UCONN MCB 2410 Genetics Exam 1

types of cell division

mitosis and meiosis

Epistatic gene

the gene that does the masking.

Hypostatic gene

the gene whose effect is masked.

Locus (plural = loci)

the place on a chromosome an allele is found.

Meiosis II

the second phase of meiosis consisting of chromatids separating, along with the two diploid cells splitting in two

Genotype

the set of alleles an organism has.

Recombination:

the sorting of alleles into new combinations.

Mitiosis

to make an exact copy of a cell by asexual reproduction

The Principle of Independent Assortment

when two alleles separate, their separation is independent of the separation of other alleles at other loci.

X-linked Dominant Traits

• Both males and females affected; often more females than male. • Does not skip generation • Affected sons must have affected mother • Affected daughters must have affected mother or father. • Affected fathers pass trait to all of their daughters.

Y-linked Traits

• Only males are affected. • Passed from father to all sons. • Does not skip generations.

The Concept of dominance

• The trait that remained unchanged in F1 = dominant. • The trait that disappears in F1 = recessive.

Autosomal Recessive Traits

• Usually appears in both sexes equally. • Tends to skip generations. • Affected offspring usually born to unaffected parents. • Appears more frequently among children of consanquine marriages.

Autosomal Dominant Traits

• Usually appears in both sexes equally. • Both sexes transmit to their offspring. • Does not skip generations. • Affected offspring have affected parent. • Unaffected parents do not pass trait.

X-linked Recessive Traits

• Usually more males than females. • Affected sons born to unaffected mothers (skips generations). • Never passed from father to son. • All daughters of affected father's are carriers.

Non- disjuction in meiosis I

(Left Side)

Non- disjuction in meiosis II

(Right Side)

Chromosome Mutations

- Aneuploids - Chromosome Rearrangements - Polyploids

Lethal alleles:

- Cause death usually early in development. - Can alter phenotypic ratios. - Can be dominant or recessive.

How can we investigate characteristics in humans?

-pedigrees -twin studies -adoption studies

Nondisjunction in meiosis II

2 normal gametes, 2 abnormal gametes

Human Genome:

23 chromosome pairs • 22 pairs of autosomes • 1 pair of sex chromosomes

Barr Body

A dense object lying along the inside of the nuclear envelope in female mammalian cells, representing an inactivated X chromosome.

Nondisjunction in meiosis I results

All 4 gametes are abnormal.

Chromosome Rearrangement

Alter the chromosome structure - Duplication - Deletion - Inversion

Aneuploids

Alter the number of chromosomes

Continuous characteristics

Are polygenic and influenced by the environment

Expressivity

Degree to which a character is expressed

Non-disjunction

The failure of homologous chromosomes to properly segregate

Meiosis I

The first division of a two-stage process of cell division in sexually reproducing organisms that results in cells with half the number of chromosome sets as the original cell.

Dominant Epistasis

The presence of a single copy of an allele can inhibit the expression of an allele at a different locus.

Recessive Epistasis

The presence of two recessive alleles inhibits the expression of and allele at a different locus. (e.g. Bombay phenotype)

Telocentric chromosome

a chromosome in which the centromere is located at its very end

Heterozygous (heterozygote)

a diploid organism with 2 different alleles at a given locus.

Homozygous (homozygote)

a diploid organism with 2 identical alleles at a given locus.

Incomplete penetrance

Genotype does not produce expected phenotype

Haploid

Germ cell (N)

Diploid

Somatic cells (2N)

Pleiotropy

The ability of a single gene to have multiple effects.

random assortment

The chance distribution of chromosomes to daughter cells during meiosis

Multiple alleles and Codominance

Create greater variety in genotypes & phenotypes

Submetacentric chromosome

Chromosome in which the centromere is displaced toward one end, producing a short arm and a long arm

Acrocentric chromosome

Chromosome in which the centromere is near one end, producing a long arm at one end and a knob, or satellite, at the other end.

Sex-limited

Autosomal genes expressed only in one sex

Meiosis

Cell division that produces reproductive cells in sexually reproducing organisms

Gregor Mendel (1822-1884)

Discovered the principles of inheritance using peas.

The concept of dominance:

Dominant: Heterozygote is same as one parent Incomplete dominance Heterozygote is intermediate Codominance Heterozygote exhibits both phenotypes

Gene Interaction

Genes at multiple loci determine a single phenotype.

Sex-linked

Genes on X or Y chromosomes

Sex-influenced

Genes on autosomes more readily expressed in one sex

Genomic imprinting

Genes whose expression is influenced by sex of transmitting parent

Homologous pair

Maternal + Paternal

inversion mutation

Mutation in which a chromosome piece reattaches to original chromosome but in reverse orientation

Trisomy

One additional member of a homologous pair

Epistasis:

One gene hides/masks the effect of another gene at a different locus.

Polyploids

One or more additional SETS of chromosomes

Penetrance

Percentage of individuals with a particular genotype that express the expected phenotype

Incomplete dominance ratios

Phenotypic ratio will match genotypic ratio.

recombinant

Progeny that exhibit mixing of maternal and paternal alleles on a single chromosome

Monozygotic twins

Result from a single fertilized egg. • Share 100% of their genome.

Dizygotic twins

Result from two separate eggs. • Share 50% of their genome.

Robertsonian translocation

Translocation in which the long arms of two acrocentric chromosomes become joined to a common centromere, resulting in a chromosome with two long arms and usually another chromosome with two short arms.

Linkage

When genes are located close to each other on the same chromosome

deletion mutation

a mutation in which one or more pairs of nucleotides are removed from a gene

duplication mutation

a mutation that involves duplication of a region of DNA on the same strand

Pedigree

a pictorial representation of a family history.

"or" =

add

human genome

all of the DNA of the human species 23 chromosome pairs - 22 pairs of autosomes (Homologous pairs) - 1 pair of sex chromosomes

Gene

an inherited factor that determines a characteristic

Three-point testcross

can map three linked genes.

Metacentric chromosome

centromere is in the middle

Alleles

different variations of a gene. (i.e. round vs. wrinkled seeds)

paracentric inversion

does not include centromere

Concordant-

if both members of a twin pair have a characteristic

pericentric inversion

includes centromere

Monosomy

loss of one member of the homologous pair

Phenotype

manifestation or appearance of a characteristic

"and" =

multiply

translocation mutation

mutation in which one part of one chromosome breaks off and attaches to another

Testcross

one individual of unknown genotype is crossed with another individual with a homozygous recessive genotype. • A testcross tests, or reveals, the genotype of the first individual.

Compound heterozygote

someone with a recessive trait with two different alleles for that trait.

Recombination frequency

tells you how far apart two loci are on a chromosome.