Chapter 12. Genetics

Question 1

What is heredity?

Answer 1

Transmission of traits from parents to their offspring

Question 2

Who is Gregor Mendel? Understand what questions Mendel was addressing with his famous experiments.

Answer 2

He is a scientist who worked out the rules of inheritance through a series of experiments on garden peas.

Question 3

Understand Mendel’s experimental design. Be familiar with his experiments results and conclusions. How did he ensure his lines were truebreeding? How did he control matings/crossings? Why was he successful when so many others at the time were not?

Answer 3

He had garden peas as his model organism. To ensure his lines were truebreeding, he conducted self-pollinated of 14 different phenotypes of plants for 2 years, eliminating plants that were not a true breed.
To control his matings/crossings, “monohybrid cross” pollination (crossing of true-breeds) was done.

He was successful because his trials were repeated and produced many numbers to be able to conduct mathematical analysis compared to others at that time which had more ideas rather than factual evidence.

Question 4

What characteristics are important in a good model organism for genetic study? Why were pea plants a good choice in his analysis of the transmission of traits?

Answer 4

Model organism he chose was cheap, easy to grow, easy to mate and cross, had short generation time, produced many offspring, and had easily identifiable traits.

Question 5

What is a reciprocal cross? Why did Mendel perform a reciprocal cross?

Answer 5

Reciprocal cross was done prove that paternal and maternal seeds contributed equally and did not change the result.

Question 6

What is the relationship of genotype and phenotype

Answer 6

genotype is alleles and phenotype is what is expressed as a trait

Question 7

dominant vs. recessive alleles

Answer 7

dominant alleles determine the phenotype and recessive is only expressed when it’s homozygous recessive

Question 8

homozygous vs. heterozygous

Answer 8

homozygous: allele pair that is same, heterozygous: allele pair that is different

Question 9

dihybrid vs. monohybrid cross

Answer 9

dihybrid: two traits, monohybrid: one trait

Question 10

F1 generation vs. parental generation vs. F2 generation

Answer 10

P gen – pure breed (homozygous), F1 gen – heterozygous, offspring of P1 gen, F2 – offspring of F1 gen.

Question 11

Somatic cells vs. gametes

Answer 11

Somatic (=body, diploid) cells are created by mitosis

Gametes (sperm and egg, haploid) are made in meiosis – for reproductive cycle.

Question 12

Alleles vs. genes

Answer 12

Alleles: 2 alleles in each gene, one paternal and one maternal Genes: code for a certain trait

Question 13

Wildtype alleles vs. mutant alleles

Answer 13

Wildtype (common types) allele (represented with “+” sign)

Mutant alleles are alleles that are not wildtype.

Question 14

Define and describe Punnett square

Answer 14

Prediction of offspring, shows the probability of phenotypes and genotypes of offspring.

Question 15

Define and describe Allele

Answer 15

one of two or more alternative forms of a gene that arise by mutation and are found at the same place on a chromosome.

Question 16

Define and describe Loci

Answer 16

Location of a gene on a chromosome

Question 17

Define and describe test cross

Answer 17

crossing with homozygous recessive to test if the dominant feature phenotype organism has Homozygous dominant (all offspring would show dominant phenotype) or heterozygous (50% chance that offspring shows dominant and 50% recessive phenotype).

Question 18

Define and describe linkage groups

Answer 18

all of the genes on a single chromosome. They are inherited as a group; that is, during cell division they act and move as a unit rather than independently.

Question 19

Define and describe sex linked

Answer 19

alleles in sex genes

Question 20

9. Understand the law of segregation and the law of independent assortment.

Answer 20

Law of segregation: two alleles of a gene segregate to different gametes during meiosis; each gamete contains one allele.
Law of independent assortment: each pair of alleles segregates into gametes separately from every pair of alleles (** this only occurs if the alleles are on different genes)

Question 21

Thomas Hunt Morgan

Answer 21

Experimented on Drosophila(fly) revealed extension to Mendel’s’ rules. —> to see if the rules applied to animals not just plants. He discovered linked genes (autosomal and sex linked)

Question 22

Nettie Stevens

Answer 22

She was the first to discover sex chromosomes (X and Y chromosomes)

Question 23

Alfred Sturtevant

Answer 23

Constructed first genetic map of chromosome. Student of Thomas H. Morgan.

Question 24

Why is Drosophila melanogaster a great model organism for studying genetics? What did Morgan’s lab do to find the first (known) mutant fly?

Answer 24

Cheap, easy and reproduction, many offspring,

Question 25

What is a “map unit”? What is the relationship between distance between genes and recombination frequency?

Answer 25

Recombination frequency “x” % = “x” map units apart

Question 26

What is the relationship of crossing over and genetic recombination to generating a linkage map? Be able to generate a linkage map if given a particular data set. Conversely, be able to predict an outcome if given a linkage map. Know what type of cross (genotype and phenotype) you would need to carry out in order to generate genetic distance between two genes and to generate a linkage map.

Answer 26

Closer the gene is to each other = higher chance of recombinants. Test cross(cross with homozygous recessive) is required to calculate recombination frequency.
Recombination frequency = (number of recombinants)/(number of total offspring)

Question 27

When is a trait considered a “mendelian trait”? When is it considered “non-mendelian’?

Answer 27

Mendelian trait - traits that are passed down by dominant and recessive alleles of one gene.
Non-mendelian traits
- Incomplete dominance (when allele are not completely dominant or recessive - create intermediate phenotype)
- Multiple Alleles(when a gene has more than two alleles in a population)
- Polygenic trait (when a gene produces multiple phenotypes, like eye color)

Question 28

Codominance:

Answer 28

both alleles are expressed (ABO blood group- I^A, I^B, and i))

Question 29

incomplete dominance:

Answer 29

creates intermediate phenotypes (red(rr) x white(ww)  pink(rw))

Question 30

lethal alleles:

Answer 30

alleles that are non-functional as to (when homozygous)kill the individual who inherits it

Question 31

epistasis:

Answer 31

Epistasis is a circumstance where the expression of one gene is affected by the expression of one or more independently inherited genes. For example, if the expression of gene #2 depends on the expression of gene #1, but gene #1 becomes inactive, then the expression of gene #2 will not occur

Question 32

polygenic trait:

Answer 32

traits determined by two or more genes like skin/eye color

Question 33

multifactorial trait:

Answer 33

one polygenic trait that are also influenced by environmental factors

Question 34

quantitative traits vs. discrete traits:

Answer 34

quantitative traits are ones that vary among population along a continuum (like height in different countries)
discrete traits: there is few possible phenotypes ( like a pea that is either wrinkly or round)

Question 35

What is a carrier?

Answer 35

Carrier: don’t express the disease but carry the disease.