Genetics Exam 1 (BIO2200) -Birchler Mizzou

Gametophyte

Haploid (gamete producing) plant stage (pollen)

Sporophyte

Diploid (spore producing) plant stage
(leaves, flowers, etc.)

Gamete

Haploid end-products of meiosis (sperm/egg)
(spores are the meiotic end-products in plants)

Zygote

Fertilized egg (fused gametes)

Allele

-alternative gene forms (different sequences)
-different forms of the same gene
(dominant alleles; recessive alleles)

Gene

-section of DNA (Sequence of A's, C's, G's, & T's)
-basic unit of inheritance

Meiosis

Cell divisions for chromosome REDUCTION

Mitosis

-proliferates (increases) the genetic constitution of the zygote
-cell division: parent cell = two identical daughter cells

Haploid

one chromosome set (1n; humans=23)

Diploid

Two sets of chromosomes (2n; humans=46)

Segregation

alleles of the same gene separate at meiosis I

Independent Assortment

Alleles from different genes separate randomly because on different chromosomes

Parental Generation

usually homozygous dominant x homozygous recessive - if true breeding

First Filial Generation

Usually heterozygous for different alleles

Second Filial Generation

Resultant cross of two F1's (3:1; 9:3:3:1)

P1

parental generation (pure)

F1

the first filial generation in a cross; the offspring of the parental generation

F2

the second filial generation; offspring resulting from the crossing of individuals of the F1 generation

sum rule

probability of either one of two mutually exclusive events occurring is the SUM of their individual probabilities.
(ex: 1/4 + 1/4 = 1/2)

product rule

probability of two independent events occurring simultaneously is the product of their individual probabilities
(ex: 1/2 x 1/2 = 1/4)

prokaryote

-NO nucleus
-NO mitosis or meiosis
-multiply by DNA replication and separation of cell wall
-circular genome
-MOST PROMINENT LIFE FORM
ex: bacteria, blue-green algae

eukaryote

-Nucleus
-Linear chromosomes
-Cell multiplication by mitosis
-Meiosis occurs in the life cycle
-Fertilization or other type of gamete fusion
ex: yeast, fungi, plants, animals

dominant

character that produces F1 phenotype

recessive

character that reappears in the F2

genotype

genetic constitution of each individual (AABB or AaBb)

phenotype

appearance of an organism as a result of the genotype (AABB = Tall and dark;
aabb = short and light)

homozygous

two identical alleles for trait (AA or BB)

heterozygous

Having two different alleles for trait (Aa or Bb)

testcross

heterozygote from F1 x homozygous recessive from P

monohybrid

crossing two individuals heterozygous at one locus (gene)

dihybrid

Crossing two individuals heterozygous at two genes

probability

number of times an event is expected divided by the number of opportunities

autosome

non-sex chromosome

autosomal dominant

1. trait occurs in every generation; at least one parent affected
2. when one parent affected, about 1/2 of the progeny affected
3. the probability that an additional child will be affected is 1/2
4. Unaffected individuals do NOT produce affected offspring
5. two affected parents can produce unaffected offspring

autosomal recessive

1. parents are usually unaffected (i.e. tends to skip generations)
2. Approximately 1/4 of children in a family are affected
3. the probability that an additional child will be affected is 1/4
4. Traits result from matings of relatives
5. two affected parents CANNOT have an unaffected offspring

hermaphroditic

condition is when individuals of a species produce gametes of both sexes (ex: most plants)

homomorphic sex chromosome

pair of chromosomes like any other (not cytologically distinct) but differ for the major sex determination gene. (ex: fishes, amphibia, reptiles)

heteromorphic sex chromosome

one of the homologues carrying the major sex determination gene becomes degenerate or otherwise cytologically distinct. (THIS IS THE CASE IN HUMANS)

homogametic sex

the sex with a pair of the same sex chromosomes
ex: XX females in humans; ZZ males in birds

heterogametic sex

the sex carrying different types of sex chromosomes
ex: XY males in humans or WZ females in birds

hemizygous

Having only one copy of a gene or chromosome segment instead of the usual two

X linked

a gene on the X chromosome

Y linked

a gene on the Y chromosome

Sex limited

expressed in one sex or the other but the gene can be located anywhere in the genome

X linked dominant

1. affected males pass trait to all daughters but to no sons
2. affected females pass the trait to 1/2 of their sons and 1/2 of their daughters

X linked recessive

1. many more males than females show trait
2. offspring of affected male will not be affected. All daughters will be carriers and 1/2 of her sons will be affected
3. Sons of affected males do not inherit X from fathers so they are not affected nor a carrier

