Genetics final exam

genetics

science of heredity and variation

transmission, population, and molecular

3 subdivision of genetics

alleles

alternate forms of a gene

heterozygous

two different alleles

homozygous

two of the same alleles

phenotype

what they look like

genotype

what alleles they carry

Mendel’s principle of segregation

traits are controlled by pairs of factors, which segregate from each other when the gametes are formed. One alleles is passed from paternal and one from the maternal

dihybrid cross

a cross between F1 offsprings, involving two traits

monohybrid cross

a cross involving one trait

Mendel’s principle of independent assortment

genes for 2 different traits segregate independently when the gametes are formed

Law of dominance

some alleles are dominant, others recessive. One dominant allele will display the effect of the dominant allele

Law of segregation

each gene is present in two alleles, which segregate when the gametes are formed - each offspring inherits one parental and one maternal copy

Law of independent assortment

different genes segregate independently when the gametes are formed

What is the common ratio of a dihybrid cross

9:3:3:1

disease

defects in enzymes results in

Alkaptonuria

inborn errors of metabolism (Archibald Garrod)

mutant genes

Defective enzymes are caused by

George Beadle and Edward Tatum proposed this

one gene one enzyme hypothesis (later changed to one gene one polypeptide)

many traits (and heredity diseases) are

complex (not caused by a single gene)

risk factor

each genetic factor that increases chance of showing trait

haploid

1N

diploid

2N

Meiosis

How are chromosomes transmitted to somatic cells

Meiosis 1: Early prophase 1

chromatin begins to condense following interface

Meiosis 1: Mid prophase 1

synapsis aligns homologous pairs and chromosomes condense further

Meiosis 1: Late prophase / prometaphase

chromosomes continue to coil and shorten. nuclear envelope breaks down.

chiasma

site of crossing over

crossing over causes

genetic variation

metaphase 1

homologous pairs line up one the metaphase (equatorial) plate

anaphase 1

homologous chromosomes (each with two chromatids) move to opposite poles of cell

telophase 1

the chromosomes gather into nuclei and original cell divides

Meiosis 2: prophase 2

chromosomes condense again, following a brief interphase (interkinesis) in which DNA does not replicate

Meiosis 2: metaphase 2

centrosomes of the paired chromatids line up at the equatorial plates of each cell

Meiosis 2: telophase 2

chromosomes gather into nuclei and the cell divides

Products after Meiosis 2

4 cells has nucleus with a haploid # of chromosome

independent assortment

chromosomes line up randomly (possble arrangements 2^(# of chromosomes - 1))

how many chromosomes do humans have

23 pairs, 46 total

meiosis generates genetic variation by

crossing over and independent assortment

cohesin

in mitosis and meiosis, holds together sister chromatids until anaphase

shugoshin

a protein that protects cohesin from degradation during meiosis. “guardian spirit”

Prokaryotic chromosomes

circular, in cytoplasm, single chromosome, no histones, DNA alone

Eukaryotic chromosomes

linear, in nucleus, multiple chromosomes, contains histone proteins, occurs as chromatin

Chromatin is made up of

DNA and histone proteins

analyze chromosomes by

size, banding pattern, centromere position

karyotype

complete set of chromosomes in a cell (used for determining evolutionary relationship btw species)

homologous pair of chromosomes

same genes in same location, alleles can be same or different, and same centromere positions

autosomes

pair of complete karyotupes (one from each parent)

Sutton and Bover

linked chromosomes to medelian inheritance

sex linked characteristics

genes on x chromosomes are x linked, genes on y chromosomes are y linked

chromosomes theory of inheritence

genes are located on chromosomes

Thomas Hunt Morgan

explained sex linked characteristics through fruit flies.

non disjuction

failure of chromosomes/chromatids to separate during meiosis (can result in down syndrome)

aneuploidy

an increase or decrease in the # of individual chromosomes

monosomy

only one sex chromosome (ex: turner syndrome)

trisomy

an extra chromosome in a set (ex: edward’s syndrome)

causes of aneuploidy

mitotic spindle function problems (loss of centromere, gain of centrosomes, or checkpoint failures)

Trisomy 21

Down Syndrome:; extra chromosome in set 21

polyploidy

presence of more than two complete sets of chromosomes

autopolyploidy

polyploids created by chromosome duplication with a species

allopolyploidy

polyploids created by hybridization btw two species

example of autopolyploidy plant

potato , banana, sweet potato

example of allopolyploidy

tobacco, wheat, strawberrycreated from hybridization of different species like oats and cultivated wheat.

importance of polyploidy

increase in cell size, larger plant attributes, and evolution (rise to new species)

structural change to chromosomes

deletion

structural change to chromosomes

duplication

structural change to chromosomes

inversion

structural change to chromosomes

nonreciprocal translation

structural change to chromosomes

reciprocal translocation

structural change to chromosomes are important because they can

cause gene loss and increase # of copies of a gene

fragile sites

constrictions or gaps in chromosomes that are prone to breakage under certain conditions

copy # variation (CNVs)

differences in the # of copies of particular DNA sequences

reproduction

zygote (diploid) → meiosis (produces gametes: sperm or eggs) → gametes (haploid) → fertilization (produces zygote)

males (biological sex)

small gametes

females (biological sex)

large gametes

variation in human sex genotypes: XO

female, shorter, underdeveloped sex organs, broad chest, and neck folds

variation in human sex genotypes: XXY

male, taller, underdeveloped testes, reduced facial and pubic hair

variation in human sex genotypes: XYY

male, taller

variation in human sex genotypes:XXX

female

SRY encodes a protein called

testis determining factor; master switch to start male development

dosage compensation

equalize the x chromosome expression in males and females (2x in males, ½ for females)

x chromosome inactivation

barr body is condensed and inactivates x chromosome randomly (causes infertile females)

in cats x-activation causes

calico coat color

autosomal recessive traits

skips generations, appears in males and females, affected has to receive allele from both parents

autosomal dominant traits

in every generation, in males and females, affected individuals must have at least one affect parent

x linked recessive

skips parents, more frequent in males (inherited from mother), all affected males will pass to daughter

x linked dominant

every generation, more frequent in females, and all daughters of affected men will be affected

y linked

every generation, only males

genetic counseling

using pedigrees to calculate risk of inheriting traits

one trait can be affected by

more than one gene

epistasis

alleles for one gene masks or suppresses the effect of another gene

recessive epistasis

a form of epistasis where a recessive allele at one locus masks the effects of alleles at another locus.

dominant epistasis

a form of epistasis where a dominant allele at one locus masks the effects of alleles at another locus.

complementary gene interaction

one dominant allele at each gene locus to display wild type phenotypes

complementation tests

can be used to determine if two mutations are caused by alleles of the same gene

mutation

where new genes come from

incomplete dominance

neither trait is dominant, observed when phenotype is quantitative rather than discrete

co-dominance

both alleles expressed simultaneously

complete dominance

shows dominant allele only

lethel alleles

Tay Sachs disease (TT and Tt - normal, Tt - tay Sachs (lethal))