens in Red Blood Cell= None

Mendelian Genetics 3

Heterozygotes will express only the dominant trait according to the principle of dominance. Principle of segregation states that alleles of a gene will separate during gamete production, such that a gamete has one allele of each gene. Principle of independent assortment proposes that genes affecting different traits are passed down to offspring independently of each other. Mendelian principles allowed biologists to link inheritance of traits with events of meiosis.

Diploid Dominance

In diploid-dominant life cycles, most cells present during the life of an organism are diploid, and the only haploid cells produced are the gametes. Fusion of gametes during fertilization produces the first diploid cell of a new individual (zygote). In multicellular organisms, the zygote undergoes mitosis and cytokinesis to produce all of the cells in a new individual. Only a fraction of the cells in an individual, called germ cells, will be capable of undergoing meiosis to produce new gametes. Most animals, including humans, follow a diploid-dominant life cycle.

Haploid Dominance

In haploid-dominant species, the "body" of the organism (ecologically important part of the life cycle" is haploid. During sexual reproduction, special haploid cells from two individuals that are designated + and - mating types join to form a diploid zygote, which immediately goes through meiosis and cytokinesis to form four haploid cells called spores. Although the spores are haploid like the parent organisms, they contain a new combination of genes from the two parents. Spores can remain dormant for various time periods, but eventually when conditions are favorable, they will undergo many rounds of mitosis and cytokinesis to form a new, multicellular individual that is haploid. Most fungi follow a haploid-dominant life cycle, but there is tremendous amount of variation in the specific steps of the cycle between different species.

Incomplete Dominance

Incomplete dominance is a non-Mendelian pattern of inheritance where heterozygotes express a phenotype that is intermediate to the phenotypes of homozygous individuals. RR (red) x rr (white) Rr (pink) Self-fertilization 1/4 RR (red), 1/2 Rr (pink), 1/4 rr (white)

Mendelian Genetics

J. Gregor Mendel was an Austrian monk who used experiments with garden peas to establish rules of trait inheritance in 1865. His research was ignored until long after his death. Considered the founder of genetics Mendel chose to use garden peas for his research. -inexpensive, easy to grow, many seeds, visible traits, mate control

Alternation of Generations

Land plants and some algae follow a third major life cycle known as alternation of generations, in which organisms alternate between haploid and diploid stages that are both multicellular. A diploid individual, called a sporophyte, undergoes meiosis and cytokinesis to produce haploid spores. These spores undergo mitosis and cytokinesis to produce a multicellular, haploid stage called a gametophyte. Gametes are produced by gametophytes through mitosis and cytokinesis and later fuse to produce a zygote, which grows into a sporophyte.Size and relationships between the sporophyte and gametophyte depend on the species. In ferns, the sporophyte and gametophyte live independently of each other, and the diploid sporophyte is what we think of as the fern. In flowering plants, the diploid sporophyte is very large and gives rise to structures that most people recognize. In contrast, the gametophyte stage is much smaller and found inside the flower. In mosses, the situation is reversed, and most of what we recognize as the plant is the haploid gametophyte.

Pedigrees

Pedigrees are family trees that also provide information about the inheritance of traits square= male circle= female filled= trait

Principle of Dominance

Purebred peas with round seeds were crossed with purebred peas with wrinkled seeds, while hybrid offspring were allowed to self-fertilize. Male parents (produce round seeds) x female parents (produce wrinkled seeds) All produce round seeds Self-fertilization 3:1 5474:1850 Monohybrid cross Round trait= dominant trait Wrinkled trait= recessive trait

Principle of Independent Assortment

Purebred peas with yellow and round seeds were crossed with purebred peas with green and wrinkled seeds, while hybrid offspring of that mating were allowed to self-fertilize. Hypothesis of independent assortment: Alleles of different genes do not stay together when gametes form. r= recessive allele for seed shape (wrinkled) y= recessive allele for seed color (green) Male parent: RRYY Female parent: rryy Offspring: all RrYy Hypothesis of dependent assortment: Alleles of different genes stay together when gametes form. R= dominant allele for seed shape (round) Y= dominant allele for seed color (yellow) Male parent: RRYY Female parent: rryy Offspring: all RrYy Dihybrid cross

Quantitative Traits

Quantitative traits vary on a continuous scale in populations rather than fall into categories. -height -metabolic rate -blood pressure -hair color Quantitative traits are influenced by multiple genes (polygenic) and environmental factors.

Sex-Linked Inheritance

Reciprocal crosses switch the phenotypes of male and female parents, and different results indicate sex is an important factor. Sex-linked inheritance is caused by genes located on the sex chromosomes (X or Y). X and Y symbols are used with uppercase and lowercase letters to represent alleles.

Mendelian Genetics 2

Self-fertilization (normal reproduction) -Female organ (receives pollen); male organs (produce pollen which produce sperm); eggs Cross-fertilization (experiments) -Collect pollen from one individual and transfer it to the female organ of a flower on another plant after removing its male organs

Life Cycles Introduction 2

To prevent the number of chromosomes from doubling each time cells from two parents fuse, a special type of nuclear division called meiosis is used to produce gametes that have only half the number of chromosomes found in other cells of the organism. However, when meiosis occurs in the life cycle of an organism varies considerably between species. Most species can be grouped into one of three life cycles: diploid dominant, haploid dominant, and alternation of generations.

Genetics

Traits are individual characteristics that can range from visible to molecular to behavioral. Genetics is a branch of the biological sciences that concerns inheritance of traits (heredity). Genotype refers to the alleles of individuals, while phenotype refers to observable traits. Genotype and environmental conditions can both influence the phenotype of individuals. Height= heavily dependent on genotype but can be affected by environmental conditions (nutrition, disorder, etc.)