Z/W sex chromosomes

Birds and butterflies, wild strawberries

incomplete dominance

heterozygote is intermediate between two homozygous types
(ex: red and white flower colors in homozygotes; heterozygote is intermediate = "pink")

codominance

heterozygote shows phenotype of both homozygotes.
(ex: blood groups (AB))

multiple alleles

refer to a series of alleles with different effects

lethal alleles

-some alleles have a phenotypic effect as heterozygote, but exhibit a recessive lethality.
-allele causes a dominant phenotype when heterozygous, but when homozygous, there is a recessive lethality
RATIO= 1:2:1

pleiotropic

term applied to mutations that have multiple effects such as no tail and lethality. Lethality is due to loss of necessary biochemical function or incorrect development.

semilethal

only some individuals of a genotype die - lethality can be conditional or affected by environment.
(ex: fruit fly alcohol dehydrogenase ADH. If flies lack ADH, they are viable, unless they encounter alcohol then they die)

epistasis

an allele of one gene eliminates the ability to recognize alternative phenotypes produced by a second gene.
(ex: Labrador retrievers can be black or brown: B-black, b-brown. Another gene E/e does not allow color deposition in coat. When homozygous recessive ee = golden retrievers whether BB, Bc, or bb at the other gene (locus). The ee genotype block the ability to see the B vs. b difference.)

complementary genes

refer to the situation in which mutations in different genes give the same phenotype. If cross them together, they have a normal phenotype. They are NOT alleles. They do NOT segregate from each other.
(ex: pigment genes in albinos. both genes are required for a particular phenotype. They give 9:7 ratio in an F2 because the two genes are on different chromosomes and either homozygote give the same phenotype.)

duplicate genes

-two genes either one of which can provide normal function.
-BOTH must be mutant to produce phenotype
-If they reside on different chromosomes then in the F2 self, there will be a 3:1 ratio for one gene and 3:1 ratio for the other gene. Therefore 1/4x1/4 = 1/16 mutant which will produce a 15:1 ratio. (common in plants that are polyploids with multiple copies of the genome present)

penetrance

the percentage of individuals of a genotype that show the phenotype associated with a that genotype.
-in some cases not every individual with the mutation shows a phenotype that deviates from normal

expressivity

the degree that a genotype is exhibited in the phenotype. (a mutant phenotype can be expressed at different levels of severity)

Linkage

different genes on the same chromosome will not show independent assortment

Sporophyte makes

spores

Gametophyte makes

gametes

Describe the evolution of the genetic material (approx. times before present for the beginning of the earth, divergence of prokaryotes and eukaryotes, beginning of mitochondria and chloroplasts, emergence of diploidy in plants and in animals and the emergence of multicellularity)

1. age of the earth: 4.5 - 5 billion years
2. divergence of prokaryotes and eukaryotes estimated at 3.5 bya based on ribosomal RNA divergence
3. Mitochondria into eukaryotes via endosymbiosis = 1.8 bya
4. Chloroplasts into eukaryotes - 1.5 bya (blue-green algal endosymbiont)
5. diploidy in animals = 5-600 mya
6. diploidy in plant lineage = 400 mya
7. dinosaurs/ abundant first mammals = 150-200 mya

What was the first form of life?

Ribonucleic acid (RNA)

Know how a gene on a pair of homologous chromosomes with different alleles (A and a) goes through the process of mitosis

They will separate during anaphase, with each daughter cell receiving one of two sister chromatids, meaning one daughter cell will get the A allele and the other will get the a allele, resulting in two genetically identical daughter cells each with one copy of the chromosome carrying either the A or a allele

Know how a gene on a pair of homologous chromosomes with different alleles (A and a) goes through the process of meiosis

the homologous chromosomes will pair up, potentially exchange genetic material through "crossing over" (recombination), and then separate, resulting in gametes that can carry either the A allele or the a allele, leading to the segregation of alleles and creating genetic diversity in offspring

Know how two genes with different alleles (A/a and B/b) on different chromosomes go through the process of mitosis

each allele will be distributed randomly to the daughter cells, resulting in all possible combinations of alleles (AB, Ab, aB, ab) appearing in equal proportions in the new cells due to the separation of chromosomes during anaphase

Know how two genes with different alleles (A/a and B/b) on different chromosomes go through the process of meiosis

When two genes with different alleles (A/a and B/b) are located on different chromosomes, during meiosis, they will independently assort, meaning each allele from one gene (A or a) has an equal chance of being paired with either allele from the other gene (B or b), resulting in four possible gamete combinations: AB, Ab, aB, and ab, each with a 25% probability of occurring